SPERMOGENESIS AND SPERM STRUCTURE IN THREE SPECIES OF PATELLOIDA AND ONE SPECIES OF NIPPONACMAEA (PATELLOGASTROPODA: ACMAEOIDEA)

The spermatozoa of Patelloida profunda albonotata, P. saccharina,P. pygmaea and Nipponacmaea schrenkii (Lottiidae) are describedby transmission electron microscopy. All have ect-aquasperm,typical of invertebrates using external fertilization. The spermof all four species have a cylindrical nucleus (length: breadth> 4: 1 in P. p. albonotata and P. saccharina; <4: 1 inP. pygmaea and N. schrenkii) which tapers towards the roundedanterior end. All have an acrosome with a posterior acrosomallobe which extends into the centre of the subacrosomal space.In P. p. albonotata and P. saccharina the acrosomal contentsare undifferentiated and the posterior lobe extends to the nucleus,being separated from it by flocculent material. In P. pygmaeathe acrosomal contents are differentiated, the lobe is relativelyshort and the subacrosomal space is filled with material witha fibrous appearance. The acrosome of N. schrenkii is undifferentiatedand the posterior lobe is no more than a bulge. The sperm ofP. p. albonotata and N. sacchrina have a small (0.25 µmlong) cytoplasmic collar which surrounds the axoneme anteriorlywhereas in P. pygmaea and N. schrenkii the cytoplasmic collaris longer (1 µm) and is swollen by an electron-dense vesicle.The composition and function of this vesicle is unknown. Thespermatozoa of Patelloida and Nipponacmaea have structural featureswhich are similar to sperm of the Lottiidae providing some supportfor the placement of these genera in the Lottiidae as proposedby Lindberg & Hedegaard (1996) and Sasaki & Okutani(1993) respectively. The similarities of the sperm of P. pygmaeato N.schrenkii raise some doubts about the tax-onomic statusof the former species. Spermiogenesis in all four species issimilar to that described for other Acmaeoidea and Patelloidea.In P. pygmaea and N. schrenkii, however, in addition to theacrosomal vesicle, the Golgi body produces a number of electron-densevesicles which fuse and eventually form a single vesicle inthe collar of the mid-piece. (Received 24 October 1996; accepted 10 February 1997)     

Selective site segregation in Patelloida (Chiazamea) Pygmaea (Dunker) and P.(C.) Lampanicola Habe (gastropoda: Patellacea) on a Hong Kong shore

Although originally described as a separate species, Patelloida (Chiazacmea) lampanicola Habe has subsequently been regarded as a “form” of P. (C.) pygmaea (Dunker). The conical shape of the shell in the former was assumed to result from the settlement and growth of some individuals of the population upon shells of intertidal Batillaria (Potamididae).This paper reports upon an analysis of a population of limpets resident on a small sand flat in Hong Kong and it is concluded that Patelloida (C.) lampanicola is distinct from P. (C.) pygmaea. This conclusion is based upon differences in radula teeth structure, shell morphometrics and behaviour. Furthermore it has been demonstrated that the earlier confusion surrounding these species results from a very nice example of selective site segregation. P. (C.) pygmaea inhabits stones and empty shells (in this region of its total range) embedded in the sand but can occasionally does reside, up to a length of 4.2 mm, upon Batillaria shells. Thereafter the flattened form of the limpet shell, on a round substratum, presumably makes such individuals more susceptible to either predation or dislodgement. The high-coned Patelloida (C.) lampanicola, on the other hand, almost exclusively colonizes living Batillaria (particularly B. zonalis and B. multiformis) shells but can, with little or no significant alteration in form, also colonize stones. Patelloida (C.) lampanicola has a positive behavioural response towards Batillaria and is clearly living in symbiotic association with the potamid. The benefits accrued by both are discussed.Thus, the limited hard substratum of a primarily soft shore environment has been segregated by these two limpets; one occupies the stones and oyster shells, the other the dense cover of epifaunal potamid snails.     

