Caligus kajii, Ohtsuka, Susumu & Boxshall, Geoffrey A., 2019

Ohtsuka, Susumu & Boxshall, Geoffrey A., 2019, Two new species of the genus Caligus (Crustacea, Copepoda, Siphonostomatoida) from the Sea of Japan, with a note on the establishment of a new species group, ZooKeys 893, pp. 91-113 : 91

Caligus kajii sp. nov. Figs 4 , 5 , 6 , Table 2

Material examined.

JAPAN • 38 adult ♀♀ and 14 adult ♂♂; parasitic on body surface of Platycephalus sp. (total length 58 cm) collected from a depth of 15 m off Shimonoseki, Yamaguchi Prefecture (34°00.686'N, 130°53.756'E); morning of August 24, 2016; S. Ohtsuka leg.

Types.

Holotype. JAPAN •1 ovigerous adult ♀; parasitic on body surface of Platycephalus sp. (total length 58 cm) collected from a depth of 15 m off Shimonoseki, Yamaguchi Prefecture (34°00.686'N, 130°53.756'E); morning of August 24, 2016; whole specimen (NSMT-Cr 26754); S. Ohtsuka leg. Allotype. JAPAN•1 adult ♂, same data as in holotype; partly dissected on 1 slide, body in vial (NSMT-Cr 26755); S. Ohtsuka leg. Paratypes. JAPAN•1♀, same data as in holotype; partly dissected and bodies in vials (NSMT-Cr 26756); 36♀♀ and 13♂♂, same data as in holotype; whole specimens (NSMT-Cr 26757); S. Ohtsuka leg.

Description.

Female. Body length of holotype 6.16 mm, 4.86-6.16 mm in holotype and female paratypes (mean ± standard deviation = 5.49 ± 0.32 mm, N = 38). Dorsal cephalothoracic shield subcircular, almost as long as wide ( Fig. 4A ). Lunules ( Fig. 4A ) relatively small. Pediger 4 almost completely fused to genital complex. Genital complex ( Fig. 4A ) subquadrate, about 1.14 times longer than wide, produced posteroventrally into pair of rounded processes between which paired copulatory pores located ( Fig. 4B ). Spermatophores ( Fig. 4B ) attached to copulatory pores via fine tubules; spermatophore proper globular, ca. 0.12 mm in diameter. Paired egg strings of holotype female containing 22 and 24 eggs. Abdomen ( Fig. 4A, B ) 1-segmented, about as long as wide. Caudal ramus ( Fig. 4A, B ) furnished with rows of setules along inner and outer margins; seta II minute, located near base of seta III on subterminal ventral surface, seta III subterminal, setae IV-VI terminal, well developed, seta VII minute, located at inner distal corner.

Antennule ( Fig. 4C ) 2-segmented; proximal segment bearing 26 setae on anteroventral surface; distal segment with 1 subterminal and 11 terminal setae and 2 short aesthetascs. Antenna ( Fig. 4D ) 3-segmented, heavily sclerotized; proximal segment with acutely pointed posterior process; middle segment subrectangular, unarmed; distal segment abruptly curved inward at distal quarter, armed with proximal seta and minute middle seta. Postantennal process ( Fig. 4E ) as long as distal segment of antenna, smoothly curved inward, with 2 multisensillate papillae basally; similar multisensillate papilla located adjacent to base of process. Mandible ( Fig. 4F ) with distal part bearing 12 teeth. Maxillule ( Fig. 4G ) consisting of anterior papilla bearing 3 setae of unequal length and triangular, plate-like posterior process. Maxilla ( Fig. 4H ) 2-segmented, lacertus (syncoxa) unarmed; brachium (basis) ca. 1.5 times longer than lacertus, with flabellum at about anterior one-third of length; calamus about 1.5 times longer than canna. Maxilliped ( Fig. 4I ) heavily sclerotized; corpus (protopod) elongate, about 1.7 times as long as subchela, with low proximal lobe located at about 30% along myxal margin, plus minute setule in distal quarter of corpus; shaft (endopod) and claw incompletely fused; claw with antero-proximal barb reaching beyond mid-length. Sternal furca ( Fig. 4J ) with tines widely separated at base and bluntly pointed.

