J. Phycol. 5, 140-149 (1969)

T H E “HYSTRICHOSPHAERID” RESTING SPORE OF T H E DINOFLAGELLATE PYRODINIUM BAHAMENSE, PLATE, 19061.2

David Wall and Barrie Dule Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543

SUMMARY

Germination experiments demonstrate that the “hystrichosphere” called Hemicystodinium zoharyi, which previously has been found only as a microfossil organism, is the resting spore stage in the life history of Pyrodinium bahamense, a modern bioluminescent, thecate dinoflagellate. T h e morphology of this spore, together with new details of the thecal structure and ontogeny of P. bahamense, is described, and it is con- cluded that Pyrodinium is closely related to Gonyau- lax but worthy of retention as a discrete genus. T h e geological history of P. bahamense is traceable to the Eocene through fossil occurrences of its spore, and i t is suggested that additional pyrodinioid dinoflagel- lates which now are extinct were represented in Lower Tertiary seas by another hystrichosphere genus, called Homotryblium. Selected aspects of the physiology and ecology of modern dinoflagellate resting spores are discussed briefly with special reference to Pyro- dinium.

INTRODUCTION

Recent investigations (9,10,25-27) have shown that numerous thecate dinoflagellates belonging to the gen- era Gonyaulax, Protoceratium, Peridinium, Scripp- siella, Diplopsalis, Diplopsalopsis, and Diplopeltopsis (Order Peridiniales) produce morphologically distinc- tive resting spores during their life histories. Study of these spores promises to provide important infor- mation which can contribute toward an improved understanding of contemporary dinoflagellate syste- matics, ecology, and physiology for the phycologist. These dinoflagellate resting spores also are of partic- ular interest to paleontologists because such spores are identical or homologous with certain microfos- sils known as hystrichospheres and fossil dinoflagel- lates (9,20,25,26) which have a prolific fossil record reported in a voluminous literature (4). This investi- gation demonstrates that one hystrichosphere, Hemi- cystodinium zoharyi (Rossignol) Wall, is the resting spore of a modern bioluminescent dinoflagellate, Pyrodinium bahamense Plate and discusses some of the systematic and evolutionary implications arising from this correlation.

1 Received November 20, 1968; revised January 2,1969. 2 Contribution N o . 2245 from the Woods Hole Oceanographic

Institution.

Pyrodinium bahamense was described originally by Plate (17) from Waterloo Lake near Nassau in the Bahamas and additional illustrated comments were appended many years later by Tafall (23) and Marga- lef (15,16). Lindemann (13) allocated Pyrodinium to the family Gonyaulacaceae. The species P. baha- mense is best known for its bioluminescence in the tropical waters of the Bahamas, Persian Gulf ( I ) , coastal waters of the eastern Pacific ( 2 3 , and particu- larly in southern Puerto Rico (15,16) at Phosphores- cent Bay.

The hystrichosphere Hemicystodinium zoharyi was recorded originally as a microfossil in Early Pleisto- cene marine sediments in southern Israel (18,19) as Hystrichosphaeridium zoharyi Rossignol and subse- quently given its current paleontological generic assignment when it was found in deep-sea cores from the Caribbean Sea (24). Living specimens are re- ported here for the first time.

MATERIALS AND METHODS

Bottom sediment samples containing viable resting spores were collected from shallow water marine environments in Smiths Sound (St. Georges Island), Bermuda, in February, 1968 and from a series of bays including Bahia Fosforescente and Bahia de Jobos in southern Puerto Rico and Isla de Vieques during April, 1968. The samples from Bermuda were kept at temperatures close to those encountered during collection (15.5 C) and immersed in bottom seawater from the collection site until the spores were incubated a t Woods Hole in March and April, 1968. Samples from Puerto Rico and Isla de Vieques were collected from warm waters (ca. 26 C) and also maintained in bottom seawater from the site of collection at approximately the same temperature.

Individual spores were isolated by micropipette and placed in a small amount of medium suspended inside a Palmer-Maloney nannoplankton counting cell (25) after the sediment sample had been cleaned by a short sonification treatment and sieved through a 37 p mesh screen. Details of this technique have been described elsewhere (2297). Specimens from Bermuda were placed in an incubator a t 26 C and those from Puerto Rico and environs at 27 C to induce germination. During incubation the spores received a 14-hr light/lO-hr dark cycle with cool white fluorescent light at intensities of 5000-8000 lux.

Plankton hauls containing dense populations of Pyrodinizirn baliamense were collected in early April, 1968 from Phosphores- cent Bay, Puerto Rico, and Ensenada Honda, Isla de Vieques. Cultured specimens of the species for comparison kindly were supplied by Mr. William H. Biggley of Johns Hopkins Univer- sity, Baltimore.

140

P Y K O D I N l l l h l KESTINC; SPORE5 141

TABLE I . SynoPs~s of germination data f o r Pyrodinium ha- hamense sfmres from Ilennuda (Fehnmry, 1968) incubated at

26 C.

Commencement Spores Spores Thecae Days token of incubation incubated geminated c,btained to excyst

March 13 7 0 N o germination No germination 1 11-13

March 14 7 0 March 15 3 March 16 7 4 3 10-15 March 17 1 1 1 0 15 R.larc11 18 4 0 N o geriiiiriation March 19 13 2 2 12 March 2F 10 7 5 f i March 27 ti 4 10 2-4 March 29 4 4 8 < 4 April 3 6 6 I 2-4

__- - ____ - _ ~ _ _ _ _ ~ ~ ~ ~

_ _

r

- - _- Total 82 31 40

-

RESULTS

Eighty-six resting spores (82 from Bermuda) were inc.ubated between March 13 and April 22, 1968 and 35 germinated. The spores that germinated eventu- ally produced around 46 dinoflagellate thecae wliicli were identified as P y r o d i n i u ~ ~ bnhamense b y com- parison with descriptions in literature and reference to naturally occurring populations and cultured specimens. Of tlie spores from Bermuda, tlie 14 placed into incubation a t 26 C on 13 and 14 March failed to germinate, but 10 oiit of 42 spores subjected to the same treatment between 15 antl 19 March germinated after 10-1 5 tlays of incubation. Finally, 21 oiit of 26 spores wliicli were incubated in t.lie period March 26 to April 7 germinated after 2-6 clays of incubation under the same conditions (Table 1). Four spores from southern Puerto Kico were incubated ( 3 from Rahia de Jobos and 1 from Phos- phorescent Bay) at 27 C. These all excysted after 2-5 days and eventually produced 6 thecae as a few cells underwent ecdysis to form more than 1 tlieca between April 12 and 22.

