The biology of Rumina decollata(Linnaeus) Pulmonata: Achatinidae

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Authors Rascop, Ann-Marie, 1936-

Publisher The University of Arizona.

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THE OF R U m E l BECQLLATA (LIHMAETJS)

: w ■ : •Aaa^Mairie Base op > ,. V -

'; A Thesis Submitted. ,t-6 the Faculty o f the■ * DEPARTMENT OFZGOLOGI

V: la Partial Fulfillment of the Requir©meats- For the Degree o t ' ■

' - , MASTER OF SCIENOEla the Graduate College: -

: ; WiWRSlTt OF ARIZONA ‘ ■

1 9,6 0

STATEMENT BY AUTHOR

This thesis has been submitted ia partial f m l o f re

TABLE OF GOHTENTS

latroauytios ■ ■ . 1"Taxoaomy .

\ Lea'cySitSes , 4.v Glassi’fi'eatisa : - - : ■ ■ . : ; . ."'4 '

- Ifomeaolafure T - ' ■ \ , 5Blstributioa 8Food Habj-ts 10Aaatbiay and. Histology, of the jDigestire System • 13Anatomy and Histology of the Reproductive System 20Reproductioa 24Growth and Bevelepment / ; 31Estivatioh ,; / . , -M...Oxygea CoastmptioB ■ 4lSummary 4?Bibliography 5©

I l S t o l M W S

l

ti#ts a

# #

Ruraiaa deeoXXeta. Morphology of ShelX'at Variotes Ages 55Xa if6sly hatched, lateral view X6 11)' HewXy hatched, apical view Xo 2 Si# weeks, previous to decollatioa X k 5 Ni#e week# 9 after first decollation X44 Adult, previous to fourth decollation XI 2/55 Mtilt ̂ aftey fourth decollation XX 2/36 Becollatioh partition tif adult 9 apical view X5

Htoaiga decollata Histplogy pf the Digestive System ' ' ' ■ § $- 1 -Cellular d#t&ll pf palivary glapd showing

collecting thhules and cells 2 Ciliated columnar ppitheliusj of crop

■ 3 Arrangement Of ga$triO epithelium in stomach k Ciliattd columnar epithelium, of intestine 5 Cellular d#tuiX of digestive gland fubui©

and intsftubular tissue

Rumin# doooliata R#prod#tiy#.#mctures ' . |f1 Adult X3 ' ;2 #utf#nii#'5. si# mo#h# 23 S fh&tid sdult x|4 AdUlt 9 estivating 3E3

INTBODUGTIOH

The phylum Mollueca represents a group of diverse animals whose number of known genera and species is seeond only to that of the arthropods» The mollusks vary greatly not only in form and structure, but also in the range of habitats which they occupy in the sea, freshwater and on the land. The Pulmonates are the most diverse in habitat with marine, brackish waterv freshwater and terrestrial forms® The importance ©f freshwater snails as inters mediate hosts for trematode parasites of birds, mammals and man has been recognised for a long time. More recently, the importance of land snails as agricultural pests has been realised:. When the numbers of these forms increase, as they are at the present time, their eradication will present am insurmountable problem. Mass poisoning programs haye been unsuccessful in eradicating freshwater snails and have been equally ineffective against land snails^ Both forms have the capacity to avoid, molluscieides by remaining dormant until normal conditions again prevail.

Fortunately, there are those who are aware of the threat that the increasing land snail populations present and are.directing their efforts toward finding safe and practical control measures. At present, a control program for the giant African snail, Aohatina fulica, is being investigated at the University of Arisona by Dr. Albert R. Mead. The Aohatina have increased to such an extent in numbers and range in the islands and tropical mainland areas of the south and west Pacific that they have - become m seri0ms

agriemltural pest „ It is believed that Eiamina deeollata possesses the potential to become an equally important pest in the somthern tJnited States o It is interesting to note that Aehatina fttlica and Eo deeollata are members of the same molluscan family9 the Achatin- idaev and are strikingly similar in many respects» Because of these similarities and because the- importation of live Aehatina into the United States is prohibited9 Bo deeollata is currently being substituted for Aehatina in biological control experiments directed toward eradication of the latter» It is hoped that the control program will also prove effective against the increasing populations of Bo deeollata within the United Stateso Without doubt, this species is the most serious snail pest ini Arizona today

■ fhe study of E® deeollata, therefore., was undertaken to supply information which might prove helpful to those investigating biological control methods of Aehatina

■> ’■ ' ■■■ ' ' ' 5 The: writer is indebtefi. to many in t-he: Department of Zoology

at the University of Arizona for their, help in various phases ofthis works Espeoial thanks are extended to Dro Albert R. Meadl forhis goidan.ee and adviee in many aspeets of the -study and in thepreparation of this thesis 5 to DraWilliamEoBrowm for his interestand times spent in the construetion of oxygen consnmption equipment |and to Dr0 Eo lendell Coekrim and Br« William J0 MeSauley .for helpfulsuggestions and- time spent in examining'the manuscripto

Description? The shell of Rumina decollata has a tapering eylin=> drleal- forms There are four and one=half t© six slightly convex whorls in the admitse The.apex of.the shell is trmneate^ dme to the periodi© loss of. the last two or three whorls 9 andi is sealed by a slightly convex plmg (fig«, 6S p..'.55)-* The aperatmre of the shell is oval and smooth = The average length of. the shell in the admits is 28 msu and the average disateter of the. largest and most recent formed whorl is 12 mmo The average diameter of the apical .convex plmg is 6 mm»

Shells containing living animals appear dull brownish gray in color? but those which are empty are a creamy tan» Newly hatched individmals have an extremely thin transparent shell'which iis tah in color with a smooth opalescent surface« The whorls of young Snails are more convex than those of the. adults= Subsequent: growth of the shell results in the. formation of striae at right angles tb the sutures of the whorls„ These become progressively more pfdnouneed with the increasing size of the: shells©

The dorsal portion of that part of the; body which extends . beyond the: shell ̂ s • aperature:. is dark gray in color and. is finely ..granulated:© - The ventral surface: or base: of thes fleshy foot is yellowish gray in.color and smooth© .

Classification: The following, arrangement gives the, taxonomic categories within which Rumina decollata is now placed:

- ' ■ ' . ■ ■ 5:;Zhylma Mollusea - '

Glass Gastropoda.©rder Pulmonata

Suborder Styloma.atoph.ora , Family Achatiaidaei

Subfamily Smbuliaiaae HomenelAture: Bumiaa decollata has been the subject of a great-deal of coafusioa as far as molluseaa. taxonomy is eoncernedo This animal hds paraded under no less than fourteen geaerie ahd- seven, specific trivial nameso Host ©f these invalid names wereiapplied! to Bo dec.ollata at a time when shell morphology (1®©®$ eonchology) was the basic criterion for identification and nomenclature of snails ® Investigators discarded the animals and retained their sheiie»̂ failing to realize that theiinternal anatomy offered far : more stable, criteria for identification than the: highly variable; shells o Much of the confusion which surrounded the identification of this species can be attributed to- the; great variability of the shell of this animal»: The young snails appear quite -differentfrom the adults.® It was for this reason that Bisso -created the new species ©rbitina truncatella and Orbitina incemparabilis, which were both based ©a juvenile forms of B® deGellata® Adult forms are equally variable, both within the same population arid between populations from different areas® Kaltenbaeh (1951) has attributed the variation in shell form between populations of Berth African B® decollata to environment® Snails inhabiting agricultural areas where a fair amount of moisture is present

