Dirona albolineata MacFarland, 1905

Description

A fairly large nudibranch usually about 25 mm long, but reaching up to 180 mm in body length. The body is semi-translucent, ranging from whitish-grey through pale salmon-pink to pale violet between individuals. Conspicuous opaque white lines run along the lateral edges of the leaf-shaped cerata, the anterior margin of the oral veil, and the dorsal midline of the tail. A similar white line runs along the stalk of each rhinophore and the two meet on the midline of the head. The cerata surfaces are smooth, and the radular formula is about 32 × 1.1.1.1.1.

Distribution

Originally described from California, with MacFarland's manuscript name made available through the publication by Cockerell & Eliot. Subsequently recorded along the north-east Pacific from Kachemak Bay, Alaska, to San Diego, California, with isolated records from Japan and the Russian Far East (the taxonomic status of Japanese material has yet to be assessed).

Etymology

The specific epithet albolineata combines the Latin albus ("white") and lineatus ("lined"), in reference to the diagnostic white lines along the oral veil, cerata, tail, and rhinophores. The species is widely known by the English common name "Alabaster Nudibranch".

Remarks

A broad-spectrum predator, feeding on bryozoans, hydroids, small gastropods, and ascidians. The family Dironidae, of which Dirona is the type genus, is unusual among cladobranch-like nudibranchs in having unbranched digestive gland (not entering the cerata) and lacking cnidosacs — features that place it as a distinct lineage outside the typical aeolids.

---

References

• Dirona albolineata MacFarland MS, in Cockerell & Eliot, 1905, Cockerell T.D.A. & Eliot C. (1905). Notes on a collection of Californian nudibranchs. Journal of Malacology. 12(3): 31-53.
• シロスジアケボノウミウシ（新称）, スーザン・ミドルトン他. (2015). 海の美しい無脊椎動物. 創元社.
• Dirona albolineata, Behrens D.W., Hermosillo A., Fletcher K. & Jensen G.C. (2022). Nudibranchs & Sea Slugs of the Eastern Pacific. Molamarine.