Schizobrachium polycotylum Meisenheimer, 1903a
Overview
This is a large, naked pelagic snail, 3 cm long, with a semi-transparent body. There are two dichotomously branching lateral arms, a median arm is absent. Uniquely the number of suckers is extremely high (>1000). A posterior gill is absent (though small crests are sometimes seen), the lateral gill is reduced but present. The posterior footlobe is typical in size as are wings and lateral footlobes. It is a carnivorous species that lives at great depths in all oceans (Schizobrachium polycotylum).
Taxonomic Description
The acetabuliferous arms are dichotomously branched and covered with extremely small suckers. They can number over a thousand (Tesch, 1950). The greatest number of suckers is found on the finest branches of the arms. Only Meisenheimer (1903b) found a posterior gill composed of two simple crests at the ventral side of the body pole. A lateral gill is absent according to all known descriptions, but Tesch (1950) pictured a "fold in the skin of no importance" at the place where the lateral gill when present is normally found. As simple lateral gills easily become lost by fixation, the real absence of a lateral gill is dubious. The specimen figured also shows a 'lateral gill'. A dorsal gland patch is present. The radula formula is 6-1-6 up to 8-1-8; the teeth are variable in size and shape. The median tooth, with large basal plate, always has two cusps and its hollow anterior border ends at both sides in more or less pronounced corners. The cusp of the first lateral tooth is straight or bends slightly to the median line, while the cusps of the other laterals point in an anterior direction. The jaw supported by a thin membrane, is composed of numerous slender spines with an open space in the middle. Under the jaw, globular cells are found while at the right under the radula a group of smaller cells with perhaps a secretory function are found. Hook sacs are voluminous having numerous slender hooks, about 20 at each side.
Body length up to 32 mm.
Juveniles
A special description is not available.
Reproduction
This species is a protandric hermaphrodite
Ecology
This species is carnivorous.
Distribution
It occurs in the S-Indian Ocean and is probably circumpolar, although it is also found in the tropical Atlantic, N-Atlantic and tropical Pacific Ocean, see the Schizobrachium polycotylum map. The records given in the map surely do not reflecting the real dispersal of this bathypelagic species. Probably the greater number of records in colder areas is due to an occurrence of animals at shallower depths compared to the tropic vertical range.
Types
Schizobrachium polycotylum Meisenheimer, 1903b: 410.
Holotype: not present in HMEB, u.s.
Type locality: 34°14'S 80°31'E. Coll.: CVDE, stat. 169.