Fabrizio Marcondes Machado

A New Species of Cyamiocardium Soot-Ryen, 1951 from Shallow Waters off Brazil, with a Discussion on the Anatomical Characters of the Cyamiidae (Bivalvia: Cyamioidea)

Abstract. Cyamiocardium domaneschii n. sp. is described from shallow waters off the Southeastern coast of Brazil. An anatomical study provides comparisons with other Cyamioidea. It has a small shell (up to 3.1 mm in length), valves with a rounded contour, external radial sculpture, a distinct large prodissoconch, and hinge structure characteristics of the genus Cyamiocardium Soot-Ryen, 1951. Three well-defined pallial openings are present; tentacles border the anteriormost part of the pedal opening and the inhalant and exhalant apertures. The inner demibranchs are larger than the outers, do not have interlamellar junctions, and form a spacious brooding chamber. It is dioecious and developing oocytes are covered by a thin follicular tissue, which persists as a covering of each brooded young. Offspring are retained up to the juvenile stage, and are attached to the gill filaments by a long stalk. The foot has a narrow, grooved ventral sole; no byssus threads were observed. An active burrowing or crawling behavior is suggested for C. domaneschii n. sp., as there are well developed statocysts. This finding of a cyamiid from Brazil represents the extension of the geographical distribution of this family further north in the southwestern Atlantic Ocean. This study also reveals that some anatomical characters are variable in the genus Cyamiocardium: in C. denticulatum (Smith, 1907), there are only two pallial openings and its foot does not have a ventral sole. The attachment of young to the gills are not related to nourishment, and here for C. domaneschii n. sp. it is suggested that the stalk is only used as a “safety belt”, preventing embryos and juveniles to be released before the end of their development. More studies remain to be done on the anatomy of cyamioideans, particularly on living specimens; we paid attention to common characters used for discussions on the taxonomy and biology of these bivalves.

Spheniopsidae Gardner, 1928 (Bivalvia): Conchological Characters of Two New Species from off Brazil, Southwestern Atlantic

Abstract: The Spheniopsidae Gardner, 1928 comprises four living species of Spheniopsis Sandberger, 1861 and eight of Grippina Dall, 1912, the latter restricted to the Pacific Ocean, the former also occurring in the Atlantic. Spheniopsis brasiliensis new species and Grippina coronata new species are described from the Brazilian southeastern coast, based on a detailed study of their shells. They are distinguished from already described species mainly by differences in the outline of the valves, external sculpture and right hinge dentition. Shallow micro-pits present all over the outer surface of the dissoconch are viewed as similar to those already described for cuspidariids. They may, thus, represent further evidence for the relatedness of spheniopsids and cuspidarioideans. The new species from Brazil represent the first finding of these rare minute bivalves of this family from the southwestern Atlantic.

The organs of prey capture and digestion in the miniature predatory bivalve Spheniopsis brasiliensis (Anomalodesmata: Cuspidarioidea: Spheniopsidae) expose a novel life-history trait

ABSTRACT Spheniopsis brasiliensis, from depths of 17–148 m off the southern Atlantic coast of Brazil, is a predator of epipsammic micro-crustaceans which it sucks into the infra-septal chamber using a raptorial inhalant siphon and internally generated hydrostatic suction forces. Prey items, which include ostracods, are thought to be pushed into the funnel-shaped mouth using the foot. The stomach is capacious with a short style sac conjoined briefly with the mid gut and possessing a stubby crystalline style. Internal stomach architecture is simplified, with no identifiable sorting areas (unlike other cuspidarioids) and lined virtually completely by a gastric shield. The exoskeletal remains of digested prey are held in the posterior end of the stomach and not in a specialised waste storage pouch as in the con-familial Grippina coronata. The mid gut, hind gut and rectum are all extremely narrow and, thus, only the smallest of faeces can be accommodated and transmitted for anal discharge. Spheniopsis brasiliensis, like G. coronata is a self-fertilising simultaneous hermaphrodite with encapsulated lecithotrophic eggs brooded internally. Both taxa are thus ovovivaporous. It is also believed that both taxa are univoltine so that larvae and the exoskeletal prey remains are all released post mortem. Cuspidariids are generally regarded as dioecious but, recently, Cardiomya costellata has been shown to be a non-brooding simultaneous hermaphrodite. The distinguishing characters between cuspidariids and spheniopsids thus appear to be their differing reproductive strategies and life history traits.

