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Peraclis bispinosa Pelseneer, 1888a

Overview

This is a pelagic snail with a left coiled shell, 0.8 cm high; it has 5 whorls and a deep suture with radial crests. The spire is relatively high. A strong keel ends in a distinct aperture tooth. The aperture is wide, the base of the aperture is pointed towards the keeled rostrum. The shell sculpture is sometimes composed of a irregular reticulum. The sculpture disappears abruptly before the aperture border. The wings are fused into a swimming plate. This species lives usually at great depths in the Atlantic and Mediterranean (Peraclis bispinosa drawing).

Taxonomic Description

The elongate shell has 4 to 5 whorls and a deep suture (Peraclis bispinosa from oral, Peraclis bispinosa). The spire is relatively high due to the rapid increase in size of the whorls (Peraclis bispinosa apical). On the last half of the body whorl a strong keel ends in a distinct aperture tooth. The radial crests between suture (Peraclis bispinosa suture) and keel resembles those in Peraclis apicifulva are distinct, but more regular and thinner than in the latter. The aperture is wide and near the tooth at the end of the keel a triangular portion of the aperture border is turned upwards forming a second tooth. The base of the aperture is pointed towards the keeled rostrum. The spirally twisted rostrum has a very well developed, broad columellar membrane. The shell sculpture is sometimes composed of an irregular reticulum with a pattern of spiral lines. The sculpture disappears abruptly before the aperture border. The operculum has about five whorls and no radial striae. Radula formula (1)-1-1-1-(1) with about 13 transverse rows (Peraclis bispinosa radula). The soft part are dark brown to black (Peraclis bispinosa living)
Shell measurements: height up to 7.5 mm, maximum diameter 6 mm.

Juveniles

The juveniles have a small left coiled shell. Embryonic shell is almost smooth, only high magnification shows faint and irregular ornamentation (Boltovskoy, 1974).

Reproduction

This species is a protandric hermaphrodite.

Ecology

This species is phytophagous and mesopelagic. The temperature range is 3.24-11.64°C and the salinity range is 34.82-35.57 °/oo S.

Distribution

Mesopelagic warm water species, restricted to the Atlantic Ocean and Mediterranean Sea, forming a true Atlanto-Mediterranean element (Atlanto-Mediterranean centre). It shares this endemic occurrence with some other bathypelagic pteropods. All other bathypelagic representatives of this group are more common in the Atlantic than in the Indo-Pacific Oceans and Red Sea. Its most northern record is northwest of Iceland at about 60°N and its most southern record is from off the W-African coast near 25°S. Avoidance of upwelling areas is not evident. Strong penetration into the Caribbean and into the N-Atlantic may be induced by current transport. The influence of surface currents on this species is, however, hard to explain as it is the most bathypelagic species, see the Peraclis bispinosa map. Records of this species in the E-Pacific by McGowan (1967) are not included in the map as they seem doubtful by the mere fact of their isolated position. Moreover, McGowan (l.c.) himself mentioned the problem of identification badly preserved specimens.

Geological Record

This form is found in the Pleistocene of the Mediterranean.

Types

Peraclis bispinosa Pelseneer, 1888: 36, pl. 1, figs. 9-10.
Types not found in BMNH.
Type locality: 28°3'15"N 17°27'W; 32°21'30"N 64°35'5S"W; 38°38'0"N 28°28'30"W; 38°11'N 27°9'W; 37°26'N 25°13'W; 28°42'N 18°6'W Coll.: CCHE stat. 8; stat. 33; stat. 75; stat. 76; stat. 78; stat. 85.

Peraclis bispinosa