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Pneumodermopsis (Pneumodermopsis) paucidens (Boas, 1886a) forma paucidens (Boas, 1886a)

Overview

This is a relatively small, naked pelagic snail, up to 0.5 cm long, the visceral mass is seen through the body wall. The skin has grayish chromatophores. There is a median sucker arm with 5 suckers, the top one is the largest. There are 12 suckers implanted on the buccal wall. A posterior gill is absent. The posterior footlobe is short (Pneumodermopsis p. paucidens j- juvenile specimen). It is a good swimmer that hunts shelled pteropods as food. It lives in all oceans in shallow and deep water layers.

Taxonomic Description

The posterior footlobe is short, gills are less developed, the lateral gill is extremely short. In young specimens, the footlobes are equal in size, but with age the posterior lobe rapidly lengthens. Median arm with five suckers, the top sucker being the largest, the two lower pairs are small and attached to long stalks (Pneumodermopsis p. paucidens B). On the buccal wall ten to twelve suckers are attached on short stalks in a single row, as shown for Pneumodermopsis p. paucidens in an illustration after Boas. Pigmentation, in the larger specimens usually consists of thickly spotted dark chromatophores, occurring all over the animal except for the wings; in Pacific specimens chromatophores are found on the wings. The penis is armed with a chitinous style. The Pneumodermopsis p. paucidens radula formula is 2-1-2, the median tooth is bicuspoid without central cusp. The number of transverse rows varies between 12 and 22. The few hooks, only 6 at each side, are short and broad.
The maximum body length is 5 mm.

Morphology and Structure

The chromosome number is 32 (2N) (Thiriot-Quievreux, 1990)

Juveniles

A special description is not available.

Reproduction

It is protandric hermaphrodite. Massy (1917) found a large number of specimens with external accessory glands. The gland found pressed out of the body was at the right ventral side the gonoduct was found connecting the internal gonad with the external accessory gland. Massy (1917: 228, 231) described the occurrence of external sexual organs also in Pneumodermopsis (P.) ciliata and it is her impression that this phenomenon is normal in this group. Pneumodermopsis (P.) paucidens reproduces in the Mediterranean in January, juveniles are found in February and in June (Franc, 1948).

Ecology

This carnivorous species feeds on Limacina bulimoides and especially Creseis spp.

Distribution

It shows a distribution comparable with that given for Pneumodermopsis (P.) ciliata, see the Pneumodermopsis p. paucidens map. The tolerance for temperature differences in this species is large. There are many records for the N-Atlantic Ocean, but for the S-Atlantic they are scarce. From these records, one may conclude that the species is present in the Atlantic between 65°N and 30°S, with the greatest population density between 65°N and 35°N. This species is also abundant in the Mediterranean. In the Indian Ocean (Arabian Sea and near Madagascar) few records are known. The records from the Pacific, based on immature specimens identified only using the radula, possibly are dubious. The forma pulex is described from the Atlanto-Mediterranean Centre and as such it is sympatric with the forma paucidens. (cf. fig. 192).

Types

Dexiobranchaea paucidens Boas, 1886: 160, 223, figs. 105-106 (Pneumodermopsis p. paucidens type).
Types: not found in ZMUC.
Type locality: Atlantic Ocean. Coll.: Prof. Dr. Behn.

Original description

De parrende Arme er repræsenterede ved 11-13 kortstilkede Sugeskaale, der sidder i en Halvkreds indenfor Mundaabningen, direkte paa Mundhulens Væg; de falder ikke i to Grupper (svarende til de to Arme), men danner en sammenhængende Halvkreds. Den uparrede Arm er temmelig lang; den bærer paa Spidsen en temmelig stor Sugeskaal (forholdsvis omtrent saa stor some den tilsvarende hos D. ciliata), lidt nedenfor denne en mindre, stilket, paa hver Side og endelig ved Basis et Par ligende (disse 4 mindre Sugeskaale er dog størrre end de i Halvkredsen). - Radulas Formel er 2.1.2; af Sidtæn- derne har den inderste et bredt Basalstykke, den yderste et smalt; Midttanden synes ganske at mangle den lille Midtspids, vi finder hos de andre Arter, men har de to andre Spidser, - Krogsæksrudimenterne bestaar af en Gruppe af 4-6 korte kraftige, svagt krummende Torne, der ikke et meget længere end de er brede ved Basis. - Gjællen lille, men tydelig.- De to bageste Fimrekranse tilstede.- Det Største Exemplar var, de udkrængede Dele ikke medregnede, 5 mm langt.
De foreliggende 15 Exemplarer er af Prof. Behn tagne i Atlanterhavet den 3/5 48 paa hand Hjemrejse fra Brasilien.

Pneumodermopsis paucidens paucidens