Caligus abigailae, 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 : 33-36

Caligus abigailae sp. nov.

( Figs. 13 , 14 )

Type material. Holotype ♀ and 19 paratype ♀♀ from 6 heads of Sphyraena obtusata Cuvier, 1829 (TC16953) caught by anglers at Amity , North Stradbrooke Island, 10 January 2016 ; 2 paratype ♀♀ from S. obtusata (TC16970) 11 January 2016. QM Reg. Nos. Holotype ♀ W53051, 10 paratype ♀♀ W53052; 10 paratype ♀♀ NHMUK Reg. Nos 2017.202–211.

Type Host. Sphyraena obtusata Cuvier, 1829 .

Site on host. Roof of pharynx, gill arches, wall of branchial cavity.

Etymology. This species is named after Abigail Whittaker, who has, over the years, provided me with considerable support and encouragement.

Description. Adult female ( Fig. 13A ) mean body length including caudal rami 3.35 mm, range 3.19 to 3.58 mm (based on 10 specimens). Cephalothorax subcircular; comprising about 36% of total body length. Free margin of thoracic portion of dorsal cephalothoracic shield extending posteriorly just beyond rear margins of lateral portions. Well developed lunules present ventrally on frontal plates. Genital complex bottle-shaped, i.e. with rounded convex lateral margins, widest towards posterior end and narrowing anteriorly, about 1.4 times longer than maximum width; fifth legs located ventrally close to posterolateral corners ( Fig. 13B ). Genital complex about 2.2 times longer than abdomen. Abdomen 1-segmented; about 2.0 times longer than wide in dorsal view; bearing paired caudal rami distally; anal slit terminal. Caudal rami with parallel sides, just longer than wide, measured at midpoints of margins. Each ramus armed with short hirsute seta at inner distal angle, slightly longer hirsute seta at outer distal angle, minute hirsute seta located just ventral to outer distal seta, and 3 long plumose setae on distal margin.

Antennule 2-segmented; large proximal segment with 25 plumose setae arrayed along anteroventral surface and 2 setae located dorsally; short distal segment bearing 12 elements (10 setae plus 2 aesthetascs) around apex, plus isolated seta on posterior margin. Antenna ( Fig. 13C ) comprising proximal segment bearing weakly defined posteriorly-directed spinous process; middle segment short, subrectangular, unarmed; terminal segment forming recurved claw bearing long proximal seta and slender distal seta. Post-antennal process ( Fig. 13C ) with weaklydeveloped, more-or-less straight tine ornamented with 2 multisensillate papillae on basal part and single multisensillate papilla on adjacent ventral cephalothoracic surface. Rounded swelling present between base of antenna and post-antennal process.

Mandible of typical stylet-like structure, with 12 marginal teeth ( Fig. 14A ). Maxillule ( Fig. 13D ) comprising anterior papilla bearing 3 unequal, naked setae and posterior, tapering process. Maxilla 2-segmented ( Fig. 14B ), comprising elongate unarmed syncoxa and basis: basis bearing membranous subapical flabellum on anterior margin, and terminating in 2 subequal claw-like elements (calamus and canna); calamus slightly longer than canna, ornamented with strips of serrated membrane arranged obliquely around surface; canna ornamented with bilateral strips of serrated membrane. Maxilliped subchelate ( Fig. 14C ); proximal segment robust, with transverse fold and swelling on myxal surface; distal subchela with apical claw; short, slender seta present on concave margin.

Sternal furca ( Fig. 13E ) with slightly divergent tines, with bluntly-rounded tips.

First swimming leg pair ( Fig. 13F ) joined by slender intercoxal sclerite; sympod with inner and outer plumose setae derived from basis. Endopod represented by process on posterior margin of basis, bearing 2 minute setal vestiges on apex. Exopod 2-segmented, directed laterally and forming main axis of leg; first segment robust, about 2.9 times longer than wide and armed with small outer (anterior) spine and ornamented with row of setules along posterior margin; second segment short, with bulbous swelling on posterior surface at base of spine 2, armed with 3 short plumose setae along posterior margin and 4 distal elements along oblique distal margin. Distal elements as follows: spine 1 (anterior-most) longest ornamented with row of robust denticles; spines 2 and 3 progressively smaller, each with rows of spinules and accessory process; seta 4 about as long as spine 3, shorter than segment.

Second leg biramous, with flattened protopodal segments and 3-segmented rami. Coxae of leg pair joined by intercoxal sclerite bearing marginal membrane posteriorly; each coxa with plumose seta and surface sensilla. Basis armed with outer naked seta; ornamented with surface sensilla, marginal membrane posteriorly, and flap of membrane anteriorly, reflexed back over dorsal surface of segment. Exopod 3-segmented ( Fig. 13G ); first exopodal segment with inner plumose seta and bilaterally serrate, curved outer spine extending obliquely across lateral side surface of ramus; segment 2 with smaller but similar outer spine extending across surface, plus inner plumose seta; segment 3 with 2 outer spines (proximal spine small and bilaterally serrate, distal spine with unilateral row of fine setules); apical spine with marginal membrane laterally and pinnules medially, and 5 inner plumose setae. Endopodal segments 1 and 2 ( Fig. 13H ) armed with 1 and 2 inner plumose setae respectively; segment 3 with 6 plumose setae; outer margin of first endopodal segment expanded distally and ornamented with stout setules around convex expansion.

