Capillaria plectropomi n. sp. (Nematoda: Capillariidae), a new intestinal parasite of the leopard coral grouper Plectropomus leopardus (Serranidae) off New Caledonia

A new nematode species, Capillaria plectropomi n. sp. (Capillariidae), is described from the intestine of the leopard coral grouper Plectropomus leopardus (Lacepède) from coral reefs off New Caledonia. The new species, belonging to the subgenus Neocapillaria Moravec, 1987, differs from other congeneric species of this subgenus from marine fishes mainly in the length (168–186 μm), shape and structure of the spicule. It is characterized, in the male, by the presence of two well-developed dorsolateral caudal lobes, a pair of lateral papillae, a heavily sclerotized spicule with many rough transverse grooves in the middle part, a spinose spicular sheath, and in the female, by eggs measuring 60–66 × 27 μm without protruding polar plugs. The buccal cavity contains a small finger-shaped stylet. Capillaria plectropomi n. sp. is the first known species of this genus parasitizing fishes of the perciform family Serranidae.


Introduction
The present knowledge of the diversity and biology of capillariid nematodes (Capillariidae) is fragmentary, especially where species parasitizing marine fishes are concerned. In addition, the taxonomy of these pathogenic parasites based on morphological features is rather difficult; therefore, capillariids remain frequently unidentified in faunistic surveys, being reported only as Capillaria (s.l.) sp. or Capillariidae gen. sp. [8]. The fauna of these parasites in marine fishes off New Caledonia remains almost unknown, because to date only two nominal species, Pseudocapillaria echenei (Parukhin, 1967) and P. novaecaledoniensis , are known to parasitize Echeneis naucrates Linnaeus (Echeneidae) and Pristipomoides argyrogrammicus (Valenciennes), respectively, in this region. Seven other morphologically different types of capillariid females, apparently each of them representing a new species, have been reported from Carangoides oblongus Cuvier (Carangidae), Diagramma pictum (Thunberg) (Haemulidae), Fistularia commersonii Rüppel (Fistulariidae), Naso unicornis (Forsskål) (Acanthuridae), Siganus doliatus (Guérin-Méneville) (Siganidae), Stegostoma fasciatum (Hermann) (Stegostomidae) and Synodus dermatogenys Fowler (Synodontidae), but, because of the absence of conspecific males, these could not be identified to the genus and species and were designated as Capillariidae gen. spp. [9,11]. Unidentified capillariids from New Caledonian waters were also reported by Justine et al. [6] from Plectropomus laevis (Lacepède) and P. leopardus (Lacepède) (Serranidae), based on specimens collected from these hosts while studying the parasites of marine fishes off New Caledonia by J.-L. Justine between 2003 and 2011. Closer examination of the specimens from the latter host revealed that they represent a new species, which is described herein.
The leopard coral grouper Plectropomus leopardus (maximum body length 120 cm, weight 23.6 kg) is a tropical marine, reef-associated commercial and game fish also used for aquaculture. It is distributed in the Western Pacific from southern Japan to Australia and eastwards to the Caroline Islands, Fiji and Tonga [4].

Materials and methods
The grouper was caught by line, brought back to the laboratory and immediately examined. The nematodes obtained were washed in physiological saline and were then fixed and preserved in 70% ethanol. For light microscopical examination, the nematodes were cleared with glycerine. Drawings were made with the aid of a Zeiss drawing attachment. Specimens used for scanning electron microscopy (SEM) were postfixed in 1% osmium tetroxide (in phosphate buffer), dehydrated through a graded acetone series, critical-point-dried and sputter-coated with gold; they were examined using a JEOL JSM-7401F scanning electron microscope at an accelerating voltage of 4 kV (GB low mode). All measurements are in micrometres unless otherwise indicated. The fish nomenclature adopted follows FishBase [4].

