Halgerda guahan Carlson & Hoff, 1993

Description

Body length 32-48 mm. Dorsum translucent white, traversed by a low reticulate network of orange ridges. The junctions of the ridges are only slightly raised and lack the prominent tubercles seen in some congeners. The dorsal ground color bears almost no additional yellow or brown markings, leaving the orange ridges as the dominant pattern; this makes H. guahan easily separable from most other Halgerda by external appearance alone. The mantle margin is bordered by an opaque white rim. Both the rhinophores and the tripinnate gill are translucent white with large scattered black spots, and a small amount of orange enters the rim of the rhinophoral sheath.

Distribution

Type locality: Anae Island, Guam (southern Mariana Islands, western Pacific). Additional records exist from several sites around Guam (e.g., Agat, Bile Bay) and from Saipan in the northern Mariana Islands.

Etymology

The specific epithet guahan is the Chamorro word for "Guam," the indigenous name of the type-locality island. Carlson & Hoff 1993 named this species together with two other new Halgerda from Guam in the same paper.

Remarks

In the molecular phylogeny of a 2023 study, H. guahan falls within a clade together with Halgerda paulayi (Red Sea) and Halgerda jennyae (Mozambique). The three species share a similar spotting pattern on the rhinophores and gills, but H. guahan is the palest of the three and is distinguished externally by the absence of dark lines along the dorsum and ridge valleys that are diagnostic of the other two. The original description appeared in Carlson & Hoff 1993, The Veliger 36(1): 16-26, which simultaneously introduced Halgerda brunneomaculata and Halgerda malesso from Guam.

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References

• Halgerda guahan sp. nov., Carlson C.H. & Hoff P.J. (1993). Three new Halgerda species (Doridoidea: Nudibranchia: Opisthobranchia) from Guam. The Veliger. 36(1): 16-26.
• Halgerda guahan, Terrence Gosliner, Ángel Valdés and David Behrens. (2015). Nudibranch and Sea Slug Identification Indo-Pacific. New World Pubns Inc.
• Halgerda guahan Carlson & Hoff, 1993, Donohoo S.A., Villalobos S.G., Hallas J.M. & Gosliner T.M. (2023). Hyperdiversity of the genus Halgerda Bergh, 1880 (Nudibranchia: Discodorididae) with descriptions of fourteen new species. Marine Biodiversity. 53(3): 42. https://doi.org/10.1007/s12526-022-01334-9