A new species of Chlamydoconcha Dall, 1884, from southeastern Brazil (Bivalvia: Chlamydoconchidae)

The second species in the genus Chlamydoconcha is described. Chlamydoconcha avalvis new species, occurs off the coast of Rio de Janeiro coast, in southeastern Brazil. The new species has very reduced valves acid a mantle surrounding the entire body, two features of the genus. The outer surface of the mantle lacks papillae except for a single cite located close to the excurrent siphon. These are distinctive characters of Chlamydoconcha orcutti Dall, 1884, from the eastern Pacific coast of North America, the single other known species of the genus. Some of the more interesting anatomical characters of the new species are: posterior pair of retractor muscles Of foot free front valves, absence of adductor muscles, gastric style sac totally separated from intestine, and the presence of a single (excurrent) siphon.

PLICATULOSTREA, A NEW GENUS OF PLICATULIDAE (BIVALVIA: PECTINOIDEA) FROM THAILAND

Plicatulostrea onca, a new genus and species of Plicatulidae, is described based on shell and anatomy. The samples were collected under intertidal rocks at Kungkrabaen Bay, Thailand. Plicatulostrea differs from other plicatulids mainly in lacking undulations or shell sculpture, by long projections of the hinge teeth of the right valve and extreme body compression. Plicatulostrea onca has a radially arranged spots at the shell surface and typical plicatulid anatomy, differing mainly by the richness of papillae on the mantle edge and by invasion of the gonad along the mantle lobes. Some comments on the anatomy of the family are also provided.

COMPARATIVE MORPHOLOGICAL STUDY OF SOME TELLINIDAE FROM THAILAND (BIVALVIA: TELLINOIDEA)

A comparative study of seven species of Tellinidae, collected at Kungkrabaen Bay, Gulf of Thailand, is presented. The species are Serratina capsoides (Lamarck, 1818), Moerella cf. Miens (Deshayes, 1854), Cadella cf. semen (Hanley, 1845), Pinguitellina cf. pinguis (Hanley, 1844), Elpidollina sp., and Tellinides timorensis (Lamarck, 1818) of the subfamily Tellininae, and Macomona sp. of the subfamily Macominae. With the objective of performing the study in a comparative and testable scenario, a phylogenetic analysis was carried out based on 43 morphological characters (94 states). A single cladogram was obtained as follows: (Serratina capsoides (Tellinides timorensis (Pinguitellina cf. pinguis (Cadella cf. semen (Moerella cf. Miens (Elpidollina sp. Macomona sp.)))))). A semelid and a solenid were operationally analyzed as part of the ingroup; polarisation was based on a plicatulid. In this analysis, Tellinoidea and Tellinidae were monophyletic, supported by 19 and 9 synapomorphies, respectively. Tellininae was paraphyletic. Good and significant morphological differences were found for all taxa, including at the species level. Some structures are reported for the first time, such as pseudogills, insertion of the pedal protractor dividing the anterior adductor muscle, and a circular muscle surrounding part of the anterior adductor muscle.

Anatomical description of Solen cf. exiguus DUNKER from Thailand (Bivalvia: Solenidae)

An anatomical description of the solenid Solen cf. exiguus DUNKER 1862, collected in the Gulf of Thailand, is provided. The anatomical features include high antero-posterior elongation; mantle lobes widely fused with each other; powerful pallial muscles; fused siphons with capacity of autotomy; wide and partially hollow foot; complete separation between gastric style sac and adjacent portion of intestine; all possible common characters of the family. Some so far exclusive attributes include short anterior pallial tentacles; pair of muscular valves at base of siphons; and arrangement of tentacles at siphonal tip. A short discussion on the taxonomy of the Solen exiguus/leanus complex is also included.

COMPARATIVE ANATOMICAL STUDY OF TWO SPECIES OF SEMELE FROM THAILAND (BIVALVIA: TELLINOIDEA)

An anatomical description of two semelids from Thailand is presented, based on samples from Kungkrabaen Bay, Gulf of Thailand. The species are Semele sinensis A. Adams, 1853, and S. carnicolor (Hanley, 1845), both with Indo-Pacific distributions. Morphology in these two species is typically tellinoidean, each with a long internal ligamental element (resilium), a distance between the inner fold of the mantle edge and the other two folds, long and branched gastric ducts to the digestive diverticula, and a stomach diverticulum located in the posterodorsal corner of the gastric chamber, projecting posteriorly. The main anatomical differentiation between the two species is in the character of the labial palps.

