Macandrewella omorii, Ohtsuka & Nishida & Nakaguchi, 2002

Ohtsuka, Susumu, Nishida, Shuhei & Nakaguchi, Kazumitsu, 2002, Three new species of the genus Macandrewella (Copepoda: Calanoida: Scolecitrichidae) from the Paci ® c Ocean, with notes on distribution and feeding habits, Journal of Natural History 36 (5), pp. 531-564 : 545-554

Macandrewella omorii new species

(®gures 3B, C, 8K±M, 11±16)

Material examined. OOE Kume Shima Is. (23 May 1989): 24 and 30; oOE Tokashiki Shima Is. (31 May 1999): 22.

Types. HOLOTYPE: 1, appendages dissected and mounted on glass slides, body in vial, collected from oOE Kume Shima Is., 23 May 1989,

CBM-ZC 5696. PARATYPES: oOE Kume Shima Is., 23 May 1989: 1 and 1, appendages dissected and mounted on glass slides, body in vials, CBM-ZC 5697, 5698; 14 and 22, whole specimens, CBM-ZC 5699. OOE Tokashiki Shima Is., 31 May 1999: 1, appendages dissected and mounted on glass slides, body in vials, CBM- ZC 5700 ; 8, whole specimens, CBM-ZC 5701 .

Body length.: 3.32±3.54 mm (3.39 Ô 0.07 mm, n 516). (oOE Kume Shima Is., 23 May 1989): 3.38±3.62 mm (3.48 Ô 0.07, n 521); (oOE Tokashiki Shima Is., 31 May 1999): 3.53±4.05 mm (3.74 Ô 0.19 mm, n 59).

Description. Female: Body (®gure 11A) robust, similar to that of female of Macandrewella stygiana . Cuticular lens (®gure 11B) present at base of bifurcate rostrum (see ®gure 12A, arrowed). Posterior ends of prosome slightly asymmetrical, right lateral process straight, directed posteriorly and curved ventrally at tip (®gure 11D) and left lateral process directed slightly outwards, reaching beyond posterior margin of genital double-somite (®gure 11A, C). Urosome (®gure 11A, C, D) short, less than one-third length of prosome; genital double-somite covered by complex spermatophore in all specimens examined (see ®gures 11A, G, 13A, C); spermatophore proper located on right dorsolateral side (see ®gure 13C), bulbous spherical structure on left ventrolateral side (see ®gures 11A, C, G, 13A, C), dropletlike structure on right ventrolateral side (see ®gure 13A, C); genital operculum (®gure 11E) linguiform, located near ventroposterior margin, reaching nearly halfway along second urosomite (see ®gure 13B, D); seminal receptacles (®gure 11E) paired; second and third urosomites with striated posterior margin; anal somite small; caudal rami (®gure 11A) as in female of M. stygiana , but setae V almost symmetrical.

Antennule reaching to anal operculum, 23-segmented; armature elements and fusion pattern as in M. stygiana . Antenna to leg 4 resembling those of M. stygiana . Maxillule with praecoxal arthrite bearing patch of setules terminally. Maxillary endopod bearing three worm-like and ®ve brush-like sensory setae (see ®gure 12C±E). Maxilliped (®gure 11F) with syncoxa having patch of long setules proximally. DiOEerences in size and distribution pattern of prominences on surfaces between M. omorii and M. stygiana slight in legs 2 (®gure 14A, B) and 3 (®gure 14C), and remarkable in leg 4 (®gure 14D): large prominences on posterior surface of rami lacking in M. omorii . Leg 5 absent (see ®gure 12B).

Male: Body (®gures 3B, 14E, F) similar to that of M. stygiana ; diOEerences as follows: ®fth pediger asymmetrical, with right process slightly larger than left (®gure 14G, H); genital somite (®gure 15A) slightly asymmetrical; second urosomite with left side more swollen laterally than right side. Caudal rami (®gures 3C, 15A, B) symmetrical.

