Caligus confusus Pillai, 1961

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 : 55-56

Caligus confusus Pillai, 1961

( Fig. 25 )

Material examined. 2♀♀ from Caranx ignobilis (Forsskål, 1775) (TC17542) 24 June 2016, QM Reg. No. W53062; 1♀ from (TC17561) 24 June 2016, 2♀♀ from (TC17579) 25 June 2016, 1♀ from (TC17702) 28 June 2016: 3♀♀ NHMUK Reg. Nos 2017.254–256. 2♀♀ from Caranx sexfasciatus Quoy & Gaimard, 1825 (TC17655) 28 June 2016, 23♀♀, 9♂♂ (TC17668) 28 June 2016; 10♀♀, 5♂♂, QM Reg. No. W53063; 4♀♀, 1♂ (TC17690) 28 June 2016, 15♀, 4♂♂, NHMUK Reg. Nos 2017.257–266.

Site on host. Gill arches.

Differential diagnosis. Cephalothorax dorsoventrally flattened with well-developed marginal membranes along lateral zones; frontal plates with lunules; thoracic zone very small, extending posteriorly about level with posterior ends of lateral zones ( Fig. 25A ). Genital complex about 1.5 to 1.6 times longer than wide; abdomen small, 1-segmented, just longer than wide; genital complex about 5 times longer than abdomen ( Fig. 25A ). Antenna with flattened membranous flange located posteriorly on proximal segment ( Fig. 25B ) instead of posterior process. Post-antennal process bifid, primary tine straight with marginal flange; associated papillae multisensillate. Posterior process of maxillule trifid ( Fig. 25B ); main (inner) tine with marginal flanges. Maxilliped of female with conspicuous ridges in myxal area ( Fig. 25C ). Sternal furca with tapering pointed tines, each with distinctive dense central core ( Fig. 25D ). Distal exopodal segment of leg 1 with 3 plumose setae on posterior margin; distal spine 1 longer than other spines; spines 2 and 3 each with accessory process; seta 4 about as long as spines 2 and 3. Leg 2 with marginal setules on endopodal segments 2 and 3; outer spine on exopodal segment 1 lying obliquely across segment 2, spine on segment 2 aligned close to longitudinal axis of ramus. Leg 3 ( Fig. 25E ) apron with raised bifid rib plus circular array of large denticles on ventral surface and corrugated adhesion pad near outer margin on dorsal surface; exopod 3-segmented, first segment with large recurved outer spine, lacking inner seta: endopod 2- segmented, distal endopodal segment with partial suture, armed with total of 6 plumose setae. Leg 4 uniramous, 4- segmented ( Fig. 25F ); exopodal segments with I; I; III spines; first exopodal segment with conspicuous sensillar ornamentation. Mean body length of female 3.61 mm, range 3.38 to 4.04 mm (based on 10 specimens).

Male with genital complex and 1-segmented abdomen forming ovoid unit. Maxillule with simple posterior process ornamented with marginal flanges and proximal adhesion pad. Maxilliped with transverse ridge fringed with membrane on proximal segment. Mean body length of male 2.20 mm, range 2.15 to 2.29 mm (based on 8 specimens).

Remarks. This distinctive species is a widely distributed and common parasite of carangid hosts. It was originally established by Pillai (1961) to accommodate material from Caranx ignobilis (as C. sansun (Forsskål)) caught at Trivandrum, India. Pillai (1961) placed in the synonymy of his new species, material previously confused with C. constrictus Heller, 1865 by Shiino (1959) and Wilson (1937b), and material confused with Caligus alalongae Krøyer, 1863 by Kirtisinghe (1937).

About 50 species of Caligus retain a 3-segmented exopod on leg 4 armed with I, I, III spines. Within these, C. confusus can be placed in a species-group characterized by a suite of character states including: the presence of a raised bifid cuticular rib and a circular array of denticles on the apron of leg 3, the possession of a large recurved hook (= the outer margin spine) on the first exopodal segment of leg 3, and, commonly, the presence of an accessory tine on the post-antennal process and on the posterior maxillulary process. This group is referred to here as the C. confusus -group.

In addition to C. confusus , the core group of species sharing these character states comprises C. aesopus Wilson, 1920 , C. bicycletus Heegaard, 1945 , C. brevicaudus , C. chorinemi Krøyer, 1863 , C. cordyla Pillai, 1963 , C. equulae Ho & Lin, 2003 , C. kurochkini Kazatchenko, 1975 , C. lichiae Brian, 1906 , C. lunatus Wilson, 1924 , C. platurus Kirtisinghe, 1964 , C. randalli Lewis, 1964 , C. regalis Leigh-Sharpe, 1930 , C. spinosus Yamaguti, 1939 , C. tenax Heller, 1865 and C. zylanica Hameed & Pillai, 1986 . Linked with the core C. confusus -group are a number of other Caligus species which share most but not all of the characteristics. Examples of such species include C. fortis Kabata, 1965 , which has a slightly curved spine instead of the large recurved hook on the first exopodal segment of leg 3, C. isonyx Steenstrup & Lütken, 1861 , and C. inopinatus Kabata, 1994 , both of which have simple instead of bifid tines on the post-antennal process and the posterior maxillulary process. The trifid form of the maxillulary posterior process in C. confusus is unique within the genus, and the form of the sternal furca combined with the presence of a hyaline membrane on the proximal segment of the antenna, help to distinguish C. confusus from all other core members of the C. confusus -group.

Caligus confusus has been reported from a wide range of carangid fishes including: Caranx hippos (Linnaeus, 1766) , C. ignobilis (and as C. sansun ), C. melampygus Cuvier, 1833 , C. sexfasciatus , C. caballus Günther, 1868 , C. caninus Günther, 1867 , Alepes djedaba (as Caranx kalla and C. djedaba ), Elagatis bipinnulata (Quoy & Gaimard, 1825) and Seriola dumerili (Risso, 1810) ( Pillai, 1961, Kirtisinghe, 1937 (as C. alalongae ), Wilson, 1937a, Lewis, 1968, Ho & Lin, 2001, 2004; Morales-Serna et al., 2014). There are also records from non-carangid fishes such as Coryphaena hippurus (Wilson, 1937, as C. constrictus ), Epinephelus tauvina (Forsskål, 1775) (Ho & Sey, 1996), and Rhabdosargus holubi (Steindachner, 1881) (Grobler et al., 2003). In Moreton Bay it was found on two previously reported hosts, C. ignobilis and C. sexfasciatus .

The geographical distribution of C. confusus includes the Indo-Pacific from the Arabian Gulf, Sri-Lanka and India, through the South China Sea to Taiwan, and across to Eniwetok Atoll, and the Pacific coast of Mexico, Columbia and Panama (Ho & Lin, 2004; Morales-Serna et al., 2014). In the Southern Hemisphere it has been reported from South Africa (Kensley & Grindley, 1973; Grobler et al., 2003) and New Caledonia ( Kabata, 1968). It was first reported from Australian waters on Elagatis bipinnulata by Hutson et al. (2011) who recorded it off the southeastern coast. This is the first report from Queensland.

Figures

FIGURE 25. Caligus confusus Pillai, 1961, female. A, habitus, dorsal; B, antenna, post-antennal process and maxillule drawn in situ; C, maxilliped; D, sternalfurca; E, leg 3; F, leg 4. Scale bars:1.0 mm on A, 200 µm on B, C, E, F, 100 µm on D.