Revision of the genus Spinosipella (Bivalvia : Verticordiidae), with descriptions of two new species from Brazil

A revision of the deep-water verticordiid genus Spinosipella is provided, based on conchological and anatomical characters. The genus is considered distinct from Verticordia (of which it was considered a subgenus) based on the strong ribs, prickly surface, reduction of lunula, relative large size, weakly spiral valve shape, and other characters. The following species are considered in the genus: (1) Spinosipella agnes new species, ranging from Florida, USA, to Rio de Janeiro, Brazil, and also including the Porcupine Abyssal Plain in the North Atlantic; (2) S. tinga new species, occurring from Rio de Janeiro to Rio Grande do Sul, Brazil; (3) S. acuticostata (Philippi, 1844), a Pliocene fossil from southern Italy; (4) S. deshayesiana (Fischer, 1862), from south and central Indo-Pacific (S. ericia Hedley, 1911, the type species of the genus, was revealed to be a new synonym of S. deshayesiana); and (5) S. costeminens (Poutiers, 1981), from the tropical west Pacific. The five species differ mainly in conchological details of the number and size of ribs, of the prickly sculpture, shape of the shell, of the hinge and the degree of convexity. Anatomical description is also provided for the two Pacific species, which differ among themselves mainly by the size of the pair of renal folds. From the standpoint of anatomical characters, the more significant are: the wide lithodesma; the elongation of the auricles, crossing the roof of pallial cavity; a tall digital fold in posterior region of supraseptal chamber; the low but wide palps; the muscular, gizzard-like stomach; the complete separation of both constituents of the hermaphroditic gonad (a ventro-posterior testicle and a centro-dorsal ovary), and a complete fusion of the visceral ganglia.

Early development, survival and growth rates of the giant clam Tridacna crocea (Bivalvia: Tridacnidae)

Tridacnid clams are conspicuous inhabitants of Indo-Pacific coral reefs and are traded and cultivated for the aquarium and food industries. In the present study, daily growth rates of larvae of the giant clam Tridacna crocea were determined in the laboratory during the first week of life. Adults were induced to spawn via intra-gonadal serotonin injection through the byssal orifice. After spawning oocytes were collected, fertilized and kept in 3 L glass beakers and raceways treated with antibiotics to avoid culture contamination. Larvae were fed twice with the microalga Isochrysis galbana and zooxanthellae were also offered twice during the veliger stage (days 4 and 6). Larval length was measured using a digitizing tablet coupled to a microcomputer. Larval mortality was exponential during the first 48 hours of life declining significantly afterwards. Mean growth rate was 11.3 mu m day-1, increasing after addition of symbionts to 18.0 mu m day-1. Survival increased to ca. 75% after the addition of zooxanthellae. The results describe the growth curve for T. crocea larvae and suggest that the acquisition of symbionts by larvae may be useful for larval growth and survival even before larvae have attained metamorphosis.

Nuculidae (Bivalvia) in the Cape Melville Formation, King George Island, Antarctica, with an overview of the bivalve fauna

Nuculid bivalves of the Cape Melville Formation (Early Miocene, King George Island) are reviewed. Ten bivalve taxa are listed from the formation in the families Nuculidae (two species), Sareptidae, Malletiidae, Limopsidae (two species), Limidae, Pectinidae, Hiatellidae, and Periplomatidae. The Nuculidae consist of two species of Leionucula Quenstedt, 1930. One of these, L. melvilleana n. sp., is described and the other consists of the two species named previously by Anelli et al. (2006), which are demonstrated to be synonymous and are assigned to the species Leionucula frigida (Anelli, Rocha-Campos, Santos, Perinotto & Quaglio 2006). This assemblage, dominated by protobranchs (89% of specimens), is a typical fauna of offshore soft substrates, with a few specimens transported from hard substrates nearby. The diversity of Nuculidae has decreased in the Antarctic region through the Cenozoic.

Early development, survival and growth rates of the giant clam Tridacna crocea (Bivalvia: Tridacnidae)

Tridacnid clams are conspicuous inhabitants of Indo-Pacific coral reefs and are traded and cultivated for the aquarium and food industries. In the present study, daily growth rates of larvae of the giant clam Tridacna crocea were determined in the laboratory during the first week of life. Adults were induced to spawn via intra-gonadal serotonin injection through the byssal orifice. After spawning oocytes were collected, fertilized and kept in 3 L glass beakers and raceways treated with antibiotics to avoid culture contamination. Larvae were fed twice with the microalga Isochrysis galbana and zooxanthellae were also offered twice during the veliger stage (days 4 and 6). Larval length was measured using a digitizing tablet coupled to a microcomputer. Larval mortality was exponential during the first 48 hours of life declining significantly afterwards. Mean growth rate was 11.3 μm day-1, increasing after addition of symbionts to 18.0 μm day-1. Survival increased to ca. 75% after the addition of zooxanthellae. The results describe the growth curve for T. crocea larvae and suggest that the acquisition of symbionts by larvae may be useful for larval growth and survival even before larvae have attained metamorphosis.