Armature and elements of legs 1-4 as in Table 2 . Leg 1 ( Fig. 5 A–C ) with protopod bearing 1 marginal bifurcate setule and 2 surface setae; endopod reduced to small knob with vestigial element at tip ( Fig. 5B ); exopod 2-segmented, proximal segment with row of setules along inner margin and outer distal seta, distal segment with 3 plumose setae along inner margin and 1 naked outer spine, 2 terminal spines each with accessory process ( Fig. 5C ), plus long spinulose seta (seta 4) terminally. Leg 2 ( Fig. 5D, E ) with intercoxal sclerite bearing semi-circular marginal membrane along posterior margin; coxa with large plumose seta at posterior corner and setule on anterior surface; basis ornamented with marginal membrane along both inner and outer edges and long setule near midpoint of inner margin; armed with minute seta at distal outer corner; rami 3-segmented; first endopod segment with notch bearing tuft of setules, second segment furnished with row of setules along outer margin, third segment with tuft of setules near base of proximal outer seta; first exopod segment with anterior marginal membrane reflexed dorsally over segment surface and long, stout outer spine directed obliquely across surface of second segment; second segment with smaller outer spine than in first segment; third segment armed with 1 reduced spine (arrowed in Fig. 5E ) and 1 moderate-size outer spine. Leg 3 ( Fig. 5 F–H ) apron (protopod) with no distinct ornamentation on surface, armed with 1 long inner seta and 1 small outer seta terminally; endopod 2-segmented, proximal segment reduced, velum developed, decorated entirely with row of setules along free posterior margin; distal segment with outer margin expanded and hirsute Fig. 5G ; exopod 3-segmented, first segment with strong, slightly curved, inward-directed outer spine not reaching distal margin of second segment, second segment with expanded, hirsute outer margin and 1 minute outer seta (arrowed in Fig. 5H ), third segment with 3 small spines plus 4 inner setae.

Leg 4 ( Fig. 5I, J ) protopod slightly shorter than exopod, bearing minute plumose seta at outer distal corner; exopod 2-segmented, with pecten at base of each exopodal spine; first exopodal segment bearing spinulose spine reaching nearly half of distance to proximalmost outer spine on second segment; innermost terminal spine more than 3 times longer than middle spine. Leg 5 ( Fig. 4B ) represented by small outer knob bearing protopodal seta and inner (exopodal) knob bearing 2 setae.

Male. Body length of allotype 4.36 mm, range 4.09-5.73 mm long in allotype plus all male paratypes (4.69 ± 0.51 mm long, N = 14). Cephalothorax ( Fig. 6A ) as in female. Pediger 4 ( Fig. 6A ) separate from genital complex, wider than long. Genital complex ( Fig. 6A, B ) about 1.4 times wider than long and about 1.2 times longer than abdominal somites combined, expanded posterolaterally into 2 knobs (leg 5), outer knob bearing 1 seta, inner (exopodal) knob with 2 setae; paired genital opercula representing leg 6 ( Fig. 6B ), each bearing 1 small terminal seta. Abdomen ( Fig. 6A ) 2-segmented, first segment small, second segment ca. 4.8 times longer than first. Caudal ramus ( Fig. 6C ) as in female.

Antennule, mandible, maxillule ( Fig. 6F ) and maxilla as in female. Antenna ( Fig. 6D ) 3-segmented; proximal segment long, unarmed, with corrugated pad distally; middle segment massive, with 1 proximal, 2 middle and 2 subterminal corrugated pads; distal segment short, with 2 fine setae at mid-length, 1 bluntly pointed process terminally and 1 membranous truncate projection subterminally. Postantennal process ( Fig. 6E ) similar to that of female, but more abruptly curved inward than in female. Maxilliped ( Fig. 6G ) stouter than in female; corpus with rounded knob proximally on posterior surface (arrowhead in Fig. 6G ) and 3 distinct processes in myxal area, proximalmost process socket-like, to receive distal tip of subchela; shaft and claw partly fused, ca. 0.67 times as long as corpus; barb about half length of claw.

