Pacific Science (1979), vol. 33, no. 3© 1980 by The University Press of Hawaii. All rights reserved

The Biology of Hastula inconstans (Hinds, 1844) and a Discussion of LifeHistory Similarities among other Hastulas of Similar Proboscis Typel

BRUCE A. MILLER2

ABSTRACT: Terebrid gastropods of the genus Hastula are found in greatabundance on fine-sand beaches throughout the tropics. Hastula inconstans, aspecies common to surf beaches in the Hawaiian Islands, is the first hastula forwhich a complete life history is known. Hastula inconstans is a primarycarnivore, preying exclusively on Dispio magna, a tube-dwelling, deposit­feeding spionid polychaete. The gastropod lives just beyond the surf zone andexhibits well-developed adaptations that permit survival in this habitat. Thebroad, fleshy foot, used in anchoring the snail in the sand and in rapid re­burrowing, is also highly modified as a "sail" which carries H. inconstans upand down the beach with the passage of waves. A highly specialized foregutcontains long retractile labial and buccal tubes, which, combined with a poisonbulb and radular teeth, rapidly sting, immobilize, and ingest prey. The snaillies buried in the sand when not feeding, but emerges when prey are detectedby distance chemoreception. Nearby prey are reached by rapidly crawling overthe sand surface, and prey at a distance are reached by using the foot to "sail"to their location. In either case, contact with the prey is first made by thepropodium of the foot, rapidly followed by proboscis eversion. After contactis made, the prey is stabbed by a radular tooth held by the buccal tube, poisonis injected into the wound, and engulfing of the worm begins. This entiresequence occurs between the passage of waves, and the snail usually reburrowsto continue feeding before the next wave arrives.

The sexes in Hastula inconstans are separate. Mating takes place above thesand while the animals are coupled and rolling freely in the surf, andapproximately 40 spherical eggs are later deposited in a capsule covering asmall piece of basalt. Larvae metamorphose when they are less than 1 mm inlength and reach 3-5 mm in length by late spring. Individuals grow between0.5 and 0.8 mm per month, reaching a maximum size of 34 mm, whichsuggests an average life-span of 3-4 years. Other hastulas with a proboscisnearly identical in structure to that of H. inconstans exhibit similar life historyaspects, including habitat choice and prey specificity. It is suggested thatfeeding types may not only be useful as a diagnostic characteristic, but also inpredicting basic life history aspects throughout the family.

GASTROPODS OF THE FAMILY Terebridae areamong the most abundant mollusks found in

tropical and subtropical sand environments,ranging from the intertidal to depths ofseveral hundred meters. Despite their abun­dance and relative ease of collection, littlehas been published on any species in thefamily. This report represents the first de­tailed life history study for any member ofthe genus Hastula, a group of small, activeanimals found primarily in shallow watersthroughout the tropics.

289

I The research reported here was supported by aNational Defense Education Act Title IV grant to theUniversity of New Hampshire. This paper is based inpart on a Ph.D. Thesis submitted to the University ofNew Hampshire, Durham. Manuscript accepted IFebruary 1979.

2 New England College, Environmental Studies Divi­sion, Henniker, New Hampshire 03242.

LJAnahola

~IPoipu

290 PACIFIC SCIENCE, Volume 33, July 1979

~-KahanaMakUa-~

Waikiki ~

Awalua",-~

~Ie~c;;J

, . ,

50 miles

FIGURE I. Map of the Hawaiian Islands, showing the location of collection sites of Hastuta inconstans.

Hastula inconstans (Hinds, 1844) is Indo­Pacific in distribution and is commonlyfound throughout the Hawaiian Islandswhere large populations of the species occuron surf-washed beaches characterized byfine, well-sorted sand, gentle slopes, and rol­ling breakers. I have never found the specieson coarse-sand beaches, nor on other fine­sand areas protected from wave action. Thelocations in which it is found generally ex­hibit open ocean conditions of salinity andtemperature throughout most of the year.

METHODOLOGY

Studies on the ecology and life history ofHastula inconstans were conducted betweenSeptember 1968 and July 1969. Observationson life history in the field and laboratorywere primarily concerned with locomotion,food and feeding, reproduction, develop­ment, growth, and predation. Animals wereobserved and collected from eight surfbeaches on the islands of Hawaii, Maui,Oahu, and Kauai using standard skin- and

scuba-diving gear. All study sites are indi­cated in Figure 1, but most studies weredone at Kealakekua, Wailea, and Poipu.

