Elysia degeneri Ostergaard, 1955

Description

A small vivid sacoglossan reaching about 19–25 mm in length and ~3 mm wide. Body elongate, rather slender, tapering posteriorly; parapodial lobes thrown into about four folds. Rhinophores short, stout and cylindrical, directed antero-laterally and slightly curved outward, beset with low sharply-pointed conical processes. Eyes located at the postero-lateral base of each rhinophore, each surrounded by a white area encircled by a pale brown ring. Foot rounded anteriorly (capable of forming a broad anterior lobe) and tapered to a blunt posterior point. Body, head and foot yellowish-green dark green, merging to pale green medially; the parapodial lobes are bordered medially with a bright orange band, edged outwardly by a broad white band, and inwardly by a sky-blue band — sometimes with an additional vermilion band between the blue and yellow. Distinguished from Elysia nealae by short, knobbed, non-tapering rhinophores and the orange-bordered parapodial lobes.

Distribution

Central and western Pacific. Records include Hawaii, the Philippines and Japan. The type locality is Waianae, Oahu, Hawaii (26 March 1923, leg. Otto Degener; holotype USNM 574929).

Etymology

The specific epithet degeneri honours Otto Degener (1899–1988), the German-American botanist who collected the type specimen at Waianae and supplied many other Hawaiian specimens to Östergaard.

Remarks

Originally described by Östergaard in "Some opisthobranchiate Mollusca from Hawaii" (Pacific Science 9(2): 124-125, 1955). The intense green colour appears to depend on commensal algae and may be subject to fluctuation; the second specimen examined (Hanauma Bay, 1950) lacked the algal pigmentation but otherwise agreed with the type.

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References

• Elysia degeneri, Ostergaard J.M. (1955). Some opisthobranchiate Mollusca from Hawaii. Pacific Science, 9(2): 110-136.
• フジイロミドリガイ（仮称）, 小野篤司. (1999). ウミウシガイドブック. TBSブリタニカ.
• Elysia cf. degeneri, Terrence Gosliner, Ángel Valdés and David Behrens. (2015). Nudibranch and Sea Slug Identification Indo-Pacific. New World Pubns Inc.