?’lie protoplasts liberated at excystment formed either motile cells which secreted tliecae, or n01111io- tile, spherical to ovoid amehoitl cells (Fig. 1) called h ypnoitls (7,26). Some hypnoids secondarily gave rise to motile, tliecate individuals, but others formed only a series of hypnoids without cell division simply by shedding tlie periplast antl leaving a trail of these delicate membranes beliind as the protoplast mi- grated very slowly by ameboid movement across the incubation chamber (Fig. 1). Protoplasts which be- came thecate cells passed tlirougli typical avalvate, prevalvatc, and valvate stages of dinoflagellate devel- opment (14). Many tliecate cells underwent ecdysis (Fig. 2) and shed their original tlieca a r i d a n inner membrane (Fig. 20) hefore secreting a new tlieca. Cell tlivisiori was not observed directly and was a rare event. Approximately 10 Iir were required for the

FIG. 1. Resting spore of Pyrodiniwn baiictmrnse germinating to produce a serics of empty prriplasts arid a Iiypnoidal cell. X 127.

.Ithecatc stage next to i ts abandoncd cmpiy theca shortly aftcr ecdysis. X 419.

FIG. 2.

development of a tliecate (valvate) individual from a newly excysted protoplast.

DESCKII’TIONS

The resting spore of Pyrodiiiizo)z bahnrnense (Fig. 3-10, 33) is spherical, unicellular, and possesses approximately 60 radiating, more or less randomly arranged, intratabnlar (5) spines. Specitnens from Bermuda, Puerto Rico, and Isla de Vieques hat1 diameters from 43 to 55 p excluding their spines, which were from 6 to 12 ru. long Ixrt constant for each specimen. ‘I’lic spore wall is transparent, almost colorless with a microgranular outer surface and a smooth inner surface. Its chemical composition is unknown, but it is able to witlistand treatments such as acetolysis which destroy cellulose thecae but are commonly used in palynology (9,lO). Wall thickness varies from less than 1 to 3 p. The spines are predom- inantly simple, circular in cross section, narrow and tubular, and have closed, slightly enlarged capitate tips which sometimes are lobed asymmetrically. Mi- crogranules ornament some spines. Smaller niini bers of the spines are bifurcate distally and sometimes sev- eral spine bases are fused.

The cell contents comprised microgranular cyto- plasm enclosing a small but conspicuous red eyespot (10-1 5 p) and nunierous starch grains which clustered together around the nucleus antl obscured it (Fig. 3). The appearance of the cell content-s varied; in freshly collected sporea from Bermuda there was little color and large areas of pale cytoplasm, but a few tlays prior to germination t.he cells became green as chromato-

142 D A V I D WALL A N D B A R R I E DALE

phores developed and there was a general dispersion of the organelles toward tlie periphery of tlie cell lumen. Contraction of the protoplasm from the spore wall occiirretl too a t this time and then a thin rricni- brane surrounding tlie protoplast was discernillle.

The spores ruptiirecl in a very cliaracteristic man- ner at germination to lorin a complex excystinent aperture called an arclieopyle (Fig. 4, 5, 33) of tlie combination type designated 2 A + W by Evitt (8). The upper liemisphere or epitract (5) of tlie spore was separated b y a suture from tlie lower hemisphere or hypotract (5) and cingiilar area. The epitract itself was divided by sutures into 8 polygonal units or opercular pieces (8) whose shapes and mutual config- uration corresponded very precisely with tlie arrange- ment of tlic epithecal plates of the tlieca of the motile stage (Fig. 33) ; thu5 they have been referred to as plate-equivalents (8). They included tlie plate-ecluiv- alents of 6 precingular plates, the first apical plate and a compound operciilar piece which represented plate-equivalents of apical plates 2’, 3’, 4’ a n d tlie apical closing pore plate, all joined together but. whose shapes were outlined by unopened sutural traces. The positions in wliicli conspicuous gapes developed in geririinated spores varied arid some vari- ations of this are shown in Fig. 33. However a11 the spore epitracts dissociated into the same 8 opercular pieces with subsequent inanipulatiori (Fig. 33E) . A prominent notch in tlie epitract and a corresponding

tral position (Fig. 5); this projection is tlie plate- equivalent oT tlie anterior siilcal platelet of the tlieca (Fig. 34C).

The avalvate stage (“gyninodinioid stage”) which clevclopecl iriirnediately following escystnierit (Fig. 11, 12) was ovoid arid eloilgated (ca. <56 p long am1 46 /J.

wide) witli a round anterior a n t l weakly indcritecl posterior. T h e tranwersc furrow was weakly tlevel- oped antl visible riiairily as a notch in the proEile wliilc tlie longiludinal sulcuc was yeen as a depression in tlie posterior end; enrh iurrow contained a long flagelluiri. Tlic cell wall w a s \;cry tliiti, transparent, arid witliorit thecal plates. TIE cell contents iricluded niiirieroiis granular green clironiatophores with a weakly 1-aclial arrangement, a small red eyespot, and an eqtratorially situated nucleus. There was a paler zone differentiated benea t l i the: cirigiiltiin. 71-his phase persisted lor approxiiiiately SO niin alter excystiiient.

l ’he Ixevalvate stage (Fig. 13) liatl a pointed ante- rior a n d a thin tlieca ant1 evidcricecl the earliest stage o f plate formation which occurred within 12 lir of cxcystnicnt. It s~7aiu with 21 rapitl spiral motion and differed only in tlie density of its cell wall froin the val~ii te stage into which it developed. The motile tliIioflagell~ttes ~ I i i c l i were produced in the labora- tory from spore geriiiinations seltloiii siirvivcd for inore t h a n 2 c lays antl were jiivenile valvate s~ages. Tliey sliowctl wine significant iiiorpliological fea-

projection on t.lie hypotract tleveloped in tlie riiidven- tiires more clearly t l i ; i i i (lid the thicker walled speci- _. .~ -

