Atlanta lesueuri Souleyet, 1852a
Overview
This is a large dextrally shelled, pelagic snail, 0.6 cm in diameter with large eyes and a single swimming fin. The shell is strongly flattened and keeled. The spire is small, smooth and straight. The shell is colourless. The operculum is relatively large. It is a carnivore predating on relatively large zooplankton and occurs in the warm water of all oceans (Atlanta lesueuri SEM, Atlanta lesueuri 2).
Taxonomic Description [after Richter, 1986]
The shell is large, smooth and colourless (Atlanta lesueuri). The number of whorls is 3.5. Radial waves or striae are found only on the body whorl. The spire is small but high, the suture is deep and clearly visible. The keel is high, relatively steep ending near the aperture, it penetrates 1/3 whorl distance in between the whorls. The aperture sinus is short and the umbilicus is narrow. The eyes (type B) are large with a large lens. The dorsal window in the pigment mantle is elongated at the anterior side into a thin transverse slit. The operculum (type B) is large with a relatively small spiral portion and it is thin and transparent. The radula is large (up to 2000 µm), its increase in width is 31% and it consists of up to 120 transverse rows. The Atlanta lesueuri radula formula is 1-1-0-1-1 in the first rows and 2-1-1-1-2 in the latter rows. A tricuspoid median tooth is formed and it is broad rectangular with straight or slightly concave frontal rim (Atlanta lesueuri rad). The Atlanta lesueuri median teeth are unicuspoid. Differences between the male and female radula are not apparent.
Shell diameter up to 4 (6) mm.
Juveniles
The juveniles have a small dextrally coiled shell. The Atlanta lesueuri veliger shell is smooth and colourless. In Atlanta lesueuri veligers the velum has 4 to 6 lobes which are very long and slender. The Atlanta lesueuri protoconch is smooth. The Atlanta lesueuri juv. specimens show 6 velar lobes and 3 shell whorls. In Atlanta lesueuri young specimens the shell is like those of the adults except for the development of the keel.
Reproduction
In this form the sexes are separate. Single eggs, 40 µ in diameter, are produced. The veliger, 300-400 µm, has a flattened, dextral shell and tetra-lobed velum. There are three stages in larval development, as in all heteropods; during these stages the foot, eyes and velum change. During metamorphosis the keel appears and the eyes gain their final organisation. Gametogenesis starts after metamorphosis and then the fin starts to develop. The velum changes during development from tetra- into hexaloboid. The three developmental stages are not reflected in the shell structure. For a full description of organogenesis and histogenesis referred to Thiriot-Quievreux (1969b).
Ecology
This species is carnivorous and epipelagic.
Distribution
The map of this species gives an incorrect picture of its distribution. Its absence in large parts of the Atlantic Ocean is due to insufficient research and identification problems and this may also be correct for the Pacific and parts of the Indian Ocean. The only possible conclusion is that it is a cosmopolitan warm water species found between 40°N and 30°S, see the Atlanta lesueuri map.
Types
Atlanta lesueuri Souleyet, 1852: 380 (1841), pl. 20, figs. 1-8.
Lectotype: MHNP, shell dissolved (alcohol collection). Paralectotype: MHNP, 3 spec. with dissolved shell (alcohol collection).
Type locality: Atlantic Ocean. Coll.: Eydoux and Souleyet.