GENERAL MORPHOLOGY

The shell of Hastula inconstans is glossy,reaches a maximum length of approximately34 mm, and exhibits the flared aperture typ­ical of other hastulas. Shell color within apopulation is fairly uniform and often sim­ilar to the color of the sand beach habitat.Because of the wide range of beach colors inHawaii, color among populations from dif­ferent beaches is extremely variable, withindividuals shading from light tan throughpure black (Figur~ 2).

The animal has a large, fleshy foot, shorteyestalks, and a long siphon which is ex­tended to the sand surface when the snail isburied. One of the most characteristic fea­tures of Hastula inconstans and the otherHawaiian hastulas is the nature of the fore­gut and the distinctive behavioral patternsassociated with this type of feeding appa-

Biology of Hastula inconstans-MILLER 291

FIGURE 2. Variation in shell color among Has/uta incons/ans populations from different Hawaiian beaches: a,Waikiki, Oahu; b-e, Poipu, Kauai;f-h, Kealakekua, Hawaii; i-j, Awalua, Maui.

ratus. Termed a type IIA polyembolic pro­boscis (Miller 1970), its most distinctivefeature is a specialized poison apparatusuniquely suited for rapid prey capture.

LOCOMOTION

Both the morphology of the foot andgeneral locomotory behavior of hastulasdiffer markedly from animals of the genusTerebra. The foot of Hastula inconstans isvery fleshy and has a broad propodium. It iscapable of rapid contraction and maintains a

degree of flexibility not evidenced in otherterebrids living in less rigorous habitats.

Locomotory behavior was studied in thefield and laboratory using techniques de­scribed by Miller (1975). There are two basicmovements involved in locomotion: a for­ward gliding of the foot to a position an­terior to the shell, followed by cessation ofpropodial movements and contraction of thebody musculature to advance the shell andvisceral mass. I call one complete cycle astep. Compared with most other terebrids,locomotion in hastulas is very fast, averag­ing from 20 to 30 steps per minute. In

..

292

addition, hastulas exhibit a locomotory be­havior not seen in other genera of terebrids.First described as the "sail effect" byKornicker (1961), it permits the animal tomove rapidly up and down the beach byusing its broadly extended foot as a sail tocatch the waves.

Use of these locomotory behaviors is de­pendent upon both the size of the animaland severity of surf conditions. When thewaves are small or absent, the animal doesnot crawl on the sand surface, but ratherremains deeply buried, with the long ex­tensible siphon extending above the sandsurface. The animal tends to bury itself to adepth roughly equal to the length of its shell.

Calm conditions are rare on the beaches itinhabits, however, and waves of 1 m or morein height generally wash the shore. Underthese conditions several millimeters of sandare agitated with the passage of each swell,and the shells of small animals are thenuncovered. Following the passage of a wave,Hastula inconstans may exhibit one of threebehavioral patterns, presumably dependingon the presence or absence of prey in thevicinity: In the absence of prey, the snailimmediately burrows back into the sandbefore the passage of the next wave. If preyare detected, the snail may either begin rapidlocomotory behavior over the sand in theimmediate area, or exhibit the sail effect(described in detail below).

With stronger wave action, 5-10 mm ofsand may be overturned during the passageof each wave, and the smaller specimens ofHastula inconstans are completely dislodged.Under these severe conditions, reburrowingis not successful, and the small snails glideback and forth just beyond the surf zonewith the foot completely extended. Evenunder this extreme wave action, the largerspecimens are rarely completely dislodged.

Since sand trails are rapidly eradicated inthe field, it is impossible to determine thedistance or general direction an animalcrawls each day. Specimens of Hastulainconstans have been observed crawling atall hours of the day, but evidence to bepresented later indicates that the peak periodof feeding, and hence locomotion, takes

PACIFIC SCIENCE, Volume 33, July 1979

place during the night and early morninghours. This is consistent with data forspecies of Terebra (Miller 1975).

FOOD AND FEEDING

Introduction and Methods

Several references exist concerning foodand feeding in terebrids of the genusHastula. Hedgpeth (1953) suggests thatH. salleana may prey on the beachclam Donax, although this is not prob­able. Marcus and Marcus (1960) studiedH. cinerea on the beaches of Sao Paulofrom Ubatuba to Cananeia. Although theyhad no success in feeding the animals, setaein the gut suggested that the prey atUbatuba may be Nerine agilis.

