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Pneumodermopsis (Pneumodermopsis) ciliata (Gegenbaur, 1855b)

Overview

This is a relatively large, naked pelagic snail up to 1.5 cm long, with a mainly transparent body which shows the reddish brown of the visceral mass shining through the body wall. The skin has purple and black chromatophores. There is a median sucker arm with 5 suckers of which the anterior two are large, oval and pointed. There are two lateral arms each with 8 suckers. A posterior gill is absent. The posterior footlobe is long. It is a quick swimmer that hunts shelled pteropods as food. It lives in the N-Atlantic and N-Pacific Oceans in shallow and deep water layers where it can occur in mass blooms (Pneumodermopsis ciliata).

Taxonomic Description

The body is slender, the lateral gill is large and it hangs free from the lateral side in the middle of the body. Head and body clearly separated. The transparency of the skin is variable. The median footlobe is long, the median foot tubercle is moderately developed. Lateral arms with 7 to 8 sessile suckers (Pneumodermopsis ciliata organs), rather short; median arm with 5 suckers of which the posterior two and the top sucker are small and the anterior large pair are typical. Small, young specimens (0.8 mm long) have a radula formula 3-1-3 and 8 to 9 hooks, while older specimens (5.0 mm long) have the formula 7-1-7, up to 8-1-8, with 30 to 40 hooks (Pneumodermopsis ciliata 1, Pneumodermopsis ciliata 2, Pneumodermopsis ciliata 3). Specimens with the formula 5-1-5 and 6-1-6 have about 18 to 25 rows of teeth, their body length is 2 mm and the ciliated rings are still present, the number of hooks is 30-40 (Pneumodermopsis ciliata hooks). The first lateral teeth are sometimes found with a slight dentation or sometimes without. Though the suckers in the median arm are variable, the present species always differs from other species due to the two large anterior suckers. When sexually active the genital organs may become so large that the body and the position of the alimentary organs are completely transformed. In this species, specimens are found with a gonad externally of the body, hanging at the right side under the wings. This was observed in specimens of 3 mm and larger.
The maximum length of the body is 15.0 mm.

Juveniles

The protoconch, which is lost after a few days, is nearly globular. The colour is faint brown especially in the incision between protoconch I and II (Pneumodermopsis ciliata protoconch). Protoconch II is small, forming just a rim on protoconch I. The aperture of the protoconch is slightly oval (Pneumodermopsis ciliata line drawing).

Reproduction

This species is a protandric hermaphrodite.

Ecology

This is a carnivore species feeding on Thecosomata and Cladocerans.

Distribution

With the data available at this time, only an extremely discontinuous range can be recognised. This species is only found in the N-Atlantic, Atlanto-Mediterranean centre, Indian and N-Pacific Oceans, see the Pneumodermopsis ciliata map. From this distribution it is clear that it is an eurythermic species, and thus the discontinuity is not merely due to a more neritic character. Meristic and morphological differences are known for populations of cold and warm waters.

Types

Pneumodermon ciliatum Gegenbaur, 1855: 74.
Types were never indicated.
Type locality: near Messina. Coll.: Gegenbaur.

Pneumodermopsis ciliata