Paedoclione doliiformis Danforth, 1907

Description

A minute gymnosomatous pteropod (sea angel) reaching about 5 mm in body length. The cephalic tentacles are very short and the parapodia are rounded-quadrate. There are two pairs of buccal cones (asymmetrical) and conspicuous ciliated bands behind the head, near the mid-body, and near the posterior end. Adults are shell-less; the body is gelatinous and mostly transparent, with an orange visceral mass visible through the anterior part. The species is the only known shell-less pteropod that retains larval external features into adulthood (paedomorphosis / neoteny).

Distribution

Originally described from Casco Bay, Maine, USA (Danforth, 1907). Not collected again for 61 years after its original description, until rediscovery in 1968 from Nova Scotia, Canada, and the Gulf of Maine. Okutani (2017) (Umiushi-Tsushin No. 94) records the species from the temperate and cold waters of the Pacific, including coastal Hokkaido in Japan.

Etymology

The specific epithet doliiformis combines the Latin dolium ("barrel") and the suffix -formis ("shaped"), referring to the barrel-shaped body. The genus name Paedoclione combines Greek paedo- ("young, juvenile") with the related genus Clione, meaning "young Clione".

Japanese vernacular name

According to Okutani (2017), the Japanese name "Ikuo-hadaka-kamegai" originates from the nickname "Ikuone" — a portmanteau coined by the underwater photographer Ikuo Nakamura (中村征夫) from his own given name "Ikuo" and "Clione" — when he first photographed the species in waters off Hokkaido.

Remarks

The sole species in the genus Paedoclione. Okutani (2000) (Marine Mollusks in Japan) had initially proposed the Japanese name "Ikuo-hadaka-kamegai" for a different species, Pneumoderma atlanticum pacificum (改称, "renamed"), but Okutani himself revised this in 2017, reassigning the name to Paedoclione doliiformis, which is the currently accepted application.

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References

• Paedoclione doliiformis n. g., n. sp., Danforth C.H. (1907). A new pteropod from New England. Proceedings of the Boston Society of Natural History. 34: 1-19.
• イクオハダカカメガイ (改称) Pneumoderma atlanticum pacificum (misappl.), 奥谷喬司. (2000). 日本近海産貝類図鑑. 東海大学出版会.
• イクオハダカカメガイ Paedoclione dolliformis (Danforth, 1907), 奥谷喬司 (2017). わが国近海に見られる浮遊性巻貝類—VII 裸殻翼足類. うみうし通信 94: 8-9.
• イクオハダカカメガイ Paedoclione doliiformis (Danforth, 1907), 中野理枝. (2018). 日本のウミウシ. 文一総合出版.