Caligus neoaricolus, 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 : 89-96

Caligus neoaricolus sp. nov.

( Figs. 39–41 )

Type material. Holotype ♀, 14 paratype ♀♀, 12 paratype ♂♂, 1 immature ♀ paratype from Neoarius graeffei (Kner & Steindachner, 1867) (TC17881) 4 July 2016, QM Reg. Nos Holotype ♀ W53085, 1 paratype ♀♀ and 1 immature ♀ paratype W53086, 6 paratype ♂♂ W53087; 7 paratype ♀♀ and 6 paratype ♂♂ NHMUK 2017.283– 292; 1 paratype ♂ from (TC17597) 26 June 2016, 1 paratype ♂ from (TC17624) 27 June 2016.

Additional non-type material. 1♀ from Netuma proxima (Ogilby, 1898) (TC18830) 0 1 August 2017, NHMUK 2017.294. 1♀ (possible contaminant) from Sillago maculata Quoy & Gaimard, 1824 (TC17904) 5 July 2016;1♂ incomplete (possible contaminant) from Gerres sp , juveniles (collected 26 June 2016).

Type Host. Neoarius graeffei (Kner & Steindachner, 1867) .

Site on host. Body surface.

Etymology. The name of this species alludes to the genus of the type host.

Description. Adult female ( Fig. 39A ) mean body length including caudal rami 5.91 mm (range 5.73 to 6.24 mm) (based on 10 specimens). Cephalothorax about 1.18 times longer than wide; comprising about 54% of total body length. Free margin of thoracic portion of dorsal cephalothoracic shield extending posteriorly just beyond rear margins of lateral portions. Lunules present ventrally on frontal plates. Genital complex 1.13 times longer than wide; narrowing slightly anteriorly and with linear lateral margins ( Fig. 39A ). Genital complex about 1.4 times longer than abdomen. Abdomen 1-segmented, about 2.0 times longer than wide; carrying paired caudal rami distally; anal slit terminal. Caudal rami 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 plumose setae on distal margin.

Antennule ( Fig. 39B ) 2-segmented; proximal segment with 25 plumose setae along anteroventral margin and 2 setae located dorsally; distal segment bearing 12 elements (10 setae plus 2 aesthetascs) around apex, plus isolated seta on posterior margin. Antenna ( Fig. 39C ) comprising proximal segment with small sharply-pointed, posteriorly-directed spinous process; middle segment subrectangular, unarmed; terminal segment forming strongly curved claw with proximal sclerotized swelling bearing small seta, and armed with stout distal seta. Post-antennal process ( Fig. 39C ) weakly curved, ornamented with 2 multisensillate papillae on basal part; plus single multisensillate papilla on adjacent ventral cephalothoracic surface.

Mandible of typical stylet-like structure, with 12 marginal teeth ( Fig. 39D ). Maxillule ( Fig. 39C ) comprising anterior papilla bearing 3 small naked setae and slender, tapering posterior process. Maxilla comprising elongate syncoxa and basis: syncoxa unarmed but bearing opening of maxillary gland; basis bearing subapical membranous flabellum on anterior margin, and terminating in 2 subequal, claw-like elements (calamus and canna) ( Fig. 39E ): calamus just longer than canna, ornamented with strips of serrated membrane arranged obliquely around surface; canna with linear strips of serrated membrane. Maxilliped subchelate ( Fig. 39F ); slender proximal segment with fine transverse ridges on myxal surface; distal subchela with small inner seta.

Sternal furca ( Fig. 39G ) with weakly divergent, tapering tines.

First swimming leg pair ( Fig. 40A ) with sympods joined by slender intercoxal sclerite; sympod with inner and outer plumose setae; endopod represented by unarmed process on posterior margin of basis, bearing minute vestiges of 2 setae apically. Exopod 2-segmented; directed laterally and forming main axis of leg; first segment robust, about 2.5 times longer than wide and armed with small outer (anterior) spine and ornamented with setule row along mid-section of posterior margin; second segment armed with 3 long plumose setae along posterior margin and 4 distal elements. Distal margin elements as follows: spine 1 (anterior-most) longest and naked; spine 2 longer than spine 3, each with accessory process; seta 4 twice as long as spine 1 and longer than segment.

Second leg biramous, with flattened protopodal segments and 3-segmented rami. Coxae of leg pair joined by plate-like intercoxal sclerite bearing marginal membrane posteriorly; armed 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. Exopodal segments 1 and 2 each with inner plumose seta and large reflexed outer spines extending obliquely across ventral surface of ramus ( Fig. 40B ); outer spines ornamented with bilateral membranous strips; first exopodal segment bearing flap of membrane anteriorly, reflexed back over dorsal surface; segment 3 with 2 outer spines, proximal spine small, distal spine ornamented with membrane; apical spine with marginal membrane laterally and pinnules medially, and 5 inner plumose setae. Endopodal segments 1 and 2 armed with 1 and 2 inner plumose setae respectively; segment 3 with 6 plumose setae; outer margins of all endopodal segments ornamented with fine setules.

