Storch, V. and Jamieson, B.G.M. 1992c. Further spermatological evidence for including the Pentastomida (Tongue worms) in the Crustacea. International Journal for Parasitology 22:  95-108.

relationships of pentastomids with their putative maxillopodan and   remipedian relatives have been deduced from sperm ultrastructure   intuitively and by parsimony analysis using the PAUP program of Swofford   (1990, Version 3.01, Illinois Natural History Survey, Champaign, IL). A   remarkable degree of homogeneity in the ultrastructure of the spermatozoa   of cephalobaenids and porocephalids is demonstrated and a sister-group   relationship of pentastomids and Branchiura, first proposed by Wingstrand  (1972, Kongelige Danske Videnskab Selskab Biologiske Skrifter 19: 1-72),   is confirmed. Spermatozoal synapomorphies of the Pentastomida and the   branchiuran Argulus include: absence of an acrosome vesicle and filament   in the mature spermatozoon; presence of a pseudoacrosome, about 30mm   long, divisible into a dorsal and a ventral component (the dorsal and   ventral rod), and derived from pericentriolar structures; continuation of   the dorsal rod with the dorsal ribbon of an axonemal sheath and with   material embedding the centriolar doublets 1, 2 and 9; continuation of the   ventral rod with material embedding the more ventrally situated doublets;   presence of the axonemal sheath; presence of a connective from the dorsal   ribbon to axonemal doublet 1; presence in the spermatid of nine dense   fibres peripheral to the doublets; great elongation of the three   mitochondria parallel to the nucleus; and total incorporation of the   axoneme in the spermatozoon so that a free flagellum is absent. The sperm   of the pentastome-branchiuran assemblage appear to be the most highly evolved of the flagellate crustacean sperm.