Cuspidaria glacialis, (SARS G. O., 1878)

CUSPIDARIA GLACIALIS (SARS G. O., 1878) View in CoL

( FIGS 16, 17)

Description

Shell: Elongated, robust, inaequilateral, equivalve and slightly inflated; with a prominent and long rostrum in the posterior; smooth, valves covered by a dehiscent, thick and light brown periostracum; with a lithodesma.

Mantle: Mantle margin with one anteriorly large pedal gape, extending from the anterior adductor until almost the beginning of the inhalant siphon; posteroventral mantle margin fusion formed by inner and middle folds (Type B of Yonge, 1982); absence of a fourth pallial aperture.

Siphons: The detailed description of this structure was not possible due to the state of contraction of the specimen analysed.

Septum: Presence of a well-developed horizontal muscular septum (‘septibranch condition’) dividing the mantle cavity into infra- and supraseptal chambers; septum long and wide, perforated ventrally by five pairs of isolated septal pores.

Labial palps: Poorly developed, non-lamellate, slightly asymmetrical, with the anterior palps larger than the posteriors; anterior labial palps attached to ventroanterior mantle margin, close to anterior adductor muscle.

Musculature: Posterior and anterior adductor muscles present, isomyarian; with well-developed pedal and septal retractor muscles, both bifurcating before attaching to the shell; lateral septal muscle also present, more concentrated posteriorly; taenioid muscle absent.

Foot: Large, with a long pedal groove; byssal thread absent.

Digestive system : Funnel-shaped mouth opens into thick and muscular oesophagus that enters into anterodorsal portion of stomach; stomach large, rounded, with a dorsal short projection, internal grooves not visible; stomach connected to the short and small crystalline style sac located on the median portion of the stomach floor; crystalline style present; large preys were observed inside of stomach (gastropod and ostracod: Figs 15B, F, 16D, E); stomach surrounded dorsally and anteriorly by the gonads and digestive gland.

Reproductive system : Dioecious, only ovary is visible in this specimen; ovary closely associated to the digestive gland, covering the roof of the stomach.