A new species of parasitic copepod, Sarcotretes umitakae sp. n. (Siphonostomatoida, Pennellidae), on the rattail (Actinopterygii, Macrouridae) from the East China Sea, Japan

Abstract A new species of copepod, Sarcotretes umitakae sp. n., of the siphonostomatoid family Pennellidae is described based on female specimens from the rattail Coelorinchus jordani Smith and Pope (Actinopterygii: Gadiformes: Macrouridae) caught in the East China Sea. This species is characterized by exhibiting the following characters: the large proboscis projects strongly; the head bears paired lateral processes which are bulbous and taper into a slender horn; the twisting neck is significantly longer than the trunk; and the trunk bears an anterior constriction with a reduced abdomen.


Materials and methods
Two specimens of the rattail C. jordani infected with copepods were caught in the East China Sea off the Tokara Islands, Kagoshima, Japan on 8 October 2011 during the cruise (UM-11-06) of the Umitaka-maru, a training and research vessel of Tokyo University of Marine Science and Technology (TUMSAT). The fishes were collected using an otter trawl towed for 30 minutes between two sites (29°58.02'N, 127°43.79'E to 29°59.57'N, 127°44.28'E) around 309 m in depth and, immediately after capture, they were preserved in 70% ethanol with copepods attached. In the laboratory, copepods were carefully removed from the tissues of fishes, and then soaked in lactophenol for a whole day before dissection. The appendages of the copepods were observed after dissecting with the method of Humes and Gooding (1964). Drawings were made with the aid of a drawing tube. Morphological terminology follows Huys and Boxshall (1991). Measurements (in millimeters) are shown as ranges, followed by means and standard deviations in parentheses. The flexed part was measured along the body axis. Type specimens are deposited in the crustacean collection at the National Museum of Nature and Science, Tsukuba (NSMT). The scientific name of fish follows Nakabo (2002). Description of postmetamorphic adult female. Body ( Fig. 2A) elongate, comprising head, neck, and trunk. Total length 43.42 (from tip of cephalothorax to end of abdomen). Head (holdfast) composed of cephalosome to third pediger ( Fig. 2A, B), bearing elongate oral area projecting forward as cylindrical proboscis with multiple constrictions and mouth tube at its tip, with paired lateral processes ( Fig. 2A, B) consisting of bulbous base drawn out into highly sclerotized horn-like process. Vestige of dorsal shield of cephalothorax and tergites of first to third visible on dorsal surface of head (Fig. 2D). Two paired small sclerites on ventral surface of basal region of oral cone (Fig. 2E). Neck ( Fig. 2A) slender, longer than trunk, twisting and bearing bulge and constriction at posterior portion. Cylindrical trunk ( Fig. 2A) 12.23 long (from enlarged end of neck to abdomen), 3.08 wide at widest part bearing paired hemispherical protrusions and reduced abdomen (Fig. 2F, G). Caudal rami absent.
Remarks. Currently, three species of Sacotretes: S. eristaliformis, S. longirostris, and S. scopeli, are considered to be valid (Ho et al. 2007). Sarcotretes umitakae sp. n. differs from S. eristaliformis and S. scopoli by having the holdfast with paired bulbous swellings drawn out into an elongate, horn-like process (vs. bulbous with or without a blunt tip) and the neck approximately 3 times as long as the trunk (vs. nearly as long as the trunk in S. eristaliformis and less than 3/4 of the trunk length in S. scopeli) (Brian 1912;Hogans 1988;Boxshall 1989;Cherel and Boxshall 2004;Ho et al. 2007). The two specimens described as S. eristaliformis by Kabata and Gusev (1966) were judged to be S. scopeli on the basis of a body length of 15.8-21.2 mm, the neck being shorter than the trunk, and relative length of the proboscis (Hogans 1988;Ho et al. 2007). In addition, S. scopeli differs from the new species by the absence of the vestige of leg 4 (vs. presence) (Boxshall 1989;Cherel and Boxshall 2004). Sarcotretes longirostris has the neck longer than the trunk like S. umitakae sp. n. and only these 2 species possess an extremely long proboscis among their congeners. Sarcotretes longirostris is, however, easily distinguishable from the new species by having the following characters: slender lateral head processes without swollen basal portions (vs. a bulbous swelling with a slender process); a not defined rostral area (vs. triangular); and a large and conical reduced abdomen, protruding to posterior (vs. small and non-conical and slightly protruded to posterodorsal) (Ho et al. 2007). In addition, the trunk has an anterior constriction in S. umitakae sp. n. not shared with any of the three known species (Figs. 2A, 4D).

Discussion
Despite the fact that some morphological characters of Sarcotretes species (e.g. the shape of the holdfast, the length and flexure of the neck, and the length of the proboscis) show variability, they have been conventionally used to distinguish the species in this genus (Hogans 1988). Because these characters vary according to the site of attachment to the host and the age of the parasite, species identification using such characters may not make sense. Actually, based on those characters, Wilson (1917) had recognized 6 species as valid, but later, 4 species (S. gempyli, S. inflexus, S. lobatus, and S. nodicornis) were regarded as junior synonyms of S. scopeli by Hogans (1988). Nonetheless, we consider that such characters as the length of the proboscis and the shape of the lateral horns on the head, which were used in the key given by Wilson (1917), are useful identification characters. These characters do exhibit variability but there is no overlap between in S. umitakae sp. n. and existing species. Sarcotretes umitakae sp. n. and S. longirostris possess a strongly projecting proboscis which is not shared with other congeners. The lateral process of S. umitakae sp. n. comprising a bulge with a pointed tip is similar to that of S. scopeli and S. eristaliformis, but the greatly elongated tip in S. umitakae sp. n. is apparently distinguishable (see Brian 1912, pls. 9, 10;Hogans 1988, fig. 2b;Boxshall 1989, fig. 3; present study, Fig. 2).
Although a great care is required, it is considered that these characters can provide reliable evidence of species identity. On the other hand, all three specimens of S. umitakae sp. n. have a neck with a posterior protrusion and a constriction behind it. However, this character cannot be used to identify S. umitakae sp. n. because a similar character was observed in some specimens of S. eristaliformis and S. scopeli (see Brian 1912;Boxshall 1989).
The discovery of S. umitakae sp. n. in this study shows that there are at least 2 species of the genus in Japanese waters.