Feeding in Hastula inconstans was ob­served in both the field and the laboratoryon several occasions throughout the studyperiod and on animals collected from surfbeaches on all the islands studied. Data onfood and feeding were gathered by twomethods. Gut analyses were performed onanimals collected by sieving in the surgezone just beyond the surf with a fine-meshbag. Samples were taken during three peri­ods, 7-10 AM, 2-4 PM, and 6-7 PM, todetermine the time of feeding, the number ofprey captured each day, and the percentageof the population feeding each day. Nightsamples were not taken due to the presenceof observed inshore shark and barracuda.Food preference studies were also conductedin the field on Kauai, Maui, and Hawaii.Approximately 1 m2 of sand in the surgezone at each study site was dug up andsieved through the fine-mesh bag. All thepolychaetes remaining in the bag wereplaced in a bucket of seawater containing50-100 freshly collected H. inconstans. Theanimals were allowed to feed for 5 min andthen 20 animals from each study area con­taining prey in their proboscises were drop­ped in 70 percent alcohol, which resulted inimmediate regurgitation. Prey were then re­turned to the laboratory for identification.

Details of the anatomy of the feedingapparatus were worked out through dissec-

Biology of Hastula inconstans-MILLER

10b1mm

Sa

6

4b

2b

293

FIGURE 3. Gross morphology of the anterior digestive system of Hastuta inconstans with the proboscis everted(exposed by cutting through the dorsal mantle and body wall): 1, labial tube; la, labial cavity; Ib, sphincter of thelabial tube; 2, buccal tube; 2b, longitudinal retractor muscles of the buccal tube; 3, buccal cavity; 4b, radular sac; 4d,radular tooth; 5a, poison bulb; 6, salivary gland; 8, cephalic hemocoel; lOb, postganglionic esophagus; 16, foot; 17,eyestalk; 18, siphon.

294 PACIFIC SCIENCE, Volume 33, July 1979

FIGURE 4. Dorsal view of the organs contained within the cephalic hemocoel of Hastula inconslans: 1f, innercircular muscles of the labial tube; 2a, outer circular muscles of the buccal tube; 2b, longitudinal retractor musclesof the buccal tube; 2d, inner circular muscles of the buccal tube; 2e, lumen of the buccal tube; 3, buccal cavity; 4b,radular sac; 4c, radular caecum; 4d, radular teeth; 5b, poison gland; 6, ducts of the salivary gland; 9, nerve ring; lOa,preganglionic esophagus; lOb, postganglionic esophagus.

Biology of Hastula inconstans-MILLER

tion of fresh specimens removed from theshell after quick freezing.

Gross Morphology of the Alimentary Tract

Figure 3 illustrates the foregut of Hastulainconstans with the proboscis everted. As isthe case for all terebrids with the type IIApolyembolic proboscis (Miller 1970), theprimary functional components utilized inprey capture in H. inconstans are a longeversible labial tube, terminating in an an­terior sphincter and containing a long re­tractile buccal tube that can be extendedbeyond the labial tube. The cephalic he­mocoel contains the longitudinal retractormuscles of the buccal tube and severalorgans that enter into the muscular buccalcavity (Figure 4). The radular sac and ra­dular caecum open into the buccal sac on theventral wall of the buccal cavity. A smallbipartite salivary gland overlies the pregan­glionic esophagus and opens through twoducts into the buccal sac on both sides of theradular caecum. The coiled poison glandleads from a large muscular poison bulblocated in the right half of the cephalichemocoel and enters the ventral wall of thebuccal cavity posterior to the opening of theradular apparatus. The short, thin-walledpreganglionic esophagus passes through thenerve ring and continues as a long postgan­glionic esophagus, tubular stomach, andslender intestine.

Diet and Feeding Behavior

Analyses of gut contents were made on 66specimens of Hastula inconstans collectedfrom Kealakekua Beach on Hawaii, andprey preference records were obtained for 60H. inconstans from Kauai, Maui, andHawaii. The results of gut analyses areshown in Table I. While there are severalspecies of polychaete worms living in thesurf beach habitats studied, both gut an­alysis and feeding preference records indicatethat H. inconstans in Hawaii feeds exclusive­lyon the spionid polychaete Dispio magna.This deposit feeder inhabits fine sand onmany of the surf beaches in Hawaii, utilizing

295

a pair of ciliated palps that stretch overthe substratum to gather food particles. Itlives buried in the sand to a depth of up to0.5 m in a burrow lined with a fragile mucoidsecretion and is generally found where thereis sufficient water agitation to keep thedetritus moving. Greatest abundance of theworm occurs in the surge and lower surfzone, and densities of 100-300 animals persquare meter are common on fine-sandbeaches such as Kealakekua on Hawaii,Wailea on Maui, and Poipu on Kauai.

