Caligus alepicolus, 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 : 39-42

Caligus alepicolus nom. nov.

( Figs. 16 , 17 )

Syn: Caligodes alatus Heegaard, 1945

Material examined. 1♀ from Alepes apercna Grant, 1987 (TC17073), 13 January 2016, QM Reg. No W53054 .

Site on host. Gills.

Redescription. Adult female ( Fig. 16A ) body length 6.03 mm, including caudal rami. Cephalothorax subcircular (1.94 mm long x 2.16 mm wide); comprising about 32% of total body length. Cephalic portion of dorsal cephalothoracic shield well developed, raised dorsally and with strongly defined and rigid posterior margin. Thoracic portion of dorsal cephalothoracic shield small, posterior margin not reaching as far as rear margins of lateral portions. Lunules present ventrally on frontal plates. Genital complex with paired, broad-based, sheath-like posterior expansions arisiring laterally and enclosing anterior part of abdomen from 3 sides: genital complex shorter than abdomen, measured along midline. Abdomen indistinctly 2-segmented ( Fig. 16A, B ); elongate, 1.68 times longer than wide and longer than genital complex; first segment expanded laterally: anal somite short, carrying 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 ( Fig. 16C ) 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. 16D ) with proximal segment lacking posterior process; middle segment short, subrectangular, unarmed; terminal segment forming slender recurved claw armed with slender proximal and distal setae. Post-antennal process ( Fig. 16D ) small with short tine; ornamented with 2 bisensillate papillae on basal part and single bisensillate papilla on adjacent ventral cephalothoracic surface.

Mandible of typical stylet-like structure, with 12 marginal teeth. Maxillule ( Fig. 16D ) comprising anterior papilla bearing 3 unequal setae and posterior, tapering process with tiny area of thin integument. Maxilla 2- segmented, comprising elongate unarmed syncoxa and basis: basis bearing membranous but spiniform subapical flabellum on anterior margin, and terminating in 2 subequal claw-like elements (calamus and canna). Calamus longer than canna ( Fig. 16E ), ornamented with strips of serrated membrane arranged obliquely around surface near tip; canna ornamented with bilateral strips of serrated membrane. Maxilliped subchelate ( Fig. 17A ); robust proximal segment unarmed but with rounded swollen myxal margin; distal subchela with slender seta proximally, apical claw strongly curved, ornamented with surface striations.

Sternal furca ( Fig. 16F ) with short, more-or-less parallel tines, median space between tines square-sided.

First swimming leg pair joined by slender intercoxal sclerite; sympod with inner and outer plumose setae derived from basis, ornamented with patch of large surface denticles ( Fig. 17B ); 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 2.9 times longer than wide, armed with small outer (anterior) spine and ornamented with row of setules along posterior margin; second segment short, armed with 3 reduced plumose setae on posterior margin and 4 distal elements along oblique distal margin as follows: spine 1 (anterior-most) longest with marginal row of minute serrations; spines 2 and 3 progressively smaller, each with unilateral serrated membrane plus accessory process; seta 4 naked, longer than spine 3, shorter than segment.

Second leg ( Fig. 17C ) biramous, with flattened protopodal segments and both rami 3-segmented. 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. Exopodal segment 1 with inner plumose seta and large serrate outer spine aligned with longitudinal axis of ramus, bearing flap of membrane anteriorly, reflexed back over dorsal surface of segment; exopod segment 2 with outer spine directed distally plus inner plumose seta; segment 3 with 2 small outer spines, 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. 17D ) forming flattened plate closing posterior section of cephalothoracic sucker. Protopodal part flattened joined by plate-like, intercoxal sclerite forming apron; ornamented with extensive flap of 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 origin of endopod; antero-lateral corner with corrugated surface, ventral surface with lateral line of denticles plus rosettelike array of denticles closer to mid-line and raised, bilobed rib-like process. Exopod 3-segmented; first segment armed with slightly curved outer claw directed over ventral surface of ramus, lacking inner seta; second segment with outer spine and inner seta; third segment with 3 spiniform elements on outer margin plus 4 plumose setae on inner margin; outer margins of segments 2 and 3 ornamented with rows of slender setules. Endopod 2-segmented; first segment expanded laterally to form flap-like velum closing off space between rami, free margin of velum ornamented with row of fine setules, armed with inner plumose seta; compound distal segment with 6 plumose setae increasing in length from outermost to innermost.

