Halgerda formosa Bergh, 1880

Description

A medium-sized Halgerda, reaching up to 45 mm in life (20 mm wide, 8 mm high). The ground colour in life is translucent grey to greyish-white, traversed on the back by orange longitudinal lines and reticular networks, with conspicuous flat depressions between them. A median dark purple round spot stands in front of the rhinophores; behind the gill on the back lie two more similar spots, with further spots on the upper face of the tail. The rhinophores and gill rachides are also dark purple, the gill leaves yellowish; the head is pale yellow and the foot border yellow. In alcohol the red tones fade and the dorsum is dominated by white anastomosing ridges set against grey or leaden interstitial fields, the ridge intersections somewhat yellow. The mantle border is fairly wide, flat, and rather thin.

Distribution

Type locality: Japanese coast. Also recorded from Mauritius (Indian Ocean) and widely across the Indo-West Pacific.

Etymology

The Latin adjective formosa (feminine) is from forma ("form, shape"), meaning "beautiful, well-formed" — a descriptive epithet evoking the conspicuous reticular dorsal pattern.

Remarks

The species is the type of the genus Halgerda. The reticulate white dorsal ridges and dark purple round spots make the species readily recognisable within the genus.

---

References

• Halgerda formosa, B., Bergh R. (1888). Nudibranchien vom Meere der Insel Mauritius. In: Semper C. (ed.), Reisen im Archipel der Philippinen. II. Wissenschaftliche Resultate. Bd. II, Abt. II (Malacologische Untersuchungen Bd. III), Heft XVI: 755-814. Wiesbaden: C.W. Kreidel's Verlag.
• Halgerda formosa, Terrence Gosliner, Ángel Valdés and David Behrens. (2015). Nudibranch and Sea Slug Identification Indo-Pacific. New World Pubns Inc.