As in other terebrids (Miller 1975), feedingappears to be initiated by distance chemore­ception. Observations in the laboratoryindicate that worm extract will elicit emer­gence from the sand, rapid propodial un­dulation, and limited swelling of the cephalichemocoel. Marcus and Marcus (1960) in­dicate that the anterior of the foot ofHastula cinerea is heavily innervated, prob­ably serving as an important sensory organ.This also appears to be true in H. inconstans,for under most conditions complete swellingof the cephalic hemocoel will not occur untilthe propodium of the foot comes into con­tact with pieces of prey or sections of theprey tube (Figure SA). When this occurs,relaxation of the retractor muscles, alongwith contraction of the circular muscles,leads to eversion of the labial tube andextension of the buccal tube through it. It isnot known how the radular tooth is movedinto position, but Smith (1967) is probablycorrect when he states that contraction ofradular sac muscles carries a tooth into thebuccal cavity, and peristalsis then moves thetooth to its normal functional position at thetip of the buccal tube. As the broad footsearches rapidly through the sand, the sphinc­ter of the labial tube remains in close contactwith the sand surface, and the radular toothheld by the extended buccal tube can be seendarting in and out. When the anterior end ofDispio magna is sensed by the propodium,the labial tube rapidly moves toward theworm and the buccal tube may extend to aconsiderable distance beyond the sphincter(Figure 5B). As the radular tooth comes intocontact with the worm, the poison bulbappears to contract, causing the entire body

296 PACIFIC SCIENCE, Volume 33, July 1979

FIGURE 5. The rapid ingestive phase of feeding behavior in Hastufa inconstans: A, feeding behavior is elicited bybringing a Dispio magna into contact with the propodium of the foot; B, after stimulation of the propodium, thelabial tube everts and the long buccal tube bearing the radular tooth searches for the prey; C, following impalement,the buccal tube rapidly retracts and the labial tube extends to engulf the prey; D, E, the labial tube retracts and thenextends a second time to further engulf the prey; F, when the labial tube inverts for the second time, the labial cavityis full and further ingestion occurs slowly.

Biology of Hastula inconstans-MILLER 297

298 PACIFIC SCIENCE, Volume 33, July 1979

TABLE I

ANALYSIS OF PREY CHOICE OF Hastula inconstans

POSITION OFNUMBER OF NUMBER OF PREY IN GUT MAXIMUMSPECIMENS SPECIMENS NUMBER OF

DATE EXAMINED COLLECTION SITE PREY WITH PREY Fore Hind PREY PER SNAIL

13 Oct. 1968 18 Kealakekua, Hawaii Dispio magna 4 I 318 Feb. 1969 48 Kealakekua, Hawaii Dispio magna 13 4 93 May 1969 20* Wailea, Maui Dispio magna 20 20I June 1969 20* Poipu, Kauai Dispio magna 20 20

18 June 1969 20* Kealakekua, Hawaii l)ispio magna 20 20

• Results of food preference test.

of the snail to lunge violently. On severaloccasions a milky substance could be seenflowing from the tip of the buccal tube. Thetooth is thus not fired at prey as reported byJaeckel (1952), but rather is used as Smithsuggests, merely to make an opening to ad­mit the discharged poison. As soon as thepoison has been injected, the labial tubebegins to engulf the worm and the buccaltube rapidly contracts to pull the worm in(Figure 5C, D, E).

Prey capture is a rapid process, and in thelaboratory a considerable portion of theworm may be completely engulfed in lessthan 1 min. Once the labial cavity is full,further rapid ingestion cannot occur and thesnail begins to crawl (Figure 5F). In thefield, the entire process of prey capture takesplace between the passage of successivewaves, and as soon as the poison has beeninjected, Hastula inconstans begins toburrow into the sand, entering nearlystraight down so that only the spire of theshell is exposed before the next wave passes.The snail continues to reburrow until theshell is completely covered and free fromwave disturbance. Feeding then continues ata slower rate until the worm is completelyingested.