- ■ ■ 6 have broader shells with fewer whorls® Those inhabiting semiarid: regieas have narrow shells with a greater-ntamber of whorls» With only the shell being nsed in identifioation% it is understandable - why . so many new spesies names' were; based' mp©a' the ■ same.1 animale ,

The following synonymy gives the generi© and specifie trivial names which have.been applied to Bumina deeoliata since

BmKina deeoliata (linnaens) ''1758 Helix deeoliata linnaens * .Systema Matnraetenth edition

P= ■77'3v- ■ ' : -V; ■■■ ■ ;1787 Rhinoceros deeollatus G o Menschen, . % Mnsenm - #eversiannm 178? o '1789' - Bnlim'as decollatns . (!♦ ) #0 Brnguiere-,, Eney elope die

rdi

1841 Eupa trmacatella L0 Pfeiffer9 Symbo ado Histo Heli= ce.orum $ 1:43° '

1842 B-glimas trtmcatms Pfeiffer« ibidem.1845s Gylindrella decollata (Myst) R0 Ac Philippi, Abbildo u»

Besehro Goacho,.2(2):47„1848 Bulimus matilatms Lo Reeve, Genohologia Iceaiea, V,

Balimas, mdo 331» •2855 Sira deeollata Aa Schmidt, Halle, Abhaadlo HaturWo Verv,', - 1?5 . , 424 : '1855 Subuliaa decollata H° Adams,■ Seaera ©f Recent Mollusca,

•2sli0o1855' Subulina cmtilata H#aAd§ms, ibidem.i860 Bulimus paiyae R o f,« Lowe, Pr© ere actings - of the Linnean

Society, 1860:201.' 1869 ’ Stenogyra decollata W 0. G0 Binney, Land,.and- Freshwater

• Shells of HorthAmeriea, Smithsonian miscellaneous collections, 8(5)$228. ’

1873 Stenogyra truncata A0 Moussoa, Revision de la fame malacologique des Canaries 9 p

DISTRIBUTION

Rumina decollafra is indigeBoas in. the Eediterraneam , regions ©f Ernrbpe, Asia and Africa. In the Western Hemisphere:,It has been reported from the following locations,;. Wilmington, North Carolina| Charleston, Sonth Carolina| Savannah, Georgia| Pensaeola, Florida; Mobile and Bemopolis, Alahama; lay Sto lomis, Mississippi; New Orleans, Louisiana; Dallas, Austin, Sehulenherg, New Braunfels and Brownsville, Texas; missions near San Antonio, Corpus Christi and Del Dio, Texas; Tucson and.Mesa, Arizona; Savanna, Cuba; Bermuda, and many places;in Mexico 0 This species was introduced'in Philadelphia, hut survived the: colder weather for only two years (Johnson, 1899)0

The introduction of R » decollata in the New World is most; likely the result of commerceo One author reports that the> animal, was brought into Cuba with, plants from. Italy (Crosse-, 1890)« Tie; adult snails or their eggs would he well hidden in the soil of potted plantso

It is interesting to note that P. decollata foundi in Mobile, Alabama and New ©rieans, Louisiana, oecurredl in the Old. French parts of the cities (Smith, 1913)» In all prohabilityv this species was accidently imported; with helix ■■ pomatia, a large garden snail which the French prise as a delicacy

' ■ , : •■■■■' ' ■ . . : 9 eeaturyo Its iatroductioa into new areas may have been deliberateor accidektalo If the latter be' the case., the manner of accidental, introduction is not definitely known0 Since the animal first

, appears as a garden pest in one location and then spreads as its numbers increaise, there, is the likelihood that it is unwittingly introduced with nursery stocko This seems to be the situation in the two Arisona .locations where this snail has been foundio It is important to have all nursery stock in interstate commerce inspected to prevent further introduction.of this and- other destructive sp@eies». , ' ■

FOOD HABITS

The food habits of Rumiaa dedollata classify it as an omnivorous animal® Practically any plant or animal material whie& cam be ingested^ is inelmded is the bill of fare of this snail® In nature., they have been observed to eat decaying leaves and fruit, grass, paper, old wood, and vegetables and other cultivated: garden plants (Showers, ms)® A great deal of damage to plants is the result of this snail eating through the roots® The young snails begin to eat the feeder roots of plants after hatching, a practice which usually results in the death of the plants®

The following is a list of foods and materials ingested by j|o decollata in the laboratorys

potato orange hard=boiled egg whitecarrot grapefruit ground beefspinach tomato egg shellscelery green pepper filter papercucumber watermelon paper towelscabbage Pablum aquarium cementlettuce milk , ' ,

'When food was not provided, the snails ingested! the soil, and fecal material within the containers» Snails which were put in am aquarium for observation of reproductive activity began to eat the rtibber=like cement holding.the aquarium together ®

Some authors have reported the cannabalistie tendencies: of B, decollata® Johnson (1899) observed this species eating Helicella ericetorum and Taylor (1919) reported that a colony of Helix memoralis at Charleston, South Carolina, had been devoured by B® decollata® Binney used them as scavengers to clean shells®

. . - 131He reported that when a Helix was placed in a box with them,, one of the Rumina would immediately attack itg introduce itself into the inner whorls of thes Helix and completely remove the animalc ' Binney also reported that R, deeollata attacked Snceinea ovalis and ate the shell as well as the., animal (Pilsbry, 19^6) 0

la the lahdr.atory 9 this species attacked adult Helix aspersa1, snails which were, several times larger than they0 The Helix-were never attacked immediately after they were; placedl in a container with Rumina as reported by Binney s but at times would Crawl among the latter for days without being harmed Usually the Helix were attacked in the evening and only their empty shells were found in the morningo They were attacked even though other food was availableo ©nly once was.the■attack and devouring of a. Helix observed^ One of the Rumina passing close to a Helix suddenly began to rasp and tear at the latter» The; Helix movedt away , but the Rumina pursued! it, continuing to rasp and tear at iteuhtil^find.lly^i&i' HilixpMthdhtwelhtQvi-t&:lM&ell, The Rumina. extended its body into the shell and continued to tear at the: Helixa literally eating it alive0 One Rumina after another would satisfy its appetite by feeding upon the Helix until the entire animal was removed from its shell®

The Rumina were.never observed to attack each other, but they would quickly devour a dead Rumina or any other dead snail®

Rumina deeollata has a voracious appetite and will continue eating until almost the entire length of the digestive

.. .. . ' ■, : , 12: traet is filled.0 Snails were dissected just after they had. finijshad eating and the digestive tract was found to contain food from the posterior esophagus to the reetum= These snails have been observed! to indulge in anofher meal a few hours after a first© Food passes qmickly through the digestive tract and snails may defecate as soon as one hour after finishing a mealo

AHAT©MY AKB-HISTOMSI::- ' OP fHS BISBSTIVE SfSfBB -

Ahatosiieai studies of the digestive and: reproductive systems of Humina deeollata were accomplished by anesthetizing the animals with ehloretone or nembutol# A saturated solution of chiefetohe was prepared by dissolving the erystalsin, hot boiled tap water (Mead, 194-2)» The snails were placed in test tubes containing the cooled1, ehloretone solution® Any air at the top of

