Heterorhabdus papilliger ( Claus, 1863 )

Lee, Seok Ju, Jeong, Man-Ki, Seo, Min Ho & Soh, Jang Han Choi and Ho Young, 2021, First record of Heterorhabdus papilliger (Calanoida, Heterorhabdidae) from Korean waters based on morphological and molecular features, Journal of Species Research 10 (1), pp. 78-85 : 79-83

Heterorhabdus papilliger ( Claus, 1863) ( Figs. 2-4 )

Heterochaeta papilligera Claus, 1863, p. 182 , pl. 32, figs.

10-13, 15; Giesbrecht, 1892, p. 372, pl. 20, figs. 4, 7, 8, 10, 15, 17, 22, 23, 34-36, pl. 39, figs. 40, 53.

Heterorhabdus papilliger : Sewell, 1932, p. 300, fig. 97; Bradford-Grieve, 1999, p. 83, fig. 50; Park, 2000, p. 106, fig. 75; Mulyadi, 2004, p. 186, fig. 106.

Materials examined. ( MABIK CR00247438) one female dissected and mounted on seven slides, collected from off Jeju Island , Korea (33°25′N, 127°53′E) on 17 May, 2019; ( MABIK CR00247439 ) ; one male dissected and mounted on four slides, same locality as the above female specimen. Six additional individuals from the same locality were used for molecular analysis and length measurement. Description. Female. Body length 1.96-2.15 mm (n = 4). Prosome length 1.39-1.50 mm. Body elongate; cephalosome clearly separate from first pedigerous somite, with groove halfway along dorsal margin; anterior margin of cephalosome round in dorsal view, with tubercular rostrum in mid-anterior part; rostrum with a pair of slender filaments; fourth and fifth pedigerous somites fused ( Fig 2A, B ). Posterior margin of prosome symmetrical and broadly rounded ( Fig. 2A, B ). Urosome composed of four somites, fourth somite incompletely fused with caudal rami; genital double-somite widest at middle, smoothly inflated dorsally,greatly protruded ventrally, almost symmetrical laterally, with ratio of with width-length ratio of 80: 100; first three urosomites each with row of triangular spinules on dorsoposterior margin ( Fig. 2A- E ). Proportional lengths of four urosomites and left caudal ramus 38: 19: 15: 85: 20 (= 100). Caudal rami and anal segment indistinctly separated ( Fig. 2C, D ). Left caudal ramus extending beyond posterior end of right ramus by about 1/6 its length as measured along medial margin ( Fig. 2C ). Dorsal appendicular seta of left caudal ramus little longer than that of right caudal ramus. Fourth marginal seta of left ramus much thicker than other marginal setae and longer than body ( Fig. 2C, E ) .

Antennule reaching about posterior end of third urosomite, 25-segmented; not all aesthetes clearly distinguishable from setae ( Fig. 2J ). Segments 2-19 each with 1 middle and 2 distal setae/aesthetes ( Fig. 2J ).

Legs 1 to 4 biramous, each with 3-segmented endopod and 3-segmented exopod; with inner marginal seta at coxa ( Fig. 3A- D ). Basis of leg 1 with inner marginal seta, have small hooklike process on outer margin ( Fig. 3A ). Basis of leg 2 to 4 without seta ( Fig. 3B- D ). Setae and spine formula of leg 1 to 4 as follows (spines, Roman numerals; setae, Arabic numerals):

Leg 5 symmetrical; basipod, endopod, third exopodal segment, and inner spine of second exopodal segment similar in length ( Fig. 3E ). Endopod extending beyond distal end of second exopodal segment. Distolateral cor- ners of first and second endopodal segments pointed; inner marginal setae provided with long setules for proximal halves and short setules for distal halves ( Fig. 3E ). Outer spines of exopod relatively small, all pointing in a distolateral direction.

Male. Body length 1.96-2.00 mm (n = 2). Prosome length 1.38-1.42 mm. Similar in habitus to female except urosome. Urosome 5-segmented; first to fourth urosomites each with row of triangular spinules on dorsoposterior margin; only second urosomite with row of triangular spinules on posterior margin in ventral side ( Fig. 4A- D ). Leg 1 to 4 similar to female.