No definite conclusions can be reachedconcerning the peak feeding period ofHastula inconstans. Animals will feed in thefield and laboratory any time they are pre­sented with prey, and they have been ob­served feeding throughout the early morninghours in the field. However, gut analyses of48 animals collected from Kealakekuashowed a higher percentage of prey in the

upper digestive tract at 10 AM (14 percent)than at 4 PM (5 percent). William Stewart, agraduate student at the University of Cali­fornia, Santa Barbara (1968, personal com­munication), found that H. cinerea, a surf­dwelling species from Florida, usually feedsat night on the spionid worm Nerine agiUs.

Ingestion and Digestion

Estimates on the duration of the inges­tive and digestive processes were. obtainedthrough gut analyses of animals fed in thelaboratory and dissected at intervals of 4-40hr after feeding and through observations onthe amount of time elapsed between inges­tion and defecation.

Evidence indicates that the entire feedingprocess in terebrids of the genus Hastula isof similar duration to that of species of thegenus Terebra (Miller 1975). Capture, im­mobilization, and initial ingestion of theprey are rapid, but once the labial cavity isfull, ingestion of the entire worm continuesat a considerably reduced rate for 5-10 hrafter capture. Digestion begins in the upperesophagus and prey remains are found in theintestine 18-24 hr after ingestion begins.Feces in the form of setae and sand arevoided considerably later, usually not ap­pearing in the rectum until 2 days after preycapture.

Use of the "Sail Effect" as a Method ofPrey Capture

Hastula inconstans and other surf-dwellinghastulas differ from other terebrids in their

Biology of Hastula inconstans-MILLER

response to water agitation. As has beenshown for certain bivalves (Reese 1964),hastulas kept in a container of still watershow little or no movement. However, uponagitation of the water, the foot immediatelyextends and rapid propodial activity begins,a factor that may be of importance in thefeeding response.

Initiation of feeding in Hastufa inconstansappears to be partially dependent on thepresence and intensity of beach surge. Onthe rare occasions when wave action on thebeach is reduced or absent entirely, no has­tulas are seen crawling, and it is probablethat little feeding takes place under suchconditions. During periods of moderatesurge action, sand agitation is sufficientlystrong to expose partially both the prey andthe hastulas and the latter begin searchingmovements with their propodia while theybury back into the sand.

One of the most curious phenomena as­sociated with locomotion and feeding in thehastulas is the so-called "sail effect" firstreported by Kornicker (1961) for Hastufasalleana along the Gulf of Mexico. He claimsthat the foot of H. salleana is used not onlyto plough through the sand, but also as a sailto enable an animal to move into deeperwater when it is about to be stranded abovethe swash zone of a falling tide. Assumingthat H. salleana is indeed exposed as the tiderecedes, this is a reasonable explanation.

The sail effect is also very obvious inHastufa inconstans, a species that lives wellbelow the swash zone where danger fromstranding presents no problem. In thisspecies, the sail effect appears to serve as abehavioral adaptation for feeding by enab­ling an animal to move from one part of thebeach to another with great rapidity. I wasfirst made aware of this while taking bottomsamples in the surge zone, when large num­bers of H. inconstans tended to concentratein the area from which the sample had beenremoved. By digging successive core samplesfrom the sand in the same area and thenobserving this disturbed area during thepassage of several waves, it soon becameapparent that the animals are initially attrac­ted to prey by distance chemoreception andthen moved into the area of disturbance by

299

use of the sail effect, as diagramed in Figure6. This rapid feeding behavior consists of thefollowing sequence of events. As an incom­ing wave passes over the bottom where sandhas been disturbed, fragments of spionidworms and their tubes are carried shore­ward. As the water containing these frag­ments passes over the buried hastulas, theysense the prey, crawl to the surface, flip ontheir side as described by Kornicker (1961),and are carried seaward in the backwash.When the disturbed area is reached, thepropodium digs in and the animal flips over.Propodial searching movements immediatelybegin, the labial tube rapidly everts, andwhen a worm is located, feeding ensuesbefore passage of the next incoming wave.

Feeding Rates

Studies on feeding rates were done onanimals collected at Kealakekua Beach fromOctober 1968 to June 1969. Of 66 animalsdissected for gut analyses, nine containeddigested or partially digested remains ofDispio magna in the esophagus and stomachand nine contained setae and sand grains inthe rectum. Since it takes longer than 24 hrfor prey to pass through the digestive tractinto the rectum, the first group representsthose animals which had fed less than 24 hrbefore collection time, and the second grouprepresents those that had fed the previousday. This would suggest an approximatefeeding rate of 14 percent per day for theentire population, a figure that is compara­ble to the 17 percent feeding rate found forthe entire Terebra gouldi population at Ahuo Laka Island (Miller 1975).