Bivalves of the São Sebastião Channel, north coast of the São Paulo state, Brazil

The north coast of the Sao Paulo State, Brazil, presents great bivalve diversity, but knowledge about these organisms, especially species living subtidally, remains scarce. Based on collections made between 2010 and 2012, the present work provides a species list of bivalves inhabiting the intertidal and subtidal zones of the Sao Sebastiao Channel. Altogether, 388 living specimens were collected, belonging to 52 species of 34 genera, grouped in 18 families. Tellinidae, Veneridae, Semelidae, Ungulinidae, Mactridae, Solecurtidae, Corbulidae, Cardiidae, Lucinidae, Cooperellidae, Nuculidae, Psammobiidae, Donacidae, Solenidae, Periplomatidae, Thraciidae and Arcidae were the most representative families in this collection. Among the identified species, Caryocorbula caribaea , Codakia pectinella and Diplodonta punctata were intertidally abundant, while Macoma uruguayensis and Pitar fulminata were subtidally abundant.

Functional morphology of Cardiomya cleryana (d'Orbigny, 1842) (Bivalvia: Anomalodesmata: Cuspidariidae) from Brazilian waters: new insights into the lifestyle of carnivorous bivalves

Of the more than 800 Recent species of Anomalodesmata only 16 have been studied alive. The Septibranchia, comprising a number of carnivorous bivalve superfamilies, are no exception to this generalization and, until recently, no living member of this group has been studied since the 1980s. Collected from the shallow, shelf seabed off Brazil, Cardiomya cleryana is one of only a few species to have its morphology described in recent years and the first ever anomalodesmatan to be filmed alive. Important anatomical features such as a greatly extensible foot to secure itself in the sediment with a single byssal thread, exhalant siphon inter-tentacular projections and micro-papillae on the surface of the siphonal tentacles are described. Observations on the species’ behaviour have revealed a lifestyle hitherto not recorded for any septibranch, indeed any anomalodesmatan. The anchoring mechanism of C. cleryana using an extraordinarily long byssal thread is described for the first time. The life position of C. cleryana is at 45° to the sediment-water interface whereas other cuspidariids have been considered to orient themselves vertically. An anatomical comparison between Cardiomya and Bathyneaera has revealed close affinities. This study thus provides new insights into the morphology and behaviour of the Cuspidariidae.

Shell morphology of a new Brazilian species of the family Kelliellidae, with a brief review of the genus Kelliella (Mollusca: Bivalvia)

The bivalves of the families Vesicomyidae and Kelliellidae are common bottom inhabitants of the deep-sea, with some taxonomic controversy concerning the smaller forms of the former, which are frequently confused as species of the latter. Based on specimens collected from shallow waters of the southeastern Brazilian coast, a new species of Kelliella is described, through a detailed description of its shell, which is compared with those from other species already referred for this genus. Its minute valves with rounded contour and a marked lunule are very similar to those of K. miliaris, the type-species of kelliellids, differing in only some details of the hinge dentition. Most species of the genus Kelliella are currently assigned to the genus Vesicomya, causing great difficulties as far as knowledge of the real diversity of the family Kelliellidae. This study represents part of a continuing work on new discoveries regarding the marine molluscs of the southwestern Atlantic. Here, a review of the genus Kelliella is provided, highlighting some shell features that will be important in future comparative studies between these bivalve families.

Shell Morphology and Sperm Ultrastructure of Solen tehuelchus Hanley, 1842 (Bivalvia: Solenidae): New Taxonomic Characters

Abstract: Solen tehuelchus Hanley, 1842 is currently the only razor-clam reported from Brazilian waters. Although its shell is well known and similar to the other Solenoidea, their anatomical aspects are poorly studied. Recently some living specimens of S. tehuelchus were obtained from a Brazilian beach, allowing the removal of their testes for an ultrastructural analysis. In order to add a new anatomical feature for this species and provide a brief comparison between some related taxa, the shell and sperm ultrastructure were described in detail. The present study showed that characteristics of the spermatozoa of S. tehuelchus are similar to those of other solenids, although certain sperm ultrastructural characteristics such as a short acrosome with an electron-dense base and rounded nucleus are also similar to the species Tagelus plebeius (Lightfoot, 1786) (Solecurtidae). Herein, we have added new anatomic and taxonomic data hitherto unknown to science. The sperm morphology of S. tehuelchus, might in the near future bring new insights into the systematic of Solenidae.