Pennella instructa Wilson 1917

Pennella instructa Wilson, 1917

(Fig. 12)

Synonyms. Pennella zeylanica Kirtisinghe, 1933

Type host and locality. Xiphias gladius, northwest Atlantic Ocean.

Morphology. Size: 122–163 mm. Papillae: full coverage, generally spherical, variable in size and shape, found in distinct bands or groups. Holdfasts: two lateral only. First antenna with five segments, second with two segments. Plumes: dendritic, complex branching

Remarks. A valid species. One of the largest species of Pennella. Found on swordfish (Xiphias) and sailfish (Istiophorus) in the Atlantic, Indian and Pacific Oceans and Mediterranean Sea (Wilson 1917; Kirtisinghe 1932; Devaraj & Bennet 1972; Hogans et al. 1985, 1986; Speare 1995; Mattiucci et al. 2005). Pennella instructa superficially resembles another large Pennella, P. filosa which is found on the same host species and sometimes found on the same individual host (Hogans et al. 1985). Well-executed original description and figures (Wilson, 1917); redescribed by Hogans (1986). This parasite exhibits two lateral holdfast horns only (P. filosa may have three), always directed posteriorly, and a cephalothoracic papillae field which is configured in distinct bands (on P. filosa the papillae are random, not organized in groups or bands). Pennella instructa has a two-segmented first antenna; P. filosa exhibits 3 segments on this appendage. Pennella instructa exhibits a somewhat variable second antenna, the structure of the terminal segment is not consistent between specimens; whether this is due to age, atrophy or site of infestation is not known. Unlike P. filosa which generally infests only muscle tissue, P. instructa is often found with the cephalothorax embedded in the tissues of an individual organ (ex: ovaries) or inserted into the dorsal aorta of the heart of the host (Wilson 1932; Hogans et al. 1985; Merella et al. 2003).