A NEW SPECIES OF THYSANOTE KRØYER, 1863 (COPEPODA: SIPHONOSTOMATOIDA: LERNAEOPODIDAE), A FISH PARASITE FROM THAILAND

Background. Thysanote Krøyer, 1863 (Copepoda, Siphonostomatoida, Lernaeopodidae) comprises 19 species of marine parasite that infect fishes. This report establishes a new Thysanote species based on new collections of copepods. The taxonomic status of this genus is not fully understood and therefore more relevant contributions are needed. Materials and Methods. The species description is based on male and female specimens collected from the olfactory sacs of spotted scat, Scatophagus argus , captured off Thailand in 2003. The specimens were studied using standard light and scanning electron microscopy techniques. Results. The studied specimens were assigned to Thysanote based on the presence of maxillary-and posterior processes and they exhibited unique characteristics such as distinctly short length of their maxillary-and posterior processes. Conclusion. Based on their unique characteristics, a new Thysanote species is erected, and named Thysanote chalermwati n. sp., thus bringing the number of congeners to 20.

Etymology: the species name, Thysanote chalermwati, is intended to honour Dr Kashane Chalermwat who hosted one of the authors (S.O.) during his stay in Thailand.

FEMALE
Body elongate (5.67 mm long) ( Fig. 1) consisting of cephalothorax and genital trunk. Cephalothorax (1.41 mm long) cylindrical, in line with genital trunk, constituting one-third of body and slightly shorter than "maxillary arms" (second maxillae). Cephalothorax diameter at base similar to that of genital trunk. Cephalothorax tapering slightly towards anterior end. Genital trunk (3.26 mm long), constituting two-thirds of body, cylindrical, longer than "maxillary arms". External layer of cuticle thick, probably elastic, with dense wrinkles, resembling elephant skin.
Thoracic appendages: not located, probably absent. Posterior processes (Figs. 1, 11) located on posterolateral margins of trunk; better developed than maxillary processes. Two short and branching (palm-like) processes on each side of body, each consisting of three toe-like processes. Dorsal-most process and ventral-most one showing signs of secondary branching. Perianal area (Fig. 16) slightly raised, located in centre of posterior margin (Fig. 11), flanked by reduced caudal rami.

MALE
Similar to male of Parabrachiella. Body moderately elongate (1.22 mm long) (Figs. 18-21) consisting of two parts of comparable length: cephalothorax, with 6 pairs of appendages, and slender genital trunk. Distinct dorsal shield (Fig. 18), cephalothorax (0.57 mm long) at angle to genital trunk, separated from latter by constriction. Genital trunk (0.7 mm long) slightly longer than cephalothorax. Dorsal-and lateral parts of body behind dorsal shield covered by wrinkled thick cuticle.
Mandible, not studied. First maxilla (Fig. 24) similar to that of female; ventral exopod more pronounced and with longer seta.
The most recent comprehensive discussion and the identification key for species of the genus Thysanote was provided by Kabata and Tareen (1981). It did not include the two most recent contributions, namely T. polyfimbriata and T. nudibranchiata (cf. Pillai 1981, Pillai et al. 1977). Their inclusion into the Kabata and Tareen (1981) key should be easy: T. nudibranchiata does not have maxillary processes and T. polyfimbriata has a multitude of maxillary-and posterior processes with branched, pointed tips, giving them a "bushy" appearance.
T. chalermwati n. sp., the new species described above, distinctly differs from its congeners, mainly in having very small (vestigial) maxillary-and posterior processes.
The description of this new species was presented in 2005 at the 9th International Conference on Copepoda, held in Hammamet, Tunisia, but without publishing its name or other details (Piasecki et al. 2005). It is worth to mention, however, that Thysanote sp., recently found by Yuniar et al. (2007) in Indonesia, from the same fish, is probably conspecific with the one presently described by us. The paper of Yuniar et al. (2007) contains only overall photograph with no morphological description and therefore the parasite is identified at the generic level only.