Tritonia tetraquetra (Pallas, 1788)

Description

A large tritonid nudibranch reaching up to about 215 mm in length. Background colour is highly variable, from translucent white through pink to deep red. The foot is broader than the dorsum, and a fine opaque white line outlines the edges of the foot, dorsum, rhinophore sheaths, and oral veil. The oral veil bears 12–16 long slender filaments.

Distribution

Originally described from material taken in the Kuril Islands. Subsequently recorded broadly across the North Pacific, from Kamchatka, the Kuril Islands and Hokkaido in the north-west Pacific to Alaska and as far south as Puget Sound on the north-east Pacific coast.

Etymology

The specific epithet tetraquetra combines the Latin tetra- ("four") and quetrus ("cornered"), meaning "four-cornered" or "square-sided", in reference to the cross-sectional shape of the body.

Remarks

Feeds primarily on octocorals and sea pens. Widely used in neuroscience under the name Tritonia diomedea as a model for escape swimming and learning/memory; T. diomedea is regarded as a junior synonym of this species.

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References

• Limax tetraquetra, Pallas P.S. (1788). Marina varia nova et rariora. Nova Acta Academiae Scientiarum Imperialis Petropolitanae. 2: 229-249.
• オオバンハナガサウミウシ (新称), Trochuina tetraquetra, 馬場菊太郎. (1968). オオバンハナガサウミウシ(新称) 北海道尻岸内沖に産す. 採集と飼育. 30(8): 257-258.
• ホクヨウウミウシ, 中野理枝. (2019). 日本のウミウシ. 第二版. 文一総合出版.