Holotype. Japan • adult ♂; Ashibe Port, Iki Island, Nagasaki Prefecture (33°48.544'N, 129°45.231'E); night, May 24, 2014; partly dissected and mounted on 1 slide, body in vial (NSMT-Cr 26753); S. Ohtsuka leg.

Male. Body 4.02 mm long. Cephalothorax (Fig. 1A) slightly longer than wide. Pediger 4 (Fig. 1A, B) incompletely fused to genital complex. Genital complex (Fig. 1A, B) about 1.1 times wider than long, about 1.2 times longer than abdominal somites combined, produced posterolaterally into 2 knobs representing leg 5 (Fig. 1C), armed with 1 and 2 setae. Paired genital opercula (Fig. 1C) representing leg 6, each bearing 2 minute unequal setae terminally. Abdomen 2-segmented, second somite ca. 1.7 times longer than first. Caudal ramus (Fig. 1B) furnished with row of fine setules along inner margin; setae II and III located close together subterminally; setae IV–VI well developed; seta VII minute, located at inner distal corner.

Figure 1. 

Caligus chinglonglini sp. nov., adult male, holotype A habitus, dorsal view B postcephalothoracic trunk, dorsal view C leg 5 and gonopore on right side, ventral view D antennule, ventral view E antenna F postantennal process G mandible H maxillule I maxilla J maxilliped K middle process on myxal margin of maxilliped corpus L distal process on myxal margin of maxilliped corpus M subchela of maxilliped N sternal furca.

Antennule (Fig. 1D) 2-segmented; proximal segment with 26 setae, distal segment with 11 setae and 2 aesthetascs. Antenna (Fig. 1E) 3-segmented; proximal segment unarmed, with adhesion pad distally; middle segment massive, unarmed, with 2 adhesion pads at mid-length and 1 pad terminally; distal segment small, multi-layered flap with 2 small setae proximally. Postantennal process (Fig. 1F) moderately curved, with 2 bisensillate papillae proximally plus bisensillate papilla on adjacent ventral cephalothoracic surface. Mandible (Fig. 1G) with 11 teeth on margin subterminally. Maxillule (Fig. 1H) represented by anterior papilla with 1 thick and 2 fine setae and posterior dentiform process with rounded prominence subterminally. Maxilla (Fig. 1I) 2-segmented, lacertus (syncoxa) unarmed, brachium (basis) slender, with large hyaline membrane at terminal third, plus long calamus and short cana apically. Maxilliped (Figs 1J–M, 3B) heavily chitinized, 2-segmented; corpus (protopod) massive, with 3 unequal processes along myxal margin, proximal process low, middle process with multiple tips, distal process largest, with irregular, undulating distal margin; shaft (endopod) as long as and incompletely fused to claw to form subchela; barbel located on rounded inner basal process of claw. Sternal furca (Fig. 1N) with divergent tines originating close together, rounded at tip.

Armature and elements of legs 1–4 as in Table 1. Leg 1 (Fig. 2A) with massive protopod bearing 1 inner and 1 outer small plumose setae plus bifid setule on outer margin; intercoxal sclerite slender, unornamented; endopod reduced to club-shaped process located near base of exopod; exopod 2-segmented, first segment with row of fine setules along inner margin and 1 naked seta at outer distal corner, second segment with 3 large plumose setae along inner (posterior) margin and 4 elements terminally, middle two of which each bearing accessory process. Leg 2 (Fig. 2B–D) with intercoxal sclerite ornamented with trapezoidal marginal membrane along posterior margin; coxa with large plumose seta at posterior corner and minute setule on anterior surface; basis ornamented with marginal membrane on both inner and outer edges, bearing 1 minute seta on knob at outer distal corner (Fig. 2C) plus setule near midpoint of inner margin; endopod 3-segmented, outer margins of second and third segments with dense patches of minute setules; exopod 3-segmented, first segment with long outer spine directed obliquely across surface of second segment, second segment with relatively short outer spine, third segment with small outer knob (arrowed in Fig. 2D), 1 reduced outer spine, 1 short terminal spine and 5 plumose setae increasing in size from apical to innermost. Leg 3 (Fig. 2E–G) apron (protopod) without surface processes, bearing well developed inner seta and 1 minute outer seta, plus 2 relatively long setules along posterior margin; outer basal margin of apron undulating; endopod 2-segmented, proximal segment small, with 1 long plumose seta; velum developed, hirsute along free posterior margin; second segment expanded along outer margin (Fig. 2F); exopod 3-segmented (Fig. 2G), proximal segment small, with slightly curved outer spine not reaching distal border of next segment, middle segment with 1 inner plumose and 1 outer naked seta, third segment with 3 spiniform setae increasing in size distally plus 4 inner setae.

