Caligus chiastos Lin and Ho, 2003

Maran, B. A. Venmathi, Ohtsuka, Susumu & Jitchum, Pailin, 2012, Occurrence of Caligid Copepods (Crustacea) in Plankton Samples Collected from Japan and Ŋailand, with the Description of a New Species, Species Diversity 17 (1), pp. 87-95 : 88-89

Caligus chiastos Lin and Ho, 2003

Caligus sp.1: Roubal et al. 1983: 21. Caligus chiastos Lin and Ho, 2003: 148 ; Hayward et al. 2008: 57; Venmathi Maran et al. 2009: 797.

Material examined.On e adult (KMNH IvR 500, 510), Gulf of ffiailand, St.1, 11°46 .4'N , 99°48.3'E, day time on 11 November 2006, plankton net.

Description. M ale . Body 2.55 mm long excluding setae on caudal rami. Cephalothoracic shield longer than wide, 1.48× 1.20 mm. Fourth pediger wider than long, 0.24× 0.36 mm. Genital complex longer than wide, 0.41× 0.42 mm. Abdomen 2-segmented, 0.47× 0.19 mm, longer than wide. Caudal ramus longer than wide and armed with 3 long and 3 short setae.

Armature on rami of legs 1–4 summarized in Table 1.

Remarks.ffi e body length of 2.55 mm is smaller than in previously recorded males: 2.70 mm o Taiwan ( Lin and Ho 2003), 2.82 mm o Malaysia ( Venmathi Maran et al. 2009). Caligus chiastos is characterized by the armature of legs 2 and 4: the proximal outer spine on the exopod of leg 2 crosses over and is longer than the subsequent spine, which is unusual in the genus Caligus ; and the exopod of leg 4 is armed with elements I-0; I, III.

ffiis is the rst report of C. chiastos from a plankton sample and also the rst record of the occurrence of any pelagic caligid from ffiailand. Caligus chiastos was rst reported on the wild reef-associated snapper Chrysophrys auratus (Forster, 1801) from Australia ( Roubal et al. 1983), followed by a report from wild reef-associated crescent sweetlip Plectorhynchus cinctus (Temminck and Schlegel, 1843) in Taiwan ( Lin and Ho 2003).

In culture farms of southern blue n tuna Ŋunnus maccoyii in Australia, a large number of adults (maximum intensity: 42 individuals per host; maximum prevalence: up to 20%) were recovered, while chalimus stages occurred not on this host but on di erent benthic shes living near the cages; this implies ontogenetic host-switching ( Hayward et al. 2008). Recently, adults of this species were also found on cultured snapper Lutjanus johni (Bloch, 1792) in Malaysia ( Venmathi Maran et al. 2009).