Thliptodon diaphanus (Meisenheimer, 1903b)
Overview
This is a small naked pelagic snail, smaller than 0.8 cm long, with a mainly transparent body and visceral mass is seen through the body wall. The wings are implanted laterally in the middle of the barrel-shaped body. Posterior and lateral footlobes are separate. It is a rather quick swimming carnivorous species. It is epipelagic and mesopelagic occurring in all oceans. (Thliptodon diaphanus swimming, Thliptodon diaphanus drawing).
Taxonomic Description
The body is transparent (Thliptodon diaphanus swimming) by its very thin skin. The body shape is variable, from droplet-shaped with an extremely large head to barrel-shaped with a head section not larger than the body section. The lateral and posterior footlobes are always distinctly separated. A median foot tubercle is, according to some authors, present. The Thliptodon diaphanus radula formula is 3-1-1-1-3 and about 8 rows are present (Thliptodon diaphanus radula after Bonnevie, Thliptodon diaphanus radula). The median plate is very fragile, thin and transparent; its borders are drawn out at each side. In the description by Meisenheimer (1903a), the median plate has not been described. Though the variation in the plates is considerable, dentation is not found. The intermediate plates show a short top cusp and sometimes 2 to 4 small cusps near its top. The lack of dentation is not confirmed by all authors, sometimes minute dentation is found.
Body length up to 8 mm.
Juveniles
A special description is not available.
Reproduction
This species is a protandric hermaphrodite. A completely separated stalked accessory sexual sucker is situated posterior of the penial aperture (Thliptodon diaphanus penis). This sucker sits in between the sucker attached to the base of the penis as in Clione limacina and Thliptodon gegenbauri and the median foot tubercle as found in Pneumodermopsis. The sheath of the penis is strongly folded, with the penis laying at its blind end. The appendage of the penial sheath contains a glandular channel which is divided into two parts by a longitudinal fold. This channel resembles a prostate though its function is still obscure. The efferent duct of this 'prostate' crosses the basal part of the outstretched penis to reach the seminal groove at the penis. The stalked sucker below the penis has a separate gland.
Ecology
This species is a carnivore.
Distribution
It is found in deep as well as surface layers, though usually at greater depth in the Atlantic and Indo-Pacific Oceans. The distribution seems identical to that of the less common Thliptodon gegenbauri thought this species is restricted to warm and transitional waters. It is widely distributed as seen in the Thliptodon diaphanus map.
Types
Pteroceanis diaphanus Meisenheimer, 1905: 59, pl. 16, fig. 10.
Types: only 1 spec. HMEB 61152 is preserved.
Type locality: 2°37'N 3°28'E, 1°57'S 7°41'E, 0°58'S 99°43'E, 6°54'N 93°29'E, 2°57'S 67°59'E, 13°3'N 46°42'E, Col. CVDE, stat. 55, 65, 190, 208, 227, 271