(Fig. 18)
Synonyms. Pennella bocconii Lamartinier, 1798, P. branchiata (Blainville, 1822)
Type host and locality. Antennarius sp (?), Atlantic Ocean.
Morphology. Size: 20–25 mm. Papillae: full coverage, clavate and tubiform, simple branching. Holdfasts: two only, short. First antenna with three segments, second with two segments. Plumes: simple, single or double.
Remarks: A valid species. Found so far only on sargassum fish of the family Antennaridae. Redescribed from Histrio histrio, Atlantic Ocean (Hogans 1988a). Possibly found on another frogfish, Anntenarius sp. (Mediterranean) (Brian 1908), but this record is not based on adequate descriptions or figures. Previously confused with P. diodontis, but P. sagitta is the smallest Pennella and is a separate, distinct species (Hogans 1988a). Pennella sagitta has been repeatedly shown by many authors to be a soft, delicate parasite with uniform external morphology among specimens (Hogans 1988a and references therein).