Anchistrotos kojimensis Do and Ho, 1983

Lee, Sue Yeon, Yoo, Jung Sun & Kim, Seung Tae, 2017, New host and first description of a male Anchistrotos kojimensis Do and Ho, 1983 (Copepoda: Cyclopoida: Taeniacanthidae) from Korean waters, Journal of Species Research 6, pp. 8-14 : 9-13

Anchistrotos kojimensis Do and Ho, 1983 ( Figs. 1-3)

Korean name: Go-ji-ma-tti-a-ga-mi-i (ŀmŔƦỌḣffiḑ)

Anchistrotos kojimensis Do and Ho, 1983, p. 1 , figs. 1-19; Dojiri and Cressey, 1987, p. 148; Suh, Shim and Choi, 1992, p. 297, fig. 4; Kim, 2014, p. 166, figs. 102-104.

Material examined. 2 adult females and 2 adult males (1 vial, NIBRIV0000293069) collected from yellowfin goby, Acanthogobius flavimanus (Temminck et Schlegel) ( Perciformes : Gobiidae ) at Gamak Bay (34°74 ʹ 72 ʺ N, 127°65 ʹ 92 ʺ E), southern Korea, 25 September 2009; 1 adult female and 1adult male (1 vial, NIBRIV0000293070) from Ernogrammus hexagrammus at intertidal mudflat in Wando Island (34°35 ʹ 71 ʺ N, 126°73 ʹ 89 ʺ E), 15 March 2013.

Diagnosis of female. Body ( Fig. 1A) 1.46 mm long (excluding caudal setae) and 0.47 mm wide. Prosome composed of broad cephalothorax (first pedigerous somite fused with cephalothorax) and progressively narrower second to fourth pedigeorus somites. Posterodorsal surface of cephalothorax with dorsal frame, sclerotised structure. Urosome ( Fig. 1B) comprised of genital somite and 4 free abdominal somites. Second to fourth pedigerous somites 462 × 213, 356 × 163 and 237 × 103 μm, respectively. Urosome comprising genital somite and 4 free abdominal somites. Genital somite 191 × 134 μm; genital apertures positioned dorsolaterally near midway of somite. Proportional length (%) of first to fourth abdominal somites 29.7: 24.4: 15.8: 30.1 = 100; first to third abdominal somites naked; distal abdominal somite with 2 transverse rows of spinules anteriorly and row of spinules near insertion of each caudal ramus. Caudal ramus ( Fig. 1B) weakly tapering, approximately 2.24 times longer (85 μm) than wide (38 μm), bearing 7 setae (seta I minute; arrowed in Fig. 1B); setae II and III with row of minute spinules at base; setae IV ornamented with medial row of bristles and lateral row of spinules; seta V (448 μm) long, with outer row of spinules only. Rostral area ( Fig. 1C) wider than long, bears inverted U-shaped, with sclerotized plates. Longest egg sac ( Fig. 1A) 648 μm long, eggs arranged in 4 rows.

Antennule ( Fig. 1C) 6-segmened, with armature formula: 5, 15, 8, 4, 2 + 1 aesthetasc, 7 + 1 aesthetasc. Antenna ( Fig. 1D, E) 3-segmented (second and third endopodal segments fused); composed of coxobasis and 2 endopodal segmentes; coxobasis with distal seta; proximal endopodal segment with inner seta; second endopodal segment bears 2 unequal pectinate processes, 3 claw-like spines and 4 unequal setae; large pectinate process with seta and several rows of spinules medially; short pectinate process with long seta and row of spinules ( Fig. 1E). Postantennal process ( Fig. 1F) stout and slightly curved.

Labrum nearly hemicircular, with fine spinules along posterior and lateral margin (not figured). Mandible ( Fig. 1G) with broad expansion proximally and 2 large and 1 small, broad, conical spines. Paragnath ( Fig. 1H) with basal patch of setules and single row of minute spinules. Maxillule ( Fig. 1I) lobate, small knob-like process posteriorly, bears 2 long and 4 short naked setae (one spiniform seta with denticles at tip); longest seta (arrow in Fig. 31) with row of minute spinules at tip. Maxilla ( Fig. 1J) 2-segmented; syncoxa with numerous pores; basis armed with spinulate terminal process and 2 subequal elements (spine with unilateral row of spinules; seta naked). Maxilliped ( Fig. 2A) 3-segmented; first (basal) segment large, irregularly-shaped, with naked seta; second segment (corpus) with 2 proximal naked setae and distomedial protrusion; terminal segment elongate, curved distally, bearing 2 subequal long (76 μm) and small (59 μm) naked setae, with approximately 19 minute spinules medially to apically and well-developed inner basal protrusion ornamented with hyaline membrane.

Leg 1 ( Fig. 2B, C) with 3-segmented exopod and 2-segmented endopod; suture incomplete between 2 distal segments of exopod. Legs 2 ( Fig. 2D, E), 3 ( Fig. 2F), and 4 ( Fig. 2G, H) with 3-segmented rami. Inner coxal seta present in legs 1-3, but absent in leg 4.

