Atlanta peroni Lesueur, 1817
Overview
This is a medium sized, dextrally shelled, pelagic snail, 1 cm in diameter with large eyes and a single swimming fin. The shell is large, strongly flattened and keeled. The colourless spire is very small, near the keel a brown colour may be seen. The operculum has a very small spire. It is a carnivore predating on relatively large zooplankton. This species occurs in the warm waters of all oceans (Atlanta peroni 1, Atlanta peroni 2).
Taxonomic Description [based on Richter, 1993]
Shell smooth, calcareous, flatly coiled with up to 6 whorls (Atlanta peroni). A high keel surrounds the entire shell circumference and penetrates between the younger whorls in full grown specimens. The inner lip of the shell aperture may be bent and separated from the preceding keel. The base of the keel is sometimes brownish and it penetrates between the last and the preceding whorl. The first whorls increase regularly, while the third and fourth whorl are relatively small. The spire is flat, with sharp apex and it is very small, with 4 whorls. In some specimens sculpture lines cover the first three whorls. The suture is moderately deep, the umbilicus is relatively wide and deep. The whorl formula (cf. Tokioka, 1961) varies between 1 : 0.25 : 0.09 and 1 : 0.50 : .27. The whorl formula applied to the soft parts (cf. Van der Spoel, 1972a) varies between 1 : 2 : 3 : 5 and 1 : 4 : 5.5 : 8. The operculum is variable in shape. The operculum (type B) is micro-oligogyre. The eyes are type B. The shape of the eyes is high cuboid, the retina thus has a narrow base. The radula with the formula 2-1-1-1-2, is ribbon-shaped with only a small width increase; there are 60 transverse rows; the lateral teeth have a high basal plate; the additional teeth are smaller than the lateral teeth (Atlanta peroni radula). There is sexual dimorphism in the radula: in males, the additional teeth are short and hook-shaped; in females, they are longer and less curved. The lateral teeth are tri- or bicuspoid.
Maximum shell diameter up to 11 mm.
Juveniles
The Atlanta peroni veliger has a small, dextrally coiled shell. The shell is pink-reddish and is smooth except for some growth lines. The bi- or trilobed velum has very long slender lobes. Atlanta peroni protoconch I and II are smooth. In Atlanta peroni young specimens there is a slight compression of the lateral sides of the whorls (Atlanta protoconchs).
Reproduction
In this species the sexes are separate.
Ecology
It is an epipelagic carnivore. Predators of the present species include the fishes Centrobranchus nigrocellatus, Alepisaurus ferox and Alepisaurus brevirostris.
Distribution
The intricate synonymy and insufficient descriptions of this species produced a scarcity in zoogeographical data. The species is cosmopolitan between 40°N and 25°S. Most striking is the high abundance in the N-Atlantic Ocean and its rarity in the southern part. Atlanta peroni is common in the Mediterranean and it is one of the few species also found in the Arafura Sea, see the Atlanta peroni map. Diurnal vertical migration is found in the upper metres of the water.
Geological Record
This species is occurs in the Adriatic in the Younger Dryas.
Types
Atlanta peroni Lesueur, 1817: 390, pl. 2, figs. 1-2.
Lectotype: MHNP, damaged (alcohol collection) Paralectotypes: MHNP, 4 damaged spec. (alcohol collection).
Type locality: Atlantic Ocean. Coll.: RANG.