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 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)     

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)     

A GENETIC ANALYSIS OF SYMPATRIC SUBPOPULATIONS OF THE SIBLING SPECIES LITTORINA SAXATILIS (OLIVI) AND LITTORINA ARCANA HANNAFORD ELLIS

A detailed analysis of shell characteristics (four parameters)and allozyme allele frequencies (eight to nine polymorphic loci)of sympatric Littorina saxatilis and Littorina arcana subpopulationsfrom Filey Brigg on the east coast of England supports theiridentification as closely related but separate species. Oneenzyme system, esterase-2, was nearly species diagnostic. Resultswere generally comparable with an earlier study of the two speciesfrom East Lothian, Scotland. Littorina saxatilis was again foundto be more variable than L. arcana. (Received 14 December 1983;     

Mating for convenience or genetic diversity? Mating patterns in the polygynous ant Plagiolepis pygmaea

Several genetic and nongenetic benefits have been proposed toexplain multiple mating (polyandry) in animals, to compensatefor costs associated with obtaining additional mates. The mostprominent hypotheses stress the benefits of increased geneticdiversity. In social insects, queens of most species mate onlyonce or have effective mating frequencies close to one. Yet,in a few species of ants, bees, and wasps, polyandry is therule. In these species, colonies are usually headed by a singlequeen, whereas multiple queening adds diversity in several ofthe remaining species, especially in ants. Here we investigatedmating frequency, inbreeding and relatedness between the queensand their mates in the polygynous ant Plagiolepis pygmaea, andthe effect of polyandry on the genetic diversity as a functionof the effective population size of individual colonies. Ourresults show that polyandry occurs frequently in the species.However, queens are frequently inseminated by close relatives,and additional sires add little genetic diversity among offspringof individual queens. In addition, the increase in diversityat the colony level is only marginal. Hence, contrary to establishednotions, polyandry in P. pygmaea seems not to be driven by substantialbenefits of genetic diversity. Nonetheless, very small or asyet unidentified genetic benefits to one party (males, workers,queens) in conjunction with low costs of mating may favor polyandry.Alternatively, nongenetic factors, such as convenience polyandry,may be more important than genetic factors in promoting polyandryin P. pygmaea.     

Scanning electron microscopy of Heterocapsa pygmaea sp. nov., and evidence for polyploidy as a speciation mechanism in dinoflagellates

The thecal morphology of three isolates of the marine dinoflagellateHeterocapsa pygmaea sp. nov. are here examined by manning electronand light microscopy. The thecal tabulation of these isolatesis p.p., c.p., 5', 3a, 7', 6c, a.s., r.s., l.a.s., l.p.s.,[?a.a.s. and p.a.s.], 5' ' and 2' ' and is identical to thatof H. niei and H. illdefina. The assignment of thecal platesto various series is based on interpretation of plate homologiesamong peridinioid genera. The above formula represents the basicpattern for Heterocapsa. The cell dimensions of four Heterocapsaspecies are determined; Heterocapsa pygmaea is the smallestspecies. Heterocapsa pygmaea differs from the next largest species,H. niei, in having approximately half the number of chromosomesand as such can be interpreted as a case of polyploidy. If so,this is the first evidence of polyploidy as a speciation mechanismin the Pyrrhophyta. ¹Present address: Department of Botany, Duke University, DurhamNorth Carolina 27706 ²Present address: The Biological Laboratories, Harvard University,Cambridge, Massachusetts 02138     

SYSTEMATICS OF POTAMACMAEA FLUVIATILIS (BLANFORD): A BRACKISH WATER PATELLOGASTROPOD (PATELLOIDINAE: LOTTIIDAE)

