Spawning behaviour and egg capsules of Concholepas concholepas (Mollusca: Gastropoda: Muricidae)

Observations on the spawning behaviour of the commercially important muricid snail Concholepas concholepas are reported. The sequence of events relating to external transportation, molding and hardening, and attachment of the egg capsules to a substratum were timed and divided into 6 major events. The snails studied in the laboratory spawned between April and Septemer. These results and data from the literature reveal an all-year-round spawning activity for the species. The frequency, size and time of spawning were studied over 1 year. Spawning activity always began at night, suggesting that the species retains its spawning rhythm in the laboratory. These was a direct relationship between length of the snail and size of the capsules spawned. No nutritive eggs were found; the number per capsule varied between 668 and 14,250 according to capsule size. Hatching time varied between 69 and 128 days at 13.5° to 14.5°C.     

Field observations on the rhythmic behaviour of Nerita textilis (Gastropoda: Prosobranchia)

Field observations on Nerita textilis Dillwyn inhabiting rocky cliffs at Sar Uanle (Southern Somalia) revealed that during the resting phase some of the snails are scattered on the upper cliff and some are clustered at lower levels. During feeding they all migrate downward, but to different extents. Maximum activity of both groups occurs during low water (LW) between midday and midnight. During spring tides (ST), the scattered snails reside higher up and make smaller feeding excursions than during neap tides (NT). During ST, some clustered snails join the belt of scattered individuals, while the trend reverses during NT. A diurnal and a tidal component appear in their periodicity.Publication of the Centro di Studio per la Faunistica ed Ecologia Tropicali del C.N.R. Researches on the coast of Somalia. The shore and the dune of Sar Uanle, No. 14.     

Isotopic composition, growth rates and biological behaviour of Chamelea gallina and Callista chione from the Bay of Trieste (Italy)

Shells of the bivalve molluscs Chamelea gallina L. and Callista chione L. from the Bay of Trieste (northern Adriatic) were analysed for their oxygen and carbon isotopic composition. The main purpose of this study was to obtain detailed information on the biological behaviour and, particularly, on the growth rates and the settlement time of these two species. Isotopic measurements were carried out on "spot" samples collected from the umbo to the ventral margin of each shell. The results obtained from nine specimens of C. gallina (plus some 20 specimens studied only for the isotopic composition of their initial umbo and for the last section of their ventral edge) and from two specimens of C. chione allow the following conclusions: (1) the calcium carbonate of C. gallina shells is not deposited under isotopic equilibrium conditions with the environmental variables (temperature and oxygen isotopic composition of seawater); (2) this species usually initiates precipitation of carbonate during the springtime, although some late summer-early autumn generation also occurs; (3) the rate of calcium carbonate deposition decreases with increasing age, and the overall accretion rate is a rather slow one; (4) there is a negative correlation between the carbon isotopic composition and the size of each shell; (5) the mean growth rate of the shells can be easily evaluated according to the oxygen isotopic composition of the spot measurements; (6) the specimens of C. chione do not precipitate the calcium carbonate of their shells in isotopic equilibrium with environmental conditions; (7) their accretion rate is rather fast during the first years of their life and progressively and considerably reduced after about 5 years; (8) the carbon isotopic composition of these shells does not show the marked evolution towards more negative values shown by C. gallina, suggesting that neither respiratory CO₂ nor carbon species derived from the oxidation of organic matter are systematically used for the precipitation of shell carbonate; and (9) a marked preference for the warmer half of the year is shown by the oldest specimen of C. chione (12 years).     

Studies on the defensive behaviour ofHypselodoris species (Gastropoda: Nudibranchia): Ultrastructure and chemical analysis of mantle dermal formations (MDFs)

The mantle dermal formations (MDFs) ofHypselodoris webbi (D'orbigny, 1839), andH. cantabrica (Bouchet and Ortea, 1980) are globular sub-epidermal structures located in the cephalic and caudal regions. Histologically they consist of an accumulation of vacuolate cells surrounded by a basal lamina and an outer muscular capsule. Chemical analysis ofH. webbi MDFs reveals the presence of high concentrations of longifolin, a well known deterrent furanosesquiterpenoid that had been previously isolated from this species. In the present paper it is demonstrated that the great majority of longifolin accumulated in the mantle ofH. webbi is stored in the MDF vacuolar cells. This finding strongly suggests that such structures act as chemical weapons against predation, mainly protecting vital organs such as the head, rhinophores and gills.     

