The Vetigastropoda and the systematics of streptoneurous Gastropoda (Mollusca)

The status of the Vetigastropoda, created 1980 to unite zeugobranch and trochoid archaeo-gastropods, is reconsidered and confirmed in the light of recent investigations. The most important synapomorphic characters of the Vetigastropoda are the ctenidial sense organs (so-called bursicles), the epipodial sense organs, and the special structure of the oesophagus. The conditions of the archaeogastropod oesophagus are comparatively described.
An examination of the relationships of the Vetigastropoda establishes the archaeogastropod nature of the Architaenioglossa. It also demonstrates the monophyletic origin of all higher gastropods, including the Caenogastropoda (s.str.) as well as the Pentaganglionata (= Euthy-neura). The Campanilidae, Valvatidae, Rissoellidae, Omalogyridae, and the Allogastropoda (= Architectonicoidea and Pyramidelloidea) share characteristics with both of the above-mentioned groups, but cannot be classified within any of them. These groups are regarded as subsequent offshoots between the caenogastropod and the pentaganglionate level of organization. The level of Archaeogastropoda is redefined by the hypoathroid/dystenoid nervous system and simple tentacle nerves; the remaining Streptoneura are classified as Apogastropoda with epiathroid nervous system, parapedal commissure, and bifurcated tentacle nerves.     

HOMOLOGY OF THE PALLIAL AND PULMONARY CAVITY OF GASTROPODS

The development and morphology of the pallial and pulmonarycavities of various gastropods has been investigated using epoxy-resinserial sections. In the veliger larvae of Cellana sandwicensis(Patellogastro-poda), Gibbula adansonii (Vetigastropoda), Modulustectum (Caenogastropoda) and Ovatella myosotis (Pulmonata) theformation of the pallial cavity is nearly identical. After shellformation a shallow dorsal pallial groove develops beneath themantle edge. During the late veliger stage, the ectoderm formsa deep invagination along the bottom of the pallial groove onthe right side of the larva, giving rise to the pallial cavity.In the ellobiid O. myosotis the pallial cavity becomes the lung(=pulmonary cavity), without any major post-metamorphic modification.Thus, the lung of this species is clearly homologous with thepallial cavity of prosobranchs. The lung of pulmonates withveliger development, as well as of fresh water basommatophoransand stylommatophorans, can be shown to be homologous by comparisonof adult morphology. In contrast to previous views, the pulmonatelung should be regarded as truly homologous with the pallialcavity of prosobranchs and opisthobranchs. In the onchidiidpulmonate Onchidium cf. branchiferum, the larval pallial cavityshifts posteriorly after metamorphosis, where it gives riseto a lung and a cloaca. Contrary to previous interpretations,it can be shown that the onchidiid lung is homologous with atleast part of the pallial cavity. Smeagol climoi has only asmall pallial cavity and no separate lung. The previously described‘lung’ is shown to be a gland. The re-evaluationof the development and morphology of the pulmonate lung hasimportant systematic implications: (1) The pulmonary cavitydoes not represent a synapomorphic character of pulmonates.(2) The gymnomorphs cannot be separated from the remaining pulmonatesbased on lung development. (3) The lack of a lung in the smeagolidsmight give reason to reconsider this group's systematic placementwithin the pulmonates.     

THE FINE STRUCTURE AND FUNCTION OF THE ANAL GLAND OF THE MURICID NUCELLA LAPILLUS (NEOGASTROPODA) (AND A COMPARISON WITH THAT OF THE TROCHID GIBBULA CINERARIA)

The fine structure of the anal gland of Nucella lapillus isdescribed, and compared with that of Gibbula cineraria. It isconcluded that the glands are not analogous in function andare unlikely to be homologous. The anal gland of Gibbula isa small rectal diverticu-lum near the anal papilla, lined bymucus-secreting cells. The evidence suggests that the largeanal gland of Nucella extracts macromolecules and cations fromthe blood, metabolizes or sequesters them in lyso-somes andultimately expels the resultant residual bodies by apocrinesecretion. It has large reserves of lipid and glycogen, andthe abundance of melanin indicates that it is a major site oftyrosine degradation. The invariable presence of bacteria inthe lumen, and of pits in the epithelium to house them, impliesa symbiotic relationship in which the bacteria metabolize anddegrade the cell debris, some of which is resorbed. The lossof the anal gland in bucci-nids and nassariids is accompaniedby great reduction in size and importance of the rectal sinus,and increase in complexity of the kidney. (Received 31 December 1991; accepted 23 January 1992)     

