SOME BEHAVIOURAL AND ELECTRICAL RESPONSES OF SCROBICULARIA PLANA (BIVALVIA:TELLINACEA) TO SIPHONAL WOUNDING

Water pumping, valve movements and heart rate have been recordedfrom Scrobicularia for short periods of normal behaviour andthen after siphonal wounding. Scrobicularia exhibits regularand repetitive pumping periods interrupted for only 2–3s after siphonal wounding, without the regularity of these periodsbeing affected. Wounding does not prevent animals from usingtheir inhalant siphons for deposit feeding. A preliminary investigationof neural responses to stimulation has shown that wounding thesiphon causes minimal disturbance to the animal, a brief (2s)burst of nerve activity occurs, the siphon is retracted, butvalve adduction does not occur. In contrast to this tactilestimulation of the mantle edge always elicits a large burstof impulses in the posterior adductor nerve, valve closure results,usually for 14–15 s. ¹Present address: Dept of Zoology, University of Cape Town,Rondebosch 7700, South Africa. (Received 2 February 1981;     

Siphons and siphonal grooves in the digestive systems of the Echinoidea (Echinodermata)

Here we use histological sections and, to a limited extent, scanning electron microscopy to ascertain whether siphons or siphonal grooves parallel the stomach of five sea urchin species representing five higher taxa in the Echinoidea. We find a siphonal groove in Centrostephanus coronatus of the Diadematidae and in Caenopedina diomedeae of the Pedinidae; we find a siphon in Tromikosoma panamense of the Echinothurioida and in Strongylocentrotus purpuratus of the Camarodonta; and we find a hemisiphon in Aspidodiadema hawaiiense of the Aspidodiadematidae (it is currently unsettled whether this last group belongs in the Pedinoida or the Diadematoida). Several recent accounts of echinoid gut anatomy have claimed that species in the Echinothurioida have a siphonal groove instead of a siphon and that species in the Diadematidae and Pedinidae have siphons instead of siphonal grooves. The present work shows that these claims are mistakes and confirms that Holland and Ghiselin (1970) correctly described the distribution of siphons and siphonal grooves in the Echinoidea.     

Ecological Aspects of Some Coral-Boring Gastropods and Bivalves of the Northwestern Red Sea

More than 17 molluscan species were obtained from burrows incoral substrata at Al-Ghardaga (Hurghada on maps) on the RedSea coast, six of which in particular bore into livingcolonies.The species reported in this paper belong to the families Mytilidae,Coralliophilidae, and Gastrochaenidae. The direction of boringin living corals is to the outside, the borers keeping pacewith the growing coral layer to maintain their burrows open.Coral growth is generally of a higher rate than that of borers,and burrows are accordingly mostly much larger than their inhabitants.There is evidence in such cases that burrows form initiallyby growth of coral around the settling young. Boring of Lithophagaspecies is mostly due to the abrasive action of the shell whichmoves straight and posteroventrally without any rotation. Incoralliophilids,boring is also executed mechanically by the turning movementsof the shell. Boring in dead coral is directed inwards, andburrows are nearly as large as the borers. The latter avoidthe blocking of their burrows (e.g., by a living coral incrustation)either by great siphonal extension (Rocellaria) or the freeends of the shell may be strengthened to maintain the capabilityof boring in the opposite direction (Lithophaga laevigata).Both L. luevigata and Modiola chmamomeus bore mainly mechanicallyby the rocking movements of the shell. Chemical boring is stilla possibility,particularly in the posterior narrow region ofburrows of Modiola lodging the extended pallial siphons whichare deprived of any effective mechanical devices for boring.Therole of boring algae in rarefying bored coral material hasalso to be included as an indirect chemical factor.     

