Pennella diodontis Oken, 1816

(Fig. 7)

Synonyms. Pennella cervicornis Heegaard, 1943, P. plumosa (Dekay, 1844) Type host and locality. Diodon sexmaculatus, Philippines.

Morphology. Size: 24–28 mm. Papillae: partial coverage, clavate and club-like, consistent in size and shape, not found in organized groups. Holdfasts: two only, short. First antenna with three segments, second with two segments. Plumes: simple, single.

Remarks. A valid species. Original description from porcupine fish, Diodon sexmaculatus (= D. holacanthus) (Oken 1816); redescription from the same host species, Ceylon (Kirtisinghe 1932; Fig. 7). Considered incorrectly as infesting two host genera: Lophius and Diodon (Wilson 1917) . The history of P. diodontis was often confused with that of P. sagitta (Wilson 1917), however, P. diodontis reported from Lophius was an error of Blainville (1822) based on a poor description and incorrect host identification; P. diodontis is in fact a parasite of porcupine fish ( Diodontidae: Diodon) and P. sagitta is found so far only on frogfish (Antennaridae: Histrio, possibly Antennarius)). Lasarus and Sreenivasan (1977) reported P. diodontis from the moorish idol (Zanculus canascens (= Z. cornuta) in the Indian Ocean. The single habitus figure and brief description are not sufficient to confidently place their specimens (eight) in P. diodontis . However, the size of the parasite (26mm) and the cephalothoracic papillae (few small at center, and larger branched papillae around the cephalothorax periphery) are reminiscent of the species. As a parasite of Diodon, P. diodontis is a small species with uniformity in most structures between specimens (Hogans 1988a), however, its cephalothoracic papillae may vary slightly in arrangement and number depending on the individual parasite (Hogans 1988a; Heegard 1943).