小地老虎雄性附腺细微结构和功能及高温的影响

本文通过光镜、电镜和生化分析等方法,研究了小地老虎Agrotis ypsilon(Rottemberg)雄性附腺的细微结构和功能,结果表明：(1)雄性附腺是一对管状腺,基段粉红色,中段桔红色,端段乳白色。形态分化在蛹前期完成,分泌功能在羽化后4天进入旺盛期;(2)附腺细胞属蛋白质合成型,具有旺盛的合成蛋白质的能力,胞内含有致密的粗面内质网和游离核糖体颗粒,大量的分泌液泡均匀地分布在细胞质中;(3)顶浆分泌和局部分泌是腺体的二种主要分泌方式, 前者分泌的颗粒物为糖蛋白性质(Pas阳性),后者吩泌的网状物为非糖蛋白性质(Pas阴性),二者在腺腔内呈有规则的放射状排列“4”雄性附腺分泌物具有种的特异性,小地老虎、棉铃虫和粘虫等夜蛾科昆虫分泌物的蛋白电泳谱带存在明显的种间差异,高温(32℃)抑制了雄性附腺分泌某些蛋白质的能力,从而改变精液的成分。     

ANATOMY AND RELATIONSHIPS OF THE BONE-FEEDING LIMPETS, COCCULINELLA MINUTISSIMA (SMITH) AND OSTEOPELTA MIRABILIS MARSHALL (ARCHAEOGASTROPODA)

The anatomy of Cocculinella minutissima (Smith, 1904) and Osteopeltamirabilis Marshall, 1987 is described. Both species belong tothe Lepetelloidea and are closely related to Addisonia Dall,1882, the anatomy of which has been recently described by theauthor. Commonly derived (symapomorphic) characters of all threegenera are found especially in the genital system (hermaphrodites,tcstis and ovary separated, with separated ducts, open seminalgroove to the unmodified right cephalic tentacle), and in thealimentary tract (paired oesophageal glands). Distinct similaritiesin genital and excretory system (large right kidney isolated;hermaphrodites, separated gonads) with the Pseudococculinidae,Pyropeltidae and Lepetellidae justify a uniting superfamilyLepetelloidea, the anatomy of which is quite different fromthat of the Cocculinoidea (Cocculinidae and Bathy-sciadiidae) Osteopelta has retained certain primitive characters (rhipidoglossateradula, true stomach), but is specialized in having a snout-likehead, a concentrated cerebropedal ring, and secondary gill leaflets(vestigial gill in Cocculinella, distinct gill leaflets in Addisonia).Cocculinella and Addisonia share additional synapomorphic featuresof the posterior alimentary tract (reduction of stomach, intestineforms a large sac, midgut gland contains dark granules). Severalaut-apomorphies of each genus justify their status as distinctfamilies. Relationships to the (coiled) Choristellidae, whichfeed on empty egg-cases of sharks or skates (as do addisoniids)and have a cocculinellid-like radula type, are discussed ^*Present address: Insitut fr Zoologie der Universitat, Technikerstr.25; A-6020 Innsubruck, Auttria (Received 10 March 1987;     

TURRILITIDAE (CRETACEOUS AMMONOIDEA) FROM SOUTH AFRICA, WITH A DISCUSSION OF THE EVOLUTION AND LIMITS OF THE FAMILY

The helically coiled mid-Cretaceous family Turrilitidae Meek,1876 are abundant in late Albian and Cenomanian sediments ofEastern South Africa, including representatives of the generaPseudhelicoceras, Turrilites, Hypoturrilites, Ostlingocerasand Mariella, together with a new genus, Neostlingoceras (typespecies Turrilites carcitanensis Matheron, 1842).a Hypoturriliteshomoeomorph derived from Ostlingoceras. Twenty-two species andsubspecies are described, four of them new: Hypoturrilites crickisp. nov., Mariella (Mariella) acanthotuberculata sp. nov., Mariella(Mariella) oehlerti (Pervinquière) sulcata subsp. nov.and Mariella (Mariella) gallienii evoluta subsp. nov. The systematicpart.of the paper providesa basis for the discussion of thephylogeny, and some of the evolutionary trends shown by thefamily. An annotated synopsis of all genera and species referred tothe family is also included (Received 10 March 1977;     

A COMPARATIVE STUDY OF THE MORPHOLOGY OF THE PULMONATE SNAIL PSEUDOTACHEA LITTURATA (PFEIFFER) AND OTHER SPECIES OF PSEUDOTACHEA, IBERUS AND CEPAEA

