Caligus chiastos Lin & Ho, 2003

Boxshall, Geoff, 2018, The sea lice (Copepoda: Caligidae) of Moreton Bay (Queensland, Australia), with descriptions of thirteen new species, Zootaxa 4398 (1), pp. 1-172 : 52-55

Caligus chiastos Lin & Ho, 2003

( Fig. 24 )

Syn: Caligus sp. 1. Roubal, Armitage & Rohde, 1983

Material examined. 1♀ from Lutjanus fulviflamma (Forsskål, 1775) (TC17525) 23 June 2016, QM Reg. No. W53060 ; 1♀ from Sillago ciliata Cuvier, 1829 (TC17557-8) 24 June 2016, NHMUK Reg. No. 2017.251; 1♀ from Abudefduf bengalensis (Bloch, 1787) (TC17806) 2 July 2016, NHMUK Reg. No. 2017.248; 1♀ from Acanthopagrus australis (TC17816) 3 July 2016, QM Reg. No. W53061 ; 2♀♀ from Lagocephalus lunaris (Bloch & Schneider, 1801) (TC17899) 5 July 2016, NHMUK Reg. Nos 2017.252–253; 2♀♀ from Aetobatus ocellatus (Kuhl, 1823) (TC17933) 5 July 2016, NHMUK Reg. Nos 2017.249–250.

Site on host. Body surface.

Differential diagnosis. Cephalothorax dorsoventrally flattened with well-developed marginal membranes; frontal plates with lunules. Genital complex just slightly wider than long ( Fig. 24A ); abdomen 1-segmented, 1.85 times longer than wide; genital complex about 1.4 times longer than abdomen. Antenna with small, pointed posterior process on proximal segment ( Fig. 24B ). Post-antennal process with weakly curved tine; associated papillae bisensillate with unusually long sensillae ( Fig. 24B ). Maxilliped of female with smooth myxal margin. Sternal furca with long, slender, slightly incurved tines ( Fig. 24C ). Distal exopodal segment of leg 1 with 3 plumose setae on posterior margin; distal spine 1 simple, about same length as spines 2 and 3 ( Fig. 24D ), each armed with accessory process; seta 4 about twice as long as spines and markedly longer than segment. Leg 2 with fine setules along margins of endopodal segments 1, 2 and 3; outer spines on exopodal segments 1 and 2 lying obliquely across axis of ramus; proximal outer spine on exopodal segment 3 curved and well developed, lying across blunt distal spine ( Fig. 24E ). Leg 3 with 3-segmented exopod; first exopodal segment bearing small straight outer spine but no inner seta; second segment with outer spine and inner plumose seta; third segment with 3 subequal outer spines, plus 4 plumose setae; endopod 2-segmented; first segment forming velum, and armed with inner seta; distal endopodal segment with swollen lateral margin and bearing 6 plumose setae. Leg 4 uniramous ( Fig. 24F ), 3-segmented; first and second exopodal segments with I and IV spines, respectively; each spine with pecten on surface of segment adjacent to base. Mean body length of female 3.34 mm, range 3.15 to 3.85 mm (based on 8 specimens).

Remarks. One of the most characteristic features of C. chiastos is the form of the outer margin spines on the third exopodal segment of leg 2. Unusually, the proximal spine on this segment is curved and slightly longer than the straight distal spine ( Fig. 24E ). The significance of this feature in distinguishing C. chiastos from the closely related C. acanthopagri Lin, Ho & Chen, 1994 was emphasized by Ho & Lin (2004).

Caligus chrysophrysi is very similar to C. chiastos . Indeed, the differences in body proportions are trivial. When C. chiastos was established, Lin & Ho (2003) presented detailed comparisons with C. acanthopagri Lin, Ho & Chen, 1994 but did not compare their material with C. chrysophrysi . Pillai (1985) only had a single female and presented an incomplete description of C. chrysophrysi , but it agrees with that of C. chiastos in every important respect, including the form of the proximal outer spine on the distal exopodal segment of leg 2, which is as long as the distal spine and curves across its surface, as highlighted by Lin & Ho (2003). It is possible that C. chiastos is a junior synonym of C. chrysophrysi , but the species are maintained as separate here on the basis of female body size: the females of C. chiastos range from 3.15 to 3.85 mm whereas female C. chrysophrysi is only 2.1 mm in length according to Pillai (1985). In addition, the lateral spine on the compound distal exopodal segment of leg 4 reaches well beyond the base of the outermost distal spine in C. chiastos ( Fig. 24F ) but barely reaches this spine in C. chrysophrysi .

Caligus chiastos is a pest of both farmed and cultured marine teleost fishes (Hayward et al. 2008; Venmathi Maran et al., 2009). It was described by Lin & Ho (2003) to accommodate specimens of both sexes collected from the haemulid, Plectorhinchus cinctus (Temminck and Schlegel, 1843) in Taiwanese waters. Lin & Ho (2003) also noted that the female caligid reported as Caligus sp. 1 by Roubal et al. (1983) could also be attributed to this species. Roubal et al. ’s (1983) material was collected from the sparid Pagrus auratus (as Chrysophrys auratus ) caught off Coff’s Harbour (NSW) in Australian waters. Ho & Lin (2004) listed three additional hosts, Caranx sexfasciatus Quoy & Gaimard, 1825 (Carangidae) , Otolithes ruber (Bloch & Schneider, 1801) (Sciaenidae) and Pelates quadrilineatus (Bloch, 1790) (Terapontidae) from Taiwan, and it has since been reported from cultured Lutjanus johnii (Bloch, 1792) (Lutjanidae) in Malaysia ( Venmathi Maran et al., 2009). This species is a known pest of farmed fish in Australian waters, including Argyrosomus japonicus (Temminck & Schlegel, 1843) (Sciaenidae) , Seriola lalandi (Carangidae) , and Thunnus maccoyii (Scombridae) (Hayward et al. 2007, 2008). In addition, early records of C. elongatus and C. rapax from Australian waters (e.g. Heegaard, 1962; Munday et al., 2003; Nowak, 2004) can also, in all probability, be considered as belonging to C. chiastos (Hayward et al. 2008) . In Moreton Bay C. chiastos was found on Abudefduf bengalensis (Pomacentridae) , Acanthopagrus australis , Lutjanus fulviflamma , Lagocephalus lunaris (Tetraodontidae) , Sillago ciliata (Sillaginidae) and Aetobatus ocellatus (Myliobatidae) . Having been reported from at least eleven families of actinopterygian fishes, and now from an elasmobranch, it appears that C. chiastos exhibits relatively low host specificity.

Figures

FIGURE 24. Caligus chiastos Lin & Ho, 2003, female. A, habitus, dorsal; B, antenna, post-antennal process and maxillule drawn in situ; C, sternal furca; D, distal margin of exopod of leg 1; E, exopod of leg 2, showing well developed, curved proximalouter spine of third exopodal segment;F, leg 4.Scale bars:1.0 mm on A, 200 µm on F, 100 µm on C, E, 50 µm on B, D.