Pneumoderma atlanticum pacificum Dall, 1871

Description

A small gymnosomatous pteropod (sea angel) with a body up to about 1 cm in length. The body is gelatinous, semi-transparent, and dotted with purple. The anterior body is rounded; the parapodia have round anterior margins and concave posterior margins, and the mid-lobe of the foot is heart-shaped and purple. The lateral gill is fold-like and the posterior gill is divided into four lobes. The triangular acetabuliferous (sucker-bearing) arms each bear about 50 suckers, used to capture shelled-pteropod prey. The foot is modified into wing-like parapodia for swimming. The shell is lost during larval development; adults are shell-less.

Distribution

The original description (Dall, 1871) was based on specimens collected from the west coast of North America and the North Pacific Ocean. According to Okutani (ed.) 2000 (Marine Mollusks in Japan), the subspecies is recorded from mixed water zones of the North Pacific. The nominate subspecies Pneumoderma atlanticum is distributed in the Atlantic.

Etymology

The subspecific name pacificum is the Latin neuter form meaning "of the Pacific", contrasting with the nominate P. atlanticum of the Atlantic. The genus name Pneumoderma combines Greek pneuma ("air, breath") and derma ("skin"), referring to the respiratory organ on the body surface.

Remarks

A gymnosomatous pteropod ("sea angel") allied to the genus Clione but placed in its own genus and family (Pneumodermatidae). Okutani (ed.) 2000 (Marine Mollusks in Japan) initially proposed the Japanese name "Ikuo-hadaka-kamegai" for this subspecies (改称, "renamed"), but Okutani himself revised this in 2017 (Umiushi-Tsushin No. 94), reassigning the name to Paedoclione doliiformis and excluding this subspecies from his list of 11 Japanese gymnosomatous pteropods. This site uses the provisional name "Niumoderuma-zoku no isshu" ("a species of Pneumoderma") for this taxon.

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References

• Pneumoderma pacificum n. subsp., Dall W.H. (1871). Descriptions of sixty new forms of mollusks from the west coast of North America and the North Pacific Ocean, with notes on others already described. American Journal of Conchology, 7: 93-160.
• イクオハダカカメガイ (改称) Pneumoderma atlanticum pacificum (Dall, 1871), 奥谷喬司. (2000). 日本近海産貝類図鑑. 東海大学出版会.