A new species Wardium paucispinosum (Eucestoda: Hymenolepididae) parasite from the intestine of Larus maculipennis (Lichtenstein) from Mar del Plata, Argentina is described. The distinctive features of the new species are: strobilar length 52.8 mm; 10 aploparaksoid rostellar hooks, 14 (12-17) microm long; ratio between cirrus pouch length and mature proglottid width (CPL/MPW) 0.38 (0.27-0.50); regular cylindrical evaginated cirrus, 90 x 10 microm, with distal end without spines and proximal and medium thirds covered with spines 7 microm long; simple tubular membranous vagina, 110 x 10 microm, without sclerotised portions and sphincters; eggs fusiform, 77 x 44 microm. Besides, Hymenolepis semidutctilis Szidat, 1964, from the intestine of Larus dominicanus and L. maculipennis from Santa Fe, Argentina is transferred to the genus Wardium Mayhew, 1925, based on the presence and shape of the rostellar hooks.