Ischnochiton sp.

Dell’Angelo, Bruno, Schwabe, Enrico, Gori, Sandro, Sosso, Maurizio & Bonfitto, Antonio, 2014, Chitons (Mollusca, Polyplacophora) from São Tomé and Príncipe Islands, African Invertebrates 55 (2), pp. 171-200 : 176

Ischnochiton sp.

Figs 2L–Q

Material examined: ST06: 1 specimen, length 2 mm ( BD 108 ).

Distribution: São Tomé Island.

Comparison and remarks: This specimen is characterized by a tegmental sculpture consisting of rough and closely spaced nodules, irregular in outline and irregularly distributed ( Figs 2O–P ). The dorsal girdle is beset with rectangular overlapping scales, bearing up to 11 strong ribs ( Fig. 2Q ).

Only five species of Ischnochiton are known from the northern and central Atlantic African coasts and islands, namely I. sererorum ( de Rochebrune, 1881) from Mauritania and Cape Verde Islands, I. cessaci ( de Rochebrune, 1881) from Mauritania, Senegal, Angola, Canary Islands and Cape Verde Islands, I. goreensis Thiele, 1909 from Senegal and Cape Verde Islands, I. paessleri Thiele, 1909 from Cape Verde Islands, and I. nicklesi Kaas & Van Belle, 1990 , from Senegal and Cape Verde Islands (Kaas & Van Belle 1990; Rolán 2005, 2011). However, all have a tegmental sculpture that is mainly smooth or finely granulose.

Congeners from South African Atlantic waters, namely I. textilis (Gray, 1828) , I. oniscus (Krauss, 1848) , I. bergoti (Vélain, 1877) , and I. elizabethensis Pilsbry, 1894 , could also be found along part of the southwest African coast but differ from the present specimen not only in their generally larger size, but they also have morphological peculiarities, summarized in Kaas and Van Belle (1990) and Sirenko and Schwabe (2002), that are lacking in this specimen, although their juvenile stages have not been carefully compared.

Description of a new species on the basis of the single small specimen is not justified, so it is preferable to leave the identification as Ischnochiton sp. until such time as more material becomes available.

Figures

Fig. 2. (A–D) Leptochiton denhartogi Strack, 2003, São Tomé Island, ST03, intermediate valve: (A–B) dorsal and frontal views, (C–D) detail of the sculpture of the tegmentum, close-ups of granules with aesthetes in different views; (E–H) Leptochiton sp., São Tomé Island, ST11, tail valve: (E–F) dorsal and lateral views, (G–H) detail of the sculpture of antemucronal and postmucronal areas, respectively; (I–K) Ischnochiton cf. rissoi (Payraudeau, 1826), São Tomé Island, specimen from ST06: (I) dorsal view, (J) dorsal girdle scales, (K) detail of the intermediate and tail valves; (L–Q) Ischnochiton sp., SãoTomé Island, specimen from ST06:(L–M) dorsal and lateral views,(N) detail of thehead and the first intermediate valves, (O–P) detail of the sculpture of central and lateral areas, respectively, (Q) dorsal girdle scales.Scale bars = 1 mm (B); 800 μm (I); 600 μm (A); 500 μm (E); 400 μm (L, M); 300 μm (F, K); 200 μm (N); 100 μm (J); 60 μm (G, H); 50 μm (D); 40 μm (C); 30 μm (P); 20 μm (O, Q).