A new species of parasitic copepod, Chondracanthus hoi sp. n. (Copepoda: Chondracanthidae), is described based on specimens of both sexes collected from the buccal cavity and gill arches of the silvery john dory, Zenopsis conchifer (Lowe) (Zeiformes: Zeidae), from waters off northern Argentina (35-36°S, 53-54°W). Female of C. hoi differs from its congeners by the following combination of characters: presence of five pairs of trunk processes, antennule with four knobs tipped with small setae and absence of denticles on the terminal process of maxilla. Chondracanthids and zeiform fishes have been proposed as an example of co-speciation; this assumption is derived from a series of analyses based on incomplete records of both geographical distribution and host range of some parasite species, as well as misidentification of fish hosts. These inconsistences observed during our bibliographical analyses are also discussed.
A new species of Merizocotyle Cerfontaine, 1894 (Monogenea: Monocotylidae) is described from the nasal tissues of three deep sea rajid skates: the southern thorny skate, Amblyraja doellojuradoi (Pozzi), broadnose skate, Bathyraja brachyurops (Fowler), and yellownose skate, Zearaja chilensis (Guichenot), collected off Buenos Aires Province, Argentina, southwest Atlantic Ocean. Two additional species of sympatric rajid, the white-dotted skate, Bathyraja albomaculata (Norman), and the Patagonian skate, Bathyraja macloviana (Norman), were also examined but no merizocotylines were found. The taxonomy of the Merizocotylinae is not widely accepted and, as a result, the status of Thaumatocotyle and Mycteronastes, and their proposed synonymy with Merizocotyle are currently under discussion. The new species differs from its congeners by having a unique haptoral structure, 6 peripheral loculi that are asymmetrically arranged (one much smaller, indistinctly located in the left or right side of the haptor). The presence of the new species in three sympatric species of Rajidae belonging to distinct genera and subfamilies, as well as its absence in sympatric congenerics indicates the lack of phylogenetic host specificity. Host ecology and geographical distribution appear to be more important than host phylogeny in determining the distribution of this parasite across potential hosts in the region. This constitutes the first record of Merizocotyle in the southwestern Atlantic Ocean.
Two new species of bothriocephalidean cestodes, Clestobothrium splendidum sp. n. from Merluccius australis (Hutton) and Clestobothrium cristinae sp. n. from Merluccius hubbsi Marini from the Patagonian shelf of Argentina, are described. Clestobothrium splendidum can be typified by the following characteristics: a medium-sized strobila composed of 410-528 proglottides that are much wider than long; 49-90 testes per mature proglottis, partially surrounding the ovary posteriorly; a transversely elongated genital pore situated anterior to spurious articulations; presence of a genital atrium; a globular cirrus-sac occupying 4-6% of mature proglottis width; a vagina with sphincter and three pairs of osmoregulatory canals on each side of the proglottis. Clestobothrium cristinae is characterised by its small size; 71-219 proglottides; 39-64 testes per mature proglottis, usually surrounding completely the ovary posteriorly; a rounded genital pore situated at the same level of spurious articulations; an oval cirrus-sac occupying 8-16% of mature proglottis width; and three pairs of osmoregulatory canals on each side of the proglottis. Clestobothrium cristinae shares with C. splendidum the type and distribution of microtriches, except for the central surface delimited by two lips. Additionally, type and voucher materials of Clestobothrium crassiceps (Rudolphi, 1819) from Merluccius merluccius were studied. A key to species is provided.