t

FIG. 3-29. Stages in the life histoi-) of Pprodini7r~ti bcrlini)ietisc. FIG. 3. Resting spore with protoplasmic ronteiits including pig- mented eyespot and starch granules, Bermuda. X 375. FIG. 4. CcerIniriatcd empty resting spore showing mode of dclriscence, C889, Rermuda. X 373. FIG. 5. Dissociated resting spore hylmtmct showing ventral sulcal projection, surface sediment lrom Smiths Sound. Bermuda. X 375. FIG. 6, 7. Fossil resting spore hylwtract (NerJi i todinii(j j t ioharyi) from a deep-sea core i n thc Yucatan Basin, Caribbean Core 4254330 at 600 cm. X 333. PIC. 8. G I C J U ~ of op ular pieces from a resting spore epitract reliiescnting tlic plate cquivalents of thecal apical plates 1’4’. C883. X 720. 1 ; ~ 9. C;Iou]> of olierci~lar pieces isolated from surface sediment in Smiths Sound, Rcrmutla, plate equivalents 2‘4’. X 794. FIG. 10. (;roil13 of olxwiilat pirccs (2’4’) isdatrd from an Eorcnc marinr sediment (London Clay) near Southampton containing He,,iicTSlotiiiiiii,,i z o / / u i , y i . X 971. E’ic,. 11. .ivalvate stage, C8S6. X 418. FIG. 12. ;\valvate stage, C870. X 478. FIG. 13. Prtwdvate stage with pointcd anterior, C888. X 353. FIG. 14. Apical view of juvenile cpitlieca, C892. X 490. FIG. 1.5. Antapical view of juvenile hypothcca. W66. X 552. Fic:. 16. Ventral view of dissociated juvenile h)potheca showing the small first postcingular plate (I”’), C885. X 500. FIG. 17. Ventral view o f jiivenile theca in the inidveritral l~osition witli a wcll- developcd first postcingular plate bearing 2 pores, CX91. X 867. FIG. 18. Ol,liqiic ventral vicw ot jnvenilc thcca split anterior to the cingulum with typically low sutural crests clearly defiriirig tlie plate lxittern, ( :XX i . X 549. FIG. 19. Juwnile tltcca in lateroventral view showing the small antapical spine developed at this stage, C889. X 549. FIG. 20. Jiivcnile tlicca alter ecti)sis antl loss of the pro- toplast but retaining a delicate internal membrane, (;8(j6. X 392. Frc:. 21. ..\ialvatc stage after release from ;i tlirca by ccdysis, C884. X 441. FIG. 22. Avalvate protoplast emerging from within 21 delicate mcnil~i-ane to i.estore the motile phase after cctl!sis. C884. X 437. FIG. 23. Group of dissociated thecal iilates from a jiivenilc valvatc stagc; from lcft to right tlrrse arc thr right ;+nd left snlcal plate- lets, the posterior sulcal plate. and tlic sixth posicingular iilnte, CX9L‘. X 500. 1 ; ~ . 21. Group o f tltecal plates from a juvenile thccate stage including the posterior sulcdl plate, the 13osterior intei-calary platc, and 2 sitlcal {)latclets. C88X. X 460. FK;. 2.7. Mature thccatr individual from a l>lanktnn haul in E,nsenada Honda, Isla de Vicques. showing Iironiinent apical and antapical sl>ines, cinguliir lists, and rlcvated apex. X 371. FIL. 26. Mature epithrra in apical vicw, Phosphnrrsccnt Ray, Pnerto Rico. X 464. Fic:. 27. Mature hypo- thera in antapical view, Phosphorescent Bay-, Puerto Rim. X 37.5. FIL. 28. Mature Iiyliotheca in ventral vicw, Pliosphoi-csccnt Kay. X 460. Fic . 29. Group of plates from a mature valvatc intlividnal including the large microgranular, pmrtc second postcingular- plate and a much reduced first postcingular, the anterior sulcal platelet, arid ii cingitlar plate. X 855. kit. 30, 31 . Hoi~zotl).bii~c~ri tenirispi- ~ O S U ? ~ from the E C J C ~ I I ~ Loridon <:la! of Erigland. Tic;. 10. HJpotract witli tulmlar processes. Meti-opolitan Water Rnatd Rorrliolc No. 11 at 53 f t depth. Enhorne Vallt’y, &Tkshire. X 358. FIG. 31. GIonp of opercular pieces from the baiiie locality antl horizon. Apical plate equivalents 1’-4’ and lirecingular equivaleiits 1” antl 2” includcrl. X 185. Fif;. 32. Similar group of plate eqni\,alents from 1.ondon Clay at Rinfirld Pit, Bracknell, Bcrkshire. Apical plate eqi~ivalcr~ts 2 ’ 4 ’ ~11e attached together. plate equivalent 1’ is in position but separate om the larger. piece 1)) a ~ i i t i i i~e , X 725.

< _ _ , . 1 . * , . . . . . . . . ., ...- ...,. 1. - . I ’

144 DAVID WALL AND BARRIE DALE

-_--- . I - . , b‘\, I \ \

’ _ _ _ I

-4 I 1

I I , I

‘\ ..... /

I ,- - /’ , B

L

FIG. 33. Diagrams to show position and nature of sutures dc- veloped upon germination of resting spores in the epitract of P. bahamense. A-D: Spores from Bermuda germinated in incuba- tion chambers. Solid black lines represent open siitures, broken lines represent closed sutures which open upon dissection, dotted lines represent sutural grooves which open with diffi- culty only. X ca. 625. E: Diagram to show the 8 opercular pieces and the plate equivalence of the epitract upon its dissoci- ation. X ca. 625.

mens in plankton hauls from Phosphorescent Bay and Isla de Vieques.

The juvenile valvate stages of specimens from Bermuda (Fig. 14-20, 23, 24) measured from 43 to GO in diameter and the crests bordering their epithecal and hypotliecal plates were low (2-3 p). The length of the antapical spine, arising at a corner of the antapical plate, did not exceed 5 at this stage (Fig. 19) and apical spines were absent or minute. The tabulation was well developed with the formula 4’,Oa,6”,6c,6”’,1p,l”” + 5 sulcal plate- lets (Fig. 34). The presence of G postcingular plates rather than 5 as previously reported (17,Zf) was seen clearly in the juvenile thecae. The first postcingular plate was a small rectangular plate (Fig. 16, 1‘7) which occupied the equivalent position as plate 1”’ does in Gonynulax. There were probably 5 sulcal platelets, 2

f lagel lar pore first postcinqular

left suIcaI

anterior sulcol

right accessory sulcol

right SUICOI

FIG. 34. Tabulation schemes for Pyrodinium bahamense. A: Juvenile epitheca from specimen obtained from a spore, X 723. I?: Juvenile hypotheca from specimen obtained from a spore, X i23. C : Sulcal region of specimen obtained from a spore, X 813. D: Mature epitheca from plankton in Phosphorescent Bay, X 563. E: Mature hypotheca from plankton in Phos- phorescent Bay, X 563.