' the -tube was: forced, out by inserting a eork® Snails whose; tissues' were t© be used: for histological.. studies were; kept in the: solution:: for twehty to thirty minutes = Those to be used for gross anatomical studies were kept'in ehloretone for one hour« The nembutol. solution was prepared by dissolving 3/4 grain (50 mg0)of nembutol in 75 ml o. of cooled, boiled water (Van der Schalie:, 1953)

.kept the■snails anchored! during dissection. 'A longitudinal: ■ , V ineision was made beginning just posterior to the genital atrius and extending to the pulmonary aperafcure in the mantle collar* .3ki# incision was continued through the aperature and; mantle cavityo. The thin mantle covering the visceral mass-was carefully teased away and the individual organs freed' from each other e Grgans to be studied histologically were, cut into small pieces approximately Zrsmm o square and fixed in Bouin°s Fluid or Heidenhain6s Solution for at least twenty-four hours o Tissues to be studied for. general structure were embedded- in paraffin and! cut on the microtome at a thickness of 10 fio Those to be studied for cellular: detail were cut at 5 .Sections were stained; for cellular detail with Ehrlieh8 s Acid Hematoxylin and for general structure with Mallory's Triple Staino

Information regarding the sl2e9 structure ahdi - cellular make-up of the various components of the digestive tract of Rumina decollata is based upon the: study of adult specimens of average size®, : The use of the directions "right" and; "iefti1 refers to the right and; left; of the; snail0 Since the longitudinal axis; of the shell of this snail normally lie# in a horizontal: plane,9it was found to he more convenient to use the terms dorsal and ventral to refer to structures withitethe shell abovethe longitudinal axis and those below the longitudinal axis, respectively»

The mouth is loeatedJt on the most anterior part of the head slightly ,ventral,to the first pair of tentaeleso - It is' a'horizontal slit with lip-like folds which opens into the buccal cavity*

At the anterior and dorsal part ©f the cavity, just behind the: upper lip $ there is an arehed: ehitinoid. jawv House# within a sae

the crop, which is 7 in length and somewhat flattened dorso- ventrallyo. The crop is histologically similar to the pre-esophagus except for a few slight changese The folds of the lining are' more prominent and extend farther. into the lumen. The outer layer of circular muscle is thicker and the columnar cells are more closely applied to it, therefore^ there is lessconneGtive tissue between these two layers than between the corresponding layers in the pre- esophagus @ The crop is surrounded by the salivary: glands» which are united: completely dorsally and ineompletely ventrally. The. glands extend the length of the crop and are: lobular in appearance; with finger=like projections directed toward the buccal mass. Two prominent salivary duets issue from the substance of the giandi and run eephalad to enter the posterior wall of the buccal mass, one on either- side of the pre-esophagus, The salivary glands are composed of large ovoid cells with large nuclei and clear cytoplasm and other spherical cells containing many small granules within the cytoplasm«, Small collecting tubules whose walls are made up.of small cuboidal cells, come, together to form the large salivary■r-x ■ ■ . ' ■ , . ' . .duets. These large duets are lined with larger cuboidal cells and" are covered with a thin layer of circular muscle.

The crop narrows in diameter/to form the: pdst-espphagus which is 7 mm, in length and is similar in structure to the crop except that the ciliated columnar cells are somewhat taller and thinner, V '

The post-esophagus opens into the stomach, a W-shaped t A structure, 12 mm, in length and 2 mm,, in diameter. The stomach

turns to the right and somewhat dorsaliy so that it is at a right angle to the post=>esophagus0 It ooenpies a position in the first; Visceral;whorl and , is partially emhedded within a lobe: of the; digesti%e glando The lining of the. stomach consists of club- shaped columnar epithelial cells of varying heights arranged in such a way. that they form fan-like: clusters (fig*'3 , pe 56)0 Ther,©; are no folds present» The outer covering of the stomach consists of a thin layer of circular muscle and scatteredi patches of longitudinal muscleo The muscle layers and; gastric epithelium are separated by a thin layer of connective tissue^

The digestive gland; comprises mos-S of the; bulk ©f the viseera and 0eeupies approximately three and one^half of the ter#i- #a&%#h@rls of the shell*,: The; ■ gland is made; up of numerous ' small , tubules-. which ultimately,-converg#' to form - large ducts 0 • These dm© t s join to form a single duet which opens into the posterior end of the stomach* The tubules are composed of a single layer of irregularly shaped columnar cells with, basal nuclei and numerous small .granules within, the cytoplasm above .the nuclei „ Sandwiched1, between the thin bases of the columnar cells are large ovoidtcells with large round nucleie The; cytoplasm of these cells contains numerous granules which are larger-" in size than those- in the columnar cells* large vacuoles containing stored waste materials are occasionally found within the cytoplasm of these large cells« The imtertubular spaces of the digestive gland are;, filled, with large irregularly shaped parenchymatous cellsb They eontain huge vacuoles which flatten the cytoplasm and nuclei agaljpst the cell

membranes9 The duets of the digestive gland eonsist of a single: layer ©f extremely thin eiliated tall eoiumnareells eontaiming elemgatW nucleic The duets are. thrown into profuse folds which are compressed against each other

following the angle of the shell8 s statures^ It opens to the? outside as the anus whioh is looate# within the mantle: eollar on the right side of the snails The.anus actually is ah opening within an openings the pneumostome, which serves as an air-passage: imt© the mantle cayity and: an exit for excreted wastes* The rectum consists Of an inner lining of short ciliated columnar epithelial cells thrown into very irregular lobular folds. The outer layer is made up of a very thick wall of.circular muscle and inner longitudinal muscle which extends into th® folds®

ANATOMY. AND HISTOLOGY ; P 1 THS BBPHCffiDCTiW SYSTEM

Tb® Itemapbroditle conditiea of th© PuTmeiaata resalts la a complex structural arraagemeat of the reproductive organs® The following laformatioB regarding the reproductive system, of Bumina decollata is based upon the study ef reproduetively mature adults«

The external opening of the. reprodueti.ve tract, the genital pore, is located on the right side of the head, 4 mm« posterior to the mouth= The. genital pore is harely visible, but becomes quite evident &t..the time of reproductive activity0- The pore .opens 'Into the genital atrium, a short wide tube 2*5 mm. long and 2 mm. in diametero The atrium is lined with small tightly packed columnar epithelial cells with, hssal nttclei.o There is no evidence of a basement membrane» The wall of the atrium is made up of an ex^ H tremely thick layer of longitudinal and circular muscle o

The genital atrium bifurcates into anterior and posterior branches to form the male and female"components■of" the reproduce tive system. The anterior branch is the penis, a long slender muscular tube, 8 mm. in length and 1 mm. in diameter. Its lining is similar to that of the genital atrium except that it is thrown into ragged folds. The.lining of the lower one-third of the;penis . has fewer folds than the.middle em®^third, which is profusely foldedo . The upper one=third has few folds; ;The wall of the. penis is similar in muscular structure to that;of the atrium. Attached to the apex of the penis is a long slender retractor muscle® This muscle is a branch of the retractor muscle of the right ocular

: -.I.;'.:..' : - V:;21teataelee , ' ' - -; - ' - ' ' , - - - ' .'