Potamacmaea fluviatilis (Blanford, 1867), which is known fromestuaries and tributaries that drain into the Bay of Bengal,was studied to assess available material, determine possiblerelationships between P. fluviatilis and other patellogastropodtaxa, and review the current state of our knowledge of thisenigmatic species. Radular and shell structure characters indicatethat P. fluviatilis is referable to the Patelloidinae Chapman& Gabriel, 1923. The radular tooth morphology of P. fluviatilisis similar to that of the wood-eating taxon PectinodontinaePilsbry, 1891; both taxa have multicuspid lateral teeth. Substantialhuman population increase and its accompanying habitat destructionin this region may have had deleterious effects on this uniquepatellogastropod. (Received 22 May 1989; accepted 25 July 1989)     

SPECIES DISCRIMINATION AMONG PELAGIC HETEROPODS: RESOLUTION OF THE PTEROTRACHEA HIPPOCAMPUS--P. MINUTA PROBLEM

Four species of Pterotrachea are currently recognized, two ofwhich (P. hippocampus Philippi, 1836, and P. minuta Bonnevie,1920) have very similar morphologies. These two species havebeen distinguished mainly on the basis of eye and visceral nucleusshapes; the former with wide, triangular eyes and a short, broadnucleus, and the latter with narrower, triangular eyes and ataller, more slender nucleus. Quantitative and qualitative morphologicaldata were obtained from specimens of P. hippocampus and P. minuta collectedduring two oceanographic sampling programs in the North AtlanticOcean. Comparisons of eye and visceral nucleus shapes (representedby their length to width and length to retinal width ratios,respectively), plotted against body length showed linear decreases,with no justification for the recognition of two separate species.Examination of eye shape across a wide range of body sizes showedthat the width of the retina increases disproportionately with bodygrowth (by elongation and medial upturning) beginning at a length ofabout 21-22 mm. As a result, the overall appearance of the eyeat this body size changes such that smaller animals (less than21-22 mm) have eyes corresponding with those of P. minuta, whilethe eyes of individuals larger than this body length match thoseof P. hippocampus. Several authors have distinguished femalesof the two species by the presence (P. hippocampus) or absence (P.minuta) of cuticular spines anterior to the eyes. Examinationof female specimens showed that those less than about 30 mmlacked these spines, while those above this size possessed them.Thus, cuticular spines represent a secondary female sexual characteristic. Other morphological features that have been used by previousauthors to distinguish the two species were examined and rejected.Because P. hippocampus was described prior to P. minuta, itis herein regarded as the senior synonym of P. minuta. (Received 12 June 1997; accepted 21 May 1999)     

INTRASPECIFIC AND INTERSPECIFIC VARIATION IN SHELL MORPHOLOGY OF BIOMPHALARIA PFEIFFERI (KRAUSS, 1848) AND HELISOMA DURYI (WETHERBY, 1879) FROM MOSHI, TANZANIA, ANALYSED BY MORPHOMETRIC STUDIES

Helisoma duryi, a planorbid snail species, which is a potentialbiological control agent of the intermediate hosts of schistosomiasis,was introduced in an irrigation scheme (T.P.C.) in northernTanzania in 1972. The species has been present at T.P.C. since,and during a snail survey in January 1981, a great variationin the shell morphology of H. duryi, ranging from typical H.duryi forms to forms resembling Biomphalaria pfeifferi, theintermediate host of Schistosoma mansoni in the area, was observed.The Biomphalaria- Wkc forms of H. duryi could constitute anentire population but also occasionally occurred in populationsof typical H. duryi. This study was undertaken to determine whether simple shellmeasurements, or ratios between some of these could be usefulin discriminating between H. duryi and B. pfeifferi. Followingparameters were considered: shell height, shell diameter, diameterof the umbilicus, ratio between shell height and diameter ofthe umbilicus, and the number of whorls. (Received 29 July 1983;     

A NEW OVOVIVIPAROUS SPECIES OF TECTARIUS (GASTROPODA: LITTORINIDAE) FROM NIUE, SOUTH PACIFIC, WITH A MOLECULAR PHYLOGENY OF THE GENUS

