A young parasite in an old fish host: A new genus for proteocephalid tapeworms (Cestoda) of bowfin (Amia calva) (Holostei: Amiiformes), and a revised list of its cestodes.

Abstract

A new genus, Laruella n. gen., is proposed for the proteocephalid cestode L. perplexa (La Rue, 1911) n. comb. (syn. Proteocephalus perplexus La Rue, 1911), a parasite of a ‘living fossil’, the bowfin (Amia calva), in North America. The new genus is differentiated from other proteocephalid genera by having a massive four-lobed scolex without an apical organ and bearing suckers possessing tear-shaped sphincters on their inner rim, vitelline follicles forming L-shaped lateral fields, with the vitellarium turned inwards (medially) ventrally alongside the posterior margin of the ovary, a ring-like vaginal sphincter situated at a considerable distance from the genital atrium, and ellipsoid eggs resembling those of bothriocephalid and diphyllobothriid tapeworms, except for the absence of an operculum. Phylogenetic relationships of the new genus are not resolved, but it belongs to the so-called Neotropical clade of the Proteocephalidae, which is composed mainly of Neotropical tapeworms of siluriforms and other teleosts, but also Nearctic and Palaearctic species of Ophiotaenia La Rue, 1911 from snakes and amphibians. A morphologically similar species, Proteocephalus ambloplitis (Leidy, 1887) from bass (Micropterus spp.) in North America, is provisionally retained in Proteocephalus Weinland, 1858 because its relationships to L. perplexa are not yet clear. The former species differs from L. perplexa by the presence of a large apical organ, large, elongate vaginal sphincter situated near the genital atrium, vitelline follicles limited to lateral longitudinal fields, strongly coiled vas deferens within the cirrus sac, and a convoluted vaginal canal anterior to the ovarian isthmus. Laruella perplexa reportedly has a s broad spectrum of hosts but most are likely postcyclic or accidental hosts. A list of cestode parasites reported from bowfin is provided; it includes eight species and three taxa not identified to the species level. However, only three adult cestodes, L. perplexa and two species of Haplobothrium Cooper, 1914, are typical tapeworm parasites of bowfin, but previous molecular studies indicate possible existence of a putative new species in bowfin.