The vagina is the posterior branch of the genital atrium and is a muscular tube o mm, in length and 1*5 amio in diameter»Its muscular layers are thicker than those of the penis and its. lining is.thrown into deep folds» •

.■ ,Five millimeters from its base9 . the vagina bifurcates to;form a small muscular tube, the duet of the sperm&thec&o This, : duet, about 6 mme in lengths opens into a thin bulb-like structure, the s.permatheea, which is 3 amio in length» The spermatheca and its duct aFe.: lined with eiliated- oolumnar epithelial cells' with basal huclelv The ; lining, is thrown into lobular folds 0 : :

The apical end of the vagina opens into the oviduct, a wrinkled tube, 16 mm0 in length and 2=2«3 mm® in diameter» The lining of the oviduct changes progressively from its proximal to distal- ends and- three fairly, distinct areas can- be distinguishedo The lower one=third of the ©yiduct is lined; with sparsely ciliated; cells similar to those of the: vagina„ The lining is thrown.into rugged crack=like folds® The cells of. the middle one-third are not as; thin- as those of the lower one=third, and are; more heavily , ' ciliated®;. .The- folds;. are smoother and lobular in outline b The upper one-third of the oviduct is lined with large eiliated;?e©lum= nar cells with large basal nucleie: Located within the Cytoplasmin the apex of each cell is an unidentified oval structure larger than:; the'; nucleUs ® - The: lining is, thrown into: deep crevices, :fhe; ■ wall of the oviduct is made up of. an oUter thin layer of circular muscle beneath which is a thick meshwork of irregularly shaped

cells with granular nuclei and web«=-like cytoplasmic, -strands«, This tissue makes up the hulk of the oviduct wall and supports the columnar cell lining=

■ Attached to the. oviduct throughout its entire length is the vas deferens„ a slender"tube^ s5 mm, in diameter« The vas deferens consists of a thick wall of mostly circular muscle and a lining of densely ciliated columnar epithelial cells which is thrown into lobular foldsa The vas deferens continues downward over the vagina where its attachment endse It .proceeds along: the top of the: genital atrium as a free tube, turns anteriorly and ehters the.integument of the penis0 It continues upward beneath the integument to the apex of the penis, where it opens directly into the lumen of the peniso

The:' apical, end of the oviduct.and 'the-apical eh& of ther vas deferens come together to form a short common duct, the sperm~ oviduct® This duet is lined.with ciliated euboidal cells and the folds of,the lining are similar in structure to those, of the upper one^third of the oviduct® It is embedded within the albumen gland, a crescent^shaped'structure, 15 mm® in length and in dia=.meter® The gland is composed of compacted tubules made up of short columnar cells containing large round granular nuclei and unidetttifiedi oval structures similar to those .found in the upper one-third of the oviduct . The tubules ultimately ©pen into, the ■ spermoyiduct ® ' ■;

Also opening into the spermoviduct is the hermaphroditic duet. This is a long, thin, much coiled and twisted tube which

penetrates the albumen gland to open into the spermotridueto Its liriing is eomposed of V’ery thin densely eiliated columnar cells and its coTefing is made up of a thim layer of circular muscle,.The cells of the lining alter in height from short to tall in such a way that they give the lumen of the duet a scalloped appearance^ The hermaphroditic duct conveys sperm and ova from the ovotestis to the spermoviducts The ovotestis is embedded within the last, one and pne=half whorls of the digestive gland and is composed of 'lobes Which are lined by a thin layer of germinal epithelium«Both ova and spermatozoa arise from the germinal epithelium, although the latter are formed in much greater abundance. Ihen mature, the ova and spermatozoa are released and are swept into the lumen of the. ovotestis and into the hermaphroditic, dticto

BEPHGBTJCTIOST.

Hegmapliroditisin is present im S-gmiaa deeollata and gives this small a biological advantage in that ,every, individual is a potential reproductive partner #or any other individual of the species, (theoretically, one hundred per cent of the reproduetively mature- individuals are able' to produce youngc This is in direct, contrast to dioecious animals.

This species is extremely well adapted in its reproductive activities® ■ The reproduetive/behavior.and: anatomy- are not sufficiently complex to become limiting factors in perpetuating this 1 species

V . ; : ■■ : v ; ' . ■ :■agressor or "male" partner of a copulating.pair0 The "male" pur= sues a partner by approaching one individual after another until "he" is accepted by a "feiaale»" The -genital pore is quite evident in the "male" and1 sometimes the genital atrium and the base of the penis may be bulging outward during the entire time a copulatory partner is being pursued, The "male" may approach several individuals without success = They will either withdraw and move away ■or show complete indifference by drawing themselves into their shellso When a receptive "female" is found, a period preparatory to copulation follows® During this time, which may be as short as ten and.as long as thirty minutes,:the "male" moves around the rather quiescent "female," coming into frequent contact with "her" with "caressing" movements

evident ¥y this times and ^eglns t© iuige6 The two snails move very slowly' until the two gehitai atria touche Both oeular ten^ tacles or only the right ones are drawn in during copulation0 Insemination is accomplished when the "male" directs the bulging has© of the penis into the vaginal opening of the “femaleo'*, Ihen ohservihg copulation with the hinocular dissecting scope, one is able to see the evagination of the penis through its •rather translucent base as it passes into the vagina of the "female»̂ The exposed base of the penis ehlarges greatly for an instant as the sperm mass is passed into the spermatheea (=semlnal receptaele) of the "female0n The penis invaginates. as it is. withdrawn from the vaginao The actual insemination.of the'"female" takes •uo longer.than twenty seconds0 The "female" may immediately inseminate the "male" while the genital atria are in contact or "she" - may withdraw and a period of as much as twenty minutes may follow during which both individuals are very still and move only occasionallyo The genital atria may decrease in size to the extent that they are barely visible, or they may remain bulging outward in one or both individuals» g short period of "caressing" may preeeed the insemination of the "male" by the "female„" When the mutual insemination has been aecomplishedg both individuals immediately set about the task of ridding' themselves of the thick ■ mucus which was. secreted prior to copulation* Frequently they will rasp at each other in their attempts to consume1 the mucus, with the result that one partner or the other contracts momentarily After the mucus is removed, this procedure Sometimes taking as long

; ; ■ ' . - .■ ’ ■ . 22 ,as fifteea minmtes, the two snails move off with,no further regard for one anothero fhe entire edpuiatory sequence, whieh includes the preparatory phase, actual eopulation and the post eopulatory phase, has been observed to take place in at- time as short as ope- half hour and as long as one hour and twenty minutes»

In the second pattern of eopulatory behavior4 there is, Po definite agressor or apparent differentmatiem of Mmaleh and "female" partners« Gopulatory tendencies: seem to arise spontan- ebusly in two individuals who are in close contact with one anothero This has been observed especially when the snails were crowded around food. The two individuals follow the-same general pattern of eopulatory behavior outlined above except that there is no - definite display of : "male" or "female" tendencies^. ■ Which individual is inseminated first appears t© be purely a matter of chance0

This animal.is easily disturbed during eopulatory activity an|:‘'U slight jarring of either of the snails results in their drawing themselves into their shells® They may be sufficiently disturbed to prevent further eopulatory activity or they may resume activity after a short while® Actual copulation in R® deeoilata is simple and quickly affected in contrast to some of the Pulmoaates in which the structure of the genitalia is such that prolonged periods of sperm transfer are required= ■ ;

