Abstract
The aim of the study is to describe in detail, for the first time, the internal and external anatomy of Cyrtopleura costata, which displays ellipsoid and elongated valves with beige periostracum, the anterior adductor muscle unites the valves in the pre-umbonal region, with abduction capacity in its dorsal half, sparing the ligament. Two accessory valves are identified: the mesoplax (calcified) located in the umbonal region; and the protoplax (corneus) above the anterior adductor muscle. Internally there is a pair of well-developed apophysis that supports the labial palps and the pedal muscles, and support part of the gills. The posterior half of mantle ventral edge is fused and richly muscular, working as auxiliary adductor muscle. The siphons are completely united with each other, the incurrent being larger than the excurrent. The foot is small (about ⅛ the size of the animal). The kidneys extend laterally on the dorsal surface, solid, presenting a brown/reddish color. The style sac is well developed and entirely detached from the adjacent intestine. The intestine has numerous loops and curves within the visceral mass. The fecal pellets are coin-shaped. The present study certainly may be used as comparative scenario for specimens from other regions of the species range.
Highlights
The bivalves are the second largest class of the phylum Mollusca in diversity and, of high economic and ecological importance (Bieler & Mikkelsen, 2006; Bieler et al, 2013; Gomes-dosSantos et al, 2019)
Like other representatives of the family, C. costata has sculpture on the surface of the valves that are adapted to substrate abrasion and indicate a preference for a particular type of substrate, as well as phylogenetic relationships (Ito, 2005)
The mesoplax is chitinous, which may be due to the low abrasion suffered by the valves within of the burrowed sediment (Morton, 1973; Turner & Santhakumaran, 1989; Fiori et al, 2012; Voight & Segonzac, 2012)
Summary
The bivalves are the second largest class of the phylum Mollusca in diversity and, of high economic and ecological importance (Bieler & Mikkelsen, 2006; Bieler et al, 2013; Gomes-dosSantos et al, 2019). Bivalves constitute an ideal group to answer biological questions around morphological adaptations to dig, drill, swim and attach on several substrates (Bieler, 2006; Bieler et al, 2013). The magnitude of megadiverse groups, such as Mollusca, hampers large-scale research, and in classical morphological studies, it is usual a functional single organ anatomy characterization. In this framework, morphological generalizations for other groups and specimens are common. There are scant attention to soft parts anatomy, with studies focusing only on description of the shell, the taxonomic importance of the internal organs
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