Caligus seriolicolus, Boxshall, 2018

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 : 121-123

Caligus seriolicolus nom. nov.

( Fig. 56 )

Syn: Parapetalus spinosus Byrnes, 1986

Material examined. 1♀, from Seriola hippos Günther, 1876 (TC18352) 28 March 2017,

QM Reg. No. W53111.

Site on host. Unknown.

Differential diagnosis. Cephalothorax dorsoventrally flattened with well-developed marginal membranes along lateral zones; frontal plates with lunules ( Fig. 56A ); thoracic zone small, posterior margin about level with posterior margins of lateral zones. Genital complex about 1.1 times longer than wide measured along midline and with conspicuous posterolateral processes formed by fifth legs ( Fig. 56B ): genital complex about 1.7 times longer than abdomen. Abdomen 2-segmented, first free abdominal somite dorsoventrally flattened, wider than long and with rounded posterolateral processes; anal somite about one third width of preceding somite, bearing caudal rami. Antenna ( Fig. 56C ) with well developed posterior process on proximal segment. Post-antennal process bifid ( Fig. 56C ), main tine slightly curved; associated papillae multisensillate. Posterior process of maxillule bifid; smaller outer tine arising near base of main (inner) tine. Maxilliped of female with small process proximally on surface of myxal area; claw strongly recurved. Sternal furca with angular, incurved tines, bearing conspicuous flanges. Leg 1 with anterior process (arrowed in Fig. 56D ) and extensive patch of small spinules on sympod; distal exopodal segment with 3 short plumose setae on posterior margin; distal spine 1 longer than other spines; spines 2 and 3 each with accessory process; seta 4 just longer than spine 1, about as long as segment. Leg 2 with expanded convex margin on endopodal segment 1 ornamented with spinules; with marginal setules on segments 2 and 3; outer spines on exopodal segments 1 and 2 aligned close to longitudinal axis of ramus. First exopodal segment of leg 3 with large recurved outer spine but lacking inner seta ( Fig. 56E ); apron with strongly-bifid, raised rib-like process plus circular array of large and conspicuous denticles on ventral surface and corrugated adhesion pad on outer margin and dorsal surface. Leg 4 uniramous, 4-segmented; exopodal segments armed with I; I; III spines. Leg 5 ( Fig. 56B ) comprising elongate posterolateral process on genital complex, with distinct papilla at apex bearing 3 plumose setae, protopodal seta located proximally on lateral margin of process. Body length of female 4.24 mm.

Remarks. This species was originally described as Parapetalus spinosus Byrnes, 1986 , based on material of both sexes collected from Seriola hippos caught off Coffs Harbour, New South Wales (Byrnes, 1986). In their major review of the Caligidae, Dojiri & Ho (2013: 297) concluded that P. spinosus is not a species of Parapetalus and they considered it “most likely a species of Caligus bearing close resemblance to Caligus parapetalopsis Hameed & Pillai, 1973 ”. However, in the same work Dojiri & Ho (2013: 299) stated that “the widely expanded genital complex and abdomen [of Caligus parapetalopsis ] suggest a closer affinity to Parapetalus than to Caligus ”, and they pointed out that Ho & Lin (2010) had treated C. parapetalopsis as a valid species of Parapetalus . These contradictory remarks simply highlight the lack of any clear generic distinction between Parapetalus and Caligus .

The shared possession of the characteristic suite of features of the C. confusus -group by both Parapetalus parapetalopsis and P. spinosus provides robust evidence that they should be classified within that species group. Both possess an unusually broad genital complex with prominent lobate fifth legs and an unusually broad abdomen, but there seems to be no valid reason to treat these features as of generic level significance. It is proposed here to return Parapetalus parapetalopsis (Hameed & Pillai, 1973) to its original combination, as Caligus parapetalopsis Hameed & Pillai, 1973 , and to transfer Parapetalus spinosus Byrnes, 1986 to Caligus . This latter action would create a secondary homonym, because the name is preoccupied by Caligus spinosus Yamaguti, 1936 , so the replacement name Caligus seriolicolus nom. nov. is proposed. The name refers to the host genus.

Caligus seriolicolus nom. nov. exhibits the characteristic suite of features of the C. confusus -group: a 3- segmented exopod on leg 4 armed with I, I, III spines, the raised bifid cuticular rib and a circular rosette-like array of large denticles on the apron of leg 3, the large recurved hook on the first exopodal segment of leg 3, and the presence of an accessory tine on both the post-antennal and posterior maxillulary processes.

The body length of the Moreton Bay female, 4.24 mm, falls within the range of 3.47 to 4.90 mm given by Byrnes (1986) for his material from New South Wales. This is only the second report of this species and Seriola hippos is the only known host.

Figures

FIGURE 56. Caligus seriolicolus nom. nov. female. A. habitus, dorsal; B, posterior part of genital complex, ventral view showingfifth legsand flattened ventral lobes concealing oviductopenings; C, antennaand post-antennal process, drawn insitu; D, leg 1 with anterior process arrowed; E, leg 3. Scale bars:1 mm on A, 0.5 mm on B, 200 µm on C–E.