THE ANATOMY OF CALLOCARDIA HUNGERFORDI (BIVALVIA: VENERIDAE) AND THE ORIGIN OF ITS SHELL CAMOUFLAGE

Callocardia hungerfordi (Veneridae: Pitarinae) lives in subtidalmuds (220 to 240m C.D.) and is covered by a dense mat of mudthat, effectively, camouflages the shell. The periostracum is two layered. The inner layer is thick andpleated, the outer thin and perforated. From the outer surfaceof the inner layer develop numerous, delicate (0.5 mm in diameter),calcified, periostracal needles. These penetrate the outer periostracum.Mucus produced from sub-epithelial glands in the inner surfaceof the mantle, slides over the cuticle-covered epithelium ofthe inner and outer surfaces of the inner fold and the innersurface of the middle mantle fold to coat the outer surfaceof the periostracum and its calcified needles. Increased productionat some times produces solidified strands of mucus which bindmud and detrital material into their fabric to create the shellcamouflage. Calcified periostracal needles have been identified in othervenerids, including some members of the Pitarinae, but how theyare secreted and how the covering they attract is producedand, thus, how the whole structure functions, has not been explained. (Received 7 December 1998; accepted 5 February 1999)     

THE LIFE CYCLE, POPULATION DYNAMICS, GROWTH AND SECONDARY PRODUCTION OF THE SNAIL BRADYBAENA FRUTICUM (MULLER, 1774) (GASTROPODA PULMONATA) IN NORTHERN GREECE

The life cycle, population dynamics, growth and secondary productionof the pulmonate land snail Bradybaena fruticum were studiedin northern Greece. The demographic analysis of the populationsof B. fruticum revealed that a) two cohorts exist in the fieldthroughout the year b) the reproductive period started in thebeginning of summer and c) growth was increased during springand autumn. According to von Bertallanffy' method B. fruticum needs 5 yearsto attain its maximum size in the field of 25.40 mm. Mortalityrate increases and life expectancy decreases with increasingage. Net reproductive rate (Ro) was equal to 3. 15 and per capitarate of increase (r^c) was equal to 1. Annual secondary production, calculated by Hynes' size frequencymethod, revealed a mean annual density of 5.9 individuals/m²,a mean standing crop (B) of 8.09 g/m²/year and an annual production(P) of 1.92 ± 0.11g/m²/year. Annual turnover ratio (P/B)was equal to 2.37. (Received 25 May 1989; accepted 17 March 1989)     

NOTOLIMEA CLANDESTINA A NEW SPECIES OF NEOTENOUS BIVALVE (BIVALVIA: LIMIDAE) ENDEMIC TO THE STRAIT OF GIBRALTAR

Notolimea clandestina new species (Bivalvia: Limidae) is describedfrom the littoral of the Strait of Gibraltar. The small size(1 mm) and the persistence of the larval hinge suggest a neotenousspecies. Its area of distribution is likely to be restrictedto the Strait of Gibraltar. (Received 7 July 1993; accepted 2 December 1993)     

THE OCCURRENCE OF ANOPAEA (BIVALVIA : INOCERAMIDAE) IN THE ANTARCTIC PENINSULA

The genus Anopaea represents a small but distinctive group ofinoceramid bivalves that apparently remained functionally endobyssate.The somewhat unusual morphology (for an inoceramid) probablyresults from structural modifications tofacilitate sedimentpenetration at a high angle and anchorage by an antero-ventralbyssus. Although never as common as thecontemporary genera Retroceramusand Inoceramus, Anopaea is now known from temperate bivalveassemblages in both the Northern and Southern Hemispheres. Itpersisted from the Late Jurassic (Tithonian) to the Early Cretaceous(Neocomian), and possibly even later. (Received 26 June 1980;     

AGE AND GROWTH OF LITHOPHAGA LITHOPHAGA (LINNAEUS, 1758) (BIVALVIA: MYTILIDAE), BASED ON ANNUAL GROWTH LINES IN THE SHELL

The life span of Lithophaga lithophaga was found to be >54 years when the annual growth lines in longitudinal shellsections were counted. The age determination was confirmed bya) length frequency histograms, b) the time taken for the formationof annual and reproduction rings and c) by determining the agein different parts of the shell. The age of individuals of thesame length varies, for example, individuals with a length of5.0 ± 0.2 cm range in age from 18–36 years. Theoldest individuals were found at depths of 1–5 m. Maximumgrowth (75%) was observed from the end of spring to the beginningof summer. The increase in length of the borehole, which was1.5 times greater than the length of L. lithophaga, was continuousand occurred at a faster rate in winter. Parameters, such as,shell length, age, axes, the occurrence of abnormal, white andpearlcontaining forms and wetflesh weight varied significantlywith depth. There was no variation in the ratio of boreholevolume/shell volume. On the basis of the above parameters, andalso the population density, each depth at which samples werecollected, was graded. Depths of 2–4 m were found to bethe most suitable for growth and habitation. Depths of 0–1m were most inhospitable due to strong wave action and the directeffect of the atmosphere. (Received 15 August 1994; accepted 17 March 1995)     