of which were thicker than the remainder and porate, namely, the anterior sulcal platelet and the posterior sulcal platelet (Fig. 34C). The former was subtrian- gular with a prominent posterior indentation which marked the anterior margin of the flagellar pore and an anterior border which projected into the epitheca to meet the first apical plate: it was surrounded laterally by plates I”, l c (left) and 6” (right) and posteriorly by plate 1”’ and the small right accessory plate which occurred between the right extremity of the girdle and the flagellar pore. The large posterior sulcal platelet lay slightly toward the right ventral area of the hypotheca and its V-shaped posterior margin extended completely across the hypotheca to touch postcingular plate 5”’ to the right and one facet of the antapical plate to the left; it tapered anteriorly toward the cingulum and its anterior mar- gin had 2 small prongs. Specimens from Puerto Rico and Isla de Vieques, whether they were germinated from cysts or were more mature specimens from

PYRODINIUM RESTING SPORES 145

plankton hauls, had a reentrant angle in the right side of their posterior sulcal plates (Fig. 27). There were probably 2 delicate sulcal platelets (the riglit and left sulcal platelets) lying between the posterior platelet and flagellar pore and they occupied the deepest part of the sulcal groove.

Mature specimens, represented by specimens from plankton hauls from Phosphorescent Bay and Isla de Vieques (Fig. 25-28), had thick thecae with pro- nounced apical spines and antapical crests comparable with those of the type specimens from the Bahamas (17). Strong crests were present along the margins of all the thecal plates with the exception of the apical closing platelet, the right lateral margin of the first apical plate, the plates of the cingulum, and the sulcal platelets. T h e depth of the sulcal groove was greater in mature than in juvenile forms, and in the former, the first postcingular plate became infolded and was difficult to examine but was present never- theless and usually had 2 pores, as in the juvenile stage. The first apical plate in mature specimens touched the second apical plate, whereas in many juvenile forms it was occluded from contact with other apical plates (Fig. 18, 34A).

The earliest formed thecal plates were extremely thin, smooth, and porate, but after 1 or 2 clays of growth their surfaces became corrugated and the mar- gins of the pores became raised to form poroids. I n the final stages of thecal growth, the plates were markedly thicker and once again appeared to be simply porate rather than poroidal since the inter- porate areas were infilled and thickened and became microgranular (Fig. 29).

DISCUSSION

Systematics and phylogeny. The systematics and taxonomy of modern thecate dinoflagellates have been based almost entirely on the morphology of the motile stage with little or no reference to other stages in the life history. As other stages become better known, especially the resting spores with their exten- sive fossil record, it is becoming obvious that they can provide additional morphological, ecological, and geological evidence of natural relationships and phy- logenies which must be recognized along with exist- ing information in the taxonomy of dinoflagellates. It is often obvious that the morphology of modern species and their thecae also require reconsideration and their descriptions need revision. For example, discovery of the resting spore of P. bahamense, corre- lation of this spore with a fossil hystrichosphere and renewed study of the morphology of the living thecate stage, provide better information for an assess- ment of its systematic and phylogenetic status than previously was available. On the basis of this infor- mation, Pyrodiniurn can be retained as a discrete genus despite certain similarities with Gonyaulax, but according to some new and revised criteria as

discussed below. The geological history and phy- logeny of pyrodinioid dinoflagellates also can be traced back to Paleocene times at the beginning of the Tertiary era through resting spores fossilized in marine sediments.

The recognition of 6 postcingular plates in P. bahamense, and not 5 as previously reported (17,23), invalidates this character as a useful criterion for distinguishing between Py~odinium and Gonyaulax, but Pyrodinizim is distinctive in other respects. Its theca has a relatively large apical closing plate, api- cal spines, strongly developed sutural crests, and a marked asymmetry of the hypotheca whereby an unusually large posterior sulcal platelet extends pos- teriorly to contact an enlarged fifth postcingular plate. The resting spore of Pyrodinizim bahamense also differs from any known in Gonyaitlax species (25), primarily by its complex combination type of archeopyle (2A+6P). Modern Gonyaulax species pro- duce a variety of distinctive resting spores and the fossil record contains an even greater array of forms, but none (except Hornotryblitim which is discussed below) possess this combination type of archeopyle; precingular archeopyles (8) characterize modern spe- cies of this genus (25) . Protoceratiitm reticulaturn (ClaparPde and Lachmann) Biitschli cysts resemble those of P. bahamense in being multispinose but they also have precingular archeopyles (8,25).

The resting spores of P. baharnense when fossilized (Fig. 6, 7) as the hystrichosphere Hemicystodinium zoharyi (whose name becomes a junior synonym of P. bahamense) enable the geological history of this spe- cies to be traced to the Lower Tertiary. The oldest occurrence of this spore reported in literature at present is Early Pleistocene (18) but it occurs in abundance in the Late Tertiary of Jamaica in the Buff Bay Series, Bowden Formation, and Manchio- neal Formation. The ages of these formations are known imperfectly, but according to their planktonic foraminifera (kindly examined for us by Dr. W. Berg- gren) they range from kf iddle Miocene to Pleistocene. Still older specimens have been found in the Eocene London Clay from near Southampton, although these records remain to be published.

Another liystrichosphere genus, Homotry bliztm Davey and Williams (Fig. 30-32), can be regarded as the oldest extinct relative of Pyi-odinizim and is found mainly in Lower Tertiary sediments ( 2 3 4 of Paleocene to Oligocene age. I t exhibits many of the characteristics which are typical of Pyrodininm spores including the same unique type of archeopyle (2A+6P) (Fig. 31, 32) and an identical overall re- flected tabulation ( 8 3 4 of 4’,0a,6”,6c,6”’, 1 p and 1”“ [not 3’ as reported by Davey PC Williams (3)]. Excel- lent descriptions of the archeopyle in Homotryblizim were presented by Evitt (8) for a species temporarily called Forma AC (probably H . temiispinostim Davey and Williams) and by Drugg PC Loeblich (6) for H .