Snails whitih had been observed eopulatihg were-isolated s© that egg laying habits could be.studied® Each member of a copulate ihg pair was placed in a small jar containing a layer of soil two inches deep® Eighteen snails were so isolated after copulation®

, Eggs asiaally were laid four days after copulation, but in a few cases eggs were not laid for six or Seiren days:. The number of eggs laid is usually eleven, this number appearing with surprising frequency. However, half of the , time the number, does•vary.from eleven^: and as- few as four and as many as seventeen eggs, have been > counted. Lamy (1929) reports that from twenty to forty eggs are laid by: deeollata, a number which appears questionable when.the: size of the animal and the capacity of the oviduct are taken into account« ! :; : ' . ' -\ . ' v 'y : ■ : ;. Tour to six clusters of eggs are laid -at- intervals of ; .\three, four or five days. S© regular egg laying schedule could be established since any one snail would lay clusters ofVeggs at irregular intervals. Hone of the snails- laid mere- than :':six:' clusters of eggs after isolation. Onee they were returned to■ the stock jars - and allowed to copulate , they would-again begin to lay eggs. In the laboratory, where environmental coBditlons were stable and food plentiful, copulation and egg laying occurred

The eggs of B. decollata are. usually laid in the ground; but if the snails find other suitable, locations, they seemto prefer- them to burrowing into the ground. Eggs have, been found .in such places as hollowed out spots in carrots and apples which the snails had been eating, in small glass feeding dishes and even within an empty . B. decollata shell. When the:eggs - are laid in the. ground, the snails tunnel through the soil by alternately extending, and then forcefully contracting their- bodies,- thereby' pulling

#ieir shells along with them. They would tunnel through the soil in the gallon jars to depths of as much as 8 em0 In small jars, they would tunnel through the two inches of soil and deposit their eggs next to the glass. Vignal (1919) collected the eggs of E. decollata from depths of as much as 12 cm. The strength with which these animals tunnel through the ground is impressive when one considers their size. When the snails have ffinished their tunneling, they back away slightly, leaving a small cavity for the egg *mass9f and then rest a few hours. When the eggs are laid, they adhere to each other in a cluster due to the mucus which, surrounds them.. 'They are white calcareous spheres approximately 2;.5 mm® in diameter. . .

After the eggs are deposited, the snails remain near them for a few hours. If the eggs are laid just heneath the surface, of the ground, the snails simply hack out of their shallow tunnels.If they have been deposited at a greater depth, the snails back away slightly, tunnel upward and emerge from the ground head first

It was possible to distinguish and isolate snails for a study of egg laying, because eggs within their oviducts, could be . seen through the translucent shell. Gravid snails were placed in empty petri dishes where they would eventually deposit their eggs, tinder these conditions, which, were abnormal as far as an egg laying environment was Concerned, the, snails laid theif.eggs at .intervals of approximately twenty minutes, provided they were not disturbed. The ocular tentacles and buccal mass remained contracted and slight rhythmic contractions of the body continued

'during egg laying® At the time ©f explusion of each egg, the right side ©f the body would bmlge greatly, the genital atrium would suddenly dilate and the egg would be quickly and smoothly ejected®

GROWTH AND DEVELOPMENT

A few days after they are laid, the eggs ofRumiha decollata begin to lose their whiteness and take on a yellow hueov Th,ey are no longer smooth and glistening, for the muons which surrounded them when they were laid has dried and revealed their rough surface. Three weeks from the time they are laid, the eggs lose their brittle calcareous nature and appear softer and leathery.At the end of four weeks, the eggs take on a definite oval shape and in three or four more days, hatching occurs.

The four and one-half week or thirty-two day period for development of the young snails within the eggs was the average time for hatching in the laboratory where room temperature was 72“F, With the heating controlled by a thermostat, the temperature in the laboratory rarely varied-, more than 2°F0 above or below 72°Fo In the early spring, before the cooling system was put into use, temperatures often rose to 78°F, and sometimes, during the day, to as high as 85°F,, with the result that eggs hatched in four weeks» None of the eggs being watched for hatching'time ever hatched in less time than twenty-four days, no matter how much the temperature had increased® Eggs placed, in an incubator at 9G°F« never hatched. The high temperature tolerance for the eggs must be somewhere between 85 and 9G°F0 When the cooling system was being used, the laboratory was kept at an almost perfect o5°F, At this temperature, the eggs hatched at approximately six weeks, A dropin. temperature of only 7 °Po resulted in a week and one-half -' . ; ' ' . 31: ' ... ' :

increase Visa time b ef or e hatching occurred« Eggs exposed to a temperature of 32°F = never hatched. No low temperature tolerance approximation was made since no refrigerated constant temperature chambers were available at the time of the study. Eggs used in .the determination of hatehing.time were kept between two pieces of moist filter paper in petri dishes® ©nly eggs which had just been laid were used and the date and time, was recorded,,, ftie filter paper'was kept moist and the eggs checked each day for hatching®

At the time of hatching, the elongated eggs begin to split' To free themselvesg the young snails literally eat their shells from around them. The shells of the young R® deeollata are 3 mm® in length, 2®3 mm® in width and have three or three and one-half whorls® The appearance of the shell has already been described:^ The body is lacking in the dark gray pigment of the adult and the internal organs can be seen through the body wall®

The young snails remain in the soil for at least a week, not moving from the spot where they hatched, but feeding on the .humus in the soil surrounding them® In nature, the young snails feed on the small feeder roots of plants®

After their week of feeding within the ground, the young .snails, now A®5 mm® in length,, begin their journey to the surface® In two or three days, depending on the depth from which they must tunnel, the young appear at the surface of the soil and begin their search for food® A great deal of time is devoted to eating and the young snails grow rapidly® : At the end of six weeks, their shells are approximately 15 mm? tn length, 6 mm® in width

and possess about eight whorls«, Their bodies have taken on a light gray color as a result of pigment development®

It is at this time, six weeks after hatching, that the phenomenon of decollation takes place„ By the end of six weeks ©f growth, all young snails have moved forward in their shells, leaving the last three whorls (the whorls which they possessed at the time of hatching, ioe®, the nepionic whorls) empty and filled with a fluid. The digestive gland which once occupied these whorls has been pulled up into the fourth and fifth whorls. The third whorl becomes, progressively delicate and m#reak may occur in it which ultimately causes its detachment from the fourth whorl However, this third whdrl is so delicate that normal movement of the snail over and through the soil results in its loss. An amusing account of decollation is given by Cooke (1895) who states that the animal SbangsM its upper whorls violently against some hard substance as if to get rid of them.

The cause of. decollation is not, as yet, understood# It is not a unique phenomenon as it. occurs.in other species of snails The mechanism probably involved the dissolving and a weakening of the shell by some chemical substance secreted by the snail.

To seal the end of the shell, a calareous convex plug is secreted directly over the exposed end of the digestive gland.It does not follow the diagonal placement of the sutures of the. shell but is at a right angle to the axis of the shell® This plug is already present before the last three whorls are lost.