EVOLUTION OF THE TELLINACEA (BIVALVIA)

The suspension feeding Astartacea appear to be among the earliestheterodonts. These organisms may have given rise to the Carditaceaand the rest of the heterodonts including the Tellinacea. Paleontological evidence indicates that the earliest Tellinaceawere suspension feeders with members that lived vertically ina burrow in shifting sand. These conditions resemble those foundin species of modern Donax in the Donacidae. From a Donax-likestate of suspension feeding evolution most likely proceededto non-selective feeders. Extant organisms that resemble thisstage are found in the Solecurtidae. A later stage resemblessome of the extant Psammobiidae. The final stage in tellinaceanevolution is the acquisition of deposit feeding with its associatedmorphology. These stages are observed in the Scrobiculariidae,Tellinidae and a few members of the Semelidae. (Received 27 April 1981;     

STRUCTURE AND FORMATION OF THE BYSSUS COMPLEX IN MYTILUS (MOLLUSCA, BIVALVIA)

A review is presented of the mechanism of byssus productionin the genus Mytilus. The pedal glands which secrete the byssusmaterial are described, followed by an account of the morphology,structure and chemistry of the byssus itself. Finally, the releaseor shedding of the byssus from the pedal tissues is discussed. (Received 10 November 1981;     

A NEW SPECIES OF LITHOPHAGA (BIVALVIA: LITHOPHAGINAE) BORING CORALS IN THE CARIBBEAN

A new species of Lithophaga is described as a small lithophaginemussel exclusively boring Madracis mir-abilis, M. decactis andM. formosa in Jamaica. The shell, musculature and pallial glandsshow modifications for live coral boring similar to those ofIndo-Pacific species of the genus. However, both the boringand posterior pallial glands are more primitive than other speciesexamined to date, interpreted as indicative of a more recentadaptation to life in a living coral habitat by this species. ^*Contribution No.359 of the Discovery Bay Marine Laboratory,University of the West Indies (Received 23 April 1985;     