146 DAVID IVALL AND BARRIE DALE

plectilzim Drugg and Loeblich. Homotryblium dif- fers from spores of modern Pyl-odiniztm only in 1 im- portant respect: whereas P. buhurneme spores possess several (up to 9) thin spines on each opercular piece of the archeopyle and numerous hypotractal spines (Fig. 6-10), Hornotryblirtm species possess only 1 large tubular spine per opercular piece and this is located in the center of each plate area (Fig. 32). From this evidence it may be postulated that the motile phase of Homotrybliiim strongly resembled the motile phase of modern Pyyodinizim bahurnenre. There is no doubt that the species that produced spores of tlie Homotyyblium type was or were abun- dant antl widespread in the Paleogene, since spores of this type have been found in abundance in tlie Eocene of England (jr), the Paleocene of Tasmania (2), antl the Oligocene of Mississippi (6),

Wall & Dale (25), in an attempt to reconstruct a broad outline of the phylogeny of meroplanktonic dinoflagellates, allocated Homotrybli7inz to an exclu- sively Paleogene lineage, but this lineage can be extended now into tlie present day by inclusion of tlie hystricliosphere Hemicystodiniitin which is corre- lated here with modern Pyrodiniztin. Pre-Tertiary representatives of Pyrodinium are unknown; the most similar Mesozoic hystrichospheres appear to be those referred to the extinct genus Hysti-icliosphaciidir~rii as typified by H . t z i biferzim (Elirenberg) Deflandre which possesses an apical archeopyle (type A) and plate-centered spines (8). Modern Pyrocliniirm and Gonyazilax thecae exhibit many similarities, but these genera probably have evolved along separate lines according to their fossil records. The resting spores of modern Gonyaulax, as represented by the type species G. spinifem (Claparede and Ladirnann) Die- sing, are spores with simple precingular arclieopyles and sutural ridges (9,25) and similar spores are ex- tremely abundant in the fossil record. One common type, referred to as Hystrichosphaew (or Spiniferites) by paleontologists, first appears in Lower Mesozoic strata, probably in the Lower Cretaceous and has a continuous record leading to modern Gonyaztlax. This lineage clearly is of much greater antiquity than that of Pyrodinium and the present day similarity be- tween Gonyaulax and Pyrodinirirn probably results from parallel evolution along two broadly related but distinct lines of descent.

The nature of modern dinof1ngel:nte spol-es. Many questions concerning the biological properties and functions of modern dinoflagellate resting spores still are unanswered and yet do concern fundamental as- pects of their life histories and ecology, especially with regard to reproduction and seasonal phenomena in marine and freshwater species. I t is unkown for example, whether these resting spores are asexual aplanospores or zygospores. Another outstanding problem is the phenomenon of dormancy and its role

in tlie life of dinoflagellates or of tlie algae in general as reviewed by Srissman (21).

Exogenous or environmental dormancy (21,22) al- most certainly is a common phenomenon in mero- planktonic dinoflagellates, including P. bahamense, but the only detailed s tudy of dormancy in a dino- flagellate spore of which we are aware was that by Huber & Nipkow (21,12) on the freshwater cysts of Ceintzum hzrundinella (Muller) Bergli from varves and plankton in Lake Zurich. These authors demon- strated that germination (excystment) in this species was retarded by low temperatures (4-7 C) but was optimal at higher temperatiires (21-24 C ) which were slightly in excess of those which facilitated optimum vegetative growth (15-20 C). They further observed that tlie germination of freshly formed cysts at 18 C was retarded strongly for 6 weeks after sporulation, but as tlie time was approached when these cysts woulcl have germinated in their natural environ- ment, germination occurred more rapidly and was followed by a greater percentage of optimal vegeta- tive growth of the motile stage. Cerutzum hirundi- nella spores are typical of the “over-wintering” type, forming in the fall and germinating in the following spring or early summer.

Resting spores of P. bahumense also appear to be tlie “over-wintering” type at Bermuda since their behavior upon storage and incubation clearly resem- bles that of C. hiindinel la and some marine species of Gonyuiilax we have described (25). T h u s resting spores could be obtained in February and stored at temperatures c!ose to the winter low for Bermuda (ca. 16 C) for at least 6 months without germination but woulcl germinate quite readily upon incubation at liiglier temperatures (26 C) in lLIarcEi and April. Upon incubation these spores also showed a tendency to germinate more rapidly and in greater numbers toward tlie end of Rilarch and in early April after failure to excyst in early March (Table l), thus re- calling tlie behavior of Ceratiztnz cysts in Huber & Nipkow’s experiments ( I f ,L2). All of our attempts to germinate spores from Bermuda were carried out at 26 C; it remains to be determined if germination was activated by previous exposure to winter temper- atures, or if a period of after-ripening could be short- ened by exposure to different temperature regimes.

It is uncertain if resting spores of P. bahamense from Puerto Rico ancl Isla de Vieques should be re- garded as “over-wintering’’ types because water tem- peratures in these tropical bays are consistently high (25 C or over). There is minimal seasonal variation in water temperature and the motile stage is present in tlie plankton tliroughout the year, for example, in Phosphorescent Bay (1 6). Nevertheless, it is signifi- cant that spores could be obtained from Phosphores- cent Hay, Ualiia tie Jobos, antl Isla de Vieques, albeit in small numbers, antl a few were germinated in the laboratory at 27 C in April. This may indicate that

dinoflagellate resting spores do riot function solely to witlistarid temperatures which are ;idverse toward the motile stage arid the Iiypotliesis that tlicse spores function as sexual zygos1)ores is attractive but 21s yct completely unproven.

The 4 spores from Pucrto Kico wliicli were geriiii- nated, were slightly atypical in possessing fewer spincs and being very thin-walled. Dormancy stiitlies in other organisms 11 a ve i ntlica t ed t 11 at tli i ck iiess of t 11 e spore wall can be related to tlie duration ol the rest- ing period ( 2 4 , thicker u~alletl specinieris Iiaving a longer period of resting. An arialogotis situation n iay exist in dinoflagellates. I n tliis context it is inierest- ing tliat Huber SC Nipkow were able to tleteriiiirie tliat longevity in freshwater dinoflagellate cysis pi-ol)al~ly is influenced by spore wall thickness since t!iic:k- walled spores oE Pe~idini7rm < i i z c ~ t i i r r ~ (Miiller) Eliren- berg were viable after 16.5 years in contrast to 6.5 years for C. hir ! ( i7d i~e /[a , these age tletcririiiiatioris being possihle with specinieiis taken from v;rrvetl setli- nients in Lake Ziiricli.

