Halgerda tessellata (Bergh, 1880)

Yonow, Nathalie, 2012, Opisthobranchs from the western Indian Ocean, with descriptions of two new species and ten new records (Mollusca, Gastropoda), ZooKeys 197, pp. 1-130 : 24

Halgerda tessellata (Bergh, 1880)

Dictyodoris tessellata . - Eliot 1905: 229 (Madagascar).

Halgerda tessellata . - Rudman 1978: 65, figs. 4C, D, 6 (Kenya); Debelius and Kuiter 2007: 236 (Maldives, South Africa); Apte 2009: 171, fig. 2p (Laccadive Islands).

Halgerda tesselata . - Yonow et al. 2002: 844, fig. 11a (Chagos) (misspelling).

Material.

Kenya: two specimens 15 × 15 mm and 9 × 5 mm, Vipingo, 25 miles N of Mombasa, rock pools at ELW, 23 September 1984, leg. J Hognerud (California Academy of Sciences CASIZ 169945). - Tanzania: photograph of single individual, Mafia Island, shallow water, May 2009, A de Villiers. - Maldives: two specimens 15 mm and 25 mm (MDV/AB/96/11), Foteo Channel, Felidhoo Atoll, 15 m depth, 05 May 1996, leg. RC Anderson & SG Buttress (California Academy of Sciences CASIZ 169996); photos of two individuals, 1986-1994, J Hinterkircher. - Mayotte: photographs of two individuals http://seaslugs.free.fr/nudibranche/a_intro.htm. - Seychelles: photos of two individuals, Lilôt, NW Mahé, 1988-1989, P Kemp.

Description.

Easily recognised by pattern of orange ridges enclosing brown depressions speckled with white. Both specimens from Kenya were examined when they were received in 1984: the 15 mm specimen was still yellow-orange, as was the foot; the brown reticulated pattern also remained. Very few spots were present on hyponotum but between the hyponotum and foot, there was a band of brown dots/patches. The smaller specimen retained an orange edge to the mantle and the foot: the dorsum was yellow-orange with the brown pattern remaining; there were more spots on the hyponotum than in the larger animal, and there were spots and patches present in a band between the hyponotum and the foot. The preserved Maldives specimens were also clearly recognizable several years after collection, with the brown reticulated pattern remaining between the ridges as well as the brown spots scattered on the hyponotum.

Distribution.

Halgerda tessellata has a wide Indo-Pacific distribution although, like some species with such a large range, it has a consistently different colour form in the Pacific: a band of white dots is present around the margin and there is dense white pigmentation on the gills ( Carlson and Hoff 1993; Yonow in prep.).