Obviously, this rate cannot be constantthroughout the year, for there are timesduring the winter months when wave actionwould be too intense for successful preycapture. Indeed, specimens are difficult tolocate under extreme surf conditions and it isprobable that many migrate into deeper,calmer waters, although it has been im­possible to make meaningful collections inthese areas during winter storms. Since theprey species maintains greatest density in theshallow surge zone, feeding in the Hastufa

300 PACIFIC SCIENCE, Volume 33, July 1979

(

B

c

E

F

FIGURE 6. Sequence of movements of Hastula inconstans exhibiting the sail effect: A, Hastula inconstans buried inthe sand as an incoming wave passes; B, the snail rapidly crawls to the sand surface; C, the apex of the shell is raisedat slack wave and thrown to one side; D, using the foot as a sail, the animal is carried seaward by the outgoingwave; E, the propodium digs into the sand and the snail rights itself; F, searching for prey commences at slack waterbefore the passage of the next incoming wave.

Biology of Hastula inconstans~MILLER

population presumably slows down duringtimes when migration occurs.

As is the case for Terebra gouldi, indi­vidual feeding rates appear to be low.Because of the relatively long time involvedin prey ingestion, it is probable that no morethan one prey specimen is eaten per day. Gutanalyses failed to show more than one preyspecimen in the guts of animals collected inthe field, and under no circumstances didany animal feed on more than one preyspecimen per day in the laboratory. Basedon an approximate feeding rate of 14 per­cent per day for the Kealakekua population,it would appear that an individual mayaverage one prey per week.

REPRODUCTION AND EGG CAPSULES

Mating

Mating in terebrids of the genus Hastula,particularly those species inhabiting surf­swept beaches, differs in several respects fromspecies of Terebra living in less rigorousenvironments. While males of T. gouldi andprobably most other terebrids living incalmer areas follow a mucous trail laid downby the female (Miller 1975), this is not prob­able in the case of surf-dwelling hastulas, forthe mucous trail would be quickly erasedwith the passage of each successive wave.Hastula inconstans lives in relatively highdensities on most beaches, and while there isno evidence to indicate the mechanism ofsexual attraction, it is possible that matingresults· from random contact of sexuallyready males and females.

The mating process also differs distinctlyfrom that of Terebra gouldi, in which matingoccurs while the animals are buried in thesand. In all situations in which mating wasobserved in the field, the mating pairs werefound in the surge zone, coupled togetherand rolling freely back and forth with eachwave. The animals remained tightly claspedtogether, and unlike the response in T.gouldi, did not separate when they weredisturbed. Duration of copulation is notknown.

Nothing is known on the length of the

301

mating season or the time of juvenile set­tling. Individuals were found mating everytime the habitat was visited.

Egg Capsules

Egg capsule deposition differs significantlyfrom the process observed in Terebra gouldi(Miller 1975). Since Hastula inconstans livesand mates on beaches of moderate waveaction and well-sorted, very fine sand, per­manently affixed egg capsules are notpossible. However, just beyond the actualzone where surf breaks is a region of surgecontaining beach litter and small bits ofbasalt rock. This material is on the surfaceof the finer sand and rolls back and forthwith the passage of each wave. Hastulainconstans appear to utilize the small round­ed bits of basalt, which are generally 1-2mm in diameter, as bases for egg capsuledeposition. It is not known whether thedeposition is accomplished with the femaleexposed to the surface and grasping thesmall basalt grains or below the surface ofthe sand where she contacts a piece of buriedbasalt. However, all the egg capsules re­corded in the field were found from surfacesieving in the litter zone with the use of thefine-mesh bag previously described.

As shown in Figure 7, the egg capsules areof approximately the same size as the basaltgranules and form a caplike covering overthem. Each capsule contains approximately40 spherical eggs, 100 J.lm in diameter.Development beyond this stage has not beenobserved. Both the small size of the pro­toconch and the variability in shell colorand sculpture among populations frombeaches in the Hawaiian Islands and fromother Indo-Pacific areas would indicate thatthe planktonic stage is either greatly reducedor absent entirely (1. B. Taylor 1968, per­sonal communication). If this is true, someof the eggs in the capsule may serve as nursecells.

