Pterotrachea coronata Niebuhr (ms. Forskal), 1775
Overview
This is a large, naked pelagic snail, up to 26 cm long, with an almost completely transparent cylindrical body and the proboscis is perpendicular to the body. Only the long-oval visceral nucleus is dark, the large eyes with black retina and the mouth organs are clearly visible. The body is elongate and cylindrical with one swimming fin. 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 (Pterotrachea coronata).
Taxonomic Description
Body long, slender and transparent (Pterotrachea coronata 2). The visceral nucleus is not stalked but sunken into the body and very slender, rod-like. A variable number of gills are found anterior to the nucleus. The fin is placed opposite and anteriorly to the nucleus, it bears a fin sucker in males. The muscles of the body wall are relatively homogeneous and the cutis is rather thin. The muscles in the fin are also fused. Numerous tubercles are found on the skin especially around the base of the fin. In males a penis with an additional clasper is present (Pterotrachea coronata penis). The proboscis is long and slender, with a relatively small buccal mass. The eyes are cylindrical with a narrow retina, its diameter may be smaller than the lens. The Pterotrachea coronata radula 3 formula is 2-1-1-1-2, the median plate has a central cusp and numerous smaller cusps at both sides (Pterotrachea coronata radula 1, Pterotrachea coronata radula 2, Pterotrachea coronata radula 4).
Body length up to 260 mm.
Morphology and Structure
For a histological description of the digestive system refer to Gabe (1952). This author proved the great affinity of the heteropods with the prosobranch molluscs also in regard to their histology and cytology. The oesophagus has a chiefly mechanical function. The salivary glands produce a mucoid substance, cells with acidophyl secretion are absent. This later type is frequent in the ventral diverticulum of the pharynx. The stomach lacks glandular tissue, so it is best considered to be a gizzard. The intestine is subdivided by Gabe (l.c.) in five parts of which section four should affect the intestinal absorption. The liver or digestive gland is composed of four cell types and produces diastases and does not execute intracellular digestion.
The organogenesis is described by Thiriot-Quievreux (1971a). The chromosome number is 31 (2N) in males and in females 32 (2N) (Thiriot-Quievreux, 1990).
Juveniles
The juveniles have a small, dextrally coiled shell. A special description is not available.
Reproduction
In this species the sexes are separate.
Ecology
This species is carnivorous and epipelagic. The species shows a temperature range of 12°C to 30°C and a salinity range of 33 to 40°/oo S. The camouflage used by this species and other Pterotrachea species is comparable to that used in cranchiid squids as shown by Seapy and Young (1986) also for Cardiapoda.
Distribution
This is the only species in the genus occurring in the centres of the oceans. It occurs in the entire Atlantic Ocean between 30°S and 40°N, although only few records with exact localities are known. It is commonly found in the Mediterranean and the Red Sea. Compared to the other oceans the Pacific Ocean seems to be insufficiently sampled, as its absence in the greater part of the ocean, seems due to insufficient sampling. See the Pterotrachea coronata map.
Types
Pterotrachea coronata (ms Forskal) Niebuhr, 1775: 117.
Types were not preserved, though the collection of Forskal is nearly complete in ZMUC. (All types of pelagic molluscs are absent in the ZMUC).
Type locality: Mediterranean.