COMPARATIVE SPERMATOLOGY OF THREE SPECIES OF DONAX (BIVALVIA) FROM SOUTH AFRICA

The fine structure of the sperm and spermatogenesis in threespecies of Donax (D. madagascariensis, D. sordidus and D. serra)are described. Although the morphology of the sperm of all speciesis very similar, each has unique features. Donax madagascariensisand D. sordidus reportedly hybridize in regions of sympatryand their spermatozoa are morphologically closer to one anotherthan to D. serra. All sperm are of the primitive type with ahead(about 2 µmu; long), mid-piece of four mitochondria andtail. The head comprises a barrel-shaped nucleus which is cappedby a small, complex acrosome. The structure of the acrosomeis typical of heterodont bivalves. During spermatogenesis thepattern of nuclear chromatin condensation is granular. Glycogenfirst appears in the cytoplasm of spermatids, and in the maturesperm is sited in the mid-piece and base of the acrosome. (Received 15 May 1989; accepted 25 June 1989)     

Distribution,growth and seasonal changes in biochemical composition for the bivalve Donax vittatus (da Costa) from Kames Bay,Millport

The bivalve Donax vittatus (da Costa) occurs in Kames Bay, Millport, Scotland,only intermittantly. Successful settlements may occur with a frequency of no more than two in twenty years. There was one such settlement in the summer of 1962. The distribution in 1967 of survivors from this settlement was mainly just below L.W.S.T. Shell ring measurements indicated that the maximum mean size was reached in 5–6 years.     

Discovery and anatomy of the arenophilic system of cuspidariid clams (Bivalvia: Anomalodesmata)

The arenophilic system of anomalodesmatan clams comprises multicellular glands, muscular papillae, and radial lines of adhesive secretion, which glue sand grains and other extraneous particles to the external surface of the shell. The presence and morphology of these organs have been established in an increasing number of taxa, but arenophilic glands were not previously known to occur in the deep‐sea, carnivorous family Cuspidariidae. Dissections, histological sections and ultrastructural examination of members of the cuspidariid genera Cuspidaria and Cardiomya revealed a functional arenophilic system positioned around the siphonal apparatus. Glands are contained in muscular papillae at the posterior tip of the siphonal sheath, from where they deposit their adhesive secretion onto the shell rostrum. Discovery of an arenophilic system in cuspidariid clams adds support to the idea that the glands are a synapomorphy of Anomalodesmata, secondarily absent in only one of the major component branches (the clade joining Thraciidae, Cleidothaeridae, and Myochamidae). Moreover, similarity between the arenophilic papillae we observed on the siphonal sheath of Cuspidaria, Cardiomya, and Myonera, and literature reports on the crown of tentacles of Multitentacula is puzzling and highlights the need for further studies of the latter genus. J. Morphol. 275:9–16, 2014. © 2013 Wiley Periodicals, Inc.     

THE STRUCTURE AND DISTRIBUTION OF PERIPHERAL CILIATED RECEPTORS IN THE BIVALVE MOLLUSCS DONAX SERRA AND D. SORDIDUS

The siphons and mantle edge of Donax serra and D. sordidus possesstwo types of ciliated sensory receptor. Type 1 has > 7 ciliawith an exposed length of 0.7–2.4 µm. Type II hasfewer cilia (2–5) which are 2–6 µm long. Athird type (Type III) described from the tips of the tentaclesof the siphon and mantle edge of D. sordidus, possesses twotufts of cilia which are 12 µm long. All three receptortypes appear to be primary receptors. Estimates of abundanceshow that receptors are most numerous on the tips of the siphontentacles (9.75 x 10³. mm^–2), and it is suggested thatthese receptors function as chemoreceptors. (Received 11 May 1983;     

The Medusa of Velella velella (Linnaeus, 1758) (Hydrozoa, Chondrophorae)

A mature medusa of Velella velella (Linnaeus, 1758) is reportedfor the first time from the North Atlantic; previously adultmedusae were known only from the Mediterranean. This specimen,collected by SCUBA divers, is the largest specimen recordedto date. Distinctive features are: two opposite adaxial-axialpairs of perradial capitate tentacles; two marginal bulbs lackingtentacles; conical manubrium with 4 perradial longitudinal gonads;perradial exumbrellar cnidae tracts; cnidome of stenoteles andmacrobasic euryteles; and zooxanthellae within the subumbrella.Since this specimen was collected near the surface and has zooxanthellae,it is likely that V. velella medusae are epipelagic.     