A population of Pseudotachea litturata (Pfeiffer, 1851) fromTarifa (Càdiz, Spain) has been studied. The morphologicalresults are compared with those from P. splendida, Iberus gualtierianus,I. alonensis, I. marmoralus, I. guiraoanus and four speciesof the genus Cepaea using, as an exploratory method, the Wagnerparsimony procedure and 18 characters of the shell, genitalsystem and karyotype have been analysed. According to this methodit seems that the taxonomical position of P. litturata in thegenus Pseudotachea is confirmed, and agrees with the phylogeneticalrelationships in this group of species. The genus Cepaea seemsto be well established, although two species groups can be distinguished:C. nemoralis—C. hortensis and C. syluatica—C. vindobonensis.These differ mainly in chromosome number, diverticulum lengthand degree of shell polymorphism. Although the present resultsdo not allow us to clarify the current taxonomical problemswithin the genus Iberus, the species studied seem to belongto a natural group (Received 15 September 1987; accepted 1 January 1988)     

THE ROLE OF LYMNAEA AURICULARIA (LINNAEUS) AND LYMNAEA PEREGRA (MULLER) (GASTROPODA: PULMONATA) IN THE TRANSMISSION OF LARVAL DIGENEANS IN THE LOWER THAMES VALLEY

Eleven species of larval digeneans are reported for the firsttime in the UK from the freshwater snail Lymnaea (Radix) auricularia.The latter replaced its congener L. peregra in a gravel pitnear Wraysbury, Berkshire in the Lower Thames Valley and hostedan assemblage of larval digeneans similar to that previouslytransmitted by L peregra. The larval digeneans of L. peregrain small bodies of water in the area were also similar to thosefound in L. auriculania in the gravel pit. This replacementin the role of the host is explained on the basis of morphological,physiological and ecological similarities of the two lymnaeidspecies. (Received 19 February 1992; accepted 27 April 1992)     

THE ANATOMY AND RELATIONSHIPS OF A MARINE VALVATOIDEAN (GASTROPODA: HETEROBRANCHIA)

The anatomy of Cornirostra (new genus) pellucida (Laseron),a marine Indo-West Pacific gastropod, is described and is shownto be similar to that of the northern hemisphere, freshwaterValvatidae. There are, however, several differences betweenCornirostra and valvatids, notably in details of the anatomyof the reproductive system, the morphology of the head-foot,the spawn and in radular characters that warrant family-levelseparation for Cornirostra. Tomura bicaudata (Pilsbry and McGinty) from Florida is alsoa member of the family. (Received 9 September 1989; accepted 30 December 1989)     

GROWTH AND MORTALITY OF THE MUSSELS CHOROMYTILUS MERIDIONALIS (KRAUSS) AND AULACOMYA ATER(MOLINA) AS INDICATORS OF BIOTIC CONDITIONS

Two mussels, Choromytilus meridionalis (Krauss) and Aulacomyaater, (Molina) were used as indicators of biotic factors thatapparently result in radically different sublittoral communitiesat two closely situated islands on the South African west coast.Specimens of both species were attached to submerged plates,which were either unprotected or protected from predation bycages. C. meridionalis grew faster and tolerated silting andsmothering better than A. ater. At Malgas Island adults of C.meridionalis are completely absent and those of A. ater scarcedue to intense predation by rock-lobsters. When protected againstpredation, growth of both species was significantly faster andsurvivership higher at Malgas than at Marcus Island, where C.meridionalis is abundant but A. ater absent. When the musselswere unprotected at Malgas, they were eaten in a few hours.At Marcus Island where rock-lobsters are virtually absent, cagedmussels grow faster than unprotected individuals and survivedlonger. Drilling whelks (mostly Nucella squamosa (Lamarck))were major predators at Marcus. Relative intensity of rock-lobsterpredation and competition between the mussels appear to controlthe structure and diversity of the sublittoral communities atthese sites, rather than physical factors. Growth rate, shellthickness and tolerance of smothering by other species determinewhich species of mussel predominates. (Received 5 April 1988; accepted 11 July 1988)     

THE ANATOMY AND RELATIONSHIPS OF THE ORBITESTELLIDAE (GASTROPODA: HETEROBRANCHIA)

