FURTHER SPERMATOLOGICAL EVIDENCE FOR INCLUDING THE PENTASTOMIDA (TONGUE WORMS) IN THE CRUSTACEA

The ultrastructure of the spermatozoa of three species of the Pentastomida is investigated: the cephalobaenids Raillietiella sp. and Cephalobaena tetrapoda, and the porocephalid Porocephalus crotali. Phylogenetic 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 30-mu-m 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.