Unusual swimming mechanism in Calycopsis borchgrevinki (Hydrozoa)

Calycopsis borchgrevinki (Browne, 1910) from Antarctic waterswas studied histologically. The entire bell is enclosed in achitin-like skin, supported by chitin-like rods in the radialmesogleal fibres. In the tentacles a thick mesogloea is presentwithout chitinous structures. The gonads are embedded in thestomach folds. It is postulated that these characters are adaptationsto ecological conditions in Antarctic waters.     

FUNCTIONAL MORPHOLOGY AND FEEDING OF DONAX SERRA ROODING AND DONAX SORDIDUS HANLEY (BIVALVIA: DONACIDAE)

The functional morphology of Donax serra and D. sordidus fromSouth African beaches was examined, and comparative measurementsmade of the rate of water filtration. The two species differin the structure and ciliation of the ctenidia, the number andspacing of the ridges on the labial palps, the direction ofciliary currents on the surface of the mantle and visceral mass,and the length and coiling of the mid-gut. The maximum ratesof water filtration recorded showed similar relationships tosize for the two species, but in D. sordidus the rate declinedrapidly with time during the observations. These differencesindicate differences in feeding strategy related to differencesin distribution and behaviour of the two species on beaches.     

Arenophilic mantle glands in the Laternulidae (Bivalvia: Anomalodesmata) and their evolutionary significance

The mantle margins of several anomalodesmatans bear multicellular arenophilic glands, the mucoid secretions of which attach sand grains and other foreign particles to the outer surface of the periostracum. These glands have been recorded for many of the anomalodesmatan families and are used as a key morphological character in recent attempts to unravel the evolutionary relationships within the Anomalodesmata. The glands occur in Laternula elliptica, L. truncata, L. boschasina and L. marilina, discharging from the top of muscular papillae at the distal tip of the siphons. The secretions are laid down as threads organized in longitudinal lines along the length of the periostracum that covers the siphonal walls. This is the first record of arenophilic mantle glands in members of the Laternulidae, a finding that not only broadens our current knowledge of the family's morphology, but assists in the reconstruction of anomalodesmatan evolutionary history.     

Mytilus edulis chilensis infested with Coccomyxa parasitica (Chlorococcales, Coccomyxaceae)

The association between the green alga Coccomyxa parasitica (Chlorococcales)and the mussel Mytilus edulis chilensis at Goose Green, Falkland Islandsis reported. C. parasitica occurred within the soft tissueswith an overall infestation rate of 16%. The highest levelsof infestation (23%) occurred in individuals from the middleof the main mussel bed, with considerably lower levels of infestation inthe upper and lower regions (<1% and 5% respectively). Noconsistent seasonal pattern in infestation rate was detectedbetween September 1993 and February 1996. C. parasitica wasmost commonly observed in tissues located in the posterior territoryof the host, in areas most directly exposed to light. Tissuesof infested mussels were rather watery and translucent and theadductor muscle appeared weak and stringy. During the summermonths when Falkland mussels are in peak reproductive condition,dry flesh weight of infested mussels was significantly lowerthan non–infected mussels of comparable size suggestingthat infestation by C. parasitica may reduce reproductive output.However it is uncertain whether poor condition of the host isdue to the presence of the parasitic alga or whether C. parasiticainfests only those mussels that are already in poor condition. ¹ Present address: 3, St Marys Walk, PO Box 530, Stanley, Falkland Islands (Received 10 June 1998; accepted 8 September 1998)     