The anatomy of two genera of the marine gastropod family, Orbitestellidae,Orbitestella and Microdiscula, is described. They possess apigmented mantle gland and pallial renal organ, lack a ctenidiumand have a simple hermaphrodite genital system with an externalpenis. They lack buccal cartilages, have a simple oesophagus,a massive jaw and a crystalline style in the stomach. The Orbitestellidaeare shown to be primitive heterobranchs, perhaps related tothe northern-hemisphere freshwater family Valvatidae. (Received 9 September 1989; accepted 30 December 1989)     

THE ECOLOGY OF THE HONG KONG LIMPETS CELLANA GRATA (GOULD, 1859) AND PATELLOIDA PYGMAEA(DUNKER, 1860): DISTRIBUTION AND POPULATION DYNAMICS

Cellana grata is a high-zoned, exposed-shore limpet with a lifespanof 3 years. Patclloida pygmaeais a low-zoned, sheltered-shorelimpet with a lifespan of I year. C. grata migrates up-shorein winter, but occurs lower on the shore in summer. This migrationis synchronized with variations in algal availability high onthe shore; such variations are, however, themselves relatedto seasonal changes in wave height. P. pygmaea is restrictedto the low shore, year round. The movements upwards in winterand downwards in summer are still evident. Algal species richnessincreased from September to reach a peak between December andMarch, and to abruptly diminish between May and June. The encrustingalgae Brachytrichia maculans, Hildenbrandia prototypus, Lithothamnionsp. and Ralfsia vcrrucosa were present year round. The timingof juvenile recruitment of C. grata and P. pygmaea was fromOctober to July and February to October, respectively. Temperaturemay be important in enhancing juvenile survival by affectingthe seasonal pattern of algal occurrence on the shore. Seasonalfluctuations in the rate of growth were recorded for both specieswith the time of fastest growth of C. grata and P. pygmaea occurringbetween October and March and September and February, respectively.Mortality of both species occurred mainly in summer. Summerheat, predation and intra-specific competition for food appearto be the major causes of death. (Received 1 December 1992; accepted 5 May 1993)     

ULTRASTRUCTURE AND HISTOCHEMISTRY OF THE POSTERIOR OESOPHAGUS OF NASSARIUS RETICULATUS (LINNAEUS)

The posterior oesophagus of N. reticulatus (Linnaeus) consistsof two histologically distinct regions. The epithelium of thethickened segment in the visceral haemocoel is virtually uniform.The cells are lipid-rich and can take up lipid from food. Inaddition, enzyme histochemistry indicates a capacity for theuptake of sugars and amino acids. The basal plasmalemma is elaboratelyinfolded and associated with numerous elongate mitochondria,features indicating an active ion pump. The physiological roleof this pump is unknown. (Received 26 March 1985; accepted 10 May 1985)     

SPERM MORPHOLOGY IN SERPULORBIS AND DENDROPOMA AND ITS RELEVANCE TO THE SYSTEMATIC POSITION OF THE VERMETIDAE (GASTROPODA)

Electron microscopic observations on the euspermatozoa (fertilizingsperm) and paraspermatozoa (infertile sperm) of Serpulorbissp. and Dendropoma sp. suggest that the family Vennetidae (sensustricto) is not closely allied to any true cerithioidean family.Vermetid euspermatozoa strongly resemble those of a number ofother mesogastropod superfamilies including the Stromboidea,Epitonioidea, Naticoidea, Calyptraeoidea, Cypraeoidea, somerissooideans and littorinoideans, and even some neogastropodtaxa. Vermetid paraspermatozoa are anudeate, with one or moretails extending from both ends of a central body region. Incontrast, paraspermatozoa of true cerithioideans: (1) have tailsextending from only the posterior region of the ‘head’(2) usually retain a condensed nuclear remnant and (3) sometimespossess an acrosome-like structure at the head apex. These results,in conjunction with anatomical work by Morton, suggest thatthe Vennetidae should be removed from the Cerithioidea and placedprobably in its own superfamily (Vermetoidea Raphinesque, 1815)as practised by some recent workers. The Vermetoidea possiblyare associable with the Stromboidea/Calyptraeoidea/Hipponicoidea/Xeno-phoroideablock within the Mesogastropoda ^*Present address: Department of Zoology, University of Queensland,St. Lucia, 4067, Queensland, Australia     

THE ECOLOGY OF THE HONG KONG LIMPETS CELLANA GRATA (GOULD 1859) AND PATELLOIDA PYGMAEA (DUNKER 1860): REPRODUCTIVE BIOLOGY