A new ovoviviparous littorinid gastropod, Tectarius (Echininiopsis)niuensis, from Niue, west of the Cook Islands, is described.This is distinguished from the only other ovoviviparous memberof the genus, T. (E.) viviparus (Rosewater, 1982) from the MarianaIslands, here redescribed in detail. The new species is remarkabletor its high-level habitat in the littoral fringe on wave-exposedkarstic limestone cliffs, for its variation in shell shape accordingto tidal level, shell colour polymorphism, calcified operculumand penis with a single mamilliform penial gland. In a cladisticanalysis of morphological characters, including single representativesof each of the three other subgenera of Tectarius (Tectarius,Echininus, Tectininus), these two ovoviviparous species appearas sister-taxa. This is confirmed by a molecular phylogeneticanalysis of the same species, based on the sequence of a portionof the 16S ribosomal RNA mitochondrial gene. Neither analysisunequivocally confirms the monophyly of Tectarius. The divergenceof DNA sequences within Tectarius suggests that the genus arosein the Upper Cretaceous, much earlier than the oldest (UpperEocene) fossils. Only 4 of the 175 species of Littorinidae areknown to be ovoviviparous (with brooding through metamorphosis)and the possible adaptive significance of this type of developmentis discussed. Hitherto, its rarity had been explained by earlyextinction of poorly-dispersed brooding taxa. However, ovoviviparitymay have persisted in Echininiopsis for at least 35 millionyears, and has not precluded colonization of islands 6300kmapart. (Received 17 September 1996; accepted 15 November 1996)     

SEXUAL DIMORPHISM OF NUCELLA LAPILLUS (GASTROPODA: MURICIDAE) IN NORTH WALES, UK

Multivariate statistical methods were employed to examine sexualdimorphism in size and shape of Nucella lapillus collected from 16sheltered sites along coasts of Anglesey and the Lleyn Peninsula, NorthWales, UK. Females were significantly larger than males in overallsize; among 12 relative measures of shell shape, two ratios (shellwidth/shell length and aperture length/shell length) were significantlydifferent between males and females, but these differences usuallydecreased with increasing age (shell length). The observed hypoallometricdimorphism could be a result of selection on increased femalefecundity, which may be positively correlated with shell sizein N. lapillus as in other gastropod species. (Received 22 November 1999; accepted 10 April 2000)     

THE ADDUCTOR AND RETRACTOR MUSCLES OF THE VELIGER OF PECTEN MAXIMUS (L.) (BIVALVIA)

In Pecten maximus (L.), retractor and adductor muscles becomefunctional in the early veliger larva. The twelve-day-old veligerhas four pairs of velar retractors, three pairs of retractorsattached to the posterior body wall and an anterior adductor.The pediveliger has in addition, pedal retractor muscles anda posterior adductor. The retractors consist of striated muscle:the adductors have both smooth and striated portions. The retractorsattach near the hinge, branch to a greater or lesser extent,then attach to specific areas of the velum, posterior body walland foot. Some features of the branching and of the dispositionof points of attachment form a pattern which exhibits mirrorsymmetry about the plane between the two shell valves. Thispattern is characteristic of the species. It is deduced thatretraction and protraction of the velum result from co-ordinatedsequences of muscle contractions. ^*Present address: Forest Products Research Centre, P.O. Box1358, Boroko, Papua New Guinea. (Received 15 June 1984;     