Evolution and systematics in Haliotidae (Mollusca: Gastropoda): inferences from DNA sequences of sperm lysin

Abalone taxonomy and systematics have remained unresolved: neither stable species-level nomenclature nor a cladistic hypothesis of relationships among species have been established. To infer the phylogeny of the genus Haliotis and to identify species using molecular data, we compared complementary DNA (cDNA) sequences of sperm lysin from 27 species-group taxa from California, Japan, Australia, New Zealand, Taiwan, Borneo, Madagascar, South Africa, Greece, France, Italy and the Azores. The lysin cDNA sequences reveal that 22 of the 27 taxa are clearly distinguishable by >20 nucleotide differences. Of the remaining 5, H. coccinea from the Azores may be a subspecies of H. tuberculata, if not a sibling species (10 nucleotide differences). The other four taxa are most probably the same species as one of the 22 taxa: the lysin sequences are almost identical between H. madaka and H. discus hannai, H. conicopora and H. rubra, H. diversicolor supertexta and H. diversicolor aquatilis, and H. tuberculata lamellosa and H. tuberculata tuberculata. The phylogeny of lysin cDNA suggests that there are three groups among the 27 species-group taxa: (1) all California species and 3 Japanese species (H. gigantea, H. discus hannai, and H. madaka): (2) 1 New Zealand species (H. iris); (3) 1 Japanese species (H. diversicolor aquatilis), Indo-West Pacific species and European species. These groups can be assigned to three previously recognized subgenera (Nordotis, Paua and Padollus) in the genus Haliotis. Two historical hypotheses are proposed to explain the biogeography and evolution within these abalone: (1) Tethyan distribution of the ancestral abalone, during the Cretaceous, followed by extinction in most of the habitat, but radiation in California and Southeast Asia which later spread to the other areas; (2) North Pacific rim distribution of the ancestral abalone, followed by dispersal to the other areas during the Paleogene.     

Spawning,larval development and settlement behaviour of Gibbula cineraria (Gastropoda: Prosobranchia) with a reappraisal of torsion in gastropods

Cultures of developing larvae of Gibbula cineraria (L.) were obtained from adults spawning in the laboratory, and these cultures were reared to settlement of the larvae at 9 days. Dispersal of the outer jelly coat of the egg appeared to be delayed in the presence of spermatozoa. Early cleavage followed the typical spiral pattern, and gastrulation was by epiboly. The trochophore larvae hatched at about 28 h, before shell-formation began. The first 90° of torsion was completed between 48 and 56 h. The second part of torsion was completed within 4 days, and preliminary attempts to retract into the shell were made at 76h. After 96 h, although torsion was complete, the larvae were still unable to retract fully into the shell. The larvae remained in a stage of swimming-attempted creeping until the 4th or 5th day after torsion was complete, but were unable to pull the shell upright until the end of this time. Throughout this stage, the velum was reduced and was finally shed. The animals all died after metamorphosis, which occurred at about 9 days, when the larval shell comprised 1 1/2 whorls, with a breadth of 250 to 300m. Settlement appeared to be passive, i.e., governed by wave action and tides. In the light of these observations, theories concerning torsion are reappraised. The advantage to the larva of torsion is not clear, as the larvae are not able to retract into the shell until after metamorphosis, yet it is clear from previous authors' observations that the first part of torsion in most gastropods involves only larval structures. This makes it difficult to suggest that torsion is entirely of advantage to the adult snails. It is thus proposed that the two components of torsion may have evolved independently. The first, relatively rapid component of torsion, resulting in 90° of displacement of the mantle cavity in relation to the visceral mass, may be of advantage to the swimming larva. The final, slower component of torsion may be of advantage to the newly-metamorphosed benthic snail, and is the only component of torsion found in those gastropods which have no free-swimming larva.     

