Temnocephala minutocirrus sp. nov., an ectosymbiont on Cryphocricos granulosus De Carlo, 1967, is described from the State of Rio Grande do Sul, southern Brazil. One hundred and nine naucorids were examined, of which 36 (33%) were positive for this species of Temnocephala Blanchard, 1849. In one sample of 94 creeping water bugs, 49 (52%) were 4th instar nymphs, 6% of which were infested; 45 (48%) were adults, either brachypterous (40 with 18 males and 22 females) or macropterous (5 with 1 male and 4 females), 67% of which were infested (29% males and 38% females). Temnocephalan eggs were found both ventrally and dorsally: fixed on coxae, trochanters, and along the sternum between fore middle, and hind pairs of legs; basal of the abdominal area; and on the scutellum, clavus, and hemelytra. Juvenile and adult temnocephalans were always devoid of body pigmentation, and were found living on the ventral body surface, preferably over the sternum, between the middle and hind pairs of legs. The most distinctive features of this new species are: 1) unusually short cirrus, slightly curved, with introvert corresponding to 37% of its total length; 2) dorsolateral 'excretory' syncytial epidermal plates, elliptic, with excretory pore relatively equatorial, closer to inner limit of each plate; 3) two pairs of large disc gland cells (paranephrocytes?) located centrally, just ahead of testes; 4) testes relatively large, but unequal in size, anterior pair smaller, always in the same zone, those of the same side, partially superposed; and (5) vagina with weak muscular wall and without muscular sphincters.
Ectocommensals; Neotropical Region; Rio Grande do Sul; South America; taxonomy
