Julia japonica Kuroda & Habe, 1951

Description

A tiny bivalved sacoglossan with both body and shell a vivid green. Although a gastropod, it carries two hinged valves and outwardly resembles a minute green clam. Shell length reaches about 8 mm. A pronounced concavity just below the umbo distinguishes it from related species. The rhinophores are rolled into cylinders and match the green body color. The animal sits on green algal blades, where its color provides effective camouflage.

Distribution

Type locality is Wakayama Prefecture, Honshū, Japan. Recorded mainly along the Japanese coasts.

Etymology

The specific epithet japonica is Latin for "Japanese," referring to the type locality in Japan.

Remarks

Feeds on the green alga Microdictyon japonicum. The family Juliidae was long known only from fossil shells and was classified among the bivalves; in 1959 Shiro Kawaguchi found living animals in Wakayama, Japan, revealing that they are in fact sacoglossan gastropods carrying a hinged two-valved shell — the famous "slug within the bivalve." The Japanese vernacular name "ユリヤガイ" originated with Kuroda 1935, who applied it to Julia exquisita; the Japanese populations were later described as the present species by Kuroda & Habe 1951.

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References

• Julia exquisita ユリヤガイ（新称）, 黒田徳米. (1935). 附録: 日本産有殻軟體動物總目録 (16). ヴヰナス. 5(4): 145-154. https://doi.org/10.18941/venusomsj.5.4_145
• ニホンユリヤガイ, 川口四郎. (1983). 二殻腹足類ユリヤガイ. 川崎医療短期大学紀要. 2: 93-100. https://doi.org/10.18928/00000643
• Julia japonica, McCarthy-Taylor J.B., Krug P.J., Muro S., Vendetti J., Maestrati P., Wong N.L.W.S., Gosliner T.M. & Valdés Á. (2025). The slug within the bivalve: molecular and morphological systematics of the family Juliidae (Gastropoda: Panpulmonata: Sacoglossa). Zoological Journal of the Linnean Society. 204(2): zlaf056. https://doi.org/10.1093/zoolinnean/zlaf056