Pterotrachea hippocampus

Pterotrachea hippocampus Philippi, 1836


This is a large naked pelagic snail, up to 8 cm long (Pterotrachea hippocampus 2), with an almost completely transparent cylindrical body and the proboscis is perpendicular to the body. Only the oval visceral nucleus is dark, the large very broad based eyes with black retina and the mouth organs are clearly visible. The body is long cylindrical with one swimming fin (Pterotrachea hippocampus 1). It hunts on large prey such as fishes, shelled pteropods and other heteropods. It lives in the warm waters of all oceans mostly in the upper water layers.

Taxonomic Description

The body is long, slender and transparent. The visceral nucleus without stalk, depressed into the body, is less slender than in Pterotrachea coronata and shows more and smaller gills. The fin, with a system of fused muscles, is placed opposite and anterior to the nucleus. A fin sucker is present in only males. Tubercles on the skin are rare though living specimens show red dots, scattered on the epidermis. The cutis is thin. The proboscis is rather slender with a relatively small buccal mass (Pterotrachea hippocampus). The Pterotrachea hippocampus eyes are triangular with a broad retina which is so strongly curved that one of the tips reaches the lens. Up to 5 tentacular protrusions on the cutis are present in females before the eyes. Another female character is the presence of an obtuse prominence on the cutis of the right side, just before the visceral nucleus. This filament is not permanent and encases only one batch of spawn. The Pterotrachea hippocampus radula formula is 2-1-1-1-2, the median plate has one central cusp with smaller cusps at both sides.
Body length up to 80 mm.

Morphology and Structure

The chromosome number is 31 (2N) in males (Thiriot-Quievreux, 1990).


In this species the sexes are separate.


The juveniles have a small dextrally coiled shell. The larvae of this species have never been documented but in all probability the following description is based on related juveniles. The planorboid shell has 2.5 perfectly smooth whorls which are scalarid as the 2nd whorl detaches from the spire. The aperture is perfectly round. The operculum has up to 5 whorls.


This species is carnivorous and epipelagic.


This species is neritic, only occurring along the coast in the Mediterranean, Atlantic and Indo-Pacific Ocean. In the Atlantic Ocean it is absent in southern parts, see the Pterotrachea hippocampus map.


Pterotrachea hippocampus Philippi, 1836: 242, pl. 28, fig. 16.
Types and type locality unknown.