ECOPHYSIOLOGICAL RESPONSES OF CERASTODERMA EDULE (L.) AND C. GLAUCUM(BRUGUIERE) TO DIFFERENT SALINITY REGIMES AND EXPOSURE TO AIR

The estuarine bivalve Cerastoderma edule and the lagoonal C.glaucum were exposed in the laboratory to different salinityregimes and the effects in the osmotic concentration of themantle cavity liquid, extrapallial fluid and haemolymph determined.The behavioural responses of the two cockles to changing salinityand exposure to air were investigated by monitoring valve movements. Both C. edule and C. glaucum are euryhaline osmo-conformerswhen exposed to different environmental salinities, but differencesare seen in their behavioural responses to sudden exposure tolow salinity and cyclic changes in salinity. C. glaucum postponedthe effect of sudden exposure to low salinity by complete valveclosure whilst C. edule partially closed its valves and intermittentlygaped during the same period. During exposure to a sinusoidalfluctuating salinity regime, C. edule responded first to thefalling salinity by retracting siphons and partially closingvalves. In contrast, C. glaucum responded more slowly to fallingsalinity than did C. edule. C. glaucum closed valves faster,accompanied by erratic adductions. During an acclimation period in a continuous automatic tidalsystem, C. edule and C. glaucum were entrained to the tidalrhythm of immersion and exposure to air and demonstrated differentresponses of valve gaping and adductions. This rhythm was lostupon continuous submergence indicating the rhythm is exogenouslyinduced. The two cockles gaped during exposure to air at lowtide, suggesting that both can respire in air, contrary to previousreports. The different physiological and behavioural responses of C.edule and C. glaucum to changing salinity and exposure to airwere found to be a reflection of their respective environments.C. edule is adapted to daily changes and stresses in its estuarinehabitat whilst C. glaucum is subjected to seasonal changes. (Received 19 September 1985;     

ETUDE ONTOGENETIQUE DE L'ORGANE SENSORIEL DU MUSCLE CRUCIFORME DES TELLINACEA

The closed cruciform muscle sense organ of Donax trunculus hasa similar origin to the open one of Scrobicularia plana. Bothdifferentiate as ectodermal pits before the cruciform muscleitself, which is issued from their wall. The sense organ ofDonax is closed immediately after the invagination of the pitand its closure is independent of the differentiation of theventral expansion which characterizes the closed sense organand of the canal which characterizes the open one. (Received 8 August 1983;     

A NEW SPECIES OF THE AEOLID GENUS FLABELLINA (NUDIBRANCHIA) FROM THE STRAIT OF GIBRALTAR

A new species of nudibranch, Flabellina insolita, is describedfrom specimens from the Strait of Gibraltar. The new speciesis assigned to the genus Flabellina on the basis of the jaws,radula and reproductive system, despite the shape of the rhinophoresand oral tentacles and the presence of small papillae flankingthe pericardium and small laminar enlargements on the dorsalsurface of the body. These features separate this species fromother aeolids. (Received 14 June 1988; accepted 19 August 1988)     

Seasonal changes in tissue weight and biochemical composition for the bivalve Donax trunculus L. on the Algerian coast

Seasonal changes in the body weight and composition of the bivalve Donax trunculus L. from Azur Plage near Algiers, Algeria, were studied during the period September 1971-June 1974. Percentage dry tissue weight was minimal in October–December and rose to reach a peak in spring or summer, the rise corresponding with rapid maturation of the gonads. Decrease in tissue weight in the autumn also coincided with a rapid decline maturity of the gonads between August and October. Lipid content increased with sexual maturity, while carbohydrate content was greatest in the autumn and declined to a seasonal minimum in April–May. The changes are compared with those for D. trunculus in other Mediterranean populations, and for D. vittatus (da Costa) elsewhere in Europe.     

