Pteraeolidia ianthina ( Angas, 1864 )

Yonow, Nathalie, Anderson, R. Charles & Buttress, Susan G., 2002, Opisthobranch molluscs from the Chagos Archipelago, Central Indian Ocean, Journal of Natural History 36 (7), pp. 831-882 : 875

Pteraeolidia ianthina ( Angas, 1864)

Pteraeolidia ianthina (Angas) : Yonow, 1994a: 127, ®gure 17D; Yonow, 2000: 125, pl. 35.

Material. Chag96/4: 15 mm; Salomon Channel, Salomon Atoll; 9 February 1996; at 6 m depth. Chag96/10: 20 mm; outer reef, Ile Anglais, Salomon Atoll; 11 February 1996; at 15 m depth. Chag96/25: 25 mm; outer reef, between Ile Boddam and Ile Poule, Salomon Atoll; 13 February 1996; at 13 m depth. Chag96/44: 22 mm; outer reef, Ile Diamante, Peros Banhos Atoll; 20 February 1996; at 15 m depth. Chag96/57: length not recorded; inner reef, Ile du Coin, Peros Banhos Atoll; 22 February 1996; at 4 m depth, with two additional individuals (photographed).

Description. Body very elongated and narrow. Dorsal coloration cream to brown, with bright blue median line. Many series of cerata, with more in the longer individuals. Cerata bulbous and longitudinally striated; coloration variable, from fawn with limited blue streaks to almost entirely blue or purple. Rhinophores fawn with white specks and purple tips or distal band. Oral tentacles long, white with three purple bands; opaque white to lime green area at base.

Geographic distribution. Indo-West Paci®c: Red Sea and South Africa to Hawaii (Yonow, 1994a, 2000).

Remarks. Rudman (1982a) reported the presence of zooxanthellae, visible as brown speckling on the head, body and cerata. The morphological adaptations to these symbionts are seen in the well-spaced clusters of cerata, each cluster a large fan-shape; not only do the cerata not shade each other, but they do not shade the zooxanthellae in the body either. The presence of zooxanthellae partly explained why P. ianthina was rarely found on a food source. Subsequently, Willan (1989) published a short note on P. ianthina found feeding on the hydroids Halocordyle distincta (Goldfuss) and Ralpharia magni W ca Watson. The question still remains, however: from which species does the aeolid collect its zooxanthellae and how does it acquire them?