In the first and all subsequent decollations, a regular

,34 .©itain of events takes place, which ©an be stunmerized as follows:An increase in size of the shell anteriorly allows the growing snail to move forward leaving the last three whorls of the shell emptyo These fill with a liquid,' the origin of which is not knownk., The empty whorls become progressively weaker e The fluid

̂ is either absorbed or evaporates through the breaks which begin to appear in the empty whorls®: A calcareous plug is secreted.,probably by the thin mantle covering the digestive gland, to pro- tect that organ from the exterior» The empty whorls are ultimately lost through normal activity®... ' : " . ■' ; .. • ■ : -' . ,4 ■■

The purpose of,decollation in certain Species of snailsis not clearly understood, but it may be an accompanying phenomenon of certain types Of growth0 The digestive gland, increasing iri bulk by intttssusception, soon outgrows the small apical whorls of the shello Since the. snail cannot discard its shell and form a new and larger one, it simply moves forward! into whorls having a greater capacity® This arrangement might be considered! analagous to ecdysis in arthropods®

The age at which this species reaches reproductive maturity has not yet been determined® Snails raised during the study

• have reached nine months of age (=25 mm® in length and 9 mm® in diameter) without beginning reproductive activity® A study of the anatomy of the young snails at six weeks of age revealed that all reproductive structures itare.epresenti^^thi.neyiapparent development of one system (male ©r female) before the other (fig® 2, p®5,7) ® Prepared sections of the ovotestis op nine month old snails

repealed that spermatogenesis hut not ©©genesis was taking place«, Shis WGuld seem to indicate that this species is protandrouS, but this point needs further investigation^ These snails would be able to inseminate another individual but could not produce eggs eveh if they themselves were inseminated» it is possible that oogenesis will not begin until the female, tract is developed enough t© accommodate the fairly large eggso

The duration of reproduetivity in Bo decollata is not: known6 Vignal (1919) kept a few specimens which laid eggs for tea yearSc, lie also had One specimen which survived for twelve years, the only record of longevity.for this species,

Adult snails grow morh slowly and decollate less frequently than young snailso They add about 5 mm. of shell e v e r y four months and decollate once or twice each year5 ridding themselves of about two whorls each time® . ■

ESTIVATION

The phenomenon of estivation is considered to be a water conserving mechanism among iland snails as well as other animals® Under unfavorable environmental conditions such as.elevatedl temperatures, decreased relative humidity and lack of fdSd, the snails will withdraw, into their shells, secrete a partition Off mucus, and lime to isolate themselves from the exterior and remain in a quiescent state until favorable environmental conditions again prevailo Metabolic activity and water loss is held to a rnintmuh during estivatioBo Breakdownof storedfoodstuffs is necessary only for cell maihtaineuce and repair, since energy requiring activity is suspendedo Nitrogenous wastes are excreted in the form of solid uric acid as a means of conserving body water

Various aspects of estivation in So decollata were invest1 gated in an effort to ascertain conditions eontribmting to its initiation and some of the effects,which it produces in this animal® " ' !.• ■■

In the laboratory, estivation was initiated by increases in temperature and decreases in relative humidityo lack of food did not result in estivation as long as the snails were-provided ■with soil which they readily ingested® When temperatures rose above SO/’Fo, as they did. in the laboratory in late spring before^ the cooling system was put into use, many of the snails began to estivate® They would draw themselves into their shells and secrete a good deal of mucus which soon dried® There was thus

, ■ ■ . . 37formed: a thin .opaque, epiphragm whieh sealed the aperature of the' shell9 Usually, the snails would burrow intlr the. soil a short distance and estivate with . the aperatureSc of the: shells buried, and the apices exposed® :

If a. rise: in temperature was not accompanied by a d6drease in relative humidity below approximately 15%9 the snails did not estivate, but a noticeable decrease in activity was observed^Plany would burrow into the soil in a manner similar to that described for estivation, but when, picked up, they would be founds slightly extended from.their shellso As the temperature decreased in the evening, the snails backed out of their shallow burrows and became active o - ■ 1

Very rarely did the relative humidity in the stock jars fall below 15%® The moist soil and liquid waste products from the snails usually kept the air: in the containers fairly humid® A few times, however,. elevated temperatures accompanied: fey a lower- relative humidity caused the soil to dry out® As a result, the snails began to estivate® They quickly became active when the soil was moistened with water®...' To test the effects of a completely moisture - free environment on Ro deoollata, twenty-five adultisnalls of approximately the' same, size were placed in a desiccator containing anhydrous calcium chloride® The temperature in the laboratory was 72°F®At least twenty snails remained actiye for the first thirty minutes® Seven snails withdrew into their shells and began secreting epiphragms after forty-five minutes® After one and one-half hours

seventeen snails hafl begum t© estivatee All remaining snails Mad began to estivate by at least two hours and twenty minutes, after being placed in the desiccator« It can:;be seen that response to , an environmental condition such as this varies greatly from one ■ individual to another,, ,

Based on these observations^ it can be said that relative humidity is the main deciding factor in initiation of estivation in Ruminao Temperature plays a secondary role, since the snails canvescape high temperatures by burrowing into the soilo Finally, food supply has no effect on estivation as long as the snails are' provided with moist soil containing organic matter» In the laboratory, the soil in the stock jars was rich in'partially . digested pflant material excreted, by the, snails o

Snails kept in empty jars displayed periods of activity and ,estivation when, temperature and relative humidity were at levels conducive to continued activitye In this instance, estivation appeared to. be a "stored food conserving mechanism^ interrupted by brief periods of Mfood searching activity^"

In considering the factors which initiate estivation in this animal, it must be emphasised that conditions■in nature might elicit entirely different responses from those ©bservedi in the laboratory® ' ' :

One of the most impressive physiological effects of estivation is the rapid decrease in metabolic activity to appoint where, it is barely perceptable® Oxygen consumption fs so slight iav-B® decoilata which have been estivating for a prolonged period

: 59bf time, that in order to record it, it was neeessary te extend - ' readiags on the Warburg :ebhMaatt.:7bl'tim@y}R'espî oiaetfe'er:fô periods';'o£ several hours, After t w days of estivation, the average oxygen consumption at 2G0G» was fbund fcti have fallen from the normal active rate of 116oj? jxlo/lGO mg, dry weight/hour to 19®5 jnl° /100 mg, dry *eight/hour, The average rate for snails which had been estivating for Six months was 5 jal»/X00 mg, dry weight/houro The rate for snails estivating.for two days illustrates the rapid’ decrease in metabolic aefivity which takes place at the beginning of estivationo That for snails estivating for six months illustrates the extremely low metabolic rate which is reached*after prdldiiged estivation, .