GROWTH

Direct observations of growth in toxog­lossans have been difficult to obtain, prim-

302 PACIFIC SCIENCE, Volume 33, July 1979

FIGURE 7. Egg capsule of Hastula inconstans containing uncleaved ova. The capsule is attached to a smallgranule of basalt.

i\ikl) &M¥¥i&fM$iM1t t!M\¥liHM1U - $ilJ!M£ :@MJ1Ji.iM!" i i@..;. ,""&Will

Biology of Hastula inconstans-MILLER 303

FIGURE 8. Length-frequency distribution of juvenileHastula inconstans from Kealakekua Bay, Hawaii,October 1968-June 1969.

arily because the specialized feeding habitsdo not permit normal survival in the labo­ratory and because tagged specimens re­leased in the field can rarely be recovered.No published data on growth exist for theturrids, but Kohn (1959) has made briefobservations on the postlarval developmentof Conus pennaceous and Miller (1975) de­termined growth rates for Terebra gouldi.

Because of the unique feeding style andspecialized habitat of Hastula inconstans, theonly conclusive data on growth rates wereobtained through periodic collecting andmeasuring of the first- and second-yearclasses. To gather large numbers of smallspecimens effectively under rather turbulentconditions, a 1.0-mm-mesh nylon bag wasattached to a metal scoop and pulledthrough the top centimeter of sand between

SHELL LENGTH(mm.)

passage of successive breakers. The sand wasquickly washed from the bag by wave tur­bulence and sampling was continued untilapproximately 400 small individuals weregathered. Collections using this techniquewere conducted at Napoopoo Beach inKealakekua Bay in October 1968 andFebruary and June 1969. Shell lengths weremeasured to the nearest millimeter with avernier caliper and animals were returned tothe beach after each measurement. The re­sults are shown in Figure 8.

The individuals collected in October withan average shell length of 7.4 mm probablyrepresent the 1968 year class. By February1969 the average shell length of this classhad increased to 9.3 mm, representing anaverage growth rate of 0.47 mm per month.Between February and June 1969 theaverage shell length increased to 12.4 mm,for an average growth rate of 0.80 mm permonth. The faster growth rate betweenFebruary and June may result from reducedsurf activity at Kealakekua when the weath­er changes from southwest winter stormsand high surf to summer dry trade con­ditions characterized by low to moderatesurf.

It was not possible to determine the timeof juvenile settling, since metamorphosisoccurs when the protoconch is less than1 mm in length (Taylor 1975) and the meshwould not retain individuals this small with­out also retaining large quantities of sand.However, since individuals collected inOctober with an average shell length of 7.4mm appear to represent the 1968 year class,and assuming that the growth rate is ap­proximately 0.8 mm per month throughoutthe summer, the larvae probably beganmetamorphosing in late spring. This isreinforced by data from the June collection,which shows the 1969 year class beginning toappear in the 3.0-5.0 mm range.

Adults reach a maximum length of 34mm, but few individuals longer than 29 mmwere found. If the growth rate of between0.5 and 0.8 mm per month is fairly constantthroughout the life-span of the species, andif growth does not significantly plateau,maximum age would be between 3 and 4years.

20 October

18 June

;(=12.4

X=::9.3 18 February

X=7.4

100

50

50

100

a: 100....III

~

::> 50Z

FIGURE 9. Hawaiian species of HaSlula with the type rIA polyembolic proboscis (O.75x): A, H. inconslans (Hinds, 1844); B, H. sirigiiaia (Linnaeus, 1758); C; H.penicillala (Hinds, 1844); D, H. heclica (Linnaeus, 1758); E, H. laula (Pease, 1869); F, H. solida (Deshayes, 1857); G, H. albula (Menke, 1843).

wo~

;en-"IjnCIln

~!T1<oa­S(1)

ww....I::::

<Z-'0-.l'0

Biology of Hastula inconstans-MILLER

PREDATION

The effects of predation on Hastula incon­stans are difficult to assess. Few empty shellshave been found washed on the beach andthose that have been found exhibit no ob­vious evidence of predation. However, somemechanism causes a significant decline inabundance between the first- and second­year classes. Two possibilities exist to ex­plain this observed reduction. During mostof the summer and fall tradewinds blowconsistently from the northeast and waveaction on the leeward surf beach is slight.With a shift in wind direction during thewinter months, waves increase in height andthe s.urf often becomes extremely heavy,even m the usually placid bays. At this timehastulas smaller than I cm in length areusually unable to remain buried in the sand'they are dislodged and tend to glide backand forth over the surface of the sand witheach passing wave. It is possible that as waveintensity increases, large numbers of thesesmall individuals could be carried into thesurf zone and eventually cast high on thebeaches.

