A new opecoelid species (Trematoda: Opecoelidae) from the threespine stickleback Gasterosteus aculeatus L. in California.

Plagioporus kolipinskii n. sp. (Trematoda: Opecoelidae) is described from the intestine of the threespine stickleback, Gasterosteus aculeatus L., from Lobos Creek, a freshwater stream in Presidio, San Francisco County, California. Plagioporus kolipinskii is morphologically somewhat similar to 4 (P. serotinus , P. angusticollis , P. macrouterinus , and P. shawi []) of the 12 currently recognized North American species of the genus, but can be readily distinguished from all 4 in possessing a much larger acetabulum and a larger ovary relative to the testes. In addition, the new species can be distinguished from P. angusticollis by a smaller cirrus sac; from P. macrouterinus by the elongated shape of its body and reduced extent of its uterus (the uterus of P. macrouterinus extends posteriorly to the intersection of the testes); from P. shawi by a much-shorter cirrus sac (which reaches the ovary in P. shawi), an unlobed ovary (as opposed to a quadrilobed ovary in P. shawi), and fewer eggs that are also larger relative to body size.