Third leg pair ( Fig. 40C ) forming flattened plate closing posterior part of cephalothoracic sucker, as typical for genus. Protopodal part flattened joined by plate-like, intercoxal sclerite forming 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. Exopod indistinctly 3-segmented; first segment armed with straight outer claw directed parallel with long axis of ramus and overlying lateral margin, lacking inner seta; second and third segments incompletely separated by partial suture; armed with slender outer spine and inner plumose seta derived from second segment and 3 outer spiniform elements and 4 inner plumose setae (derived from third segment); outer margins of segments 2 and 3 ornamented with rows of slender setules. Endopod 2-segmented; first segment expanded to form flap-like velum closing off space between rami, velum ornamented with row of fine setules along free margin; segment armed with inner plumose seta; compound distal segment with expanded and setulate lateral margin; bearing with 6 setal elements increasing in length from outermost to innermost.

Fourth leg ( Fig. 40D ) 3-segmented, comprising slender protopodal segment and 2-segmented exopod; exopodal segments separated by oblique articulation: protopodal segment armed with outer plumose seta; first exopodal segment armed with short outer spine; second segment armed with short lateral spine and 3 unequal spines along distal margin; all spines with pecten at base.

Fifth leg located posterolaterally on margin of genital complex, represented by anterior plumose seta on papilla and posterior papilla bearing 2 unequal plumose setae representing exopod ( Fig. 39H ).

Male ( Fig. 41A ) mean body length including caudal rami 5.62 mm, range 5.41 to 5.99 mm (based on 10 specimens). Cephalothorax subcircular as in female. Fourth pedigerous somite incompletely fused to genital complex. Genital complex about 1.2 times longer than wide, measured along the mid-line; with weakly convex lateral margins. Abdomen 2-segmented, separated from genital complex dorsally but fused ventrally. Caudal rami longer than wide; armed with short plumose seta at inner distal angle, 2 short plumose setae at outer distal angle, and 3 longer plumose setae on distal margin.

Antennule, mandible, maxillule and maxilla as in female. Antenna modified ( Fig. 41C ); first segment elongate; second segment reflexed, swollen proximally with surface forming corrugated adhesion pads ventrally, plus corrugated distal swelling opposing tip of claw; distal segment forming short powerful apical claw armed with 2 setae proximally. Post-antennal process more robust than in female ( Fig. 41D ).

Maxilliped ( Fig. 41E ) with weakly inflated myxal margin on proximal segment; distal subchela longer relative to syncoxa, than in female.

Legs 5 and 6 ( Fig. 41B ) each forming paired flattened processes posterolaterally on genital complex. Leg 5 represented by 3 plumose setae, 1 outer seta and 2 short inner setae representing exopod. Leg 6 represented by paired opercula closing off genital apertures; each armed with 1 long and 1 short plumose seta on distal margin, plus a minute spine.

Remarks. This new species possesses a 3-segmented leg 4 bearing I and IV spines on the first and second exopodal segments, respectively. This is a common configuration shared with nearly 90 other Caligus species, including the 14 members of the C. productus -group which are characterized by loss or major reduction of the three plumose setae on the posterior margin of the distal exopodal segment of leg 1. These can be eliminated from further comparison since these posterior margin setae are normally developed in the new species. Another 12 species, members of the C. bonito- group, all of which share the presence of large denticles on the outer margin of the second endopodal segment of leg 2, can be excluded from detailed comparison as the new species has an ornamentation of fine setules along this margin. The remaining pool of similar species is reduced to 30 by restricting further comparisons to species that have a female genital complex that is as long as or longer than wide, and an abdomen that is longer than wide. Allowing for individual variation in genital complex shape in the order of 10%, generates a short list of 13 species that exhibit a genital complex with a L:W ratio in the range of 1.0 to 1.2:1 for comparison with the new species ( Table 6).

Caligus gurnardi differs from the new species in having a genital complex that is 2.3 times longer than the abdomen ( Parker, 1965), compared to only 1.5 times longer in the new species. Four species, C. elongatus , C. tripedalis , C. ogawai and C. tenuifurcatus , all have a very broad abdomen (i.e. abdomen at least 50% of width of genital complex), whereas in C. neoaricolus sp. nov. the abdomen is only 38% of the width of the genital complex. Three of the remaining species, C. longirostris , C. rapax , and C. rufimaculatus , have a relatively short abdomen, i.e., that is only 1.4 to 1.5 times longer than wide, compared to 2.0 times longer in the new species.

