Caligus pseudorhombi, 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 : 111-115

Caligus pseudorhombi sp. nov.

( Figs. 50–52 )

Type material. Holotype ♀, allotype ♂ from Pseudorhombus arsius (Hamilton, 1822) (TC17859) 0 4 July 2016, QM Reg. Nos Holotype ♀ W53095, allotype ♂ W53096.

Type Host. Pseudorhombus arsius (Hamilton, 1822) .

Site on host. Body surface.

Etymology. The name of this species is derived from the host genus.

Description. Adult female ( Fig. 50A ) body length 4.42 mm including caudal rami. Cephalothorax slightly longer than wide; comprising about half (52%) of total body length. Free margin of thoracic portion of dorsal cephalothoracic shield extending posteriorly beyond rear margins of lateral portions. Lunules present ventrally on frontal plates. Genital complex about as long as wide, with angular posterolateral corners ( Fig. 50A, B ); complex about 2.1 times longer than abdomen. Abdomen 1-segmented; about as long as wide; carrying paired caudal rami distally; anal slit terminal. Caudal rami with parallel sides, just wider than long, measured at midpoints of margins: each ramus armed with long hirsute seta at inner distal angle, slightly longer hirsute seta sub-distally on outer margin, minute hirsute seta located just ventral to outer distal seta, and 3 long plumose setae on distal margin.

Antennule ( Fig. 50C ) 2-segmented; large proximal segment with 25 plumose setae arrayed along anteroventral surface 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. 50D ) comprising proximal segment bearing acutely pointed, posteriorly-directed spinous process; middle segment subrectangular, tapering slightly distally, unarmed; terminal segment forming recurved claw bearing short spine on swelling proximally, and minute seta near anterior margin. Post-antennal process ( Fig. 50D ) well-developed, tine curved; ornamented with 2 multisensillate papillae on basal part and single multisensillate papilla on adjacent ventral cephalothoracic surface.

Mandible of typical stylet-like structure, with 12 marginal teeth. Maxillule ( Fig. 50D ) comprising anterior papilla bearing 3 unequal, naked setae and blunt posterior, tine-like process. Maxilla 2-segmented ( Fig. 50E ), comprising elongate syncoxa and basis: syncoxa unarmed; basis bearing membranous subapical flabellum on anterior margin, and terminating in 2 subequal claw-like elements (calamus and canna): calamus longer than canna, ornamented with strips of serrated membrane arranged obliquely around surface; canna ornamented with strips of serrated membrane. Maxilliped subchelate ( Fig. 50F ); proximal segment unarmed and with ridge-like process on myxal surface; distal subchela with apical claw separated from proximal segmental part by incomplete suture; small blunt knob present on proximal part, long seta present on concave margin.

Sternal furca ( Fig. 50G ) with short, tapering, pointed tines, separated widely at base.

First swimming leg pair ( Fig. 51A ) joined by slender intercoxal sclerite; sympod with inner and outer plumose setae derived from basis; 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 3.4 times longer than wide and armed with small outer (anterior) spine and ornamented with row of setules along middle section of posterior margin; second segment armed with 3 long plumose setae along posterior margin and 4 distal elements along oblique distal margin. Distal elements as follows: spine 1 minute (arrowed in Fig. 51A ); spine 2 longer than spine 3, each with accessory process; seta 4 longer than spines 1 and 2, and markedly longer 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. 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 segments 1 and 2 ( Fig. 51B ) each with large reflexed outer spines (ornamented with strips of membrane), extending obliquely across ventral surface of ramus, plus inner plumose seta; first exopodal segment bearing flap of membrane anteriorly, reflexed back over dorsal surface; segment 3 with 2 outer spines (proximal spine minute; distal spine with membrane bilaterally); 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 first, second and third endopodal segments ornamented with fine setules ( Fig. 51C ).

Third leg pair ( Fig. 51D ) 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; long sensillae located adjacent to inner coxal seta and adjacent to origin of endopod. Exopod 3-segmented; first segment lacking inner seta, armed with weakly curved outer spine directed over ventral surface of ramus, spine ornamented with inner strip of membrane; second segment with small outer spine and inner plumose seta; third with 3 unequal outer spines and 4 inner plumose setae; outer margins of segment 2 ornamented with row of slender setules. Endopod 2-segmented; first segment forming flap-like velum ornamented with row of fine setules along free margin, armed with inner plumose seta; second with 6 setal elements increasing in length from outermost to innermost.

Fourth leg ( Fig. 51E ) 3-segmented, comprising slender protopodal segment and 2-segmented exopod: protopodal segment armed with plumose seta distally; first exopodal segment armed with slender outer spine; second with 1 lateral spine plus 3 distal spines; apical spine more than twice length of middle spine; middle spine about 1.4 times longer than shortest spine; each spine with pecten at base.

Fifth legs located posterolaterally on genital complex ( Fig. 50B ); each fifth leg comprising anterior process bearing short plumose seta (representing outer protopodal seta) and broader exopodal process armed with 2 plumose setae.

Adult male ( Fig. 52A ) body length including caudal rami 3.96 mm. Cephalothorax as in female. Genital complex 1.42 times wider than long (0.85 x 0.66 mm), measured along mid-line; with evenly convex lateral margins. Abdomen 1-segmented; about as long as wide (0.36 x 0.36 mm); carrying paired caudal rami distally; anal slit terminal. Caudal rami as in female.