Discussion
According to Moravec [9], capillariid nematodes are represented by species in 22 genera, of which nine genera comprise parasites of freshwater, marine and brackish-water teleost fishes and elasmobranchs. In having the stichosome consisting of a single row of stichocytes and males possessing two caudal lobes without a membranous bursa, the spicule with numerous rough transverse grooves on its surface, the spiny spicular sheath and the absence of lateral caudal alae, the present material belongs to Capillaria Zeder, 1800 s.s., as diagnosed by Moravec [7].
Capillaria includes parasites of all classes of vertebrates except reptiles. Moravec [8] established four subgenera for Capillaria spp. from fishes. The general morphology of C. plectropomi n. sp., in particular the structure of the male caudal end, a heavily sclerotized spicule and the absence of a vulval appendage, shows that this species belongs to the subgenus Neocapillaria Moravec, 1987 [8, 9]. To date, this subgenus includes seven species: C. acanthopagri Moravec [12].
The new species differs from all congeneric species belonging to Neocapillaria from marine fishes in the length of spicule, which is distinctly shorter in C. cooperi (120-150 lm vs. 168-186 lm) and C. hakofugu (110-150 lm) or distinctly longer in C. acanthopagri (204-285 lm), C. carioca (438-513 lm), C. navonae (210-260 lm) and C. wickinsi (534-660 lm). Moreover, in contrast to the new species, the spicules of C. acanthopagri, C. carioca and C. wickinsi have transverse grooves extending along almost their entire lengths (vs. restricted to the middle part of spicule). The spicules of C. cooperi and C. pterophylli are conical and markedly broad at their posterior parts, and a pair of papillae located anterior to caudal lobes is absent in C. hakofugu.
Whereas the hosts of C. carioca, C. hakofugu, C. navonae and C. wickinsi belong to other fish orders (Anguilliformes, Pleuronectiformes or Tetraodontiformes), those of C. acanthopagri, C. cooperi and C. pterophylli belong to Perciformes as does that of the new species. However, C. plectropomi n. sp. differs from the three last-named species in the host family, i.e., Serranidae vs. Sparidae, Callionymidae and Cichlidae, respectively. Capillaria plectropomi n. sp. is the first nominal species of this genus described from a representative of the Serranidae. Capillariids in serranids are obviously rare, as demonstrated by the scarcity of our findings in many grouper species and specimens examined in New Caledonia [6]. Smales [13] reported Capillaria sp. from Epinephelus ongus (Bloch) and E. tauvina (Forsskål) (Serranidae) off the Keppel Islands, Queensland, Australia and the possibility cannot be excluded that they are C. plectropomi.
The use of SEM has shown some details in the structure of the cephalic end in C. plectropomi that are not usually visible in capillariids under the light microscope. It is apparent from this study that the structure of lips, shape of the oral aperture and the number and arrangement of the cephalic papillae of this species are very similar to those described by Baruš et al. [2] in Capillaria anatis (Schrank, 1790), by Moravec [10] in Paracapillaria philippinensis (Chitwood, Velasquez & Salazar, 1968), by González-Solís et al. [5] in Capillostrongyloides morae González-Solís, Carrassón & Pérez-del-Olmo, 2014 or as observed in some species of Eucoleus Dujardin, 1845 (unpublished).
The present study also shows the presence of a functional stylet in C. plectropomi. As mentioned by Moravec [10], the stylet is present in the first-stage larva in all trichinelloids [1], but it is customary to assume that it is absent in the adult stage. Wright [14] observed the stylet in the dorsal portion of the buccal cavity in the adult capillariid Calodium hepaticum (Bancroft, 1893), mentioning that it can probably not be projected out of the mouth as in the conspecific first-stage larva. However, the presence of a functional stylet was clearly demonstrated in adult Paracapillaria philippinensis [3,10], Capillaria anatis [2] and Capillostrongyloides morae [5]. Its finding also in Capillaria plectropomi suggests that the functional stylet may be present in all adult capillariids.

Conflict of interest
The Editor-in-Chief of Parasite is one of the authors of this manuscript. COPE (Committee on Publication Ethics, http://publication ethics.org/), to which Parasite adheres, advises special treatment in these cases. COPE wrote: ''Editors should not be denied the ability to publish in their own journal, but they must not exploit their position. The journal must have a procedure for handling submissions from the editor or members of the editorial board that ensures that peer review is handled independently of the author/editor. This process should be detailed once the paper is published.'' In this case, the peer review process was handled by Invited Editor Dominique Vuitton.