Caligus nataliae, 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 : 84-89

Caligus nataliae sp. nov.

( Figs. 37–38 )

Type material. Holotype ♀, 1 immature ♂ paratype, from Herklotsichthys castelnaui (Ogilby, 1897) (TC17275— pooled data from 24 hosts) 19 January 2016, QM Reg. Nos Holotype ♀ W53082, 1 immature ♂ paratype W53083; 1 paratype ♀ from Neoarius graeffei (Kner & Steindachner, 1867) (TC17597) 26 June 2016, QM Reg. No. W53084.1 paratype ♀ (TC17881) 4 July 2016, NHMUK Reg. No. 2017.283.

Type Host. Herklotsichthys castelnaui (Ogilby, 1897) .

Site on host. Body surface.

Etymology. The new species is named after Mrs Natalie Latham, in gratitude for all her help with curating and labeling copepods for accession into the NHM collections.

Description. Adult female ( Fig. 37A ) mean body length including caudal rami 5.97 mm (range 5.29 to 6.56 mm) (based on 3 specimens). Cephalothorax about 1.2 times longer than wide; comprising about 60% 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 about 1.5 times wider than long with linear lateral margins, narrowing slightly posteriorly ( Fig. 37A ). Genital complex about 2.0 times longer than abdomen. Abdomen 1-segmented, about 1.3 times longer than wide; carrying paired caudal rami distally; anal slit terminal. Surface of genital complex, abdomen and caudal rami ornamented with sparsely scattered sensillae ( Figs. 37B, C ). Caudal rami wider than long ( Fig. 37B ), measured at midpoints of margins: each ramus armed with short hirsute seta at inner distal angle, slightly longer hirsute seta at outer distal angle, short hirsute seta located just ventral to outer distal seta, and 3 plumose setae on distal margin.

Antennule ( Fig. 38A ) 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. 37D ) comprising proximal segment with short sharply-pointed, posteriorlydirected spinous process; middle segment subrectangular, tapering slightly distally, unarmed; terminal segment forming recurved claw bearing sclerotized swelling proximally, and armed with slender distal seta near anterior margin. Post-antennal process ( Fig. 37D ) vestigial, ornamented with 2 trisensillate papillae on basal part; plus single multisensillate papilla on adjacent ventral cephalothoracic surface.

Mandible of typical stylet-like structure, with 12 marginal teeth. Maxillule ( Fig. 37D ) comprising anterior papilla bearing 3 unequal, naked setae and elongate, slender posterior process. Maxilla 2-segmented ( Fig. 37E ), comprising elongate syncoxa and basis: syncoxa unarmed, bearing opening of maxillary gland; basis bearing subapical membranous flabellum on anterior margin and terminating in 2 subequal, claw-like elements (calamus and canna). 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. 37F ); slender proximal segment unarmed; distal subchela with small apical claw separated from proximal segmental part by incomplete suture; segmental part armed with 1 small seta.

Sternal furca ( Fig. 37G ) with tapering parallel tines.

First swimming leg pair ( Fig. 38B ) with sympods joined by slender intercoxal sclerite; sympod with inner and outer plumose setae; endopod represented by unarmed process on posterior margin of basis. Exopod 2-segmented; directed laterally and forming main axis of leg; first segment robust, about 2.3 times longer than wide and armed with small outer (anterior) spine and ornamented with setule row along mid-section of posterior margin; compound distal segment armed with 3 long plumose setae along posterior margin and 4 distal elements: distal margin elements as follows: spine 1 (anterior-most) short and naked (arrowed in Fig. 38B ); spines 2 and 3 equal in length, both with accessory process; seta 4 naked, slightly shorter than spine 3, and markedly shorter 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. 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. Endopodal segments 1 and 2 ( Fig. 38C ) 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, extending onto surface of second and third segments. Exopodal segments 1 and 2 ( Fig. 38D ) each with inner plumose seta and large reflexed outer spine extending obliquely across ventral surface of ramus; 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 minute, distal spine curved with inner marginal membrane), apical spine with marginal membrane laterally and pinnules medially, plua 5 inner plumose setae.

