Okenia digitata ( Edmunds, 1966 )

Okenia digitata ( Edmunds, 1966) View in CoL

( Figs 2 View FIG ; 3D View FIG )

Teshia digitata Edmunds, 1966: 69-72 , figs 1-10.

MATERIAL EXAMINED. — Bengo Province. Praia São Tiago , 08°35’S, 13°21’E, 1983, 1 specimen 6 mm preserved length; GoogleMaps 1 specimen 5 mm preserved length GoogleMaps ; 1 specimen 3 mm preserved length. GoogleMaps — Cacuaco , 08°47’S, 13°21’E, date unknown, 1 specimen 6 mm preserved length GoogleMaps .

DISTRIBUTION. — The specimens from Angola represent the first reported occurrence of this species outside Ghana.

DESCRIPTION

The background body colour is white in the living animal. On its lateral border the dorsum has 16 tentacular papillae alternating between large and small ones ( Fig. 2 View FIG ). Almost every lateral papilla has, at the same height, a yellow ring, and some black spots. The whole dorsum has small black spots that are more abundant in the centre of the dorsum, being dispersed in the sides. There are two oral tentacles, which are white and similar in form to the lateral papillae. The rhinophores are white as well, with very few black spots. The gill emerges from the body and divides into three branches. Each one has seven branchial leaves. The branchial leaves are unipinnate, white with very little black and have yellow spots dispersed all over. The tail is white with black spots. In each half-row of the radula there is one inner lateral and one outer lateral tooth. The inner lateral tooth ( Fig. 3D View FIG ) is flat and wide at the base. The large cusp on the inner side has ten strong denticles. The outer lateral tooth is thin and the apex is folded, being smaller than the inner lateral.

REMARKS

The genus Teshia Edmunds, 1966 , was introduced by Edmunds (1966) for Teshia digitata Edmunds, 1966 , as different from Okenia Menke, 1830 . The main characteristic used by Edmunds to separate both genera was that Teshia had three sets of branchial leaves whereas Okenia just had one, all other features of Teshia being identical to those of Okenia . In our opinion, this difference is not enough to separate a different genus and therefore both genera are here regarded as synonyms, with Okenia Menke,1830 , having priority.

The specimens from Ghana and Angola are very similar in their colour pattern, however they s h ow s o m e d i f f e re n c e s. Ed m u n d s (1 9 6 6) described his single specimen as being grey with dark maroon spots on the dorsal and lateral areas of the body, and pale yellow spots on the flanks. The long rhinophores were grey on the stalk and maroon on the club. Gill and rhinophores were both scattered by maroon spots and small white dots. On the contrary, our specimens are white instead of grey, and have black small spots instead of maroon. The rhinophores of our specimens are white and the gill is yellow. The radula appears to be similar between the material of Ghana and Angola. Both have an outer lateral tooth, folded on the apex, much smaller than the innermost one, which has a strong cusp with eight to ten wide denticles in the inner side.

Edmunds (1966) described the gill of O. digitata as having three different sets of branchial leaves that emerge from three different points of the body. Instead, we observed that our specimens have three different sets emerging from a single point. The collector observed this character on the living animals, which after preservation cannot be properly observed. On preserved animals the gill seems to be just as Edmunds’ description except for the presence of a triangular area differently pigmented that joins the three sets of gills. We consider that the gills in both animals are similar and that Edmunds’ description could be based on preserved animals, for this reason the true nature of the gills could have been misinterpreted.