SHAPE AND FUNCTION OF THE SHELL: A COMPARISON OF SOME LIVING AND FOSSIL BIVALVE MOLLUSCS

• 1 The review is mainly concerned with Carboniferous non-marine Anthracosiidae and Myalinidae, of which only the shells are known, and with certain unspecialized non-byssate suspension-feeding bivalves which had smooth shells and burrowed shallowly.
• 2 Limited experimental evidence and observation of living bivalves suggest that in certain Recent siphonate species and in some members of the non-siphonate Anthracosiidae the shape of the shell was functionally related to movement through the sediment in the same way. Predicted optimum shapes of shells for downward burrowing and for upward near-vertical movement in sands and silts were apparently realized in the Anthracosiidae, which constituted a series of highly variable opportunistic assemblages. It is stressed, however, that the shape of the shell always appears to be a compromise between several functional requirements.
• 3 In both the early Anthracosiidae and in several analogous Recent marine genera, orientation of the long axis of the shell was the same for downward burrowing and for upward pushing, that is near the vertical, with posterior end upward.
• 4 Invasion of the Pennine late-Namurian delta took place when marine bivalves pushed upward, thereby avoiding sedimentation from delta lobes moving seaward relatively swiftly. The evolution of Carbonicola occurred at about this time (the Marsdenian Age) when the bivalves acquired a smooth elongate shell of ‘streamlined’ form, having a hinge plate with swellings and depressions on it (later to evolve into teeth). All these features tend to characterize the active shallow burrowers of today.
• 5 Entry into soft-bottom eutrophic conditions of fresh water is characterized in several unionids by increase in height/length (H/L or w/m) ratio of shell, in anterior end/length (A/L) and in obesity (T/L) (see Fig. 2, centre). These changes also took place in established faunas of Carbonicola characteristic of richly carbonaceous shales, in faunas of supposed Anthraconaia in more carbonaceous sediments of mid-and late-Carboniferous times in the U.S.A. and in Anthraconauta of the British late Carboniferous (Westphalian C and D). The genus Anthracosphaerium epitomizes the culmination of these trends in the Anthracosiidae, and species of the genus were probably epifaunal or shallowly infaunal active burrowers on soft bottoms in Westphalian upper A and B time.
• 6 Two contrasting patterns of growth characterize the shells of the widely variable unionid Margaritifera margaritifera. In the first, dorsal arching of the shell, with straightening and reflexion of the ventral margin, provides increased weight but decreased ligamental strength. In the second, in which the ‘hinge line’ tends to remain straight while the dorsal margin becomes more rounded and obesity increases, there is increased metabolic efficiency for active surface movement. The maintenance of these trends within the species, which may be regarded as secondarily opportunistic, affords a means of insurance for survival within the highly variable environments of fresh water. The same trends are recognizable in established faunas of Carbonicola, where it is likely that they performed the same function, as well as in Mesozoic and Cenozoic Unionidae.
• 7 The functional explanation outlined in paragraph (6) may be extended to provide an ecological meaning for Ortmann's ‘Law of Stream Distribution’, which states that obesity of unionid shells increases downstream. This applies broadly, within a fairly wide range of variation, a fact which again suggests ‘insurance’ of faunas against the variable hazards of fresh-water habitats.
• 8 In bivalves having considerable thickness of shell in relation to their size, and having strong umbonal development, specific gravity of the living bivalve is correlated with H/L and T/L ratios of the shell, as in the venerid Venerupis rhomboides. In this species, differences in the specific gravities of the bivalves, as well as their shape, appear to be functionally related to shallowly infaunal burrowing in different substrates.
• 9 The conclusions of paragraphs 6 and 8 provide a functional explanation, in terms of selection, for the palaeoecological ‘law’ of Eagar (1973), which is applicable to established faunas of Carbonicola in mid-Carboniferous time, and relates variational trends in two main groups of shells primarily to increases in the relative water velocities of the palaeoenvironments.
• 10 Where the growth of relatively unspecialized bivalve shells has been measured, allometric relationships have usually been found in H-L and T-L scatters. Logarithmic lines have two inflexions and linear scatters a sigmoidal form. A similar pattern of allometric growth has been found in both Carbonicola (H-L) and Anthraconauta (m-w). These patterns appear to be related to the optimum requirements of water-borne larvae, the initial byssal phase of settlement, when ability to burrow quickly is essential, and the main period of growth and activity. It is herein suggested that the final second inflexion, which indicates a falling off of gain in H/L and T/L ratios, may be a genetically controlled modification of the growth pattern which counteracts the operation of the ‘cube-square rule’ (of Thompson, 1942) and prolongs productive life.
• 11 Patterns of relative growth of the shell may be significantly modified by conditions of the habitat; both T/L and H/L ratios may be increased, with general reduction in size, in the less ‘favourable’ habitats. Both these ratios have been similarly modified, the one in the ‘natural laboratory’ of a lake formed by the damming up of streams, and the other in transplant experiments with living Venerupis. In both these latter cases, phenotypic changes took place in the same direction as those expected on the basis of natural selection. Direct response to environmental factors cannot therefore be ruled out as an agent in similar changes noted in Carbonicola and supposed Anthraconaia in paragraphs (5) and (9) and may have been operative in those of paragraphs (7) and (8).

     

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 PALLIAL EYES OF CTENOIDES FLORIDANUS (BIVALVIA: LIMOIDEA)

The structure of the pallial eye in the Limidae has neverbeenelucidated properly, largely because they are difficultto see amongthe mass of surrounding mantle tentacles and becausethey are few,small, and lose their pigmentation when preserved.Possibly two eyetypes are present, simple cup-shaped receptorsin species of Lima,like those seen in the Arcoida, and morecomplex invaginated ones inCtenoides. The pallial eyes (;18on both lobes) of Ctenoidesfloridanus are formed by invaginationof the middle mantle fold at theperiostracal groove, so thatall its contained structures are derivedfrom the outer andlight is perceived through the inner epithelia ofthis fold.The eye comprises a simple multicellular lens and aphotoreceptiveepithelium beneath it of lightly pigmented cells andalternatingvacuolated, support cells. In some species of the Arcoidea, Limopsoidea and Pterioidea,pallialeyes occur on the outer mantle fold and thus beneath theperiostracum(and shell). The pallial eyes of Ctenoides floridanus andotherpterioideans, e.g. species of the Pectinidae, occur on themiddlefold and may thus have improved vision. In the Cardiodea,Tridacniidaeand Laternulidae (Anomalodesmata) pallial eyes occur ontheinner folds. There is thus a loose phylogenetic trend, in whichCtenoidesis a critical link, of increasing eye sophisticationcorrelatedwith the historical age of the clades possessing them. (Received 16 November 1999; accepted 20 January 2000)     

TRANSPORT OF UNCONTAMINATED AND MOLLUSCICIDE-CONTAINING FOOD IN THE DIGESTIVE TRACT OF THE SLUG DEROCERAS RETICULATUM (MULLER)