A molecular phylogeny of the Patellogastropoda (Mollusca: Gastropoda)

Phylogenetic analyses of partial 18S rDNA sequences from species representing all living families of the order Patellogastropoda, most other major gastropod groups (Cocculiniformia, Neritopsina, Vetigastropoda, Caenogastropoda, Heterobranchia, but not Neomphalina), and two additional classes of the phylum Mollusca (Cephalopoda, Polyplacophora) confirm that Patellogastropoda comprises a robust clade with high statistical support. The sequences are characterized by the presence of several insertions and deletions that are unique to, and ubiquitous among, patellogastropods. However, this portion of the 18S gene is insufficiently informative to provide robust support for the monophyly of Gastropoda, or to address the division of the Gastropoda into the subclasses Eogastropoda (= Patellogastropoda + hypothetical coiled ancestors) and Orthogastropoda. These sequence data invariably group Patellogastropoda in a weakly supported clade with cocculiniform limpets, despite greater sequence divergences between Patellogastropoda and “Cocculiniformia” than between the Patellogastropoda and Orthogastropoda. Partial 18S sequences support the inclusion of the family Neolepetopsidae within the superfamily Acmaeoidea, and refute its previously hypothesized position as sister group to the remaining living Patellogastropoda. This region of the 18S rDNA gene diverges at widely differing rates, spanning an order of magnitude among patellogastropod lineages, and therefore does not provide meaningful resolution of the relationships among higher taxa of patellogastropods. Data from one or more genes that evolve more uniformly and more rapidly than the 18S rDNA gene (possibly one or more of the mitochondrial genes) seem more likely to be informative about relationships within Patellogastropoda. Received: 5 February 1999 / Accepted: 16 May 2000     

Chemical defense and evolution in the Sacoglossa (Mollusca: Gastropoda: Opisthobranchia)

Summary. Recent advances in both the systematics and the natural products chemistry of the order Sacoglossa (=Ascoglossa) in the gastropod subclass Opisthobranchia suggest a revised and improved historical account of the evolution of the group. Although the algal genus Caulerpa makes a suitable model for the ancestral food of the order, other siphonaceous algae are consistent with both morphological and chemical data. At an early evolutionary stage terpenoids are sequestered from the food, and used defensively, often with modification. With an evolutionary switch to different kinds of algal food, there is often a shift to other, related defensive chemicals. A switch to new food source sometimes leads to the abandonment of chemical defense, but in other cases there is de-novo synthesis of defensive metabolites. The synthesis of polypropionates, which are used defensively, occurs in some other gastropods, but otherwise is known only in fungi. The systematic distribution of the defensive polypropionates suggests that their defensive use has evolved several times among gastropods. Failure to detect them may mean that synthetic capacity has evolved more than once, or it may mean that they exist at low levels, perhaps having a non-defensive function. Received 9 February 1998; accepted 20 March 1998.     

Intertidal distribution and long-term movements of Littorina irrorata (Mollusca: Gastropoda)

The distribution of Littorina irrorata Say on a low-energy barrier beach on the northern Gulf of Mexico is described, and correlated with the presence of Spartina alterniflora and other plants in the upper intertidal zone. The movements of 66 individually tagged snails were followed in the S. alterniflora zone for an average of 226 days, during which time an average of 10.6 positions were recorded per snail. The snails travelled an average total path distance of at least 995 cm, but due to contorted paths, ended up an average resultant distance of only 399 cm away from their original positions. They moved an estimated resultant distance of approximately 20 to 25 cm per activity period. Despite a slight offshore movement during the fall and winter, the snails moved more parallel to the shoreline than perpendicular to it.     

Two modes of development in the morphospecies Crepidula dilatata (Gastropoda: Calyptraeidae) from Southern Chile

In Chinquihue Bay, a sheltered locality in Southern Chile, female Crepidula dilatata Lamarck brood egg masses which differ in intracapsular development. In some, all eggs develop and are hatched as free veliger larvae (indirect development). In others, only some of the eggs develop and hatch as young adults (direct development), the rest being consumed as nurse eggs. Two possible interpretations are considered: intrapopulation variation of developmental pattern in a species, and the coexistence of two sibling species. Stages of the intracapsular development are described and illustrated. Fecundity varies according to size of the female. For females brooding eggs with indirect development it is estimated at between 3840 and 85575 embryos per spawn; for females with eggs undergoing direct development, embryo production per egg mass is estimated at between 70 and 812. A comparison is made between females brooding the two kinds of egg masses. Minor differences exist in adult coloration, shape of egg capsules, egg diameters, spawning season and their abundance and distribution in the intertidal. Brooding females with eggs displaying indirect development are significantly larger than those with eggs of direct development. The latter females form chains subtidally but not intertidally as do females bearing eggs with indirect development. On these females with pelagic larvae, chains frequently include sedentary males which reach large sizes. On basal females with direct development, chains contain mostly other females, suggesting that matings are temporary and by errant males. These results are compared with existing information in the literature for other species both in this genus and in other marine invertebrates. It is concluded that two sympatric sibling species with different modes of development are present in the morphospecies C. dilatata Lamarck in Southern Chile.Devoted to Dr. E.F. Kilian, Zoologisches Institut der Universität Gießen, FRG.     