The leg 4 of C. chiastos ( Fig. 24F ) has a long outer spine on exopodal segment 1 that extends beyond the origin of the lateral spine on the distal segment. In contrast, the new species has a much shorter outer spine that does not reach halfway to the base of the lateral spine on the distal segment. Other differences include the smaller posterior process on the proximal segment of the antenna in the new species, the small size of the outer spines on the distal exopodal segment of leg 2, the shape of the sternal furca, and the relative lengths of spines 1 to 3 on the distal margin of the exopod of leg 1.

Caligus clemensi exhibits a similar arrangement of outer spines on the third exopodal segment of leg 2, to that of the new species: both have a minute pointed proximal spine and a longer blunt-tipped distal spine. The configuration of spines 1 to 3 on the distal margin of the exopod of leg 1 differs: in the new species spines 1 to 3 decrease in length in order from outer to inner, whereas in C. clemensi spines 2 and 3, with their very long accessory processes, are both longer than spine 1 ( Parker & Margolis, 1964). Another noticeable difference is the outer spines on the exopodal segments of leg 4: they are much smaller in the new species, not reaching the origin of the next most distal spine, whereas in C. clemensi each of the outer spines reaches the origin of the next spine.

The redescription of C. praetextus by Cressey (1991) reveals that leg 1 has an unusually squat shape in this species: the first exopodal segment is only 1.7 times longer than wide compared to 2.5 times longer in the new species. Spines 2 and 3 on the distal margin of the exopod have marginal membrane extending apically from about the origin of the accessory process, producing a spatulate appearance (Cressey, 1991: Fig. 158). These spines lack marginal membrane in C. neoaricolus sp. nov. The proximal outer spine on the third exopodal segment of leg 2 is longer than the distal spine and curves across its surface, just as highlighted for C. chiast os by Lin & Ho (2003), whereas in C. neoaricolus sp. nov. the proximal spine is only half as long as the distal (cf. Fig. 40B ).

In terms of body proportions C. lutjani is the most similar to the new species (cf. Table 6). Both species also share a similar configuration of spines 1 to 3 on the distal margin of the exopod of leg 1, small outer spines on the distal exopodal segment of leg 2, multisensillate papillae associated with the post-antennal process, and tapering, pointed tines on the sternal furca. The outer spines on the exopodal segments of leg 4 are much smaller in the new species, not reaching the origin of the next most distal spine, whereas in C. lutjani each of the outer spines reaches at least to the origin of the next spine. Other differences include the more strongly recurved post-antennal process in C. lutjani , and its slender maxilliped with its smooth myxal margin, compared to the more robust and ridged myxal area in C. neoaricolus sp. nov. The males differ in the proportional lengths of the two free abdominal somites: in C. lutjani the first somite is 1.24 times longer than the second, whereas in C. neoaricolus sp. nov., the first is only half the length of the second.

The material described here differs from similar congeners and these differences justify the establishment of a new species. In the type locality, Moreton Bay, its type host was Neoarius graeffei . A single female was recovered from a wash of Sillago maculata (TC17904) but this is thought to be a contaminant. Similarly an incomplete male was recovered from a container that had been used to hold a batch of juvenile Gerres sp. The partly decayed state of this male suggests that it may have been left in an inadequately rinsed dish from the previous sample.

Figures

FIGURE 24. Caligus chiastos Lin & Ho, 2003, female. A, habitus, dorsal; B, antenna, post-antennal process and maxillule drawn in situ; C, sternal furca; D, distal margin of exopod of leg 1; E, exopod of leg 2, showing well developed, curved proximalouter spine of third exopodal segment;F, leg 4.Scale bars:1.0 mm on A, 200 µm on F, 100 µm on C, E, 50 µm on B, D.

FIGURE 41. Caligus neoaricolus sp. nov. paratype male.A, habitus, dorsal; B, left corner of genital complex showing legs 5 and 6, ventral; C, antenna; D, post-antennal process, E, maxilliped. Scale bars: 1.0 mm on A, 250 µm on E, 200 µm on C, 100 µm on B, D.

FIGURE39. Caligus neoaricolus sp. nov. paratype female.A, habitus, dorsal;B, antennule, ventral; C, antenna, post-antennal process and maxillule drawn in situ; D, mandible; E, tip of maxilla; F, maxilliped; G, sternal furca; H, left corner of genital complex showing fifth leg, ventral. Scale bars:1.0 mm on A, 200 µm on B, C, G, 250 µm onF, 100 µm on D, E, H.

FIGURE40.Caligus neoaricolus sp. nov. paratype female.A, leg 1, anterior;B,exopodof leg2, anterior; C, leg 3, ventral; D, leg 4. Scale bars:200 µm on A, B, 0.5 mm on C, 250 µm on D.