Von Brand (195®) has studied: anaerobic metabolism in freshwater snails which, in order to avoid molluscicides, burrow into mud with a low oxygen content» It would be interesting to study the effects of an oxygen-free environment on estivating Ro deeollatao One might suspect, after observing the negligible amount of oxygen consumed by these animals during estivation, that ‘they, too, might be capable of anaerobic metabolism to some extent,

Gross anatomical changes accompany prolonged estivation,The most noticeable change in snails which had been estivating for six months $as the decrease in size of the digestive gland. After this length of time at room temperature (72°F0)SI it occupied the terminal one and one-half whorls of the shell, whereas it originally occupied at least three. The organ also changes in color from a golden tan to a dark dull brown. The intestine likewise

..■. > ; ;"-v ; :. ; 4©shrinks iHMSise from an average, of 32.mm0 to an average of 20/m m 9 All parts of the reproductive tract shrink proportionately in size to approximately two»thirds their normal size except the albmhen gland which shrinks to almost one=half its original sizeo

To study weight loss during estivation, twelve active adult shails were weighed and placed in,shell vials» All snails began to estivate within twenty-four hours0 They were weighed once ..a .week /for two weeks after the initial weighing and, then pnce a month until eight months had elapsed» The two weekly weighings were made to illustrate the rapid initial drop in weight

j due\t@' loss- ©f .hqdy, moistures During. the first week;of estivation, the average weight loss due to water loss mainly, was 2007% of the total body weighto Once the snails established a series of epi- ■phragms to lessen water loss and had undergone a drop in metabolic activity, the monthly readings began to represent the utilization of stored food materials and later the breakdown of body tissues® After two months the average weight loss for the twelve snails was 31o 6% of the original .body weight = At.five months the average was 43®3$^ and at the end .of eight.months it was 5 5 ° 5 & % ° All snails followed the average weight loss fairly consistehtly® At the end of the eight months the snails were brought out of estivation by dipping them: in water ® They were then killed by dr.opping them • into boiling hot water and their bodies-:were pulled from their shells® The latter were' dried, ,weighed and: their weight subtracted from all previous weighings to give weights, of the sbft bodies

' only, ,/ 1. " •. - : y : ; ; .■

OXYGEN CONSUMPTION

: - ;: Oxygen, eoHsmptioa by; Sumiaa decollata was measure & atdifYeremt tmperatures with the Warburg Constant Volume Respirometer® ; la kites ' apparatus9 gas and fluid volumes are held eQastant and , increases ©r decreases in pressure are measured; when one gas,, Changes in a#%#to These pressure changes are then converted to,' the actual amouStivST ga-S taken up« . The techniques which were- employed.•■“are descrihed by Umhreit (1957)»- ' ' Four re spirometers were, used. One was utilised as :a

thermsharometer and three for measuring oxygen consumption i," The thermobarometer recorded changes in barometric pressure and' room .and water bath temperatures 6 These were used to correct the • - readings of oxygen consumption^ The Warburg flasks and manometers were eaiibrated with mer cury * ' The manome t er • fluid Used ':wias'Fluid. An aquarium, equipped with a mechanical stirrer and two- heaters controlled by a mercury electrode-type thermostat, served ; as a constant temperature water bath, which maintained the desired temperatures to within approximately one~tenth of a degree Genti- ■ .grade*v Measurements were made at temperature intervals of 5cC«, starting at 5 and ending with 45°GS

Snails used in the measurements were repreduetively mature adults® They received no food during the 24 hours proceeding the measurements ® In this way, variations caused by metabolic break-. :down of different foods were avoided®

Because,these animals react slowly, to changes in their

environment, tjiey w6re placed, in flasks which were immersed in the water bathe The snails were allowed to acclimate themselves for one hour to the temperature at which their oxygen consumption was to be measured# Headings were taken at fifteen minute intervals for two hourss At. least six two^hour measurements were made for each different temperature® She readings were corrected, totaled and divided by two to give an. average for one hour#

Each snail used in the measurements was placed in a numbered vial after removal from the Warburg flask® Its volume

- was determined hy water displacement» A 10 ml® graduated cylinder was filled to the 5 ml® mark with boiling hot water® She snail Was carefully lowered into the water with the aperature of its sheli directed upward® It contracted violentlys forcing air from the shell and mantle cavity outward in a stream of bubbles® She volume increase in the graduated cylinder was recorded and the snail pulled from its shell® It was placed in a small pre-welghed shell vial and desiccated in an oven for 24 hours at 175eC« The vial and contained snail were weighed9 the weight of the yial subtracted and the resulting dry Weight of the snail recorded tin milligrams® The shell was not included in the determination of weight since it does not represent living respiring tissue and its sine is extremely variable due to decollation®

finally9 the actual amount of oxygen utilized.was determined,, A flask constant for each measurement was calculated after the method outlined by Hmbreit (1957)® The flask constant multiplied: by the manometer reading ^change in pressure in mm® for one

hour) equals the jilo of oxygen taken mpo This value is them divided hy the dry weight of the snail ia milligrams and multiplied! by 100 to give oxygen consumption in jilo/100mgo dry Weight/ houre

Investigations involving- the respiration of marine and freshwater mollhsks are. fairly ' hmmerous

much less effective in regulatihg a eonstaat fler of blood an#, therefore, absof%@& #t an iad oasis tent yate® ■ ■ ■ --

'The final value for oxygen consumption at eaCH temperature as presenta# •in the graph.on page-4$, derive# as ap arithmetic mean of all the.individual readings for e a # t4gpfrathra> These readings and their arithmetic means are as1 follows:

' - - 'pi.: •#$-, ml##/h#uy. ; , ...

5167 :T,17 .1*3# 1*54 .1,82 2,06 ■239 .499 .>670, . 1*17; ■ 1* 41, ,’• W ? . 1,87 v'1 2=07.230 ;.;»30l ®#2. ",1=24.' ip42; ., I060 -■ ■:.1,87, . .* .S'O'-O#.236 .311 = 701 •1* 23 ■' 1*44

1*43 1 *46

IO601,66

■i,8i ' -2,27

Arithmetic Means- 2 # o4?3 . o664 1*163 1*409 1,571 ,1,82# - 2,063

It ca$ be seem from the above that the sharpest absolute rife in oxygen. UpBSMe dec#rs between -15 ahd 20 °C

V ' : . ■■ ' 4;. ■■ :v 1$^ a$i|>@a.F8,Mt6;e of the saails varied somewhat at the? \

different temperatures during measurement of oxygen consumptiono At 5 and 100C 0 the body was ê fctended9 ̂-but the eireular muscles were d#htfa0$ed /giving th6:':%@dy' 'and . fieshy feet, a thin appear- anceo The tentacles Were invaginatedp Much water was released, from the mucons membrane covering the body0 There #as no mo've= , mente ;. At 3.5e0° the body was contracted very little- if at ailo The tentacles were occasionally evaginated for .a few minutesc Some water and mucus were secreted Very little movement: was. notedo At 20, 25 and360Cc,the body was normal in appear ance and the foot was completely extended» The tentacles were.eompletely evaginated and a t ,times were invaginated briefly» Thick mucus was secretedo There were movements of the jaw and buccal mass® Movement of the body was frequent 9 but was. hampered by the site ■ of the respirometer' fiask.. , At 35 and 40°Cc 9 the body was .extended and very much relaxed, practically to the point where it appearedi soft and flattened* The tentacles usually remained invaginated, but when they were evaginated they drooped' and swayed® The ' mucous membrane appeared almost dry, and very little mucus was secretede No movement of the body took place® At 459C®, the reactions were much.the same as the above, except that no mucus was secreted and the body actually became dry. Headings•. of oxygen consumption decreased rapidly until they reached zero, at which point death occurred® An average, of one hour of exposure ftir this' »temperatu're;'proved fatal to these animals o

46

225

200 -

175-

150-

125-

) j l . 0 2 / lOOmg.