Both antennules (®gure 15C±F) similar to those of M. stygiana except in having the second compound segment (II±IV) relatively shorter (see ®gure 7G). Mouthparts similar to M. stygiana except for presence of patch of setules terminally on praecoxal arthrite of maxillule and patch of long setules proximally on maxillipedal syncoxa.

Distribution pattern of prominences on surfaces of legs 2±4 (®gure 8K±M) with minor diOEerences from those of M. stygiana (compare with ®gure 8C±E). Large process wanting on posterior surface of rami of leg 4, as in female.

Leg 5 (®gure 14E) large, over half as long as prosome. Right leg (®gure 15H) with protopod and endopod similar to M. stygiana except for two large contiguou s protuberances between proximal and middle swellings of endopod; exopod three-segmented, ®rst segment robust with inner thumb-like swelling proximally, second segment with inner hook-like projection originating from segmental base and triangular process at midlength, third segment Y-shaped at tip. Left leg 5 (®gure 15G, I, J) with coxa as long as basis; basis with longitudinal keel-like structure along proximal half; exopod two-segmented, second segment with acutely produced triangular process subterminally and two striated elements (see`b’ and`c’ in ®gures 15I and 16) sandwiched by two plate-like structures terminally (see`a’ and`d’ in ®gures 15I and 16); endopod unisegmented, furnished with serration almost entirely along inner margin (®gure 15J).

Variation. The number and distribution of prominences and processes on legs 2±4 more or less vary among individuals. An outer promixal-most process on the posterior surface of the second endopodal segment of leg 2 is bifurcate only on the left side in a paratype (®gure 14A, B) but uni-cuspidate on both sides of the holotype.

Remarks. The new species is similar to Macandrewella joanae Scott, 1909 and M. asymmetrica Farran, 1936 in sharing the following characters: (1) the elongate linguiform genital operculum of the female; (2) the terminal segment of the right exopod of the male leg 5 with a stout outer middle process; (3) the large subterminal outer process on the second exopodal segment of the male left leg 5. The female of M. joanae bears a distinct leg 5, whereas it is lacking in the new species and in M. asymmetrica . In addition, the symmetrical caudal setae V and only one pair of lateral processes on the prosomal ends are shared only by M. asymmetrica and the new species. The female of the new species is distinguishable from that of M. asymmetrica by: (1) the lateral processes on the prosomal ends nearly reaching or extending slightly beyond the posterior margin of the genital double-somite (reaching at most mid-length of somite in M. asymmetrica ); (2) the rostrum with paired knobs subterminally (knobs absent in M. asymmetrica ); (3) the antennule reaching the anal operculum (extending only to the posterior margin of the genital double-somite in M. asymmetrica ); (4) the presence of minute prominences on the surface of the exopod of leg 4 (prominences absent in M. asymmetrica ). Since the male of M. asymmetrica was only brie¯y described by Farran (1936) and there is no additional re-description, there are potentially minor diOEerences between these two species, as follows: (1) the inner proximal process on the second exopodal segment of the right leg 5 is directed outward in M. omorii whereas inward (folded accidentally in making preparation?) in M. asymmetrica ; (2) the inner margin of the endopod of the left leg 5 is almost entirely serrated in M. omorii while it is only serrated at the tip in M. asymmetrica .

Distribution. The new species was captured only oOE Kume Shima and Tokashiki Shima Is., southern Japan (see ®gure 21).

Feeding habits. Gut contents of three adult females and two adult males were examined with SEM. A wide variety of crustacean fragments was the remains more frequently found in the guts (®gure 17). Some fragments were identi®ed as belonging to Oncaeidae spp. (®gure 17D). Radiolarians (®gure 18) and diatoms were less frequently discovered in the guts.

Etymology. The speci®c name,`omorii ’ is dedicated to Prof. M. Omori of the Tokyo University of Fisheries.