Left antennule geniculate, reaching about half of urosome; first two segments fused, segments 19 to 21 fused, segments 22 and 23 fused ( Fig. 4E ).

Leg 5 asymmetrical ( Fig. 4F ). Inner lobe of right basis relatively narrow, slightly shorter than 1/2 length segment. Inner lobe of left basis low but clearly distinguishable, and distally produced into short process. In right exopod, medial projection of second segment with large, rounded proximal lobe and without distinguishable distal lobe; whole distal margin of medial projection smoothly curved and merged into relatively large terminal spiniform process ( Fig. 4G ); outer spine of second segment relatively long and arising close to distal end of segment. Third segment of right exopod smoothly curved, about as long as combined lengths of first 2 segments; its outer spine small, located distal to midpoint of segment; terminal spine about 1/6 length of segment, and terminal lobe about 2/5 length of terminal spine ( Fig. 4G ). In left exopod, second segment with large lateral conical process terminating with small outer spine; outer spine about 2/3 length of conical process ( Fig. 4F ). Third segment of left exopod tapering distally into rather spiniform process, with small outer and long inner spine ( Fig. 4F ).

Distribution. Heterorhabdus papilliger from Korean waters was mainly collected at a depth of 75 m of the Tsushima Warm Current off Jeju Island, Korea with water temperature and salinity of about 17.1℃ and 34.6 psu, respectively. All specimens obtained were adults.

Remarks. The Korean specimens agree well with the original description and former records of Heterorhabdus papilliger by Park (1968, 2000): the genital double somite of H. papilliger females having in lateral view a more or less rounded genital prominence and an uninflated posterior ventral margin; the second exopodal segment of male right leg 5 with the medial projection with a large, rounded, plumose proximal lobe, and a poorly developed distal lobe ( Park, 2000). Additionally, we found some minor morphological features in the examined Korean specimens that were not mentioned in previous records of H. papilliger . The number of spinules on the posterior margin of each urosomite found from the dorsolateral side varied from 5 to 10 depending on the individual ( Fig. 2F- I ; Fig. 4C ). In all examined male specimens (n = 3), these marginal spinules were also present on the ventral side of the second urosomite ( Fig. 4D ), but the ventral spinules were not found on any urosomites of the female specimens ( Fig. 2E ). In spite of these morphological differences, the genetic difference for the partial mtCOI gene between Korean specimens (MW094036 and MW094037) and H. papilliger from Spain and Japan is only 0.4%, while the difference between Korean specimens is 0.5% ( Table 1; Fig. 5 ). However, the interspecific difference between H. papilliger from the Korean waters and the other six Heterorhabdus species was in the range of 14.7-20.8% ( Table 1) and similar between calanoid copepods ( Soh et al., 2012; Jeong et al., 2014). Therefore, the morphological and molecular comparison results support the occurrence of H. papilliger from Korean waters.

Figures

Fig. 2. Heterorhabdus papilliger, Female. A. habitus, dorsal; B. habitus, right lateral; C. urosome, dorsal; D. urosome, left lateral; E. uro- some, ventral; F. genital somite from different specimen, left lateral; G. genital somite from different specimen, dorsal; H. genital somite from different specimen, right lateral; I. genital somite from different specimen, dorsal; J. antennule.

Fig. 3. Heterorhabdus papilliger, Female.A. leg 1; B. leg 2; C. leg 3; D. leg 4; E. leg 5.

Fig. 4. Heterorhabdus papilliger, Male.A. habitus, dorsal; B. habitus, right lateral; C. urosome, dorsal; D. urosome, ventral; E. antennule; F. leg 5 (anterior); G. exopod of left leg 5 (left one: anterior, right one: posterior).

Fig. 5. Molecular phylogenetic analysis by the neighbor-joining method (Kimura 2-parameter model). Numbers in parentheses indicate GenBank accession number. Numbers at branch points indicate bootstrap values (1000 replicates).