Cellana grata is large, relatively long lived (3 years), withone winter breeding season each year which can be correlatedwith major seasonal climatic and hydro-logical events, e.g.,winter reduction in temperature and higher seas. C. grata ischaracterised by a relatively low value of mean annual reproductiveeffort (males: 23%; females: 18%). Patelloida pygmaea is small,short lived (1 year), with one spring breeding season each yearand devotes a large proportion of metabolic energy for reproduction.P. pygmaea showed a higher value of mean annual reproductiveeffort (males: 46%; females: 31%) than C. grata. Mature gonads of Cellana grata first appeared in June and itreached a peak maturity (100%) in September, remaining so untilDecember, i.e., the maturation of the gonads coincided withincreasing water temperatures, with spawning associated witha decrease in water temperature. Gonadal development by Patelloidapygmaea began in either July or August and reached a peak inDecember, remaining so until a major peak in spawning took placebetween April and May, i.e., gonad maturation coincided witha decline in water temperature, with spawning following thesubsequent increase. Limpet gonadal cycles are likely gearedto temperature and food supply. Spawning occurred between Novemberand December, when wave heights are typically 1 m higher thanin summer. (Received 1 December 1992; accepted 25 June 1993)     

THE ANATOMY AND RELATIONSHIPS OF ELACHISINA DALL (GASTROPODA: RISSOACEA)

Species of Elachisina are marine and extend from the Caribbeanand western North and Central America to the Philippines, Hawaiiand New Zealand. The anatomy and other morphological featuresof Elachisina ( = Microdocluis) floridana (Rehder) from theFlorida Keys are described and compared with rissoacean familiesjudged to be most closely allied. This species has a uniquecombination of characters which do not correspond to those character-setsused to define any known rissoacean family. Important featuresinclude a metapodial as well as pallial tentacles, a wide ctenidiumwith low, triangular filaments, an osphradium which is shortrelative to the ctenidium, an S-shaped loop of the intestinewhich extends into the pallial roof, long dorsal folds in themidoesophagus, a rather loosely organised nervous system, anopen prostate gland from which the pallial vas deferens exitsat its anterior extremity, glandular lobes on the penis, a non-glandularfold on the right side of the ventral channel of the capsulegland and a fold on the left side in the posterior end of thechannel, a pair of seminal receptacles lying between the albumenand capsule glands, a bursa which lies alongside the capsulegland and opens posteriorly to the ventral channel and a U-shaped,expanded section of the oviduct proximal to the albumen glandand seminal receptacles. This combination of characters is consideredto be sufficiently distinct to arrant the erection of a newfamily-level taxon to accommodate the small group of speciesjudged to be congeneric with E. floridana. The Elachisinidaeappears to be most closely related to the Rissoidae, Iravadiidaeand Hydrobiidae. (Received 19 October 1983;     

THE MORPHOLOGY, ULTRASTRUCTURE AND FUNCTION OF THE FEEDING APPARATUS OF SAYELLA FUSCA (C.B. ADAMS, 1839) (GASTROPODA: PYRAMIDELLIDAE)

Scanning and transmission electron microscopy in conjunctionwith histology and dissection were employed to investigate theforegut anatomy of Sayella fusca (C.B. Adams, 1839), a commonNew England pyramidellid snail. Certain aspects of the feedingapparatus of S. fusca, including the buccal pump and proboscisanatomy, depart from the characteristic pyramidellid plan. Somedifferences such as the position of the introvert/proboscisaperture and the common oral and stylet canal are shared withthe genera Turbonilla, Eulimella, and Pyramidella. Three characteristicsof the feeding apparatus are unique to S. fusca: (1) the buccalpump is not divided into two pouches but exists as a singlemuscular bulb; (2) the entire lumen of the buccal pump, notsimply a portion of it, possesses a cuticular lining; and (3)the salivary ducts never enter the muscular walls of the buccalpump. Histological studies of the salivary gland indicate thatthree types of secretory cells are intermittently distributedthroughout the entire gland rather than characterizing distinctregions as described for other members of the family Pyra-midellidae.In contrast to previous findings, the gland cells of S. fuscaexhibit a merocrine secretion. The taxonomic value of the buccalpump and proboscis morphology are discussed. ^*Present address: Dauphin Island Sea Lab, 101 Bienville Boulevard,Post Office Box 369–370, Dauphin Island, Alabama 36528USA. (Received 9 November 1993; accepted 1 October 1997)     