Figure 2. 

Caligus chinglonglini sp. nov., adult male, holotype A leg 1 B leg 2 C outer seta on basis of leg 2 D terminal part of exopod of leg 2, outer knob on segment 3 arrowed E leg 3 F endopod of leg 3 G exopod of leg 3 H leg 4 I terminal processes of leg 4.

Leg 4 (Figs 2H, I, 3A) with protopod bearing low outer prominence at mid-length and minute plumose seta at outer distal corner; exopod distinctly 2-segmented, first exopodal segment with long outer spine almost fused basally to segment and reaching more than half distance to origin of proximalmost outer spine on compound second segment; second segment with 1 terminal and 2 slender spines on distal margin plus lateral spine, plus 2 bifurcate processes terminally; each process complex, with 1 or 3 minute prominences basally (Fig. 2I).

Leg 5 (Fig. 1C) represented by 2 small knobs, outer knob bearing protopodal seta, inner knob representing exopod, bearing 2 plumose setae terminally. Leg 6 (Fig. 1C) consisting of genital operculum, bearing 2 terminal minute setae.

Female. Unknown.

The new species is most closely related to C. acanthopagri Ho, Lin & Chen, 1994, C. dieuzeidei sensu Shiino (1954b), and C. latigenitalis Shiino, 1954 in general appearance and in the structure of the appendages and sternal furca. As Izawa and Choi (2000) and Ho and Lin (2004b) suggested, the minor but most distinct difference can be found in the structure of the pectens of the second exopod segment of leg 4 among these three species. Those of C. chinglonglini sp. nov., C. dieuzeidei sensu Shiino (1954b) (see Discussion), and C. latigenitalis are sharply indented, whereas that of C. acanthopagri is composed of a hyaline membrane. The former three species can be distinguished by the number and shape of dentate processes (divided into 3 or 5 prominences but not hand-like in C. chinglonglini; 3 or 4 and hand-like in C. dieuzeidei sensu Shiino; 4 or 5 and hand-like in C. latigenitalis). In addition, the shape and numbers of processes of the maxillipedal myxal area differ among the males of these three species. In C. chinglonglini sp. nov. and C. latigenitalis, there are 3 processes arrayed along the myxal margin, but the middle process is furnished with serrated tips in the former but is rounded in the latter. In C. dieuzeidei sensu Shiino (1954b), there are only two processes, one quadrangular and the other low triangular, present along the margin.

Although the present new species is described on the basis of a single male, no other species belonging to the newly proposed pseudorhombi species group (see Discussion) has so far been recorded from Japanese waters except for C. latigenitalis (Nagasawa et al. 2010) in which only females were originally described by Shiino (1954a) and subsequently both sexes were redescribed in detail by Izawa and Choi (2000). These two species are distinguishable as mentioned above. In addition, C. bifurcus Shen, 1958, assigned to the same species group was described from Chinese waters based only on two females, but the non-sexually dimorphic characteristics such as sternal furca and legs differ distinctly from those of C. chinglonglini sp. nov. Therefore, the establishment of the present new species is justified.

The new species is the fourth species of Caligus found exclusively from plankton samples in Japan (see Venmathi Maran et al. 2016, table 2).

Peritrich ciliates were attached along the posterior margin of both maxillipeds (Fig. 3B, C) and on the ventral side of the cephalothorax. Epibiont suctorian and peritrich ciliates have already been recorded from species of Caligus and Lepeophtheirus von Nordmann, 1832 (Stone and Bruno 1989; Gresty and Warren 1993; Fernandez-Leborans et al. 2005). In L. salmonis (Krøyer, 1837) collected from Hokkaido, Japan, the peritrich Epistylis sp. attached mainly to the antennae and legs 2 and 3. This is the first record of the occurrence of epibiont peritrich ciliates on “pelagic caligids” (Ho and Lin 2004a; Venmathi Maran and Ohtsuka 2008; Venmathi Maran et al. 2012a, b, 2016).

Figure 3. 

Caligus chinglonglini sp. nov., adult male, holotype A terminal part of leg 4, bifurcate processes arrowed B colony of peritrich ciliates attached along posterior margin of maxilliped corpus C peritrich ciliates attached on posterior margin of maxilliped corpus. Scale bars: in mm.

The new species is named in honor of the late Dr Ching-long Lin who made a great contribution to the taxonomy of parasitic copepods together with Prof. Ju-shey Ho.

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.

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.

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.

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.

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. 5A–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. 5F–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.

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.

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.

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.

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.

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).

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