Adsorption of methylene blue onto activated carbon derived from periwinkle shells: kinetics and equilibrium studies

Periwinkle shell, an abundant and inexpensive natural resource, was used to prepare activated carbon by physicochemical activation with potassium hydroxide (KOH) and carbon dioxide (CO₂) as the activating agents at 850 °C for 2 h. The adsorption equilibrium and kinetics of methylene blue dye on such carbon were then examined at 25 °C. Adsorption isotherm of the methylene blue (MB) on the activated carbon was determined and correlated with common isotherm equations. The equilibrium data for methylene blue adsorption well fitted to the Langmuir equation, with maximum monolayer adsorption capacity of 500.00 mg/g. Two simplified kinetic models including pseudo-first-order and pseudo-second-order equation were selected to follow the adsorption processes. The adsorption of methylene blue on activated carbon derived from periwinkle shell could best be described by the pseudo-second-order equation. The kinetic parameters of this best-fit model were calculated and discussed.     

Interactions between shear rates and biofilms affecting exploratory behaviour by cyprids ofElminius modestus (Cirripedia)

The behaviour ofElrninius modestur Darwin cyprids suggests interaction between surface bacterial films acclimated to contrasting shear regimes and the range of shear rates over which observations were made. Exploratory behaviour is encouraged by filmed surfaces rather than biologically clean surfaces. Increasing shear rates encourage attachment to all surfaces, but cyprids detach from high-shear-acclimated films less often than from either low-shear-acclimated films, or clean surfaces. Furthermore, numbers of attaching cyprids are consistently lower on low-shear-acclimated films than on high-shear films.     

Imposex in Hexaplex trunculus (Gastropoda: Muricidae): first results from biomonitoring of tributyltin contamination in the Mediterranean

Imposex (the occurrence of penis and vas deferens in females) in Hexaplex trunculus collected from Malta (Central Mediterranean) in 1992 is reported. This phenomenon is related to the levels of tributyltin (TBT) in the organisms as well as in sediments. Imposex indices (relative penis size and vas deferens sequence) are used to biomonitor coastal contamination by TBT for the first time in the Mediterranean. In its response to TBT, H. trunculus is ranked as one of the most sensitive neogastropod species studied so far. Accumulation of TBT and its metabolites in the digestive glands, gonads and the rest of the body are described, and sex-related differences are shown. No preferential female mortalities are recorded in populations exposed to high levels of TBT. However, a reported shift in the size frequency distribution of H. trunculus in contaminated sites, towards bigger snails, may suggest reduced reproductive potential.     

Introduction and spread of Philine auriformis (Gastropoda: Opisthobranchia) from New Zealand to San Francisco Bay and Bodega Harbor

Specimens of Philine auriformis have been observed in the southern portion of San Francisco Bay, California, since summer 1992. Specimens from Bodega Harbor were first discovered from intertidal mudflats in April 1994 and probably represent the spread of the San Francisco Bay population to a neighboring estuary. Their numbers have increased steadily and the species is now well established in both estuaries. Examination of the anatomy of specimens collected from California was compared with that described from New Zealand. No significant differences in anatomy were detected in animals from these different localities. It is suggested that the species was introduced into California waters by release of ballast water from international shipping.     

Recruitment and juvenile survival in the sea hare Aplysia juliana (Gastropoda: Opisthobranchia)

The specificity in settling response of larval Aplysia juliana (Quoy and Gaimard, 1832) on species of its food algae, Ulva spp., provided a rare opportunity for the quantitative study of recruitment and early survival rates in a non-sessile marine invertebrate. Post-metamorphic juveniles spend about 3 weeks feeding and growing on the algae before moving to the rocky habitat of the adults. Recruitment and survival were studied by collecting weekly samples of algae and holding them in the laboratory until the recruits were large enough to be seen and reliably counted. Recruitment occurred throughout the year, although the rates were relatively low in late winter and spring. Recruitment was monitored relative to algal weight and bottom area. Variation in larval abundance and algal standing crop influenced recruitment to the study area. Mortality during the juvenile stage was very high in all cases, although the rates and shapes of the survivorship curves varied between algal species and location.     