Armature formula of legs 1-4 as follows (Roman numerals = spines; Arabic numerals = setae):

Leg 1 coxa ( Fig. 2B) with long row of setules along outer border and several rows of spinules on anterior surface; basis with distal row of spinules; first exopodal segment with long outer spine (arrowed in Fig. 2C). Legs 2 ( Fig. 2D), 3 ( Fig. 2E), and 4 ( Fig. 2F, G) distal spine on endopodal segments with acute-like at tip. Terminal endopodal segment of leg 4 ( Fig. 2F) 1.94 times longer (66 μm) and wide (34 μm). Leg 5 ( Fig. 2H) well developed, 2-segmented. Protopodal segment armed with 1 dorsolateral pinnate seta and outer patch of minute spinules. Free exopodal segment 1.98 times longer than wide, 107 × 54 μm, ornamented with patched spinules distally and having row of spinules at base of each spine and distal seta and armed with 3 spinulate spines and seta.

Leg 6 (not figured) vestigial, represented by opercular plate armed with 3 naked setae at genital opening.

Diagnosis of male. Body 0.69 mm long (excluding caudal setae). Urosome ( Fig. 3B) comprised of fifth pedigerous somite, genital somite and 3 free abdominal somites. Genital somite ( Fig. 3B) 88 × 92 μm; genital apertures positioned dorsolaterally near midway of somite. Proportional length (%) of first to third abdominal somites 33.6: 23.9: 42.5 = 100; first and second abdominal somites naked; distal abdominal somite with transverse rows of stout spinules near insertion of each caudal ramus. Caudal ramus ( Fig. 3B) 2.15 times longer (43 μm) than wide (20 μm), bearing similar elements as in female. Postantennal process ( Fig. 3C) more elongate than in female. Maxilliped ( Fig. 3D) 4-segmented; syncoxa irregularly-shaped, bearing seta; basis robust, armed with 2 proximomedial setae, 2 longitudinal rows of stout denticles on posteromedial surface and row of spinules on anteromedial surface; first endopodal segment small, unarmed; second endopodal segment forming strongly curved claw, with row of stout denticles along concave margin, 2 long setae and 1 small seta. Setal formula and ornamentation of legs 15 same as in female. Leg 6 (not figured) vestigial, represented by unarmed opercular plate on posteroventral surface of genital somite.

Distribution. Anchistrotos kojimensis has been report- ed from Japan ( Do and Ho, 1983) and Korea ( Suh et al., 1992; Kim, 2014; this study).

Hosts. Anchistrotos kojimensis are parasites of Acanthogobius flavimanus (Temminck and Schlegel) , Synechogobius hasta (Temminck and Schlegel) , and Ernogrammus hexagrammus (Schlegel) .

Attachment site. Branchial cavity wall and gill filaments.

Remarks. Anchistrotos has the following major features which provide a key for females within this genus: presence or absence on the ventral surface of anal somite, the shape of rostral area, the antennule segments, the ornamentation of maxilliped and leg 2 ( Moon et al., 2015). To date, Anchistrotos kojimensis has only been found in Japan ( Do and Ho, 1983) and Korea ( Suh et al., 1992; Kim, 2015). Previously, the male had not been observed in either country. Hence, the reported male in this study is the first for this species.

The specimens examined in this study conform to the description and illustration provided by Do and Ho (1983). However, our specimens differ from Japanese specimens in the caudal ramus bears seven setae (seta I minute), the maxillule with small knob-like process anteriorly, and the leg 5 ornamented with patched spinules distally and row of spinules at base of each spine and armed with 3 spinulate spines and distal seta of our specimens.

The characteristic features of the adult female are: (1) the rostral area with a pair of horizontally directed blunt process; (2) the caudal ramus bears 7 setae; (3) the presence of two transverse rows of spinules ventrolaterally of anal somite; (4) the tip of antenna with 2 unequal pectinate processes, 3 claw-like spines and 4 unequal setae, large pectinate process with several rows of spinules, and small pectinate process with blunt seta; (5) the presence of basal patch of setules and single row of spinules on the anterior surface of paragnath; (6) the maxillule with small knob-like process anteriorly, bears 2 long and 4 short naked seta; (7) the maxilliped with 2 subequal setae and a comparatively short terminal claw; (8) the setal formula on the distal exopodal segment of leg 2 with II, I, 5; (9) the presence of row of setules on the endopodal segments of legs 2 to 4; and (10) the second segment of leg 5 with distal seta and armed with 3 spinulate spines and having row of spinules at base of each spine and distal seta.

The complete description of male is also provided in this study. This is only the fifth species of the genus with a male description after A. onosi (T. Scott, 1902) , A. zeugopteri (T. Scott, 1902) , A. lucipetus Holmes, 1985 and A. tongyeongensis Moon, Lee and Kim, 2015 . The prominent features of the adult male are: (1) the morphological characters of cephalothorax similar to that of female but more slender; (2) the prosome 4-segmented and urosome comprised of fifth pedigerous somite, genital somite and 3 free abdominal somites; (3) the second endopodal segment of maxilliped forming a long curved claw, bearing 2 inner posterior setae and 1 inner ventral seta; (4) the distal segment of maxilliped with basal tooth and row of blunt denticles along concave margin; and (5) the presence of rows of stout spinules ventrolaterally of anal somite.

A B D C

The genus Anchistrotos is host specific to marine gobiid ( Gobiidae ) and lotid ( Lotidae ) fishes ( Kabata, 1979; Dojiri and Cressey, 1987; Venmathi Maran et al., 2014; Moon et al., 2015; this study). Hitherto, this taeniacanthid was host specific to gobiid fish, since it was already reported from A. flavimanus ans S. hasta ( Do and Ho, 1983; Suh et al., 1992; Kim, 2014). In this study, we identified a new host of A. kojimensis , the stichaeid fish, E. hexagrammus .