Antennule, mandible, maxillule and maxilla as in female. Antenna modified ( Fig. 52C ); first segment elongate; second segment reflexed, elongate, bearing corrugated adhesion pads proximally, in mid section of ventral surface, and distally; distal segment forming short powerful claw with shorter blade-like process and armed with 2 setae proximally. Post-antennal process ( Fig. 52D ) more strongly curved than in female; ornamented with multisensillate papillae as in female.

Maxilliped ( Fig. 52E ) with complex myxal margin on proximal segment produced into 2 spinous projections proximally, with tip of claw opposing base of longer process, plus rounded myxal process located distally on margin.

Legs 1 to 4 as in female.

Leg 5 ( Fig. 52B ) represented by process at posterolateral corner of genital complex; process weakly bifid at tip with outer point armed with plumose protopodal seta and inner papilla representing exopod bearing 2 plumose setae. Sixth leg represented by plate closing off genital opening armed with 1 seta and 2 minute spines on outer distal corner of genital operculum.

Remarks. This new species has a 2-segmented exopod on leg 4 and the distal exopodal segment carries 4 spines. It shares this form of leg 4 with about 90 congeneric species, although only 15 of them have similar body proportions in the adult female, with a genital complex (without posterolateral lobes) that is about as long as wide and about twice as long as the abdomen, which is itself about as long as wide. The species possessing this form of leg 4 and most closely matching these body proportions are: C. acanthopagri Ho, Lin & Chen, 1994 , C. asymmetricus , C. bifurcus Shen, 1958 , C. buechlerae Hewitt, 1964 , C. hobsoni Cressey, 1969 , C. ligatus Lewis, 1964 , C. longirostris , C. musaicus Cavaleiro, Santos & Ho, 2010 , C. nuenonnae , C. olsoni Pearse, 1953 , C. pectinatus Shiino, 1965 , C. priacanthi Pillai, 1961 , C. pterois Kurian, 1949 , C. similis Ho, Kim & Nagasawa, 2005 and C. xystercus Cressey, 1991 .

The most similar species in overall body shape is C. pterois , a parasite of Pterois species described from Indian coastal waters (see Pillai, 1985, who redescribed this species under its synonym, C. russellii Kurian, 1950 ). However, the new species differs from C. pterois in having a reduced spine 1 on the distal exopodal segment of leg 1 which is offset subapically on the outer margin. Caligus pterois , like the majority of these 15 species, has a well developed spine 1 which is about equal in length to spine 2. Only in the case of C. priacanthi is a similarly reduced spine 1 specifically mentioned ( Pillai, 1961), although spine 1 was not seen in C. xystercus according to Cressey (1991), Heegaard (1962) only observed a single distal spine in C. longirostris , and Cressey (1969) shows a spine missing in C. hobsoni . These latter 3 species are easily to distinguish from the new species by other characters: C. hobsoni has a bifid post-antennal process and bifid posterior process on the maxillule whereas the new species has simple processes. The male of C. longirostris has a clearly 2-segmented abdomen which is equal in length to the genital complex, unlike the 1-segmented abdomen that is shorter than the genital complex in the male of the new species. In C. xystercus the female genital complex is more than 3 times longer than the abdomen, rather than exactly twice as long as in the new species.

Despite sharing a reduced spine 1 on the tip of the exopod of leg 1 with C. priacanthi , the new species differs in numerous features. Spines 2 and 3 both lack accessory processes in C. priacanthi and are similar in length to seta 4, whereas in the new species spines 2 and 3 both have accessory processes and seta 4 is about 3 times longer than spine 2. The most obvious difference is the form of leg 4: in C. priacanthi all 4 spines on the second exopodal segment originate close together on the oblique distal margin of the segment whereas in C. pseudorhombi sp. nov., this segment is elongate and the proximalmost spine originates on the lateral margin with its tip only just reaching the distal margin. In addition, the outer margin spines on exopodal segments 1 and 2 of leg 2 are strongly dentate in C. priacanthi .

Figures

FIGURE 50. Caligus pseudorhombi sp. nov. holotype female. A, habitus, dorsal; B, left corner of genital complex showing fifth leg, ventral; C, antennule; D, antenna, post-antennal process and maxillule drawn in situ; E, tip of maxilla; F, maxilliped; G, sternalfurca.Scale bars: 1.0 mm on A, 100 µm on B, E, 200 µm on C, D, F,G.

FIGURE 51. Caligus pseudorhombi sp. nov. holotype female. A, exopod of leg, ventral view with distal spine 1 arrowed; B, exopod of leg 2; C, endopod of leg 2; D, leg 3, ventral; E, leg 4. Scale bars:200 µm on A–C, 500 µm on D, 250 µm on E.

FIGURE 52. Caligus pseudorhombi sp. nov. allotype male. A, habitus, dorsal; B, left corner of genital complex, ventral view showing legs 5 and 6; C, antenna; D, post-antennal process, E, maxilliped. Scale bars: 1.0 mm on A, 200 µm on B, C, 100 µm on D, 250 µm on E.