Notoxynus tertius, Kim, 2000

Kim, Il-Hoi, 2000, Poecilostomatoid Copepods from an Intertidal Mud Flat in the Yellow Sea, Journal of Natural History 34 (3), pp. 367-432 : 428-431

Notoxynus tertius n. sp.

( Figures 38 , 39 )

Material examined. Four mm, three lland one copepodid V m from the gastrovascular cavity of the mud-inhabiting sea anemone, Cerianthus ®liformis Carlgren, collected in the intertidal mud ¯at at Jakyak-do Island o Inchon, on 28 September 1996. Holotype (m), allotype (l), and three paratypes (two mm, one l) have been deposited in the US National Museum of Natural History , Smithsonian Institution. Dissected specimens (one adult pair and one copepodid V m) are kept in the collection of the author.

Female. Body (®gure 38A) narrow, almost cylindrical, stocky, 2.39 mm long, with very thin exoskeleton. Greatest width 0.61 mm. Prosome ®ve-segmented, with faint suture line between cephalosome and ®rst pedigerous somite. Epimera of prosomal somites weakly developed. Urosome (®gure 38B) ®ve-segmented, tapering, with weak segmentation. Fifth pedigerous somite distinctly wider than genital double-somite, 358 mm wide. Genital double-somite 375Ö 296 mm (1.27:1). Genital area small, located dorsolaterally at anterior third of lateral margin. Three abdominal somites 129Ö212, 79Ö188, and 96Ö 179 mm, respectively. Posteroventral border of anal somite with minute spinules. Caudal ramus 137Ö 71 mm (1.93:1), with distinctly convex inner margin and several minute spinules on terminal margin. Caudal setae relatively short and naked. Outer lateral seta located at midlength of outer margin of caudal ramus.

Rostrum semicircular and much wider than long. Antennule (®gure 38C) 487 mm long and seven-segmented. Armature formula 4, 13, 6, 3, 4 +1 aesthetasc, 2 +1 aesthetasc, and 7 +1 aesthetasc. Setae thin and naked. Antenna (®gure 38D) foursegmented, with armature formula 1, 1, 3, 6 +1 claw. Third segment very short. Terminal segment about 77Ö 34 mm (2.26:1), weakly curved. Terminal claw strongly curved. One of terminal setae very large, distinctly longer than terminal segment.

Labrum (®gure 38E) deeply incised, with unornamented, weakly tapering lobes. Mandible (®gure 38F) with broad proximal notch. Terminal lash long and spinulated. Inner margin oblique to lash, with a row of setules. Maxillule (®gure 38G) a slender lobe, with two terminal, subequal setae (in copepodid V, number of these setae being three). Maxilla (®gure 38H) two-segmented. First segment unarmed. Second segment terminating in moderately long lash bearing spinules on convex margin, with one minute outer seta, one naked seta on anterior surface, and one relatively small, distally spinulated seta on concave margin. Maxilliped (®gure 38I) three-segmented. First segment unarmed and slightly longer than wide. Second segment with two simple, unequal setae on inner margin. Terminal segment blunt, tapering, with small, blunt terminal process, one small spine and one small seta.

Leg 1 (®gure 39A), leg 2 (®gure 39B), and leg 3 with three-segmented rami. Leg 4 (®gure 39D) with three-segmented exopod and two-segmented endopod. Hairs on setae and segments sti and relatively thick. Second endopodal segment of leg 4 tapering, with two minute spiniform processes on outer margin; terminal two spines very unequal, inner one of which about twice as long as outer one. Armature formula of legs 1±4 as follows:

Leg 5 (®gure 39E) composed of one naked seta on ®fth pedigerous and free segment. Free segment distinctly tapering, 142Ö 54 mm (2.63:1), with minute spinules on surface and two naked terminal setae (outer one 110 mm, and inner one 83 mm). Leg 6 represented by two spinules in genital area.

Male. Body (®gure 39F) resembling that of female. Length 1.96 mm. Greatest width 258 mm. Urosome six-segmented, with incomplete segmentation between ®fth pedigerous somite and genital somite. Genital somite distally broadened (®gure 39G), 292Ö 296 mm. Four abdominal somites 120Ö196, 96 Ö171, 54 Ö156, and 71Ö 154 mm, respectively. Caudal ramus 113Ö 56 mm (2.02:1).

Antennule with armature formula identical to that of female. Antenna with spinules on outer margin of second segment.

Maxilliped (®gure 39H) consisting of three segments and terminal claw. First segment unarmed and longest. Second segment with longitudinal row of spinules and two identical setae on inner side. Third segment unarmed. Claw evenly curved, relatively large, proximally with one setule and one seta bearing spinules distally.

Legs 1±4 with armature formula identical to that of female. Leg 5 identical in shape to that of female, 92 Ö 47 mm (1.96:1). Leg 6 represented by two thin setae and one minute spinule on genital ¯ap; the latter located at base of inner seta.

Etymology. The speci®c name is derived from the Latin tertius , meaning`third’. The new species is named as such because it is the third known species in the genus.

Remarks. Only two species of Notoxynus have been recognized: N. mundus Humes, 1975 and N. crinitus Humes, 1982 . Notoxynus tertius can be easily distinguished from these two congeners by the armature on the endopod of legs. The endopod of legs 1, 3, and 4 in the new species carries, respectively, 2 spines +4 setae (II, 4), 2 spines +2 setae (II, 2), and 2 spines +3 setae. In the two congeners, these armatures are 1 spine +5 setae (I, 5), 3 spines +2 setae (III, 2), and 2 spines +1 setae (II, 1), respectively.

In N. crinitus and N. mundus the maxillule bears three elements, but in N. tertius it bears only two setae. It is interesting to ®nd that the maxillule in the copepodid V of N. tertius bears three setae (not two as in the adult).

Figures

FIG. 38. Notoxynus tertius n. sp., female: (A) habitus, dorsal; (B) urosome, dorsal; (C) antennule; (D) antenna; (E) labrum; (F) mandible; (G) maxillule; (H) maxilla; (I) maxilliped. Scales: A, B= 0.2 mm; C= 0.1 mm; D, E, H, I =0.05 mm; F, G = 0.02 mm.

FIG. 39. Notoxynus tertius n. sp. Female: (A) leg 1; (B) leg 2; (C) third endopod segment of leg 3; (D) leg 4; (E) leg 5. Male: (F) habitus, dorsal; (G) anterior part of urosome, ventral; (H) maxilliped. Scales: A±E, H =0.05 mm; F= 0.2 mm; G = 0.1 mm.