Third leg pair ( Fig. 38E ) 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; with corrugated expansion anterior to lateral margin membrane. Exopod 3- segmented; first segment armed with almost straight outer claw directed over ventral surface of ramus, lacking inner seta; second segment with slender outer spine and inner plumose seta; third with 7 setal elements (3 outer spiniform elements and 4 inner plumose setae); outer margins of segments 2 and 3 ornamented with rows of slender setules. Endopod 2-segmented; first segment forming flap-like velum ornamented with row of fine setules along free margin, and with inner plumose seta; compound distal segment with expanded and setulate lateral margin, bearing 6 setal elements increasing in length from outermost to innermost, ornamented with 2 sensillae on dorsal surface.

Fourth leg ( Fig. 38F ) 3-segmented, comprising slender protopodal segment and indistinctly 2-segmented exopod; exopodal segments separated by oblique articulation visible on dorsal surface only: protopodal segment armed with outer seta; first exopodal segment longer than protopodal segment, armed with slender outer spine reaching to tip of ramus; distal segment short armed with 2 unequal naked spines on apex, each with pecten at base.

Fifth leg located posterolaterally on ventral surface near margin of genital complex, represented by anterior plumose seta on papilla and posterior papilla bearing 2 unequal plumose setae representing exopod ( Fig. 37C ).

Remarks. This unusual species displays a number of distinctive features. The form of the 3-segmented leg 4 is unique. The first exopodal segment of leg 4 is longer than the protopodal segment and the second exopodal segment is very short and armed with only 2 spines. Only five species of Caligus have a 3-segmented leg 4 bearing only 2 spines on the second exopodal segment: C. centrodonti Baird, 1850 , C. epidemicus , C. labracis T. Scott, 1902 , C. mortis Kensley, 1970 , and C. sensorius . In C. centrodonti , C. epidemicus ( Fig. 28E ) and C. sensorius the first exopodal segment is shorter than the second, while in C. labracis and C. mortis the first and second segments (as measured along the inner margin) are about equal in length. Only the new species has a leg 4 exopod with the first segment more than twice as long as the second segment, and armed with I, II spines.

Other unusual features of C. nataliae sp. nov. include the vestigial post-antennal process, the long canna on the tip of the maxilla (almost as long as the calamus), the linear tapering tines of the sternal furca, plus the reduction of spine 1 on the distal margin of the exopod of leg 1. Each of these character states is found in other species of Caligus , but in no other species are they combined. When sorting these caligids freshly caught, they could be recognised by the distinctive exopod of leg 3: the second segment is relatively long (compared to the first and third segments) and the outer spine on the first segment is linear and extends the entire length of the second segment.

In Moreton Bay the new species was found on two unrelated hosts, a pelagic clupeid, Herklotsichthys castelnaui , and a bottom-living ariid, Neoarius graeffei .

Figures

FIGURE 28. Caligus epidemicus Hewitt, 1971, female. A, habitus, dorsal; B, antenna, post-antennal process and maxillule drawn in situ; C, sternal furca; D, exopod of leg 3; E, leg 4. Male, F, habitus, dorsal; G, left fifth and sixth legs, and caudal ramus, ventral view.Scale bars: 1.0 mm on A, F, 200 µm on B, E, G, 100 µm on D, 50 µm on C.

FIGURE 37. Caligus nataliae sp. nov. paratype female. A, habitus, dorsal; B, caudal ramus, ventral; C, left corner of genital complex showing fifth leg, ventral; D, antenna,post-antennal process and maxillule drawn in situ; E, maxilla; F, maxilliped; G, sternal furca.Scale bars: 250 µm on A, 200 µm on B–F, 100 µm on G.

FIGURE 38. Caligus nataliae sp. nov. paratype female. A, antennule, ventral; B, leg 1, anterior view with reduced spine 1 arrowed;C, endopod ofleg 2,anterior;D, exopodof leg 2, anterior; E, leg 3, ventral; F,leg 4. Scalebars:100 µm on A,200 µm on B–F.