Caligus paranengai, 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 : 98-102

Caligus paranengai sp. nov.

( Figs. 43–44 )

Type material. Holotype ♀, 8 paratype ♀♀, 2 paratype ♂♂ from Neoarius graeffei (Kner & Steindachner, 1867) (TC17881) 4 July 2016, QM Reg. Nos Holotype ♀ W53089, 4 paratype ♀♀ W53090, 1 paratype ♂ W53091; NHMUK Reg. Nos 4 paratype ♀♀, 1 paratype ♂ NHMUK 2017.296–300.

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

Site on host. body surface.

Etymology. The name refers to the close affinity between the new species and C. nengai Rangnekar, Rangnekar & Murti, 1953 .

Description. Adult female ( Fig. 43A ) mean body length including caudal rami 3.78 mm (range 3.50 to 3.96 mm), (based on 7 specimens). Cephalothorax about 1.07 times longer than wide; comprising about 50% of total body length. Free margin of thoracic portion of dorsal cephalothoracic shield extending posteriorly just beyond rear margins of lateral portions; additional posterior sutures present on surface of dorsal cephalothoracic shield. Lunules present ventrally on frontal plates. Genital complex about 1.04 times longer than wide; with linear, lateral margins and rounded corners ( Fig. 43A ). Genital complex about 4.0 times longer than abdomen. Abdomen indistinctly 2- segmented, about 1.1 times longer than wide; carrying paired caudal rami distally; anal slit terminal. Caudal rami wider than long, 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 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. 43B ) comprising proximal segment with short blunt posterior process ornamented with marginal flange; middle segment subrectangular, unarmed but with dorsal adhesion pad; terminal segment forming strongly curved claw with proximal swelling bearing stout seta, and armed with slender distal seta. Postantennal process ( Fig. 43B ) with broad base and distal marginal membrane, tine not developed; ornamented with 2 multisensillate papillae on basal part; plus single multisensillate papilla and sclerotized irregular process on adjacent ventral cephalothoracic surface.

Mandible of typical stylet-like structure, with 12 marginal teeth. Maxillule ( Fig. 43C ) comprising anterior papilla bearing 3 small naked setae and slender, tapering posterior process. Postoral process present as surface ridge ( Fig. 43C ). 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); 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. 43D ); slender proximal segment with 2 transverse ridges on surface near base; distal subchela with long inner seta.

Sternal furca ( Fig. 43E ) with weakly divergent, flanged tines.

First swimming leg pair ( Fig. 43F ) with sympods joined by slender intercoxal sclerite; sympod with inner and outer plumose setae. Vestigial endopod large and densely ornamented with hair-like setules. Exopod 2-segmented; directed laterally and forming main axis of leg; first segment robust, about 2.8 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) strongly developed, almost as long as segment and longer than other spines, ornamented with strip of striated membrane distally; spine 2 longer than spine 3, each with long accessory process and strip of striated membrane; seta 4 naked, markedly shorter than spine 3.

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 segment 1 ( Fig. 43G ) with large outer spine lying obliquely across surface of ramus, with large pecten at base, plus inner plumose seta; also bearing flap of membrane anteriorly, reflexed back over dorsal surface; segment 2 with outer spine aligned close to longitudinal axis of ramus and inner plumose seta; segment 3 with 2 outer spines, proximal spine minute and naked, distal spine stout with marginal membrane on apical side; apical spine with marginal membrane laterally and pinnules medially, plus 5 inner plumose setae. Endopodal segments 1 and 2 ( Fig. 43H ) 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. 44A ) 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. Both rami flattened and swollen. Exopod indistinctly 3-segmented; first segment markedly expanded laterally so wider than velum; armed with short and slightly curved outer claw almost reaching inner margin of ramus and ornamented with single lateral setule plus strip of membrane along elongate margin; second and third segments incompletely separated by partial suture; armed with short outer spine and inner plumose seta derived from second segment and 3 outer spiniform elements and 4 inner plumose setae (derived from third segment); proximal spine derived from third exopodal segment minute, middle spine short, distal spine long; 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, armed with inner plumose seta; second segment with expanded and setulate lateral margin, armed with 6 setal elements distally, increasing in length from outermost to innermost.

Fourth leg ( Fig. 44B ) uniramous, 4-segmented, comprising slender protopodal segment and 3-segmented exopod; protopodal segment armed with outer plumose seta; first exopodal segment broader than distal segments, armed with long outer spine and ornamented with membranous pecten at base of spine; second segment armed with outer spine; third segment short, armed with 2 large spines and minute vestigial spine along oblique distal margin; pectens on exopodal segments 2 and 3 each forming tuft of long setules close to base of spine. Spines on exopodal segments 1 and 2, and 2 distal spines on segment 3 each ornamented bilaterally with membrane.

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

Male. Body lengths 2.00 and 2.04 mm, including caudal rami. Cephalothorax subcircular as in female; additional posterior sutures present on surface of dorsal cephalothoracic shield ( Fig. 44C ) as in female. Fourth pedigerous somite incompletely fused to genital complex. Genital complex about as long as wide, measured along mid-line; with convex lateral margins in anterior part (to level of fifth legs). Abdomen 1-segmented. Caudal rami wider than long; 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 and maxilla as in female. Antenna modified ( Fig. 44D ); first segment elongate with marginal adhesion pad; second segment reflexed, wider proximally, surface ornamented with adhesion pads plus corrugated distal swelling opposing tip of claw; distal segment forming short powerful apical claw armed with 2 setae proximally plus small tooth-like accessory process. Maxillule as in female but post-oral process corrugated in male ( Fig. 44E ).