Another possibility is that predation mayact on the young during this time. Smallani~als dislodged from the sand keep theirwhite foot fully extended, presenting a sharpcontrast to the generally darker sand. Thecrustacean Portunus sanquinolentus is abund­ant on the beach, as is a small species offlounder, Platophys pantherius. Both of theseanimals frequent the surge zone and couldquite easily prey on the small hastulas whenthey are exposed. Gut analyses were notdone, however, to determine the feedinghabits of these species.

DISCUSSION

In addition to Hastula inconstans, I havefound four other species of Hastula with thetype IIA polyembolic proboscis commonlyliving on surf-washed beaches and threespecies living in deeper water (Figure 9).They all have a small shining shell with fewwhorls and a wide aperture. All species arenearly identical in internal morphology, with

305

a long slender buccal tube and a well­developed radular apparatus.

I have studied in detail only those speciesliving on surf beaches. They all have a broadfleshy foot, crawl and bury rapidly, andshow striking similarities in the method offeeding and choice of prey. Gut analyseswere performed on three surf species in ad­dition to Hastula inconstans and all specieswere found to feed on spionid polychaetes.Both H. hectica (Linnaeus, 1758) and H.strigilata (Linnaeus, 1758) feed on Nerinidessp., although they live in different zones ofthe beach. Hastula penicillata (Hinds, 1844)feeds on an unidentified spionid.

Spionids apparently are the preferred foodof other species of Hastula as well. Marcusand Marcus (1960) found the remains ofNerinides agilis in the gut contents of H.cinerea at Ubatuba, Brazil, and Stewart(1967, personal communication) found thesame species of worm in the guts of H.salleana from Florida.

It is too early to speculate on the taxo­nomic re.lationship of hastulas with the typeIIA feedmg apparatus. It is probable, how­ever, that species of this feeding type haveevolved from one ancestral stock and arespecialized to exploit the large numbers oftube-dwelling polychaetes occurring through­out the tropics. The study of more speciesshould make it possible to determine thediagnostic significance of this feeding type ina classification of the family. I suspect thatall species with the type IIA proboscis willprove to have similar feeding habits.Similarity in feeding habits and obvious sim­ilarities in the morphology of the shell andfeeding apparatus may serve to confirm theplacement of type IIA series in the genusHastula as proposed by H. and A. Adams in1858.

ACKNOWLEDGMENTS

I would like to thank Ruth TurnerMuseum of Comparative Zoology, HarvardUniversity, and Robert Croker, ZoologyDepartment, University of New Hampshire,for their critical advice and generous assist-

306

ance throughout the duration of this study.Special thanks go to my wife, Elsilyn Miller,for her continued support in all aspects ofthe study.

LITERATURE CITED

HEDGPETH, J. 1953. Zoogeography of theGulf of Mexico. Pub!. Inst. Mar. Sci.,Univ. Texas 3: 107-224.

JAECKEL, S. 1952. Uber Vergiftungen durchConus Arten (Gastr. Proc.) mit einenBeitrag zur Morphologie und Physiologieihres Giftapparates. Zoo!' Anz. 149:206-216.

KOHN, A. J. 1959. The ecology of Conus inHawaii. Eco!. Monogr. 29 :47-90.

KORNICKER, L. S. 1961. Tidal responses ofTerebra salleana. Ecology 42: 207.

MARCUS, E., and E. MARCUS. 1960. On

PACIFIC SCIENCE, Volume 33, July 1979

Hastula cinerea. Bo!. Fac. Filos. Cienc.Letr., Sao Paulo (Zoo!.) 23 :25-66.

MILLER, B. A. 1970. Studies on the biologyof Indo-Pacific Terebridae. Ph.D. Thesis.University of New Hampshire, Durham.213 pp.

---. 1975. The biology of Terebra gouldiDeshayes, 1859, and a discussion of lifehistory similarities among other terebridsof similar proboscis type. Pac. Sci.29: 227-241.

REESE, E. S. 1964. Ethology and marinezoology. Oceanogr. Mar. BioI. Ann. Rev.455-488.

SMITH, E. H. 1967. The proboscis and oeso­phagus of some British turrids. Trans. R.Soc. Edinburgh 67: 1-22.

TAYLOR, J. B. 1975. Planktonic prosobranchVeligers of Kaneohe Bay. Ph.D. Thesis.University of Hawaii, Honolulu. 593 pp.