Caligus pillaii, Dippenaar & Sebone, 2025

Dippenaar, Susan M. & Sebone, Makwena M., 2025, Caligus (Caligidae: Siphonostomatoida) species off southern Africa with the description of C. pillaii sp. nov., Zootaxa 5686 (2), pp. 151-197 : 191-195

Caligus pillaii sp. nov.

urn:lsid:zoobank.org:pub:FAE3CA10-9DC4-45E0-819E-6F3A02CE7F20

( Figs 33A – 35G )

Type material: Holotype ♀ (SAMC-A099214) from Thyrsites atun (Euphrasen) ( Gempylidae : Scombriformes) caught off the west coast of South Africa (Atlantic Ocean) during January 2012.

Other material examined: 2♀ from the same host.

Description of adult female: Body length from the tip of the cephalothorax to the tip of the caudal rami, excluding caudal setae 5.3 mm (5.1–5.5 mm). Cephalothoracic shield ( Fig. 33A ) suborbicular (length 2.6 mm (2.5–2.6 mm), width 2.5 mm (2.5 mm )); frontal plates with lunules. Fourth leg-bearing somite wider than long. Genital complex quadrangular (length 1.6 mm, width 1.4 mm) with slightly pointed posterolateral corners. Abdomen indistinctly 2-segmented ( Fig. 33A ) (length 0.8 mm, width 0.6 mm) about half length of genital complex, bearing caudal rami ( Fig. 34A ) (length 0.1 mm) armed with 6 setae (4 longer pinnate, 2 small naked) and setules along medial margin.

Antennule ( Fig. 33B ) 2-segmented, basal segment broad, with 23 setae of different sizes, distal segment with 14 setae (8 long (1 at about mid-length), 5 short). Antenna ( Figs 33C , 35A ) 3-segmented, proximal segment with small blunt-ending process (arrowed in Fig. 35A ), second segment quadrangular, distal segment claw with strongly curved tip, bearing 2 spiniform setae. Post-antennal process ( Figs 33D , 35A, B ) slightly curved, base with small protuberance (arrowed in Fig. 35B ) on anterior margin and 2 multisensillate papillae posteriorly, single multisensillate papilla adjacent to the base. Maxillule ( Figs 33E , 35A, C ) posterior dentiform process (mpp in Fig. 35A ) slightly curved, blunt ending, with small additional tine medially (arrowed in Fig. 35C ), anterior palp bearing 3 small setae. Mandible ( Fig. 33F ) with 14 equal sized teeth. Maxilla ( Figs 33G , 35A ) with a broader lacertus (syncoxa), branchium (basis) slender, bearing membraneous flabellum, extending to the base of calamus, calamus longer than canna. Maxilliped ( Figs 33H , 35A ) subchelate, corpus broad (without ornamentation on myxal area), subchela with ap-ical claw, armed with slender seta proximally. Sternal furca ( Figs 33I , 35A ) with divergent blunt tines, tips slightly curved inwards.

Leg 1 ( Fig. 33J ) protopod with outer and inner pinnate setae. Endopod reduced papilla. Exopod 2-segmented; proximal segment with small distolateral spine with pecten at base, medial row of setules and range of small denticles along lateral margin; distal segment with 3 posterior pinnate setae (ps in Fig. 35D ) increasing in length from basal seta to distal seta, apically bearing 3 spines, lateral terminal spine (t 1 in Fig. 35D ) slightly longer than middle spines (t2 and t 3 in Fig. 35D ) both armed with accessory processes and medial terminal seta 4 (4 in Fig. 35D ) scarcely pinnate, slightly longer than terminal spines 2 and 3. Leg 2 ( Fig. 34B ) biramous; protopod with distolateral small naked seta and medial pinnate seta; 3-segmented. Exopod first and second segments both with distolateral spine (arrowed in Figs 35E, F ) with serrated margins ( Fig. 35F ) and pecten at base and distomedial pinnate setae, both spines lying obliquely across ramus, reaching last segment; distal segment with 1 small outer spine (os in Fig. 35F ) lying obliquely across adjacent spine, 1 longer spine with serrated margins, 1 spine with serrated outer margin and setules on inner margin and 5 pinnate setae increasing in length medially. Endopod proximal segment with denticulated lateral margin (d in Figs 35E, F ) and medial pinnate seta; second segment lateral margin with fine setules (s in Fig. 35E ) and distomedially with 2 pinnate setae; distal segment with 6 pinnate setae. Leg 3 ( Fig. 34C ) biramous, protopod flattened connected to plate-like intercoxal sclerite to form apron, ornamented with marginal membrane posteriorly and along lateral margin anterior to exopod, medial and lateral pinnate setae; apron with raised bifid cuticular rib and patch of small denticles. Exopod first segment with large, recurved hook midway with a prominent accessory process (arrowed in Fig. 35G ); second segment with lateral fringe of setules, distolateral small spine and distomedial pinnate seta; distal segment with lateral fringe of setules, 3 distolateral spines increasing in length from outermost to innermost and 4 pinnate setae increasing in length medially. Endopod 2-segmented proximal segment with medial pinnate seta; second segment with 6 pinnate setae, increasing in length from outermost to innermost and lateral fringe of setules. Leg 4 ( Figs 34D , 35H ) uniramous, 3-segmented exopod with spine formula I, I, III, respectively each with pecten at base. Leg 5 ( Fig. 34E ) vestigial, anterior lobe with 1 small pinnate seta, posterior lobe with 3 pinnate setae.