Oxygen consumption by the bivalve Donax vittatus (da Costa)

The acute oxygen consumption of Donax vittatus (da Costa) freshly collected at different times from a beach at Barrassie, Ayrshire, Scotland, has been measured at different temperatures. The logarithmic relationship between oxygen consumption and body weight showed a significant difference on only one occasion, and a common regression coefficient (b) of 0.865 could be used for regressions of oxygen consumption on weight. Over the temperature range 2.9–20 °C oxygen consumption rose with temperature. There was a linear decline of Q₁₀ with temperature in the range 2.9 –20 °C. Differences in values of the constant (a) in the regression equation suggest that there is some acclimation to temperature, resulting in rotation of the rate/temperature curve counterclockwise for warm-acclimated animals, and a reduction of Q₁₀ in cold-acclimated animals. The differences in oxygen consumption which result are small and appear to have little practical significance. High levels of metabolically-inactive materials such as stored glycogen reserves lead to a reduction in the weight-specific oxygen consumption. Spawning animals show an increased oxygen consumption.     

Embryonic, Larval and Postlarval Development of the Tropical Clam, Anomalocardia Brasiliana (Bivalvia, Veneridae)

Anomalocardia brasiliana (Gmelin, 1791) is a venerid clam, distributed fromthe West Indies to Brazil, which lives shallowly burrowed inmuddy sands of mangrove lagoons in Guadeloupe. Development frominduced spawning to metamorphosed juveniles is described byusing light and scanning electron microscopy. The shell-fieldappears at the gastrula stage, 6 h after fertilization, andrapid embryonic development results in straight-hinge veligers, 18h after fertilization. These swimming veligers develop to swimming-crawlingpediveligers, then to benthic plantigrades with functional elongatedgill filaments without interruption in 15 days. The transitionalarched structures observed at the end of the pediveliger stagewere called `ctenidial crypts' to distinguish them from functionalgill filaments which exist only in metamorphosed juveniles.Metamorphosis, which occurs without a special environmental cue,is completed with the differentiation of the siphons in 300µmjuveniles. Thus, there is no delay of metamorphosis in thisspecies whereas a developmental hiatus has been described in mostplanktotrophic bivalves. Juveniles, 1 mm in shell-length withthe triangular shape, pointed posterior end and brown zig-zagstripes on the shell, typical of A. brasiliana have been obtained7 weeks after fertilization. However, a large variability ofindividual sizes and developmental stages within the same batchesmay indicate a high genetic variability. (Received 11 December 1997; accepted 30 April 1998)     

THE PALLIAL EYES OF CTENOIDES FLORIDANUS (BIVALVIA: LIMOIDEA)

The structure of the pallial eye in the Limidae has neverbeen elucidated properly, largely because they are difficultto see among the mass of surrounding mantle tentacles and becausethey are few, small, and lose their pigmentation when preserved.Possibly two eye types are present, simple cup-shaped receptorsin species of Lima, like those seen in the Arcoida, and morecomplex invaginated ones in Ctenoides. The pallial eyes (;18on both lobes) of Ctenoides floridanus are formed by invaginationof the middle mantle fold at the periostracal groove, so thatall its contained structures are derived from the outer andlight is perceived through the inner epithelia of this fold.The eye comprises a simple multicellular lens and a photoreceptiveepithelium beneath it of lightly pigmented cells and alternatingvacuolated, support cells. In some species of the Arcoidea, Limopsoidea and Pterioidea, pallialeyes occur on the outer mantle fold and thus beneath the periostracum(and shell). The pallial eyes of Ctenoides floridanus and otherpterioideans, e.g. species of the Pectinidae, occur on the middlefold and may thus have improved vision. In the Cardiodea, Tridacniidaeand Laternulidae (Anomalodesmata) pallial eyes occur on theinner folds. There is thus a loose phylogenetic trend, in which Ctenoidesis a critical link, of increasing eye sophistication correlatedwith the historical age of the clades possessing them. (Received 16 November 1999; accepted 20 January 2000)     

ERRATA

p. 183, footnote, for vittabus read vittatus p. 210. alternatus ... This entry is out of alphabetical order,and should follow after alsiosus ...