THE TANTULOCARIDAN LIFE-CYCLE - THE CIRCLE CLOSED

The discovery of a new stage in the life cycle of the Tantulocarida is reported. A sexual female, collected from a deep-sea harpacticoid copepod host, was removed from the trunk sac of the preceding tantulus larva. This female is a free-living and nonfeeding stage which presumably mates with the free-swimming adult male previously described. The female comprises a cephalothorax, probably incorporating 2 limbless thoracic somites, 2 free pedigerous trunk somites, and 3 limbless trunk somites. It also possesses paired antennules, the only well-defined cephalic appendages present at any stage in tantulocaridan life history. There is a median genital aperture, the copulatory pore, located ventrally on the cephalothorax at about the level of the incorporated first thoracic somite. This is interpreted as further evidence of a sister-group relationship between the Tantulocarida and the Thecostraca. The known life-cycle stages of the Tantulocarida are now interpreted as forming two cycles, one sexual, the other parthenogenetic.