BROODING AND NON-BROODING DACRYDIUM (BIVALVIA: MYTILIDAE): A REVIEW OF THE ATLANTIC SPECIES

The Atlantic species of the marine bivalve genus Dacrydium arereviewed, with particular emphasis on their hinge and protoconchcharacters. The basic groundplan of a Dacrydium comprises afunctional primary ligament, a paired series of primary teeth,and a posterior row of secondary teeth separated from the latterby a secondary ligament; this can be transformed into a singleseries either by loss of the secondary ligament and mergingprimary and secondary teeth, or by loss of secondary teeth andligament through paedomorphosis. Twelve species are recognized, of which eleven are illustrated.One abyssal species is not separable morphologically from theIndian Ocean D. speculum Poutiers, 1989 and is new to the Atlantic;four new species (D. wareni, D. dauvini, D. filiferum and D.balgimi) are described; a Caribbean form which is hardly distinctfrom the Eastern Pacific D. elegantu-lum Soot-Ryen, 1955, isdescribed as a new subspecies D. e. hendersoni. The larvae are brooded in D. hyalinum (Mon-terosato, 1875),D. viviparum Ockelmann, 1983 and D. balgimi. The brooding specieshave larger larvae (protoconch 210 to 315 µm long) thanthe non-brooding (protoconch 120 to 150 µm long), andreach a smaller adult size (1.4 to 3 mm instead of 4.5–5mm). A phylogenetic reconstruction is attempted using parsimonyanalysis of hinge and shell characters as well as the brooding/nonbrooding character. (Received 22 October 1996; accepted 28 November 1996)     

A REVISION OF THE DEEP-WATER OCTOPUS GENUS SCAEURGUS (CEPHALOPODA: OCTOPODIDAE) WITH DESCRIPTION OF THREE NEW SPECIES FROM THE SOUTHWEST PACIFIC OCEAN

Deep-water trawl surveys on seamounts around New Caledonia yielded62 specimens of the little-known genus, Scaeurgus. Members ofthis genus of octopuses typically occur at depths of 200–500m in temperate and tropical latitudes worldwide. Prior to thisstudy, Scaeurgus was considered to contain one to two species.The new material from New Caledonia contained a surprising diversityof Scaeurgus species from a small area: three distinct new speciesare described and limited material of a further two taxa isreported. A pygmy member of this genus is reported for the firsttime. Distributions of these new taxa are consistent with reportsof high endemism on the seamount systems in this region. Fifty-eightof the 62 specimens were collected from seamounts, with fourof the five taxa unique to a single seamount. (Received 12 January 2004; accepted 28 January 2005)     

PHYLOGENY AND BIOGEOGRAPHY OF THE ATLANTIC AND EASTERN PACIFIC HYPSELODORIS STIMPSON, 1855 (NUDIBRANCHIA, CHROMODORIDIDAE) WITH THE DESCRIPTION OF A NEW SPECIES FROM THE CARIBBEAN SEA

A new species, based on two specimens from Guana Island, BritishVirgin Islands, is described. The new species agrees with thegenus Hypselodoris in having a high body profile, a large vestibulargland and mantle glands. It differs from other members of thegenus in the Atlantic Ocean by having a reddish background bodycolour. In addition, dorsal colour patterns such as a broadcentral white line with lateral extensions and the lack of yellowlines or spots further differentiate this species. The radularformula of 52x41.0.41 and a smaller seminal receptacle are alsodistinctive. The phylogenetic relationships of 34 species andsubspecies of Hypselodoris from the eastern Pacific and Atlanticare examined using morphological characters. With the exceptionof the new species, these are characterized by a dark blue backgroundbody colour. The phylogenetic analysis of the data matrix resultedin eight most-parsimonious trees. The resulting consensus treeshows that eastern Pacific and Atlantic species of Hypselodorisconstitute a monophyletic group that is basally split into twosister clades. One clade contains the eastern Pacific speciesand most of the Caribbean species, whereas the other clade containsthe eastern Atlantic species. The new species is the sisterto the rest of the Caribbean species, which also form a monophyleticgroup. This phylogenetic hypothesis suggests that two consecutivevicariant events have affected the biogeography of Hypselodoris:(1) the closure of communication between the tropical Indo-Pacificregion and the Atlantic and eastern Pacific, completed withthe formation of the East Pacific Barrier; and (2) the riseof the Panama isthmus. (Received 19 December 2003; accepted 12 October 2005)     