Third leg pair ( Fig. 14D ) forming flattened plate closing posterior part of cephalothoracic sucker as typical for genus. Protopodal part flattened joined by plate-like, intercoxal sclerite to form apron, ornamented with marginal membrane posteriorly and along lateral margin anterior to exopod; bearing inner plumose seta at junction with intercoxal plate and outer plumose seta dorsal to base of exopod; sensillae located adjacent to inner coxal seta and adjacent to origin of endopod; apron also ornamented with rosette-like array of spinules plus prominent bifid rib on ventral surface, and corrugated adhesion pad dorsally at anterior corner; space between rami covered by short, flaplike velum ornamented with fine setules along free margin. Exopod 3-segmented; first segment armed with large recurved spine ( Fig. 14D ) directed over ventral surface of ramus but lacking inner seta; second segment with 1 outer spine and inner plumose seta; third segment with 3 spines on outer margin plus 5 plumose setae on inner margin; free outer margins of segments 2 and 3 each ornamented with rows of slender setules. Endopod 2- segmented; first segment forming velum and bearing inner plumose seta; second with 6 setal elements increasing in length from outermost to innermost.

Fourth leg ( Fig. 14E ) uniramous, 4-segmented; comprising protopodal segment and 3-segmented exopod: protopodal segment armed with plumose seta distally; exopodal segments with I; I; III spines; each spine with associated pecten.

Fifth legs located posterolaterally on genital complex ( Fig. 13B ); represented by plumose seta on anterior papilla and 2 plumose setae on posterior papilla representing exopod.

Remarks. This long-bodied species belongs to a group of species, referred to as the C. confusus group (see remarks below under C. confusus ), which is characterized by a suite of character states including: the presence of a raised bifid cuticular rib and a circular rosette-like 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, the possession of a 3-segmented exopod of leg 4 with a I, I, III setal formula, and, in some species only, the presence of an accessory tine on both the post-antennal process and the posterior maxillulary process. Within this grouping, the new species is most similar to C. clavatus Kirtisinghe, 1964 , which was described from females found on Sphyraena obtusata caught off the coast of Sri Lanka (Kirtisinghe, 1964), and C. inopinatus Kabata, 1994 which is parasitic on S. flavicauda Rüppell, 1838 in the Red Sea (Kabata, 1994). As well as the bottle-shaped genital complex and long abdomen, these three species share numerous fine details of appendage armature, including the form and ornamentation of the setal elements on the exopod of leg 1, and the form of the outer margin spines on the exopods of legs 2 and 3.

Caligus clavatus occurs on a range of other barracuda species, including Sphyraena jello Cuvier, 1829 and S. acutipinnis Day, 1876 in Indian waters (Pillai, 1967, 1985), and S. japonica Bloch & Schneider, 1801 from Taiwan ( Lin & Ho, 2002). A modern detailed description of the adult female of C. clavatus was presented by Ho & Lin (2004). It differs from the new species in its longer abdomen, which is about 2.9 times longer than wide and is equal to about 75 to 80% of the length of the genital complex, compared to 2.0 times longer than wide and about 45% of the length of the genital complex in C. abigailae sp. nov.

Caligus inopinatus is only known from the original report in the Red Sea. It has a relatively short abdomen which is only about 1.5 times longer than wide and is equal to about 35% of the length of the genital complex. In contrast, in the new species the abdomen is 2.0 times longer than wide and about 45% of the length of the genital complex. Other minor differences are apparent including the shape of the posterior process of the proximal antenna segment (bluntly rounded in C. inopinatus but tapering in C. abigailae sp. nov.) and the outline shape of the sternal furca (V-shaped in C. inopinatus versus U-shaped in C. abigailae sp. nov.).

In Moreton Bay, this new copepod was found only on the type host, Sphyraena obtusata .

Figures

FIGURE 14. Caligus abigailae sp. nov., paratype female. A, mandible; B, maxilla; C, maxilliped; D, leg 3; E, leg 4. Scale bars:50 µm on A, 100 µm on B, D, E, 200 µm on C.

FIGURE13.Caligus abigailaesp. nov., paratype female.A, habitus,dorsal; B,rightfifth legat posterolateral cornerof genital complex, ventral; C, antenna and post-antennal process, drawn in situ; D, maxillule; E, sternal furca; F, leg 1; G, exopod of leg 2; H, endopod of leg 2. Scale bars: 0.5 mm on A, 50 µm on B, E, 100 µm on C, D, F–H.