Fourth leg ( Fig. 17E ) 4-segmented, comprising slender protopodal segment and 3-segmented exopod: protopodal segment armed with plumose seta distally; exopodal segments armed with I, I, III spines, each spine bilaterally serrate and with well-developed pecten at base. Fifth legs not observed.

Remarks. Heegaard (1945) established Caligodes alatus Heegaard, 1945 on the basis of a single ovigerous female collected from “the mouth cavity of a Cardus sp. from Rambang, Java ”. The identity of the host is problematic since “ Cardus ” does not appear as a genus name in Eschmeyer’s (1998) comprehensive Catalog of Fishes. The polychelid crustacean genus Cardus Galil, 2000 was established too recently (Galil, 2000) to be relevant. In his original account, Heegaard (1945) also described Caligus bicycletus Heegaard, 1945 as cooccurring on the same host fish (“ Cardus sp.”). Subsequent records of C. bicycletus have all been from Alepes djebaba (Forsskål, 1775) (as Atule djedaba and as Selar kalla ) (see Pillai, 1985). It seems likely that the identity of “ Cardus ” as used by Heegaard (1945) is the carangid Alepes djebaba . This assumption gains some support from the second record of C. alatus , reported here, from the congeneric Alepes apercna .

The original description (Heegaard, 1945) was inadequate by modern standards, so Dojiri & Ho (2013) were unable to confirm the generic placement of this species in Caligodes in their major review. Examination of the second female of this taxon to be discovered allows the generic placement to be revisited. It does not belong in the ill-defined genus Caligodes because it does not share most of the features that serve to diagnose Caligodes according to Dojiri & Ho (2013), namely the long posterodorsal processes on the genital complex (derived from fifth legs), the enlarged spine 1 on the distal exopodal segment of leg 1, the slender exopodal spines of leg 2, and the segmentation and armature of leg 4. It does have a long abdomen, but this is found in species of several caligid genera. It also has broad-based posterior expansions at the posterolateral corners of the genital complex. Presumably Heegaard (1945) based his placement in Caligodes on the potential homology of these paired expansions with the long fifth legs of C. laciniatus . This homology cannot be confirmed, however, as setae representing the fifth legs were not observed in the Moreton Bay specimen. In the absence of any differentiating characters, Heegaard’s species should be placed in Caligus Müller, 1785 , but this creates a secondary homonym; as Caligus alatus already exists, established by Heegaard in 1943 for a parasite collected from the balistid Canthidermis Swainson, 1839 (probably C. maculata (Bloch, 1786)) in the West Indies. Although Caligus alatus Heegaard, 1943 is now recognized as a junior subjective synonym of C. balistae Steenstrup & Lütken, 1861 (Cressey, 1991) , it remains unavailable. A replacement name is required and Caligus alepicolus nom. nov. is proposed here, in reference to the host genus, Alepes Swainson, 1839 .

The affinities of C. alepicolus nom. nov. appear to lie with the Caligus confusus group of species discussed below. Members of this group are typically found on carangid hosts and share a suite of characters including the raised rib and rosette of large denticles on the apron of leg 3.

Figures

FIGURE 17. Caligus alepicolus nom. nov., female. A, maxilliped; B, leg 1;, C, leg 2, with insets showing outer spine of exopodal segment 2, and proximal and distal outer spines on exopodal segment 3; D, leg 3; E, leg 4. Scale bars: 200 µm on A, D, E, 100 µm on B, C.

FIGURE16.Caligus alepicolus nom. nov., female.A,habitus, dorsal;B, genital complex and abdomen,ventral;C, antennule; D, antenna, post-antennal process and maxillule, drawn in situ; E, distal tip of maxilla; F, sternal furca. Scale bars: 1.0 mm on A, B, 100 µm on C–E, 50 µm on F.