Peraclis moluccensis Tesch, 1903
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 body whorl increases very rapidly. The spire is strongly depressed. A keel ends in a distinct aperture tooth. The aperture is wide and its base is pointed towards the keeled rostrum. Shell sculpture is absent. The wings are fused into a swimming plate. This species usually lives at great depths and is found in all oceans (Peraclis moluccensis).
Taxonomic Description
The hyaline shell, without any sculpture, is relatively high although the spire with 3 to 5 whorls is slightly depressed. The first whorls are coiled in one plane while the last whorl may be higher than the apex because of its great breadth. The last whorl is so large that the other whorls are only seen in apical view. The aperture is wide, inflated in the upper part and pointed towards the rostrum. The last whorl, at its dorsal margin, has a keel ending in an aperture tooth (Peraclis moluccensis aperture tooth) which is directed slightly towards the apex and curving spirally with the shell. Between the keel and suture a triangular field is present with about 7 strong, irregular crests. These crests are undulate and placed closer together than in Peraclis bispinosa and Peraclis apicifulva. The rostrum is not curved, but twisted, with a narrow columellar membrane. An umbilicus is absent. Growth lines on the shell are visible and some perpendicular lines are seen under high magnification. The operculum is glassy, sinistral with 4 up to 5 whorls and shows radial striae. In some shells and in the type specimen, clear transverse crests are found on the last whorl along the suture which continue on the seven crests between the rib and suture just before the aperture tooth. The Peraclis moluccensis radula formula is (1)-1-1-1-(1).
Shell measurements: height to 3.0 mm, diameter to 2.5 mm.
Reproduction
This species is a protandric hermaphrodite.
Juveniles
The juveniles have a small left coiled shell. The embryonic shell shows rough ornamentation of irregularly ramified flat ridges (Boltovskoy, 1974) (Peraclis moluccensis protoconch).
Ecology
This species is phytophagous and mesopelagic.
Distribution
This is a cosmopolitan meso-bathypelagic species, locally not rare. Most typical is its absence east of 140°W in the Pacific and its absence in the entire N-Pacific Ocean; it penetrates only in the SW-Pacific. It is found in the entire tropical and subtropic Indian Ocean. The north-south range of this species in the Atlantic is larger than in the Indo-Pacific Ocean. It is not recorded from the Mediterranean, see the Peraclis moluccensis map. This species is most abundant below 500 m.
Types
Peraclis moluccensis Tesch, 1903: 112 (1904), pl. I figs. 7-10.
Holotype: ZMAN (alcohol collection) u.s.
Type locality: 4°30'2S 129°25'E. Coll.: CSIE. stat. 243.