THE FINE STRUCTURE AND FUNCTION OF THE SALIVARY GLANDS OF NUCELLA LAPILLUS (GASTROPODA: MURICIDAE)

The fine structure of the tubular and acinous salivary glandsof Nucella lapillus (L.) has been studied and some histochemicaland enzyme tests have been carried out. The clusters of subepithelialcells of the tubular glands secrete a glycoprotein composedof chains of tubular macromolecules resembling secretions knownto have adhesive properties which may assist in boring. Thesecretion is rich in disulphide groups, as are many toxins,and is believed to be responsible for the recently demonstratedpharmacological activity of the glands. It is proposed thatflaccid paralysis is induced in prey by envenomation with thissecretion during rasping, after soft parts have been exposedby an ‘anti-predator’ reaction to secretion fromthe hypobranchial gland of Nucella. The secretory vesicles ofboth types of gland cells in the acinous glands have heterogeneouscontents indicating that their secretions are complex. The majorcomponent in those of the mucous cells is an acid mucopolysaccharidetypical of a lubricant or releasing agent. The ciliated basalcells resemble typical enzyme-secreting cells and the majorconstituent of their secretion is a finely granular glycoprotein. (Received 8 January 1990; accepted 5 June 1990)     

THE PHYSIOLOGY AND FEEDING BEHAVIOUR OF TWO MARINE SCAVENGING GASTROPODS IN HONG KONG: THE SUBTIDAL BABYLONIA LUTOSA (LAMARCK) AND THE INTERTIDAL NASSARIUS FESTIVUS (POWYS)

Aspects of the physiology and feeding behaviour of the scavengingsnails, Babylonia lutosa and Nassarius festivus have been studiedand compared. N. festivus has a wider physiological tolerancethan B. lutosa; upper lethal temperatures being 31.5°C and28.5°C respectively and lower lethal salinities 15.5 and11.5. N. festivus was also more resistant to desiccation. N.festivus is adapted to an intertidal environment that is morevariable than the subtidal habitat of B. lutosa. The metabolicrate of adult N. festivus was two to three times higher thanthat of adult B. lutosa, the specific oxygen consumption rateof the former being 7.91±0.49x10^–6 mol of O₂.g^–1wet wt.hr^–1. This correlates with estimates of consumptionobtained for the two animals, B. lutosa eating, on average,6.57% of its wet tissue weight per day, N. festivus 15.33%.Standardization of the data for 2 g animals of both species,however, reveals no significant difference in terms of oxygenconsumption and thus the enhanced consumption by N. festivussimply reflects its smaller size. Both species are opportunisticfeeders and can survive long periods of starvation (>100days). The feeding strategies of the two are also different,N. festivus eating faster than B. lutosa, possibly because ofthe more ephemeral nature of carrion in the intertidal. Starvationaffected the feeding behaviour of N. festivus more than B. lutosaand N. festivus was able to perceive carrion from greater relativedistances than B. lutosa. (Received 27 February 1989; accepted 24 July 1989)     

DISTRIBUTION AND ABUNDANCE OF GYMNOSOMATA (GASTROPODA: OPISTHOBRANCHIA) IN THE SOUTHWEST ATLANTIC

The distribution and abundance of gymnosome gastropods in theArgentine Sea and Brazil—Malvinas Confluence during 1978–1979and 1988 were studied. The collections analyzed included 768quantitative samples obtained between 48°W and the coast,and from 35°S to 55°S. Two species were found. Spongiobranchaeaaustralis was the most frequent and abundant (up to 730 per1000 m3); its presence in the area was associated with the coreof the Malvinas Current. Clione antarctica was less abundant(maximum abundance: 230 per 1000 m³) and was also associatedwith the Malvinas Current. The geographic ranges of both speciesin the area are wider than previously described. Since the rangeof S. australis in the area extends far from the range of itsprey Clio, it is not clear whether S. australis can feed onthe thecosomatous pteropod Limacina (and not only on Clio, asdescribed in the bibliography) or it starves in that area. Duringthe 1978–1979 annual cycle, the abundance of both speciesfollowed neither the abundance patterns of their prey nor ofthe total zooplankton, and differed from each other. The residencetime of swarms of both gymnosomes were shorter than one month.As a general pattern, the aggregates are rapidly transportednorthward by the Malvinas Current and also penetrate the outershelf water, but they remain there only during a short periodand cannot preclude the final expatriation. So, the abundanceof gymnosomes in the area depends on passive migration morethan intrinsic population factors. (Received 9 July 1997; accepted 15 December 1997)