Lyonsia alvarezii, D'ORBIGNY, 1846

LYONSIA ALVAREZII D’ORBIGNY, 1846 View in CoL

( FIGS 4, 5)

Description

Shell: Subovate-elongated, thin, delicate, translucid, moderately inflated in the anterior, posterior laterally compressed; external sculpture formed by thin radial ridges with sand grains attached along the entire extension of the valves; with a large lithodesma.

Mantle: This specimen had an important part of the mantle lost during the removal of the shell, turning the analysis incomplete; presence of a fourth pallial aperture closer to the inhalant aperture.

Siphons: Inhalant and exhalant siphons similar in size and outline, short, simple, tube-shaped and separated; papillate tentacles covering the inhalant siphon; apertures of the inhalant and exhalant fringed with a ring of, respectively, ~32 and ~45 short tentacles.

Ctenidia: Eulamellibranch and plicate; complete with a large inner demibranch larger than the outer one; free edge of inner demibranch with a deep marginal food groove.

Labial palps: Large, wide, lamellate with sorting ridges, symmetrical and coiled.

Musculature: Adductormusclespresent, heteromyarian, with the posterior adductor well developed and the anterior reduced; presence of well-developed posterior and a reduced anterior pedal retractor muscle.

Foot: Elongated with a long pedal groove; presence of byssal thread.

BIVALVES AND MICRO-COMPUTED TOMOGRAPHY 53

Digestive system : The tube-shaped mouth opens into a long oesophagus that enters into the anterior portion of the stomach; elongated in shape, the stomach is connected to the also elongated crystalline style sac; style sac conjoined with an anterior coiled midgut; pericardium/ heart surround the rectum/hindgut; kidney not visible.

Reproductive system : Hermaphroditic; ovary located in the dorsal portion of the visceral mass, closely associated to the digestive gland; testis small and poor visible, located in the anterior portion of visceral mass.