Gerniinulion. Hiiber Pi Nipkuw (11) oliserved a number of pre-excystiiient modifications of ~ ~ r o t o - plast organization in C. hi~.,uncliiiclln cysts similar to those often sliowri by P . hnhnmen.se antl riunieroii; other dinoflagellate spores we have observed. These included tlie intensikation of piginentiition arid tlevelopnierit of clirortiaLoi)liores, coiiiiticiiceitient of Brownian motion or streaining oi’ cytoplasniic p r - ticles, a decrease and dispersion toward t!)e (.ell periphery of starch gram, a n d tlie differentiation o f a pale zone in the region of tlie tlcveloping triirisverse furrow. Finally, there w a s some contraction of tlie sporc contents from the cyst u d several Iioiirs Ix-fore excystnient wlicn a delicate menibraric surroiiiidiiig the protoplast could he ol)servecl For 1 lie first time; this membrane is part of the iiew cell wall of the motile stage. A similar nienilxane is ahariclotietl a t a later time when tliecae of 1’. bnhccnicizsc iiritleri~o ecdysis (Fig. 20). In the germination of desrnitl zygospores (20) a (lark mcinbranc is left within the empty zygospore. Tlic longitudinal flagclliiiri devel- oped in c. hi?.?rndinelln irriniecliately prior to excyst- ment and during the escape of the protoplast co i i l t l be seen trailing in the cyst luinen ( T I ) . A n idciitical cleveloprricnt was seen iii tlie marine species ( ; o J i y u i ( - lax spinifera arid G. digitalis (Pouchetj Kofoicl (25) where the liberated swiininer liatl on ly 1 flagellun~ Tor ;I few minutes before the trari’iverse flagelluni was developed. Tlie moment of’ excystiiieiit was not observed in P. baha?rien.w, so it is unknown w!ictlier this species lias a uniflagellatcd s tqe .

Tlie constancy of the position in which tlie excyst- merit aperture or arclieopyle tlevelops for ;I i.pecies was brought to tlie attention of mir:ropaleoiitoloRirts by Evitt (8) antl since lias been reported in iiiiiiieroiis

modern clinoElagellate cysts (25). Hu1)er X: NipkoLv (11) had oliservetl this plienomenon ill C. hii.lcndi-

? z ~ l l n many years belore, when they noted the p rom plast in tliis species was liberated tlii-uugli a split located between the ;ipical arid riglit antapical horns of tlie cyst below its apex. The act ol excystinerit ap- pears to lie a well-ordered process arid die resultant :rpertirre lias taxonomic value (8,10,2i). T h e resting spore wall remains rigid during excystnient a u t l the 1~roio1~l;ist escapes by ;~meboid iiioveiiieiit. l l i e cyst wall also appears to be impermealile t o water prior to excystment (but not to various cheriiicd treatments) aiicl tlicre is 110 swelling of tlie entire cyst. The first stage in excystineiit tliercforc appears to be ;in endoge- iioiis plienomenon, perliaps tlie enzyriatic clissoluiion 01 tlie internal surface of the spore wall along pre- formed or incipient sutures wliicli later pipe to pro- duce tlie arclieopyle. However, once (lie cyst wall is 1m;iclied ant l becomes lxrineable, swelling of a gelati- 110 tis slime layer around tlie protoplast. inay aid in excystiiient (25) . A trail of tliis gelatinous slime c i sd ly remains aLlacliet1 to tlie spore interior after exc ystinerit.

Ontogeizy. Tlie development of ;I thecate dino- flagellate following gerniinatiun of a resting spore lias not been observed often (7,1T,1?,14). I n P. bnha- riiwzsc this development follows a similar sequence a s i n h e species which have been s t itcliecl previously and the org;inisms all pass tliroug-Ii av;ilvate, pre- val\.ate, antl valvate stages, to w e T.incleiiiann’s tcrnii- nology (14). As noted earlier, several marine ant1 Ireslirvatcr species lime only 1 flagellum iminediateiy following excystnient; this iiiay represent a discrete stage in cell oiitogeiiy and one t l ia t has pliylogenetic iniportaiice for organisiris tliat are ~~redoniinaiitly bi- flagell;ited, but ;is yet it is poorly kriown. The imme- diate advantage of studying the ontogeriy of f’yl-0- di i i iu t r i has heen the eluciclation of certain features of ihc t h e d striictiire (tlie 1”’ plate arid sulcal plate- lets) which are more difficult to observe in the ma- ture fornis.

T h e Iiylmoid (iionitiotile, ameboid) stage (Fig. 1) may be ;I response to unfavorable conditions when the cell iiietabolic rate is insufficiently great to pro- duce the energy reqiiired for vigorous moveinent normilly exhibited b y tlie motile pliase. Ahlost all meroplaiiktonic dinoflagellates previorisly described (25) can produce liypnoids.

Ew1og.y o i i d pnlcoccology. ‘The present day tlis- tribiition of I ’ y o d i ~ i i ~ 7 t ~ bul iat t ie im is restricted to tropical and siilJtropicd latitudes of the Caribbean Sea (1.5,16), easiern Pacific Ocean (23). Red Sea, Per- sian Gulf ( I ) , arid h-ortli ,.itl;iritic Ocean (27). It has been found most abuntlantly in shallow water bays surrotiridetl by mangroves and salt marsh but occurs in sm:ill iuimliers to the seaward side of ericloserl bays i r i the: iieritic Lone (16) . Environimental conditions tliac 1‘;rvor a profri5e growth of Pyrodiniun? include tropical water teiriperatiires (25 C or over) for all or p i r t of tlic year, high salinities (around 35.$7(,), close

148 DAVID I\”,%LL AND BARRIE DALE

proximity to mangrove swamps, and a shallow water basinal physiography where there is relatively little water exchange with the open ocean (25J6). Resting spores of the species can survive at lower tempera- tures (15 C) as at Bermuda, but i t is unknown whether the motile phase can live under these conditions.

