Peraclis triacantha (Fischer, 1882a)
Overview
This is a pelagic snail with a left coiled shell, 0.5 cm in height; it has about 4 visible whorls and a deep suture without radial crests. The spire is strongly depressed. The aperture has two aperture teeth one of which is supported by a strong rib. The aperture is wide and rounded. The shell surface is smooth. The wings are fused into a swimming plate. This species usually lives at great depths in the Atlantic Ocean (Peraclis triacantha drawing).
Taxonomic Description
The shell and its spire are depressed and broad, the body whorl covers the three preceding whorls (Peraclis triacantha). The aperture is very broad and has two aperture teeth. One tooth is supported by a very strong rib and curls from the upper border upwards in the spiral direction. The other tooth is found at the underside of the outer aperture border and is supported by a short rib. Radial lines between the keel and suture are absent. The ribs and the rostrum are brown. The spirally twisted rostrum, with keel, has a very large columellar membrane. The umbilicus is well developed. Rostrum and second aperture tooth are both visible in apical view. The sculpture of the shell is composed of spiral lines with cross connections showing a resemblance to a reticulated pattern. The overall colour of the shell is white. The Peraclis triacantha radula formula is (1)-1-1-1-(1) with about 10 transverse rows. The operculum, with a subcentral nucleus, has five whorls and a suture bordered by many transverse lines.
Shell measurements: height up to 5 mm, maximum diameter up to 5 mm.
Juveniles
The juveniles have a small left coiled shell. A special description is not available.
Reproduction
This species is a protandric hermaphrodite.
Ecology
This species is a phytophage.
Distribution
This meso-hypoplanktonic species occurs, like Peraclis depressa, only in the Atlantic and even not in the Mediterranean. Except a the more westward penetration up to Bermuda and a penetration towards 60°N in the Gulf Stream the range of this species is completely comparable with that of P. depressa, including its presence as far south as 40°C. Motoda et al. (1972) reported P. bispinosa and Peraclis triacantha from the Indian Ocean, South of Java. These records are not included in the maps as they are dubious. It is also known from sediments of the Mediterranean (Nofroni and Silesu, 1986). See the Peraclis triacantha map.
Types
Embolus triacanthus Fischer, 1882: 49.
No types preserved in MHNP, BMNH or IRSN.