Remarks.

The female of the new species most closely resembles Caligus bifurcus , C. musaicus Cavaleiro, Santos & Ho, 2010, C. pectinatus Shiino, 1965, C. pseudorhombi Boxshall, 2018, C. pterois Kurian, 1949 and C. xystercus Cressey, 1991. All these species share a 2-segmented exopod on leg 4 armed with 4 spines on the distal exopodal segment, the female genital complex is nearly as long as wide and about twice as long as the abdomen, and the abdomen is about as long as wide. However, the present new species is distinguished from these species by the combination of the following characteristics: (1) the genital complex is as long as wide (cf. wider than long in C. bifurcus , C. musaicus and C. pterois ; slightly longer than wide in C. xystercus ); (2) the genital complex is about 2.1 times longer than the abdomen (cf. 1.2 times longer in C. bifurcus ; 2.2 in C. musaicus ; 2.1 in C. pseudorhombi ; 1.6 in C. pterois ; 3.6 in C. xystercus ); (3) the corpus of the maxilliped lacks processes (cf. ridge-like process present in C. pseudorhombi and C. pterois ); (4) the tines of the sternal furca taper distally (cf. uniform in width and with a truncate tip in C. pectinatus ); (5) the terminal exopod segment of leg 1 is furnished with 3 large spines terminally (2 in C. pseudorhombi ); and (6) the maxillipedal subchela is more than half the length of the corpus (cf. much shorter in C. musaicus ).

In males, the new species is most similar to C. musaicus , C. nuenonnae Andrews, Bott, Battaglene & Nowak, 2009, C. pterois , and C. priacanthi Pillai, 1962. These five species share the following characteristics: (1) the genital complex is laterally expanded and produced into 2 posterolateral protuberances representing leg 5, armed with 1 (outer lobe) and 2 setae (inner lobe); (2) the abdomen is completely or incompletely 2-segmented and shorter than the genital complex; (3) the maxillipedal corpus is well developed and carries anteriorly-produced processes on the myxal surface. However, the new species is easily distinguishable from these congeners by the combination of the following features: (1) the maxillipedal corpus has a rounded process on the posterior surface (absent in the other species); (2) the sternal furca has pointed tines which are widely separated (tines that are close at base and with rounded tips in C. priacanthi ; rounded in C. nuenonnae ); (3) the mxyal surface of the maxilliped carries 3 large, rounded processes along the margin, (cf. the processes are different in shape and number in the other species); (4) the posterior dentiform process of the maxillule lacks a surface ornamentation of minute prominences (present in C. nuenonnae ).

Etymology.

The new species is named in honor of the late, supremely talented carcinologist Tomonari Kaji who passed away in May 2019.

Figures

Figure 4. Caligus kajii sp. nov., adult female, paratype A habitus, dorsal view B posterior end of genital complex plus abdomen, ventral view C antennule D antenna E postantennal process F mandible G maxillule H maxilla I maxilliped J sternal furca.

Figure 5. Caligus kajii sp. nov., adult female, paratype A leg 1 B endopod of leg 1 C two terminal spines of second exopod segment of leg 1 D leg 2 E outer spines of terminal exopod segment of leg 2, reduced spine arrowed F leg 3 G endopod of leg 3 H exopod of leg 3 I leg 4 J terminal part of leg 4.

Figure 6. Caligus kajii sp. nov., adult male, allotype A habitus, dorsal view B gonopores, ventral view C tip of caudal ramus, dorsal view D antenna E postantennal process F maxillule G maxilliped, rounded knob on posterior surface of corpus arrowed H sternal furca I leg 4.