Reproductive cycle and gametogenesis in the black abalone Haliotis cracheroidii (Gastropoda: Prosobranchiata)

Seasonal changes in gonald size and stages of gametogenesis in the black abalone Haliotis cracheroidii were related to changes in environmental parameters. H. cracheroidii showed an annual reproductive cycle terminating in a synchronized spawning in late summer. Gametogenesis was initiated immediately after spawning. Gametes were present in the gonad through the winter months. Gametogenesis was initiated a second time in the spring months. Maximal gonad growth (to a gonad index of 20%) occurred during summer months prior to spawning. Changes in gonad size andperiods of initiation of gametogenesis revealed no apparent correlation with changes in seasonal water temperature. Changes in gonad size showed no apparent relation to change in day length. Total polysaccharide levels in foot tissue changed seasonally, indicating that food availability is probably not a factor in directly regulating gonad growth. Gonad index data for the chiton Katharina tunicata (collected over a 10 year period) showed no apparent correlation to seasonal change in water temperature.     

Phylogenetic relationships within Ovulidae (Gastropoda: Cypraeoidea) based on molecular data from the 16S rRNA gene

Closely interacting groups, such as hosts and parasites, sometimes provide useful models to study evolution and adaptive processes. In Ovulidae, a widespread family of specialised browsing carnivorous molluscs that feed on polyps and tissues of Anthozoa, close association with the host has produced a plethora of adaptations affecting shell morphology, colour pattern and mantle shape. These morphological characters have been widely used in ovulid taxonomy, although putative differences are often based on trivial and inconsistent variations. In this work we used a molecular approach to generate the basal phylogeny of the family. Phylogenetic analyses of mitochondrial 16S rRNA gene sequences of 32 species from 23 genera reveal unexpected taxonomic groupings from the genus up to the family level, as well as unexpected phenomena of homoplasy in conchological features. Since molecular phylogenies also provide an evolutionary framework where character transformations are polarised, we used this basal ovulid phylogeny to explore the specificity of the association and the degree of morphological adaptation to the host.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00227-005-1566-0.Communicated by R. Cattaneo-Vietti, Genova     

Reproductive effort and r-and K-selection in two species of Lacuna (Gastropoda: Prosobranchia)

The growth and spawning of Lacuna pallidula and L. vincta were measured in the laboratory over 7 months. In both cases, there were significant differences between the mean number of eggs per batch or weight of egg batches from females of the same species and also between rates of spawning by females of the same species. The reproductive effort of L. vincta, estimated by the ratio total spawn weight: body weight and by the time taken to exceed body weight in cumulative spawn, is approximately twice that of L. pallidula. L. vincta has a long-lived planktotrophic larva, while L. pallidula has direct, lecithotrophic development, and therefore in this instance planktotrophic development seems to be more expensive to the parent than lecithotrophic development. Published work on two Pacific seastars leads to the opposite conclusion, and it is suggested that the paradox can be resolved in terms of r-K-selection theory. In both cases, the r-selected species has a higher reproductive effort, notwithstanding that the snail is planktotrophic and the seastar lecithotrophic in development.     

Competition and interaction between Neosarmatium smithi (Crustacea: Grapsidae) and Terebralia palustris (Mollusca: Gastropoda) in a Kenyan mangrove

 In a Kenyan mangrove, we studied the interactions between the gastropod Terebralia palustris and the crab Neosarmatium smithi when foraging on decaying mangrove leaves. Interactions are considerable on account of their wide overlap in zonation (Rhizophora mucronata belt), food items (mangrove leaves) and activity window (diurnal low water). The snails find a leaf by a systematic transecting of the platform and eat the leaf after crawling on to it, usually en masse. The crabs rarely venture beyond 80 cm from their burrows, and once they find a leaf they quickly drag it back into their burrow, probably to reduce the strong intra-specific competition. A crab is able to drag a leaf away even if a number of snails are already feeding on it, by strongly pulling the leaf away or by pushing the snails off the leaf. The success of the “thief ” depends on both the crab's size and the number of snails on the leaf. Received: 25 July 1999 / Accepted: 27 April 2000