Fossilized spores of P. bahamense (Hemicysto- dinium zoharyi) are found in Quaternary and Lower Tertiary outcrops in low latitudes, such as in Israel (28,19) and the Caribbean (24) region. In both of these regions, in the Early Pleistocene of Israel and the Late Tertiary of Jamaica, horizons with profuse occurrences of Pyrodinium spores alternate with sedi- mentary beds containing resting spores of Gonyaulax polyedra Stein and spores of the Hystrichosphaera type which are produced by species of the Gonyaulax spinifera group. Comparable associations of cysts can be found in Bermuda within a few miles of one another: Pyrodinium cysts occur in reasonable abun- dance in Smith Sound (St. Georges Island) in a shel- tered bay, while Gonyaulax cysts are abundant in nearby Harrington Sound where Pyrodinium spores are rare. This indicates that these cysts can be formed today within a single climatic province with an annual temperature range from ca. 14.5-26 C and hence the distribution of similar cyst associations even in Pleistocene sedimentary sequences is not easily correlated with the changing palaeoclimatic conditions. A more reasonable palaeoecological in- terpretation concerns the localization of Pyrodinium in semienclosed, shallow water bays of a littoral facies, comparable with Phosphorescent Bay. Oscil- lations of sea level during the Late Tertiary and Quaternary in low latitudes often resulted in alter- nations of littoral and neritic facies and Pyrodinizim may have preferred the former and Gonyaulax the latter.

Dispersed fossilized spores of P. bahamense are not restricted to littoral facies however, but have been found in abyssal lutites at depths greater than 4000 m in the Caribbean Sea (24) and at depths of 2704 and 1276 m in the Red Sea (27). Such occurrences seem best regarded as examples of displaced microfossils, that is, where they have originated in shallow water and then carried by currents into abyssal provinces. I t is almost certain that dinoflagellate resting spores do not germinate at great oceanic depths where there is no light and temperatures are always very low and constant. As a result of their incubation experiments Huber & Nipkow (22) were of the opinion that C. hirundinella cysts could not germinate in Lake Zurich at depths of only 140 m. These experiments indicated that low temperature suppressed germina- tion, and further they observed many viable but ungerminated cysts preserved in the sediment varves (up to 16% years old).

The presence of Pyrodinium spores in deep-sea deposits may be due to their displacement from shal-

low water but their stratigraphic distribution in deep water sediments of the Red Sea (27) is not uniform throughout geological time. Here the spores exhibit fluctuations in abundance with depth in piston-cored sediments as do associated pelagic microfossils such as foraminifera, pteropods, and coccolithophorids. This stratigraphic distribution apparently reflects an in- creased abundance of the spore-forming dinoflagel- lates during interglacial and postglacial warm periods and a corresponding increase of spores to the axial trough sediments during these periods as compared with the supply during cooler glacial periods. Thus in the case of Red Sea sediments the vertical distribu- tion of Pyrodznzum spores in the sediments may have paleoclimatic significance. I t is interesting to note that here the associated dinoflagellate assemblages are dominated 11) 2 types, Nernatosphaeropszs and Leptodinzzrm, and are different from those which alternate with Pyi odznzum in the Lower Pleistocene of Israel and Late Tertiary of Jamaica. The influ- ence of Indian Ocean waters which periodically in- vaded the Red Sea during the Late Quaternary (28) may account for this contrasting situation. Interpre- tations of the paleoecological significance of Pyro- dznzurn clearly must take into account the nature of the geological province in question and the compo- sition of dinoflagellate and other microfossil associa- tions which accompany Pyi odznzum.

CONCLUSIONS

1. The hystrichosphere Hemicystodinium zoharyi (Rossignol) Wall is the resting spore stage of the ma- rine, bioluminescent dinoflagellate Pyrodinium ba- hamense Plate.

2. The thecal and resting spore morphology of P. baharnense (the type species of the genus) is suffi- ciently different from that of Gonyazilax and Proto- ceratium to warrant continued separation of these genera in taxonomy, although Pyi odinium, like Go- nyaulax, has 6 postcingular plates and not 5 as origi- nally proposed by Plate as the basis for generic separation.

3. Pyrodinzum bahamensc spores occur as micro- fossils in marine sediments as old as Eocene, indicat- ing a considerable antiquity for the species.

4. Another hystrichosphere genus, Homotryblium (Paleocene-Oligocene) basically possesses the same or- ganization (archeopyle structure, reflected tabula- tion) as Pyrodinium bahamense spores, differing mainly in showing fewer spines, and it probably represents the fossilized spores of 1 or more extinct pyrodinioid dinoflagellate species which were wide- spread globally in Lower Tertiary shallow water seas.

5. Dormancy probably is a common phenomenon in marine, meroplanktonic dinoflagellates, including Pyrodinium, but has not been investigated in any detail cince the work of Huber & Nipkow on the

P Y R ODIXl Uizl 149 RESTING SPORES

freshwater species Cci-nt i i im Iiiriindinelln in 1922 arid 1923.

6. The g.erniination ot Py~odiniuni, and other dino- flagellate resting spores involves b o i m distinctive reorganization of intracellular organelles and termi- nates in a well-ordered excystiiient process when tlie protoplast is liberated through a specific area in the spore wall to form a n excystrnent aperture died an arclicopylc. This is of the type PA+(;€’ in P. b a h -

7. P. bahurncnse passes tlirough typical avalv:rte and prevalvate stages during tliecal ontogeriy and some critical details of its niorphology are best seen in immature thecae, incliiding the first postcingular plate and sulcal platelets.

8. The present-day distribution or P. bahurr,eriae appears to be restricted mainly to littoral eriibay- merits iii tropical regions and often is associated with the presence of mangrove sw~arrips. The presence of its spores in abundance as microCossils in low lnti- tude, epicontinental sedimentary scqueiices probably is indicative of tlie I‘ormer existence of similar littoral environments but the occurrence of Py~od iv i i im spores in abyssal deposits probably rcsults from tlie lateral displacemenl of spores to great depths I‘rom shallow water, primarily duririg periods wlieri the species was able to thrive in great abundance in tlie littoral zones of the basin of deposition, for example, tlie Ked Sea Uasin.

111 e??.Ec.

ACKNOWLEDGMENT

This rcscarcli was supported by National Science Foundation Grants GB-5200 and GS-7695. Tlte authors tlrank Dr. R. R. Cuillard for his assistance and Professor W. K. Evitt for S U I J I - ’ ~ ~ -

ing thc photograph used as Fig. 32.

1.

2.

3 .

4 .

5.

6.

