Okenia cf. amoenula (Bergh, 1907)

Vallès, Yvonne, Valdés, Ángel & Ortea, Jesús, 2000, On the phanerobranch dorids of Angola (Mollusca, Nudibranchia): a crossroads of temperate and tropical species, Zoosystema 22 (1), pp. 15-31 : 16-20

Okenia cf. amoenula (Bergh, 1907)

( Fig. 1 )

Idaliella amoenula Bergh, 1907: 80-82 , pl. 8, figs 6-11. MATERIAL EXAMINED. — Luanda Province. Punta das Palmeirinhas, 9°09’S, 12°58’E, II.1987, 1 specimen 6 mm preserved length.

DISTRIBUTION. — Okenia amoenula has only been reported from South Africa (Gosliner 1987a). This paper is the first reference for this species to Angola.

DESCRIPTION

The background body colour is opaque white in the living animal. In the centre of the dorsum there are a few reddish spots and short lines of the same colour ( Fig. 1 ). The oral tentacles are white and have four yellow tips each. The dorsum has, on each lateral margin, ten short papillae with yellow pigmentation on the apex. All over the dorsum there is a network of spicules. The rhinophores are white, non-retractile, and ringed with 18 lamellae. There are 11 unipinnate (the largest one is bipinnate) branchial leaves white in colour, having the rachis yellow (in the distal region edged with two red lines). The tail has a yellow line in the centre with few red spots.

REMARKS

The single specimen collected was badly preserved, making dissection and investigation of the internal anatomy impossible. In the process of removing the foregut the radula was lost. For that reason a positive identification of the specimen could not be done.

Bergh (1907) described Okenia amoenula (Bergh, 1907) in the binomen Idaliella amoenula Bergh, 1907 , as being a white animal with three crimson lines on the dorsum, which joined together in the anterior part, and a crimson patch on the anal area. The dorsal papillae were reddish and yellow, the branchial leaves had a crimson colour, and the rhinophores were yellow. Our specimen, as well as Bergh’s, has a white background colour, red and yellow pigmentation on the lateral papillae, and the branchial leaves are also reddish (with two red lines). However, our specimen shows a few differences in colour pattern from Bergh’s material (white rhinophores instead of yellow, white branchial leaves instead of crimson), and with that described by Gosliner (1987a) from South Africa (dorsum with more red pigmentation in Gosliner’s specimen and yellow lateral papillae, but also with red spots), which could be caused by differences in size. Otherwise they are identical.

Okenia amoenula has been considered by Schmekel (1979) as a synonym of Okenia mediterranea (Ihering, 1886) . Okenia mediterranea , like our material of O. amoenula , has a yellow line in the centre of the tail with some red spots, and the rhinophores are white. However, our specimen lacks tubercles in the centre of the dorsum, which is a definitive character that separates the two species (Valdés & Ortea 1995).

Okenia amoenula is similar in colour to Okenia hispanica Valdés & Ortea, 1995 . Both species have a white background colour, a white tail with a yellow line, and yellow pigmentation on the gill. However, they are clearly distinguishable by several external features. The dorsum of O. hispanica has two large pink patches, just behind each rhinophore, and another one on the anal area, the rhinophores are pink, and the oral tentacles are white, whereas in O. amoenula the dorsum is white with red spots or lines (lacking large patches), the rhinophores are white or yellow and the oral tentacles are white with four small yellow spots. Other differences include the absence of tubercles on the dorsum of O. hispanica and the radular morphology, already compared by Valdés & Ortea (1995).

Okenia digitata (Edmunds, 1966) ( Figs 2 ; 3D )

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 ; 1 specimen 5 mm preserved length; 1 specimen 3 mm preserved length. — Cacuaco , 08°47’S, 13°21’E, date unknown, 1 specimen 6 mm preserved length .

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 ). 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 ) 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 consi- der 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.

Family POLYCERATIDAE Alder & Hancock, 1845 Genus Limacia Müller, 1781

TYPE SPECIES. — Doris clavigera Müller, 1776

REMARKS

MacFarland (1905) introduced the genus Laila MacFarland, 1905 , based on Laila cockerelli MacFarland, 1905 , as an “allied” to the genera Triopha Johnston, 1838 and Issa Bergh, 1880 , but he did not refer to the genus Limacia Müller, 1781 . The description of L. cockerelli was later completed with drawings of the radula and the animal in the living form (MacFarland 1966). Laila janssi Bertsch & Ferreira, 1974 , presents similar morphological characteristics as L. cockerelli , differing on the colour pattern and in some radular features such as a smaller number of teeth rows, a rougher rachidian plate texture and some variations on the shape of the outer lateral teeth (Bertsch & Ferreira 1974).

The genus Laila has the same morphological characteristics as the genus Limacia : pallial margin with numerous club-shaped papillae; presence of tubercles on the notum; veil appendages canaliculated; retractile rhinophores; branchial leaves non retractile; two inner lateral teeth hook-shaped, the innermost being thinner and longer than the outermost, and many outer lateral teeth quadrangularshaped. Laila and Limacia only differ in the fact that Limacia clavigera Müller, 1776 , lacks a rachidian plate in the radula, which is present in both L. cockerelli and L. janssi . Since most of the morphological features of Laila and Limacia are very similar, just the presence of rachidian plate in the radula of Laila does not seem to be enough to consider Laila as a different genus. Therefore both genera are here regarded as synonyms, with Limacia Müller, 1781 having priority. This idea was already proposed by Ortea et al. (1989).

Figures

FIG. 1. — Okenia cf. amoenula (MNHN), dorsal view of the living animal. Scale bar: 1 mm.

FIG. 2. — Okenia digitata (MNHN), dorsal view of the living animal. Scale bar: 1 mm.

FIG. 3. — A, Kaloplocamus ramosus (MNHN), rachis of the radula; B, Kaloplocamus ramosus (MNHN), inner lateral teeth; C, Kaloplocamus ramosus (MNHN), outer lateral teeth; D, Okenia digitata (MNHN), radular teeth morphology. Scale bars: A, C, 100 µm; B, 20 µm; D, 10 µm.