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Peraclis reticulata (d'Orbigny, 1836)

Overview

This is a pelagic snail with a left coiled shell, 0.6 cm high; it has 5 whorls and a deep suture without radial crests. The spire is not depressed. A keel is present but does not have an aperture tooth. The aperture is wide and oval, the base of the aperture is pointed towards the keeled rostrum. The shell surface has a regular sculpture of a reticulate pattern. The wings are fused into a swimming plate. This species usually lives at great depths in all oceans (Peraclis reticulata 2).

Taxonomic Description

The reddish or yellow horny shell is relatively highly coiled and has 4 to 5 whorls with a relatively deep suture. The last whorl has a keel, but apertural teeth are lacking. Depending on age, faint radiating crests may develop along the suture (Peraclis reticulata). Meisenheimer (1906) stated these crests are present, however, Bonnevie (1913) thought they are always absent. The aperture is rounded, a rostrum is present with a narrow columellar membrane. The shell is covered with reticulate sculpture composed of "cells" with 6, sometimes 4 or 5 corners (Peraclis reticulata 1); this sculpture disappears a short distance before the border of the aperture. The reticulate layer is not identical to a periostracum as it is composed of calcareous material. The umbilicus is very narrow or absent, the operculum has 5.5 whorls without radial striation. The radula formula is (1)-1-1-1-(1) (Peraclis reticulata lateral tooth). Young specimens of about 2 mm have 3.5 whorls with an extension of the reticulum to the last whorl.
Shell measurements: height up to 6 mm, mean diameter 3 mm.

Morphology and Structure

The two symmetrical, dorsal tentacles have a small eye each; on the short stalk a flattened disc is found covered with flat epithelium "the cornea"; the walls of the stalk are covered by a thick epithelium. The flat disc is composed of retinal tissue and a lumen below "the cornea" is filled with"lens" substance. The retinal cells are found on top of the optical ganglion under which cells with yellowish pigment form a pigmented body. Bonnevie (1913) found two peculiar cell groups of the sensory type in the mantle margin, one group at the base of the ctenidium formed an osphradium and the other group near the free mantle margin may be the mantle corner gland at the right side of the balancer. As in most Thecosomata, the salivary glands are very simple and consist of two sacs with efferent ducts to the ventral side of the oesophagus. There are two cell types in these sacs: a large type with a large chromatine-rich nucleus secreting the glandular products and a small type in the more frontal gland section with oval nuclei and eosinophile secretion.
The chromosome number is 24 (2N) (Thiriot-Quievreux, 1988).

Juveniles

The juveniles have a small left coiled shell, and the reticulation starts directly after the protoconch I. (Peraclis reticulata protoc).

Reproduction

This species is a protandric hermaphrodite.

Ecology

This species is phytophagous.

Distribution

This is a cosmopolitan, mesopelagic species, usually occurring deeper than 100 meters. Its distribution seems restricted by the subtropical front in the north and the south. Only a few records near South Georgia fall outside this range. The lack of records off most of the American west coast, the Australian west coast the African west coast and in the N-Indian Ocean are remarkable. These absences seem to indicate an avoidance of areas of upwelling, however, his does not explain its absence in the SW-Atlantic. An avoidance of halostazes, in the N and N-Atlantic, in the Indian Ocean and in the W-Pacific seems also apparent. It is found in the Red Sea, see the Peraclis reticulata map. The records of Peraclis rissoides fall within the distribution of the present species and zoogeography indicates synonymy of both.

Geological Record

This species is known from the Late Quaternary (it is almost continuously present from the start of the Riss into present) of the Red Sea. It is found in the N. Adriatic after the Boreal.

Type

Atlanta reticulata d'Orbigny, 1836: 176 (1846) pl. 12, figs. 32-35.
Syntypes: BMNH 1854.12.4.39 two fragm. of two spec. (dry collection, originally alcohol).
Type locality: Pacific Ocean 2°S. Coll.: CVAM.
Peraclis reticulata var. minor Tesch, 1904: pl. I fig. 4.
Lectotype: ZMAN (alcohol collection) Paralectotype: ZMAN, 2 spec. (alcohol collection)
Type locality: 4°30'2S 129°25'E. Coll.: Siboga. stat. 243.

Peraclis reticulata