Poromya rostrata, REHDER, 1943

POROMYA ROSTRATA REHDER, 1943 View in CoL

( FIGS 10, 11)

Description

Shell: Ovate-trigonal, inflated, thin, whitish, inaequilateral, slightly inaequivalve; posterior margin with a short rostrum; outer sculpture granulated with micro-pustules over the entire shell; without lithodesma.

Mantle: Ventral mantle margin with one anteriorly wide pedal gape, extending from the anterior adductor until the inhalant siphon; without a fourth pallial aperture.

Siphons: Separated, different in size and outline; inhalant siphon, large, modified in a raptorial appendage, typically retracted into the infra-septal chamber; exhalant siphon short, cone-like and everted in this specimen; both surrounded at the base by a ring of large siphonal tentacles, 12 around the inhalant and three around exhalant; debris attached to the siphonal walls.

Septum: Thin, ventral surface with well-defined twopaired groups of slit-like branchial apertures, with no interfilamental connections; anterior group with four and posterior with five slits. Presence of a small and lobulate hollow sac in the posterior inner floor of the septum.

L a b i a l p a l p s: N o n - l a m e l l a t e, f l a t t e n e d a n d asymmetrical with anterior labial palps large and posterior labial palps small.

Musculature: Posterior and anterior adductor muscles present and isomyarian; with posterior and anterior pedal and septal retractor muscles; lateral septal muscles not visible in this specimen; taenioid muscle absent.

Foot: Large and elongated; absence of pedal groove and byssal thread.

Digestive system : The funnel-shaped mouth opens into a thick, short and muscular oesophagus that enters the anterodorsal portion of the stomach; with a sphincter between oesophagus and stomach opening; stomach large, rounded, internal grooves not visible into the gastric chamber; stomach connected to the short and small crystalline style sac located on the median portion of the stomach floor; no prey observed inside the stomach; stomach surrounded dorsally and anteriorly by the gonads and digestive gland; two gastric caeca observed in the digestive gland; crystalline style sac conjoined with the anterior portion of the midgut; crystalline style present; pericardium/heart surround the rectum/hindgut; hindgut passes above the kidney.

Reproductive system : Hermaphroditic, ovary and testis well visible; ovary closely associated to the digestive gland cover the roof and the posterior wall of the stomach; the testis lie ventral to the ovary and consist of a pair of large lobulate sacs.

Nervous system : With circum-oesophagic, pedal and visceral ganglia observed.