Macrochiron anomalum, 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 : 410-414

Macrochiron anomalum n. sp.

( Figures 26 ±28)

Material examined. Two mm and ®ve llcollected from stagnant water on the intertidal mud ¯at at Jakyak-do Island o Inchon, on 29 September 1996. Holotype (m), allotype (l), and three paratypes (ll) have been deposited in the US National Museum of Natural History , Smithsonian Institution. Dissected specimens (one m and one l) are kept in the collection of the author.

Female. Body (®gure 26A) relatively narrow. Body length 1.19 mm. Greatest width 0.42 mm. Prosome occupying 61% of body length and ®ve-segmented. Urosome (®gure 26B) ®ve-segmented as well. Fifth pedigerous somite 159 mm wide. Genital double-somite 200Ö 162 mm, with anterior two-thirds expanded broadly and roundly. Posterior third slightly tapering. Genital area located dorsally in the middle of anterior broad part. Genital double- and ®rst two abdominal somites with serrate membranous fringe along posterodorsal and posteroventral margins. Three abdominal somites 63 Ö72, 45 Ö63, and 37Ö 55 mm, respectively. Anal somite with minute spinules along posterodorsal and posteroventra l margins (®gure 26C). Caudal ramus 55 Ö 22 mm (2.50:1), terminating in a duct with terminal pore at tip.

Rostrum short, wider than long, with angular posterior tip. Antennule (®gure 26D) seven-segmented, 313 mm long, with armature formula 4, 13, 4 +1 aesthetasc, 2 +1 aesthetasc, and 7 +1 aesthetasc; all setae naked. Antenna (®gure 26E) massive, three-segmented. First and second segment each much wider than long, with one inner distal seta respectively. Third segment with ten setae; three setae on inner margin broad, proximal two of them with spinulated inner margin, and remaining one with serrate inner margin; of seven terminal setae, one large, curved with serrate concave margin; remaining six setae comprising two long, thin, simple setae, one small naked seta, and three moderately thick, spiniform setae; the latter three setae with minute spinules on concave margin.

Labrum (®gure 26F) with two round, unornamented posterior lobes. Mandible (®gure 26G) with deep proximal notch; terminal lash long, thin, and well de®ned proximally; inner margin perpendicular to terminal lash, with one row of spinules; outer margin with proximal row of spinules and continued to serrate margin. Maxillule (®gure 26H) tapering, with three terminal and one subterminal setae. Maxilla (®gure 27A) two-segmented. First segment unarmed. Second segment drawn out into moderately long lash bearing serrate convex margin, with two setae, one of the latter large and spinulated on both margins. Maxilliped (®gure 27B) threesegmented. First segment longest, slightly tapering and unarmed. Second segment with spinules and two extremely unequal setae. Third segment slender and tapering, with one proximal and one distal setae.

Leg 1 (®gure 27C), leg 2 (®gure 27D) and leg 3 with three-segmented rami. Leg 4 (®gure 27E) with three-segmented exopod and one-segmented endopod. Seta on outer margin of basis of legs 1±4 small. Inner posterior corner of basis of legs 3 and 4 pointed. Endopod of leg 4 103Ö 31mm (3.32:1); inner of terminal spines more than twice as long as outer one; proximal seta on inner margin slightly longer than width of endopod; outer margin with small spinule at proximal one-third. Armature formula of legs 1±4 as follows:

Leg 5 consisting of one small seta on ®fth pedigerous somite and free segment. Free segment (®gure 27F) 131Ö 30 mm (4.37:1), tapering, with minute spinules all over surface and with one spine (61 mm) and one seta (42 mm) terminally. Leg 6 represented by three spinules in genital area.

Male. Body (®gure 28A) distinctly narrower than that of female. Length 858 mm. Segmentation between cephalosome and ®rst pedigerous somite incomplete. Urosome six-segmented. Fifth pedigerous somite 79 mm wide. Genital somite distinctly longer than wide, 123Ö 96 mm. Four abdominal somites 46 Ö48, 38 Ö44, 29 Ö41, and 31Ö 42 mm, respectively. All abdominal somites with denticulated posteroventral margin. Caudal ramus 54Ö 21 mm (2.57:1). Outer one of two median terminal setae truncate.

Antennule with three additional aesthetascs (indicated by dark dots in ®gure 26D): two on second, and one on third. All aesthetascs extending beyond distal end of antennule. Antenna (®gure 28C) with one extra seta on inner margin of third segment (thus ten setae).

Maxilliped (®gure 28D) consisting of three segments and terminal claw. First segment distinctly tapering and unarmed. Second segment with one longitudinal row of spinules and two extremely unequal setae on inner side. Claw long, slender, evenly curved, proximally with one long seta and one minute spinule. Other mouth parts as in female.

Terminal endopodal segment of leg 1 armed with two spines and four setae (II, 4; instead of I, 5 as in female). Legs 2±4 as in female. Free segment of leg 5 relatively short, 33Ö 12 mm (2.75:1), with nearly parallel margins. Leg 6 represented by two setae on genital ¯ap.

Etymology. The speci®c name anomalum alludes to the`anomalous’ armature of the endopod of leg 4.

Remarks. The new species is unusual in the extraordinary armature of the endopod of leg 4, in which there is one inner proximal seta in addition to the two terminal spines. This setation is characteristic of the Rhynchomolgidae , according to Humes and Boxshall’s (1996) recent revision of the lichomolgoid complex. However on the basis of the structure of other appendages, Macrochiron anomalum n. sp. clearly belongs to Macrochiron in the Macrochironidae . This incongruence suggests that the Macrochironidae and Rhynchomolgidae need to be rede®ned. A narrow boundary such as this between two families is also demonstrated by Telestacicola of the Rhynchomolgidae and Pseudomacrochiron of the Macrochironidae .

According to the key of Humes and Stock (1973), there are ®ve species of Macrochiron displaying an armature formula of III, I, 5 (rather than II, I, 5) on the terminal exopodal segment of leg 4 as in the new species. These are Macrochiron echinicolum Humes and Stock, 1973 ; M. lobatum Humes and De Maria, 1969 ; M. lytocarpi Humes, 1966 ; M. mutatum Stock, 1957 ; and M. sargasii Sars, 1916 . No more species with this armature formula have been added to this genus since. These ®ve species can be di erentiated from the new species by the following characteristics which are not observed in the new species.

Macrochiron echinicolum has a distally broadened free segment of leg 5; M. lobatum has a distinct lobe on the ®fth pedigerous somite near the base of leg 5 and a needle at the tip of rostrum; M. lytocarpi has a needle at the tip of rostrum, a single terminal claw on the antenna, and a genital double-somite broadened near the middle; M. mutatum has a two-segmented endopod of leg 4, a single terminal claw on the antenna, and a slender leg 5 (ratio of L/W more than 6); M. sargasii has a long, evenly narrowed leg 5 (ratio of L/W more than 7).

Figures

FIG. 26. Macrochiron anomalum n. sp., female: (A) habitus, dorsal; (B) urosome, dorsal; (C) distal part of urosome, ventral; (D) antennule; (E) antenna; (F) labrum; (G) mandible; (H) maxillule. Scales: A = 0.2 mm; B= 0.1 mm; C, F±H= 0.02 mm; D, E= 0.05 mm.