Attachment site: On gill filaments.

Etymology: The species is named in honour of NK Pillai who redescribed C. cornutus .

Remarks: This species belongs to the Caligus - confusus group due to the presence of a raised bifid cuticular rib and the array of denticles on the apron of leg 3 (see Fig. 34C ); a large, recurved hook on the first exopodal segment of leg 3 (see Figs 34C , 35G ) as well as an accessory tine on the posterior dentiform maxillary process (see Fig. 33E , arrowed in Fig. 35C ) and the protuberance on the post-antennal process (see Fig. 33D , arrowed in Fig. 35B ) ( Boxshall 2018). The accessory tine on the maxillule dentiform process of C. pillaii n. sp. is very small (see Fig. 35C ) while the protuberance on the post-antennal process is on the anterior margin (see Fig. 35B ) similar to those of C. chorinemi Krøyer , C. equulae Ho & Lin (both sides), and C. abigaila Boxshall. Of all the species in the C. confusus -group, C. pillaii n. sp. is easily distinguished by the accessory process on the large, recurved hook (see Fig. 35G ) on the first segment of the exopod of leg 3. The presence of two clawlike spines on the first exopodal segment of leg 3 is one of the distinguishing features of Midias spp. ( Dojiri & Ho 2013) but, in C. pillaii n. sp. this seems more like an accessory process on the distolateral spine/recurved hook ( Fig. 35G ) than a second claw (cf. Fig. 111c in Dojiri & Ho (2013)).

The current specimens are very similar to that described and illustrated by Pillai (1985) as C. cornutus Heegaard , collected from Sphyraena jello Cuvier and S. obtusata Cuvier (Carangiformes: Sphyraenidae ) off India. However, the holotype male of C. cornutus was synonymized with C. lobodes (Wilson) ( Boxshall & Bernot 2023) and therefore the redescription of the female of C. cornutus by Pillai (1985) is thus by implication considered to be C. lobodes (Bernot, Boxshall pers. comm.). Thus, C. pillaii n. sp. is described as a new species.

Caligus pillaii n. sp. is the sixth Caligus species ( C. coryphaenae , C. dakari van Beneden , C. mulli , C. pelamydis and C. zei Norman & Scott ) reported from T. atun off South Africa ( Dippenaar 2004; Dippenaar 2024).

Figures

FIGURE 33. Caligus pillaii n. sp. adult female: A. dorsal habitus; B. antennule; C. antenna; D. post-antennal process; E. maxillule; F. mandible; G. maxilla; H. maxilliped; I. sternal furca; J. leg 1. Scale bars: A 0.5 mm; B, C, D, E, G, H, I, J 100 µm; F 10 µm.

FIGURE 34. Caligus pillaii n. sp. adult female: A. caudal ramus; B. leg 2; C. leg 3; D. leg 4; E. leg 5. Scale bars: A 50 µm; B, C, D, E, 100 µm.

FIGURE 35. Caligus pillaii n. sp. adult female: A. cephalothorax, ventral view (a2 = antenna; arrow = posterior process; pap = post-antennal process; mpp = maxillule posterior process; mx2 = maxilla; mxp = maxilliped; sf = sternal furca); B. postantennal process (arrow = protuberance); C. maxillule (arrow = additional tine); D. leg 1 exopod distal segment (4 = terminal seta 4; ps = posterior setae; t1, t2, t3 = terminal spines); E. leg 2 (arrows = distolateral spines; d = denticles; s = setules); F. leg 2 exopod (arrows = distolateral spines; os = outer spine; d = denticles); G. leg 3 exopod (ds = distolateral spine; arrow = accessory process); H. leg 4 exopod.