REYEKENCES Boant, A. 1931. Peridineen aus dem Persisclic~~ Golf und dem Golf yon Oman. (:OOKSON, I. C. Fi EISENACK, A. 1967. Some Early Tcrtiar) microplankton and pollen grains from a deposit near Strahan, \Vestern Tasmania. Proc. Roy. Sor. T’irtorict 80: 131-40. D.4veu, R. J . 8c W x L t h h i s , ‘2, L. 1966. T h e genus Hys- tricliosplineridiziff1 and its allies. In Davey, K. J., Downie, C.; Sar.jeant, W. A. S., 8c Williams, G. L., Studies 0 1 1 Meso- zoic mid Cainoioic dinoflngellate cyris. R7111. Brit. M I L . ~ ~ I L J ? L Geol. SztfiJ111. 3:53-106. I)OW-NIE, C. eC SARIEANT, W. A. S. 1964. Bibliography and index of fossil dinoflagellates and acritarchs. Geol. Sor. A m . Mcrrr. 94, 180 pp. -&- 1%6. The moi-phology, terminology and classification of fossil dinoflagellate cysts. In L)ave), R. J., Downie, C:., Saricant, W. ,4. S., 8c Williams. G . L... Studies on Ncsozoic arid Cainozoic dinoflagellatc cysts. l < i i / l . A1-i/. Aliiseicm Geol. Sirpfil . 3. 10-7. DRUC;~, W. S. & LOEBLICH, A. R., JR. l9F5. Some Eocene and Oligocene pliytoplarikton from the Gulf Coast, 1J.S.A. Ti i la~2e St7,die.r Grol. 5:181 -94.

Ar-cti Prolistenk. 74188-97.

7.

8.

9.

10.

11.

12.

13.

14.

I.?.

16.

17.

18.

19.

20.

21.

22.

23.

24.

25.

26.

27.

28.

ENTZ, C,. 1926. Bcitrsge zur Kenntriis tler Pcridincen. 1. Zur hforphologie und I5iologic yon Peritl i~iicim Uorgei 1,cm- me mi aiin. Arch. Pro i i s ten k. 563%44(;. EVITT. W. R. 1967. IXnollagcllate studies. 11. The archeo- Pylc. .Stonford Unii!. Pztbl. L i?z iu . Ser. G P O / . Sci. 10, 83 pp.

Rc UAVIDSUN, S . E. 1964. Dinoflagellate studies. I. IXrioflagcllate cysts arid therac. Stnuforel U , ~ i v . Pzibl. ~ n i i i . .Fey. Geol. Sci. 10, 12 pp. Evi-c.r, W. R. XC WALL D. 1968. Dinoflagellate studies. IV. l’licca and cyst of recent ti-esliwater Peridiniirm lim- b c i t r r v i (Stokes) Lemincriiiann. Stoirford O n i i ) . Pt ihl . U n i n . S P J - . Ceol . Sci. 12, 15 pp. HURFR, G. 8c Kipnow, F. 1922. Expci-imentcllr Unter- sucliungen iiber tlie Entwicklung von Cenltiutn hirundi - ?f?lln 0 . F . M . Z. notan. 14:337-71. ___ Fi __- 1923. Esperiinen tellc Untcrsuctiungen iiber Entwicklung und Formhildung voii Cercrtizim hiwn- dirtella 0. F. h,Iiiller. Flora 116:114-215. LINIXMANN, E. 1928. Yeridineae (DinoClagcllalae). 111 Englcr, A. Fi Prantl, K., Die mliirlichen Pf la~zzenf~na i l i en , Wilhclni Engelmarin, Leipzig. Vol. 2. 1-104. -~ 1929. Expcrimcntelle Studien iiber die Fortpflanz- ungsersclieinunen der Siiss~vasserl7ericli1ieeii auf Grund von Kcinkulturen. A ~ c l r . Pre~ l i~ te i ik . 68:l-104. \ilmi:&Lm. R. 1957. Fitoplanc~on de las costas de Puerto Kico. 1 m . Prsg. 6:39-52. - 1961. Hidrogi-afia y fitoplancton de un drca marina cle la costa rr~eridional de Puerto Rim. I?z7). Pesq. 18:33-O6. PI A W , I,. f‘yrodinitim baliomense n. g., 11. sp. die I.c.iirlit-Peridinee des “k’euersees” von Kassau, Bahamas. Arct i . Protistrnk. 7:411-28. ROSSICSOL, M . 1961. Analysc 1,ollinique de sediments marins (2uaternaires en Israel 11. SPdiments Pleistoches. Pullrfi Sfiorfs 4:12148.

1964. Hystrichosphc‘res d u Quaternaiie en Mbdi- ~c t i - a i ik orientale, tlans les sediments Pl6isroc12nes ct les boues marines actnelles. CTARR, R . C. 1955. Lygospore germination in Co$m.o?-i?trri hotfyti.7 var. s i ib l?6i f i id imf . SLSSVAN, .4. S . 1965. Physiology of dormancy and ge rm- 113 tion in tlie propagules of cryptogamic plants. I n Lang, Anton [Ed.], Encyr lopef f in of Plant Physiology, Springer- Verlag, N.Y., Vol. 15, Pt. 2, 933-1025.

~ Fi HALVORSON, 1%. 0. 1966. S ~ J O W S , Their l h r - ni(tJtcy a n d Gerniinntion, Harper 8c Row, K.Y., 354 pi>. TAFAT.I., 0. B. F. 1942. Novas sobre alguitos dinoflagrla- dos plancthicos niaIinos dc Wxico, con dcscripci6n de i iuevas espccies. W A L I . , L). 1967. Fossil microplankton in dccp-sea cores from thc Caribhcan Sea. Palaeontology 10:99-123.

~ ~ _ _ & I).II.E, H. 19(iX. hfodcrn tlinoflagcllate cysts and crolution of tlie Peridiniales. M i r r-obafeoTLtoLogy 14:265- 304. - & - 1968. Quaternary calcarcous dinoflagel- latrs (Calciodinellidae) and tlirir natural affinities. J .

W A I I , , D., GUII.LARD, K. K. L., 8c D.\i.k, B. 1967. Marinr tlinoflagcllate cultures from resting slmrcs. Pf~ycologirr 6: 83-86. ~ \ ’ A I . I , I). eC WmREiv, J. S. 1969. Dinotlagcllatrs in Red Sea piston corcs. In Dcgens, E. T. Bc Ross, D. ji. [Eds.], H o / 11riiie.r and Recent H e n q Metal DufmilJ ~ J I l l re Red Sea.

Springer-VciIag, N.Y. (in Jxess).

~ _ _

1906.

R ~ P . :I.lio-of,crleoiitul, 7:83-9.

A m . J . Hot. 12577-81.

A n . Esc. A‘ac. C i e w . Riol. 2435 4 7 .

pcl/C’O?LlcJl. 42: 1395-408.