Maxilliped ( Fig. 44F ) with proximal segment more robust than in female; ornamented with transverse cuticular ridges proximally as in female, but with rounded distal process on myxal margin of proximal segment; distal subchela robust, armed with long seta and with small area of thin cuticle on claw.

Sternal furca ( Fig. 44G ) short with flattened spatulate tines, each with marginal flange.

Legs 1 to 3 as in female. Leg 4 as for female except exopodal segments 2 and 3 with normal membranous pectens ( Fig. 44H ) not tufts of spinules.

Leg 5 ( Fig. 44I ) forming paired processes located laterally on genital complex; each represented by exopodal process armed with 2 plumose setae, plus (protopodal) seta on adjacent surface. Leg 6 located posteriorly; represented by oblique operculum closing off genital aperture armed with 2 plumose setae around outer distal margin.

Remarks. This species is very closely related to C. nengai Rangnekar, Rangnekar & Murti, 1953 which was originally described on the basis of material from a marine catfish, Nemapteryx nenga (Hamilton, 1822) (as Arius nenga ), caught off Bombay, India ( Rangnekar et al., 1953). Subsequently, a mutilated female from a specimen of Tachysurus sp. caught off Trivandrum, India was described as Caligus distortus Pillai & Natarajan, 1977 ( Pillai & Natarajan, 1977). However, Ho et al. (2000) formally recognized C. distortus as a junior subjective synonym of C. nengai and provided a detailed redescription of the female based on Taiwanese material. The material from Moreton Bay is identical in many respects to the material redescribed by Ho & Lin (2004); both share a number of unusual characteristics, such as the pattern of sutures on the dorsal cephalothoracic shield, the flanged postantennal process, the hirsute endopod of leg 1, the laterally expanded first exopodal segment on leg 3, and the presence of tufts of setules replacing the pectens on the second and third exopodal segments of leg 4. Despite these similarities, there are a few important differences: the abdomen of the female is wider than long and 1-segmented in C. nengai , but longer than wide and indistinctly 2-segmented in the Australian material; there is a long slender posterior process on the antenna of female C. nengai , whereas in the new species there is a bluntly rounded posterior process ornamented with a membranous flange ( Fig. 43B ); the maxilliped of female C. nengai has 4 medial tooth-like protuberances on the proximal segment whereas in the new species there are paired transverse ridges in this position ( Fig. 43D ). These differences are sufficient to justify the establishment of a new species, C. paranengai sp. nov.

Ho & Lin (2004) mentioned and figured only 2 large spines on the distal exopodal segment of leg 4 in the Taiwanese material of C. nengai , but in the Moreton Bay females a minute third spine is present proximally in both sexes. This might be an additional difference between the species but the vestigial spine is partly concealed by the setular tuft representing the pecten in the female and could easily be overlooked.

The new species and C. nengai appear related to Caligus arii Bassett-Smith, 1898 as redescribed by Pillai (1985) since both species share the unusual leg 3, with its large lamellate rami, as well as the hirsute ornamentation of the vestigial endopod of leg 1. However, this latter character state is also present in some other caligids parasitic on catfish hosts, including Hermilius longicornis Bassett-Smith, 1898 (cf. Ho & Kim, 2000: Fig. 3J ) and Lepeophtheirus longipalpus Bassett-Smith, 1898 (cf. Pillai, 1985: Fig. 151D) and has been inferred as being due to convergence between parasites using closely related hosts.

Equally intriguing are the numerous derived character states shared with Parapetalus hirsutus (Bassett Smith, 1898c) : these include the presence of setulose tufts (rather than pectens) associated with the spines on the second and third exopodal segments of leg 4, the hirsute vestigial endopod of leg 1, the unusual pattern of sutures on the dorsal cephalothoracic shield ( Fig. 43A ), and the reduced post-antennal process. In addition, the first exopodal segment of leg 3 is transversely expanded and is ornamented with a conspicuous marginal sensilla, as in the new species. The expansion of the segment is not as extreme as in the new species and C. nengai , but this is a very unusual configuration within the Caligidae . The affinities of P. hirsutus appear to lie with C. nengai and C. paranengai sp. nov., rather than with other members of the poorly defined and heterogeneous genus Parapetalus . It is proposed here to return it to its original combination, Caligus hirsutus , as established by Bassett-Smith (1898c).

The extent of the sexual dimorphism exhibited by C. paranengai sp. nov. is unusual: the sternal furca and leg 4 both show marked sexual dimorphism, in addition to the more typically dimorphic limbs such as the antennae and maxillipeds.

Figures

FIGURE 3. Anuretes amplus sp. nov., paratype female. A. habitus, dorsal; B, antennule, ventral; C, antenna, post-antennal process, maxillule and post-oral process, drawn in situ; D, mandible; E, left maxilla and maxillary whip, drawn in situ; F, maxilliped;G, sternal furca. Scale bars:0.5 mm on A, 50 µm on B–C, E–G, 25 µm on D.

FIGURE 43. Caligus paranengai sp. nov. paratype female. A, habitus, dorsal; B, antenna and post-antennal process drawn in situ; C, maxillule and postoral process, drawn in situ; D, maxilliped; E, sternal furca; F, leg 1; G, exopod of leg 2; H, endopod of leg 2. Scale bars:1.0 mm on A, 100 µmon B,C, E, G, H, 200 µm on D, F.

FIGURE 44. Caligus paranengai sp. nov. paratype female. A, rami of leg 3, ventral; B, leg 4. Paratype male, C, habitius, dorsal; D, antenna, E, maxillule and postoral process, drawn in situ; F, maxilliped, G, sternal furca; H, exopod of leg 4; I, left side of genital complex showing legs 5 and 6. Scale bars:200 µm on A, B, 1.0 mm on C, 100 µm on D, G–I, 50 µm on E, F.