Pterotrachea minuta Bonnevie, 1920
This is a large naked pelagic snail, up to 5 cm long, with an almost completely transparent cylindrical body and the proboscis is perpendicular to the body. Only the oval visceral nucleus is dark and the large eyes with black retina and the mouth organs are clearly seen. The body is long cylindrical, with one swimming fin. It hunts large prey like fish, shelled pteropods and other heteropods. It lives in the upper layers of the warm waters of all oceans (Pterotrachea minuta 3, Pterotrachea minuta 2, Pterotrachea minuta 1).
Small slender species, without a shell. The visceral nucleus is placed far posteriorly so that only a small tail with four muscle bands is found behind it (Pterotrachea minuta). The visceral nucleus is elongated and is three times as long as broad. About ten very small gills are present near the top of the nucleus. The eyes are triangular with broad bases. The proboscis is relatively small. The Pterotrachea minuta radula formula is 2-1-1-1-2. The fin is found dorsally about halfway between visceral nucleus and eyes. It is small and bears a small fin sucker in males. The muscles are fused together in the fin except for the marginal area. The long trunk has a thin cutis. Round tuberculate spots are found dorsally on the trunk especially at the area of the fin base. This species is intermediate between Pterotrachea hippocampus and Pterotrachea coronata in regard to shape of its visceral nucleus and eyes.
Body length up to 50 mm.
The juveniles have a small dextrally coiled shell. The larvae of this species have never been described adequately, but the following description is probably given for the true juveniles. The thin shell with 2.5 whorls and clear transverse striation, is planorboid. The aperture is perfectly round. The operculum has up to 5 whorls.
In this species the sexes are separate.
This species is carnivorous and epipelagic.
It may also be neritic, though its distribution is far less known than that of other species in this genus. The affinity between Pterotrachea hippocampus and the present species is close and it should be noted that both are nearly sympatric. Its abundance in the Panama area and localities east of New Guinea are, however, not found for Pterotrachea hippocampus, while the latter is much more abundant in the Mediterranean than Pterotrachea minuta, see the Pterotrachea minuta map.
Pterotrachea minuta Bonnevie, 1920: 13, figs. A4, B4, pl. 4, figs. 47-52.
Holotype: ZMVB 23259 (alcohol collection).
Type locality: 29°8'N 25°16'W Coll.: CMSE, stat. 49.