By X-ray analysis of food transport in the alimentary tractof Deroceras reticulatum it was shown that even ten hours afteringestion of a thorium sulfate-containing bait, this materialcan be detected in the crop. After 2.5 h, some parts of labelledfood passes down from the anterior to the posterior part ofthe gut. After 13 h, thorium sulfate-containing material canbe observed only in the gut. After 19 h, no more labelled materialis present in the alimentary tract of the animals. After addition of Cloethocarb, the animals feed on only smallamounts of food. The labelled material only enters the anteriorpart of the gut. After ten hours, the food does not move anymore and does not leave the crop even 19 h after feeding. After molluscicide application, the crop epithelium is moreinfolded than in control animals and the cells are elongated.After 30 h, cells protrude into the lumen of the digestive tract. (Received 11 May 1992; accepted 26 June 1992)     

SEXUAL DIMORPHISM OF SHELL SHAPE AND GROWTH OF VILLOSA VILLOSA (WRIGHT) AND ELLIPTIO ICTERINA (CONRAD) (BIVALVIA: UNIONIDAE)

Shell shape and growth of two unionacean species, Villosa villosaand Elliptio icterina, are analyzed with univariate and multivariatetechniques. The relationship of shape variables to size variablesis examined. Under the lognormal assumption, parametric testsof these allometric relationships are valid. Variables describingthe ventro-posterior region of the shell are shown to be thebest of those tested for discriminating between the sexes ofboth species regardless of statistical method. Neither speciesexhibits size sexual dimorphism. Shape sexual dimorphism ofV. villosa is constant during adult growth, but the more subtledimorphism of E. icterina changes as adults continue to grow. (Received 20 January 1986;     

THE REPRODUCTIVE BIOLOGY OF THE AMPULLARIID SNAIL POMACEA URCEUS (MULLER)

Investigations of the reproductive biology, life cycle and populationdynamics have been undertaken to assess the potential of Pomaceaurceus as a culture species in Trinidad. The species is dioeciousand evidence from microscopic gonad analyses, together withmaturity indices and size frequency distributions in the population,all indicate that the reproductive cycle is annual. Adults spawnat the end of the rainy season months. Hatching and early developmentof the young occur in the dry season (January to May) whileadult females aestivate. The total developmental period variedbetween 22 to 30 days. Mean fecundity is 54 eggs/female witha range of 21 to 93 for egg masses deposited in the field andthose produced under laboratory conditions. ^*Present address: Zoology Dept., University of Aberdeen, TillydroneAve., Aberdeen AB9 2TN. Scotland. (Received 13 January 1988; accepted 11 April 1988)     

GENETIC STUDIES OF ALLOZYME VARIATION IN LEUCINE AMINOPEPTIDASE IN THE LAND SNAIL HELIX ASPERSA (MULLER)

In the land snail H. aspersathe enzyme LAP has two loci, LAP-1and LAP-2, both of which arc monomeric enzymes under the controlof multiple alleles, the alleles being codominant. None of theobserved ratios in the pheno types in the experimental progenywere significantly different from Mendelian expectation. ^* Present Address: Bournside School, Cheltenham, Glos. (Received 1 September 1981;     

THE EFFECTS OF POPULATION DENSITY ON GROWTH RATE IN LIMICOLARIA FLAMMEA MULLER (PULMONATA: ACHATINIDAE)

Density effects on growth and sexual maturity in laboratory-keptLimicolaria flammea MÜller are described; high densityresults in low growth, higher mortality and a delay in sexualmaturity. (Received 9 April 1991; accepted 11 June 1991)     

THE FUNCTIONAL MORPHOLOGY OF THE ANTARCTIC BIVALVE THRACIA MERIDIONALIS SMITH, 1885 (ANOMALODESMATA: THRACIIDAE)

The functional morphology of the Thraciidae is poorly understood.Although some morphological aspects of several members havebeen described, only Trigonothracia jinxingae from Chinese watersis known in detail. Thracia meridionalis is the only representativeof the family in Antarctic waters, and is common in AdmiraltyBay, King George Island, where it inhabits muddy sediments.Thracia meridionalis shares many features with Tr. jinxingaethat are typical of most Anomalodesmata, i.e. a secondary ‘ligament’of thickened periostracum, extensively fused mantle margins,ctenidia of type E, a ctenidial-labial palp junction of categoryIII, a stomach of type IV and simultaneous hermaphroditism.Thracia meridionalis is, however, strikingly different fromTr. jinxingae in a number of ways, such as the presence of afourth pallial aperture, statocysts of type B₃, heterorhabdicctenidia, direct communication between the mantle chambers,a deep-burrowing habit (individuals lying on the left shellvalve), siphons that retract into mucus-lined burrows, a stomachwith extensive sorting areas, a rectum which passes over thekidneys and separate male and female gonadial apertures. Thereis, therefore, a greater range of morphological diversity withinthe Thraciidae than previously suspected. (Received 27 April 2004; accepted 30 November 2004)