Caligus lethrinicola Boxshall & El-Rashidy, 2009, n. sp.

Caligus lethrinicola n. sp. Type material: Holotype female, partly dissected in alcohol, reg. No. MNHN-Cp 2969. Type locality: Récif au large de Nouméa, New Caledonia, 22 ° 34.529 ’S 166 ° 32.974 ’E. Collected on 27 November 2003 by J.-L. Justine (JNC 988 C). Host: on gills of Lethrinus rubrioperculatus Sato, 1978 Etymology: the species name is based on the generic name of its host, Lethrinus and – icola, meaning inhabitant. Female body (Fig. 1 A) dorsoventrally flattened, caligiform; body length 2.75 mm; maximum width of cephalothoracic shield 1.10 mm. Cephalothorax incorporating first to third pedigerous somites; dorsal cephalothoracic shield provided with conspicuous marginal membrane laterally and with well defined striated border located ventrally internal to lateral margins of dorsal cephalothoracic shield (Fig. 1 B). Frontal plates carrying large lunules and provided with marginal membrane. Nauplius eye visible dorsally through cuticle (Fig. 1 A). Fourth pedigerous somite forming narrow ‘waist’ between cephalothorax and genital complex. Genital complex longer than wide; length 0.91 mm and width 0.80 mm. Abdomen 2 -segmented (Fig. 1 A) longer than wide, length 0.54 mm and width 0.25 mm. Caudal rami dorsoventrally flattened, armed with 2 small and 4 large plumose setae (Fig. 1 A). Antennule typical for family; 2 -segmented with tapering first segment and elongate second segment. Antenna damaged on both sides; basis with spinous process near inner distal corner (Fig. 1 D). Postantennal process strongly recurved; 2 bi-setulate papillae present on basal part of process plus 1 on adjacent surface; small process located on ventral cephalothoracic surface just medial to process (Fig. 1 D). Oral cone typical for genus: mandible stylet-like (Fig. 1 C) bearing 12 teeth on one side near apex. Maxillule with basal portion incorporated into ventral cephalothoracic wall; anterior papilla bearing 3 unequal setae; posterior lobe forming tapering spiniform process (Fig. 1 D). Maxilla (Fig. 1 E) well developed, brachiform, comprising unarmed syncoxa (lacertus) and basis (brachium) bearing long calamus and shorter canna at apex, plus flabellum just distal to mid-length on anterior margin. Flabellum comprising serrated membrane. Maxilliped comprising slender corpus (Fig. 1 F) and distal subchela representing fused endopodal segments plus heavily sclerotized terminal claw. Corpus unarmed. Subchela subdivided by irregular suture line; bearing single seta about at level of suture. Sternal furca with slightly incurved tines (Fig. 1 G); pair of small sclerotized swellings located on ventral cephalothoracic wall either side of furca. Leg 1 (Fig. 1 H) with sympod bearing outer and inner plumose setae. Endopod vestigial. Exopod 2 - segmented; large, robust first segment carrying outer distal spine, and with smooth inner margin; second segment with 3 distal margin spines, outer most simple, second and third with bifid tips (Fig. 1 H), plus inner distal angle seta located on ventral surface close to distal margin, inner margin naked. Leg 2 biramous (Fig. 2 A-B); protopod comprising coxa and basis; coxa short, bearing long, plumose seta on posterior margin; basis long, armed with short, naked, outer distal seta and provided with extensive reflexed flap of marginal membrane along inner margin and another reflexed flap of membrane dorsally, along outer margin (not figured). Both rami 3 -segmented. First exopodal segment elongate, with large outer spine reflexed over middle segment, and inner plumose seta; inner margin setulose. Second segment with reflexed outer spine. Third segment with tiny naked spine proximally, adjacent spine with broad flanges bilaterally, and terminal spine (flanged along outer margin and plumose along inner). Endopod (Fig. 2 B) directed medially; first segment with inner seta and with lateral margin ornamented with distal tuft of fine pinnules; second segment elongate, with thickened lateral margin ornamented with row of spinules along outer edge, and 2 inner plumose setae; third segment with 6 plumose setae. Leg 3 pair (Fig. 2 C) fused with expanded, flattened intercoxal sclerite to form broad transverse plate. Intercoxal sclerite with extensive flap of membrane along posterior margin. Coxa and basis incompletely fused, with large plumose (coxal) seta located posteriorly. Basis with plumose outer seta; posterior and lateral margins each with extensive flap of membrane. Rami originating close together on basis, base of exopod concealed ventrally by flap-like velum, ornamented with membrane along free margin. Exopod broad, 3 - segmented; first segment short and highly sclerotised, small, reflexed, outer spine lying transversely across ventral surface of ramus; second segment armed with outer spine and inner plumose seta, plus long setules along outer margin; third segment armed with 2 naked outer spines plus 4 short, plumose inner setae. Endopod 2 -segmented, comprising small, proximal segment with inner plumose seta, and distal segment armed with 6 plumose setae (Fig. 2 C). Leg 4 uniramous (Fig. 2 D); coxa and basis fused, bearing plumose basal seta laterally. Exopod 2 - segmented: first exopodal segment armed with long outer spine and ornamented with single marginal setule; distal segment bearing 3 flanged spines, distalmost longest; each spine with pecten at base. Leg 5 comprising outer basal seta on lateral surface of genital complex plus 2 (exopodal) plumose setae located immediately medial to isolated seta (Fig. 2 E). Leg 6 represented by paired, unarmed lobes closing off genital apertures. Remarks: In common with Caligus productus Dana, 1852, the new species lacks any trace of the three plumose setae on the posterior margin of the second exopodal segment of leg 1. However, it differs from all other species that share this character in the spine formula of the fourth leg exopod – which bears I, III spines rather than I, IV found in all other species lacking the leg 1 setae. This combination of characters is unique in the genus, and allows us to identify this species as new despite the incomplete state of the antennae and the lack of a male. It shares some other characters typical of the productus -group species, such as the relatively large lunules, the strongly recurved postantennal process, the presence of a small process medial to the postantennal process, and the presence of a marginal setule on the first exopodal segment of the fourth leg. An interesting character present in the new species is the striated ventral border extending around the lateral margins of dorsal cephalothoracic shield internal to the margin membrane. It is distinctly notched in the vicinity of the post-antennal processes. We infer that this border enhances attachment to the surface of the host. This striated border has not been discussed extensively but we note that it also occurs in Caligus epinepheli Yamaguti, 1936, C. pagrosomi Yamaguti, 1939, and C. schelegeli Ho & Lin, 2003 (see figures in Ho & Lin 2003), and C. sciaenops Pearse, 1952 (see figures in Pearse 1953). We suspect this character is more widely distributed in the group, but for most species only dorsal views are given and its presence cannot be confirmed.Published as part of Boxshall, Geoff A & El-Rashidy, Hoda H., 2009, A review of the Caligus productus species group, with the description of a new species, new synonymies and supplementary descriptions, pp. 1-26 in Zootaxa 2271 on pages 5-6, DOI: 10.5281/zenodo.19095