Experimental Elucidation of the life Cycle of Acanthobothrium parviuncinatum Young, 1954 (Cestoda: Onchobothriidae) from the Round Stingray, Urobatis halleri (Myliobatoidea), in Southern California, with a Redescription of the Adult Worm

The life cycle of the cestode Acanthobothrium parviuncinatum includes a copepod as the first intermediate host, a small benthic fish as second intermediate host and the round stingray, Urobatis halleri, as the final host. Hexacanth embryos within nonoperculate, untanned eggs, collected from round stingrays developed in the tidepool copepod, Tigriopus californicus, into procercoids with an apical organ/sucker and cercomer, within 10 d post-exposure at 21°C, followed by development into a plerocercoid with bothridia. When infected copepods were fed to arrow gobies, Clevelandia ios, nonlacunate plerocercoids, each bearing four acetabula, in the form of nonretractable bothridia, were found within 2 d, attached by their apical sucker deep between villi in the small intestine. By 33 d post-infection at 21°C, plerocercoids approached the size of plerocercoids found in naturally infected fish hosts. At 44 d post-infection, two experimentally infected gobies were fed to a laboratory reared round stingray where seven mature adult worms were found 31 d post infection at 21°C. Additional studies are necessary to determine if plerocercoids in the first intermediate host are directly infective to round stingrays. Identification of experimental plerocercoids and adult worms as A. parviuncinatum was confirmed using 28S rRNA gene sequences. A second plerocercoid morphotype present in small benthic fish was identified as A. olseni. Adult A. parviuncinatum can be distinguished from all other species found in Southern California elasmobranchs by possessing narrow hooks with a bent outer prong, fewer than 13 testes and a genital pore in the anterior third of the proglottid. The adult and pleroceroids of A. parviuncinatum are reported from Morro Bay to Tijuana Estuary, California. This study documents the first complete experimental life cycle in the Onchobothriidae, which includes 12 genera and over 300 species, and only the fourth life cycle known for all elasmobranch tapeworms. The biological characteristics of U. halleri, with its diverse parasite fauna, and abundance in nearshore waters, provide significant opportunities to examine the biology of an array of elasmobranch tapeworm taxa.