THE GENUS HAMINOEA (GASTROPODA: CEPHALASPIDEA) IN PORTUGAL, WITH A REVIEW OF THE EUROPEAN SPECIES

The study of specimens of Haminoea collected on the coast ofPortugal, together with the re-evaluation of historical specimensused by Nobre (1938–40) in his main work on the Portuguesemolluscs, recognized the presence of two species, Haminoea navicula(da Costa, 1778) and H. orbignyana (Férussac, 1822),and confirmed the misidentification of H. orbignyana as H. elegans(Gray, 1825). Anatomical analysis found intraspecific variabilityin the radula of H. navicula and H. orbignyana and in the seminalduct of the latter. The systematic value of taxonomic featuresincluding the shell, external morphology, animal coloration,radula, jaws, gizzard plates, prostate gland, seminal duct,penis and egg-masses is discussed. For all European speciesbut H. orbignyana, identification is only possible when anatomicaldata are considered, and the most relevant character is themale reproductive system. SEM images of the penis and prostateof H. navicula and H. orbignyana are given for the first time.A synoptic table for the recognition of the European speciesis provided. (Received 21 January 2005; accepted 17 June 2005)     

REDESCRIPTION OF PHYLLIDIOPSIS SINAIENSIS (YONOW, 1988) (NUDIBRANCHIA: DORIDOIDEA: PHYLLIDIIDAE), WITH A REVIEW OF THE RED SEA PHYLLIDIIDAE

Phyllidiopsis sinaiensis (Yonow, 1988), of which only one single preservedspecimen had been known, was rediscovered in the northern RedSea. The dorsal colour-pattern of living individuals is presented forthe first time, and the anatomy of P. sinaiensis is describedin detail. Major features of the holotype previously used tocharacterise the species are shown to be artifacts. Principaldistinguishing characters of P. sinaiensis include the centraltubercle ridge, large and multicompound, broad based, pink tubercles,bicoloured black and pink rhinophores, the very elongate muscularoesophageal segment, the distinct stomach and the extremelylong, convoluted prostate that is bound together by connectivetissue. In some specimens, the bases of the tubercles may fuseleading to a predominantely pink dorsum with only a few blacklines. Phyllidiopsis sinaiensis appears to be among the mostcommon nudibranchs in the Gulf of Aqaba. The fact that it has notbeen reported since its original collection in 1980 can be explainedby being confused with the externally similar, well-known speciesPhyllidiella pustulosa (Cuvier, 1804). A review of the phyllidiidfauna of the Red Sea reveals eleven valid species that can allbe identified with the key presented herein. With four out of elevenspecies, phyllidiid endemism (36%) is high in the Red Sea. This isin contrast to recent palaeobiological hypotheses of a post-glacial originof the Red Sea coral reef fauna.     

LABORATORY EXPERIMENTS ON BEHAVIOUR AND MOVEMENT OF A FRESHWATER MUSSEL, LIMNOPERNA FORTUNEI (DUNKER)

Experiments on the movement and behaviour of a freshwater musselLimnoperna fortunei (Dunker) were conducted m the laboratory.Small mussels of 5–12 mm shell lengths moved over 100cm during a day within plastic containers, with a maximum distanceof 300 cm. However, their movement was concentrated during thefirst five hours of the experiments. The distance moved decreasedwith increasing shell length, and mussels larger than 27 mmmoved less than 20 cm. Both small (< 15 mm) and large (>15mm) mussels showed negative photo-taxis and positive geotaxisunder the light, but positive geotaxis of small mussels tendedto be weak in darkness or under the shade Small mussels hadstrong thigmotaxis with a preference for settling in the angledcrevices between the vertical walls and the flat bottoms ofthe containers Small mussels tended to aggregate, after movement,and the presence of large mussels facilitated secretion of byssalthreads by the small mussels. The possible adaptive significanceof these behaviours and movement are discussed in relation toresponse to predation and dislodgement by waves or water current (Received 11 September 1995; accepted 18 December 1995)