Permian non-marine bivalves of the Falkland Islands and their palaeoenvironmental significance

We describe the occurrence of non-marine bivalves in exposures of the Middle Permian (Capitanian) Brenton Loch Formation on the southern shore of Choiseul Sound, East Falklands. The bivalves are associated with ichnofossils and were collected from a bed in the upper part of the formation, within a 25 cm thick interval of dark siltstones and mudstones with planar lamination, overlain by massive sandstones. The shells are articulated, with the valves either splayed open or closed. At the top of the succession, mudstone beds nearly 1.5 m above the bivalve-bearing layers yielded well-preserved Glossopteris sp. cf. G. communis leaf fossils. The closed articulated condition of some shells indicates preservation under high sedimentation rates with low residence time of bioclasts at the sediment/water interface. However, the presence of specimens with splayed shells is usually correlated to the slow decay of the shell ligament in oxygen-deficient bottom waters. The presence of complete carbonized leaves of Glossopteris associated with the bivalve-bearing levels also suggests a possibly dysoxic-anoxic bottom environment. Overall, our data suggest that the bivalves were preserved by abrupt burial, possibly by distal sediment flows into a Brenton Loch lake, and may represent autochthonous to parautochthonous fossil accumulations. The shells resemble those of anthracosiids and are herein assigned to Palaeanodonta sp. aff. P. dubia, a species also found in the Permian succession of the Karoo Basin, South Africa. Our results confirm that (a) the true distributions in space and time of all Permian non-marine (freshwater) bivalves are not yet well known, and (b) there is no evidence for marine conditions in the upper part of the Brenton Loch Formation.

NEW FOSSIL RECORDS OF PLEISTOCENE MARINE MOLLUSKS IN SOUTHERN BRAZIL

Fossils of the gastropods Diodora patagonica, Zidona dufresnei, Olivancillaria carcellesi, Lamniconus lemniscatus carcellesi and the bivalve Arcinella brasiliana are registered for the first time from the outcrops of Chui Creek, on the coastal plain of Rio Grande do Sul State, southernmost Brazil, together with other taxa previously known elsewhere. The specimens were collected in a shallow Pleistocene marine facies exposed at the base of the banks of the creek, in a fossil concentration possibly formed by storm events. The taxa described here live in shallow environments (with the exception of A. brasiliana and Z. dufresnei) with sandy bottoms (except for D. patagonica, T patagonica, B. odites, C. rhizophorae and A. brasiliana). The presence of L. lemniscatus carcellesi, found living today only in Uruguay and Argentina, indicates a wider distribution for this taxon during the late Pleistocene.

Production of Excirolana armata (Dana, 1853) (Isopoda, Cirolanidae) on an exposed sandy beach in southeastern Brazil

The somatic and gonad productions of the cirolanid isopod Excirolana armata were analyzed by taking monthly samples from December 2003 to November 2005 on Una beach, So Paulo state (24A degrees S), southeastern Brazil. Sampling was performed along three fixed transects established from the base of the foredunes to the waterline. Weight-specific growth rate was used to estimate the E. armata somatic production for 2004 and 2005, separately. The gonad production was estimated based on the monthly reproductive potential (mean number of eggs/embryos per female x monthly abundance of ovigerous females with near-release broods) for 2004. The annual somatic production of E. armata population varied from 15.57 to 17.25 g AFDW m(-1) year(-1) and the somatic production/biomass ratio (P (s)/B) from 3.55 to 3.14 year(-1) for 2004 and 2005, respectively. The P (s)/B ratios were higher for males (4.02 and 3.19 year(-1) for 2004 and 2005) than for females (3.10 year(-1) for both years). The annual gonad production (P (g) = 1.07 g AFDW m(-1) year(-1)) contributed about 15 and 6% to the total production (P (s) + P (g)) of females and the population, respectively. The proportion of gonad to somatic production of females (P (g)/P (s)) increased with individual size (ca 90% in the 7.5 mm size class), and the annual weight-specific gonad production (P (g)/B ratio) was estimated to 0.24 year(-1). The high P (s)/B ratios estimated for E. armata derive from the fast growth of individuals and show the importance of this population to the energy flow on Una beach ecosystem. However, the low percentage of juveniles verified in this population and in other studies of populations of the genus Excirolana is discussed as an important source of underestimation of P (s)/B ratio.