dry weight /hour

100-

7 5 -

5 0 -

2 5 -

20 25 3530 40T e m p e r a t ure O

Rumi na de c o l l a t o Oxygen Co nsumpt i on

S l H M t

- SuBiiaa decolla,ta (L«,) ? a laad snail native to t'k© Mediterranean regions :@f, ■Sttrd̂ o-e- Asia m#;A#ioa,. keoo##' im the .southern United States and hag' extended its range westward as -tar as Tucson and Mesa, Apiz.dha0 Tho ititroduction and spread of this apeeies-appear td have taken plaee thrdugh traffic ig commerce.The isolated populations found in Arizona seem to indicate that the animal mas unknowingly introduced with nursery stdeko ' " .„

go decollafa is an omnivorOhs asimhl:with -a_voracious appetite« It will accept a wide variety of items as food. This species9 therefore ? has a , distinct .'advantage direr other snails whose range is limited by more restrieted feeding habits, $t also, •possesses ‘ cannibalistic tendencies Which permit it to destroy Other snails competing with it in a given locality. '

: In this hermaphroditic animal % reproductive SfhWldr-is simple and highly effective ih greatly increasing the number ,of Ihdlylduals in a short p#l#d of: time^: About four days' after /- copulation, each snail lays a cluster of approximately eleven eggs ;and will lay up to five more clusters at intervals of three to five. days. The.- eggs, are usually laid in-ths'ground'.' They .hatch ; ' within four and ©ne^half weeks at a temperature Of ?2 °C«, in nature, the eggS are laid near the roots of plants, the latter serving .food for the newly hatched snailS:,. The young: emerge ■' ;;at the surface of the ground approximately ten days after hatching.They grot .'rapidly -and ■st^iho end. of s#. weeks their shells measure

M length and t.#,- tn %i#h^ #ereas ;#ey were:# in• ; ■ .: . , .. . ■' , 4? ' : . , „ . ' . '' ■ . -.

length:,and; wa® in ■wiith at the time #f '. B̂ SS: aftesr •;1 ■the young snails have reached six - weeks of age^ deeollation (loss of the apieal whorls) takes place® This phenomenon occurs at regular'intervals, as the.snails increase - % .Si##® :Spermatozoa, but ho ova are produced in the ovotestis of young snails nine months of age. The time at which actual reproductive aetivity begins ' has net yet been determined s -i?he duration -of' reprb'iuotive activity in this species has been reported as ten years in snails .-'kept im captivity® The■ only record of ■ longevity is one in whidh'^ Snails were reported: to. have been kept, in captivity • for1 twelve yearso 'ill aspects of the life history of this shall point'to-

v/vnhv^planation..for./this species* success in increasing- its .numbers' and Its range® ■.

. Under laboratory 'e.ondition.s.» estivation in -fe« decollata js ■ initiated' by 'a: decrease - In 'relative /humidity b'#low-' 1^# /ahd, an ,// increase in temperature above .80°P® The snails withdraw into their shells and secrete a series of epiphragms to prevent loss of body water® Mefabeiissi. falls ;ti. imperceptible' levels, and, variow /,• / , changes take place in the body tissues® Snails estivating at room temperature for eight months lost/ an',.average; of 55®56% Of their : '/ active body Weight®■ Estivation is an important aspect of the. > physiology Of these animals and attests to their capacity to over- : come the threat of,- advefse environmental conditions«, " /.:

The oxygen consumption of this animal is erratic due to the primitive vascular system which it possesses® At 15 °C», oxygen consumption was found to .be 0664 jil.=/mg.o dry weight/hour® It

^ : /;' r ,;': - r-:̂ F ':, rose sharply at 20 ° G =.to I0I65 ylo/mg® dry weight/hour, nearly. twice the amotxpt for 150Ce Oxygon consumption continued, to rise: ■steadlly/wlth •temp.orathr^^ '©f 55 and 40°^., nntll at 40*0 »,It waa Bo##5. j%l»/Ag« dry #l.#$/h##r«, $he sharp rise at 20ec«, seems t© smggest vtliat tfeie 4e the ©ptimns- level of oxygen consumption for R 0 decollata* Death 'doonrS ir this animal after exposure i o ; ■ : - a temperature of 45 9C» for approximately one houre

'.v ;■ :: . .

Adams, Ho and A«, Adams® 1858a The genera of recent Molluseas ¥ol« II® londoa, J« Van Voorst» 661 pp0

Haker, P® §® 1938? The Molltisca of the- shell heaps o* .:esearg~tieyes of Northern Algeria® Ltigan Museum, Beloit College® Ball® no® 5? p, 187-225® '

Blggs^ Hi- Ba «$o 1.953= Humina. decollata L® in cantlvlt#® Journ®of Conchology, London,. 19(8) s279.®

Hihaey, Wo 6= ■ 1859» The terrestrial air-breathing Mollusks ofthe Haited States®' Vblol¥« .Boston, Little. & Brown« 207 pp«

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Emery* D.L. 192%. Collecting in southern Florida, the Bahamas : and Cuba. ' Eantilus* 3#i^. " ' :

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P L A T E I 55

Rumi na d e c o l l a t e M o r p h o l o g y o f S h e l l a t V a r i o u s A g e s

FIG . l a — Newl y h a t c h e d , l a t e r a l v iew X 6

FIG . l b — N e w l y h a t c h e d , a p i c a l v iew X 6

F I G . 2 — Six w e e k s , p r e v i o u s t o d e c o l l a t i o n X 4

F I G . 3 — Nine w e e k s , a f t e r f i r s t d e c o l l a t i o n X 4

F I G . 4 — A d u l t , p r e v i o u s t o f o u r t h d e c o l l a t i o n X I ^

F I G . 5 A d u l t , a f t e r f o u r t h d e c o l l a t i o n X 1^

F I G . 6 — D e c o l l a t i o n p a r t i t i o n of a d u l t , a p i c a l v i e w X 5

56PLATE 2

043m m.

E x p l a n a t i o n of F igures

CM— C i r c u l a r musc l e CT— Col l ec t ing t ubu l e I T — Intertu bu l ar cel l LM—Longi t ud i na l muscle V V a c u o l e

Rumina d e c o l l a t e Histology of t he Digest ive S y s t e m

F I G . I — C e l l u la r d e t a i l of s a l i v a r y g la nd showing c o l le c t i n g t u bu le s and c e l l s

F I G . 2 — C i l i a t e d c o l u m n a r e p i t h e l i u m of c r o p

FI G 3— A r r a n g e m e n t of g a s t r i c e p i t h e l i u m in s t o m a c hF I G . 4 — C i l ia te d c o l u m n a r e p i t h e l i u m o f i n t e s t i n e ,

F IG. 5 — C e l l u l a r d e ta i l o f d i g e s t i v e g la n d t u b u l e an d i n t e r t u b u l a r t i s s u e

P L A T E 357

Explanation of Figures

A Albumen glandD S — Duct of spermathecaE Egg within oviductG A— Genital a t r ium HD— Hermaphrodi t ic duct0 OviductP PenisP R — Penis re t ractor muscleS Sper ma the caSO— Sperm oviductV VaginaVD— Vas de f e r e ns

Rumina d e c o l l a t e Reproduct i ve S t r u c t u r e s

FIG. I Adult X 3 F I G . 3 Gravid adul t X3

FIG. 2 Juveni le, six months X 3 F I G . 4 Adul t , * es t i v a t ing X 3