Caligus laticaudus Shiino, 1960

(Fig. 34)

Material examined. 2♀♀ from Gnathanodon speciosus (Forsskål, 1775) (TC17577) 25 June 2016, QM Reg. No. W53078; 2♀♀ (TC17106) 13 January 2016, NHMUK 2017.276–277;1♀ from Caranx sexfasciatus Quoy & Gaimard, 1825 (TC17673) 28 June 2016, NHMUK 2017.278; 3♀♀ from Kyphosus bigibbus Lacepède, 1801 (TC17792) 1 July 2016, QM Reg. No. W53079; 1♀ (TC17864) 4 July 2016, NHMUK 2017.279;1♂, 1 chalimus from Heniochus acuminatus (Linnaeus, 1758) (TC17874) 4 July 2016, NHMUK 2017.280; 1♀ from Pseudolabrus guentheri Bleeker, 1862 (TC17662) (in body wash) 27 June 2016, NHMUK 2017.281; 1♀ from Pagrus auratus (Forster, 1801) (TC17060) 13 January 2016, NHMUK 2017.282.

Site on host. Roof of mouth.

Differential diagnosis. Cephalothorax dorsoventrally flattened with well-developed marginal membranes along lateral zones of dorsal cephalothoracic shield; frontal plates with small lunules (Fig. 34A). Genital complex about 1.2 to 1.3 times wider than long; abdomen 2-segmented; anterior somite typically distinctly wider and with more strongly convex lateral margins than posterior, but distinction less marked in some specimens; genital complex longer than abdomen, narrowing anteriorly; transverse posterior margin with paired swellings close to base of abdomen. Antenna without posterior process on proximal segment. Post-antennal process with nearly straight tine; associated papillae multisensillate. Maxilliped of female with large myxal process (Fig. 34B). Sternal furca with short, blunt, slightly incurved tines (Fig. 34C). Distal exopodal segment of leg 1 with 3 plumose setae on posterior margin; distal spine 1 markedly shorter than other spines (Fig. 34D); spines 2 and 3 without accessory processes; seta 4 slightly shorter than spines 2 and 3. Leg 2 with outer margin of first endopodal segment unornamented (Fig. 34E); endopodal segments 2 and 3 with patches of fine setules extending onto ventral surface; outer spines on exopodal segments 1 and 2 aligned close to longitudinal axis of ramus (Fig. 34F); proximal spine on third exopodal segment more than half length of next spine. Leg 3 with 3-segmented exopod (Fig. 34G); first segment bearing small straight outer spine with cuticular flange at base of spine, lacking inner seta; second segment with small outer spine plus inner seta; third segment with 3 spines increasing in length distally, plus 4 plumose setae. Leg 4 uniramous, 4-segmented; exopodal segments with I; I; III spines; each spine with elongate strip of membrane (modified pecten) on surface of segment adjacent to base (Fig. 34H). Mean body length of female 3.36 mm, range 3.28 to 3.42 mm (based on 8 specimens). Length of adult male 2.51 mm.

Remarks. Caligus laticaudus was re-described in detail by Ho et al. (2000) based on material from Taiwan. Most of the Moreton Bay material conforms exactly to Ho et al. ’s description in all aspects of limb structure and armature, and the basic habitus is the same with a conspicuously swollen anterior somite of the indistinctly 2- segmented abdomen. This configuration is the same as in the typical material described from Japan by Shiino (1960), as well as in material from India (Pillai, 1985) and Taiwan (Ho & Lin, 2004). However, the material caught in Moreton Bay on Pagrus auratus and Pseudolabrus guntheri has a more slender abdomen, with the anterior somite less markedly swollen (Fig. 34A). Material recently described from Korea also had this more slender abdomen (Moon & Kim, 2012), similar to that of the Moreton Bay material. However, in the absence of any other differences, the Moreton Bay material is identified as C. laticaudus .

Caligus laticaudus belongs to a group of species referred to here as the Caligus diaphanus- group. This group is characterized by numerous shared features including: the lack of a posterior process on the proximal segment of the antenna, a vestigial or weakly developed tine on post-antennal process, the lack of accessory processes on spines 2 and 3 on the distal exopodal segment of leg 1, the alignment of the outer spines of exopodal segments 1 and 2 of leg 2, the presence of patches of fine setules extending over the surface of endopodal segments 2 and 3 of leg 2, and the presence of strips of membrane (modified pectens) associated with each spine on exopodal segments 1 to 3 of leg 4. In addition to C. diaphanus von Nordmann, 1832 and C. laticaudus, this group also includes: C. pelamydis Krøyer, 1863, C. stromatei Krøyer, 1863, C. cybii Bassett-Smith, 1898, C. robustus Bassett-Smith, 1898, Caligus platytarsis Bassett-Smith, 1898, C. rotundigenitalis Yü, 1933, C. seriolae Yamaguti, 1936, C. tanago Yamaguti, 1939, C. pagelli Delamare Deboutteville & Nunes-Ruivo, 1958, and C. kapuhili, 1967 . Özak et al. (2017) redescribed Caligus macrurus Heller, 1865 and reduced Sciaenophilus van Beneden, 1852 to synonymy with Caligus, thereby transferring the type species, as C. tenuis (van Beneden, 1852): both C. macrurus and C. tenuis share this suite of characters and belong in the C. diaphanus -group. The presence of very small accessory processes on spines 2 and 3 on the distal exopodal segment of leg 1 in C. macrurus was visualised by scanning electron microscopy (Özak et al., 2017), and similar vestigial processes may be present on spines 2 and 3 in other members of the group even though they appear to be absent under the light microscope. Caligus kanagurta Pillai, 1961 has a somewhat atypical leg 4 with the pectens modified as arrays of long setules at bases of exopodal spines but it shares the lack of a posterior process on the antenna, a vestigial or weakly developed tine on post-antennal process, the lack of accessory processes on spines 2 and 3 on the distal exopodal segment of leg 1, the alignment of the outer spines of exopodal segments 1 and 2 of leg 2, and the presence of patches of fine setules extending over the surface of endopodal segments 2 and 3 of leg 2. Caligus kanagurta should also be included in the C. diaphanus -group.

The males of species in the C. diaphanus -group are characterised by the possession of an accessory tine on the sexually dimorphic antenna.

Caligus laticaudus was originally described from Japanese waters (Shiino, 1960) and has since been reported from India (Pillai, 1961), Einewetok Atoll (Lewis, 1968), Taiwan (Ho et al., 2000), China (Ho & Lin, 2004), Korea (Moon & Kim, 2012), and Malaysia (Leong, 1984). This is the first report of C. laticaudus from Australian waters.

The type host was Pagrus major (Temminck & Schlegel, 1843) (as Pagrosomus major) (Shiino, 1960). Pillai (1961) subsequently recorded it from Filimanus heptadactyla (Cuvier, 1829) (as Polynemus heptadactylus) and Rhabdosargus sarba (Forsskål, 1775) . According to Ho & Lin (2004), its hosts in Taiwan are Caranx melampygus Cuvier, 1833, Lutjanus vitta (Quoy & Gaimard, 1824), L. russellii (Bleeker, 1849), Parapristipoma trilineatum (Thunberg, 1793), Polydactylus plebeius (Broussonet, 1782) and P. sextarius (Bloch & Schneider, 1801) . Other hosts include Acanthurus olivaceus Bloch & Schneider, 1801, Evynnis japonica Tanaka, 1931, Parastromateus niger (Bloch, 1795) (as Formio niger), and Liza haematocheila (Temminck & Schlegel, 1845) . All six of the host species reported here are new host records.