Macandrewella stygiana, 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 : 534-545

Macandrewella stygiana new species

(®gures 2, 3A, 4±7, 8A±J, 9)

Material examined. OOE Tokashiki Shima Is., 31 May 1999: 8 and 17. Types. HOLOTYPE: 1, appendages dissected and mounted on glass slides, body in vial, CBM-ZC 5691. PARATYPES: 1 and 2, appendages dissected and mounted on glass slides, body in vials, CBM-ZC 5692±5694; 2 and 4, whole specimens, CBM-ZC 5695.

Body length.: 3.23±3.84 mm (mean Ô SD 53.45 Ô 0.26 mm, n 56).: 3.25± 3.81 mm (3.55 Ô 0.21, n 56).

Description. Female: Body (®gure 2A) robust. Cephalosome completely fused to ®rst pediger, protruding anteroventrally into bifurcate rostrum; rostrum (®gure 2B, C) with pair of slender ®laments; single median cuticular convex lens (®gure 2B, C) present at base of rostrum (see also ®gure 3A, arrowed). Fifth pediger almost fused with preceding somite, with suture visible dorsally and ventrolaterally; posterior margin (®gure 2A, D±G, H, I) asymmetrical, with two pairs of processes, dorsolateral projections lamellar, with serrate margin, ventrolateral processes curved ventromedially at tip, nearly reaching posterior end of genital double-somite; right ventrolateral margin produced medially into round lobe partially covering leg 5 (®gure 2I; see also ®gure 4A).

Urosome (®gure 2H, I) short, approximately one-®fth as long as prosome; genital double-somite over half length of urosome. Genital double-somite asymmetrical, with anterodorsal swelling on left side (®gure 2H) and posterodorsal protrusion on right side (®gure 2H); genital area covered by attachment disc of simple sausagelike spermatophore (compare with ®gure 11A, C, D, G in M. omorii ) in some paratypes (®gure 2I); single genital operculum located midway. Second and third urosomites with striated posterior margin; fourth urosomite (anal somite) almost telescoped into preceding somite. Caudal rami (®gure 2A, H) almost symmetrical except for setae V in which left seta is much longer and thicker than right seta; seta

I minute; seta II located dorsally near base of seta IV; seta VII originating from inner ventrolateral side, bent outward.

Antennule (®gure 5A, B) consisting of 23 free segments, reaching nearly to prosomal end. Fusion pattern and armature elements as follows: I-3, II-IV-61 ae (II-2, III-21 ae, IV-2; one seta on IV missing in ®gure 5A), V-21 ae (one seta missing), VI-2, VII-21 ae (two setae missing), VIII-2, IX-21 ae, X±XII-41 ae, XIII- 1, XIV-21 ae, XV-1 (missing), XVI-21 ae, XVII-1 (missing), XVIII-1 (missing), XIX-1, XX-2, XXI-11 ae, XXII-1, XXIII-1, XXIV-11 1, XXV-11 1, XXVI-11 1, XXVII±XXVIII-51 ae (including two rudimentary setae). Distal seta on tenth segment spiniform; two anterior setae on terminal segment vestigial. Antenna

(®gure 5C, D) with coxa bearing plumose inner seta and outer row of setules; basis with two inner setae of unequal length; endopod two-segmented, proximal segment bearing two setae subterminally and patch of ®ne setules terminally, distal segment with eight setae (one missing in ®gure 5C) on middle lobe and seven setae on terminal lobe; exopod indistinctly seven-segmented, setal formula 0,1,1,1,1,1,11 3. Mandible (®gure 5E, F) with heavily sclerotized gnathobase bearing spinulose seta and eight teeth, ®ve of which are ¯attened with broad edge, and others with minute, acutely pointed prominences at tip; basis bearing two spinulose inner setae; endopod two-segmented, proximal segment with two setae, distal segment with nine setae and patch of ®ne spinules; exopod ®ve-segmented, setal formula 1,1,1,1,2.

Maxillule (®gure 5G) with elongate praecoxal arthrite bearing one minute, seven sclerotized spiniform, two hirsute and three serrate setae; coxal endite with two setae; coxal epipodite bearing nine setae (one missing in ®gure 5G); basis completely fused with endopod; ®rst and second basal endites bearing three and ®ve setae, respectively; baseoendopod with seven setae terminally; exopod lobate, bearing eight setae and patch of ®ne setules along outer margin. Maxilla (®gure 5H, I) compact; ®rst praecoxal endite bearing four setae plus rudimentary element; second praecoxal to second coxal endites each with three setae and patch of ®ne spinules; basis furnished with two worm-like sensory, one spinulose and one heavily sclerotized seta; endopod (®gure 5I) indistinctly three-segmented, ®rst to third segments bearing three brush-like, two brush-like and three worm-like sensory setae, respectively. Maxilliped (®gure 5J) elongate; syncoxa with two worm-like sensory setae proximally and single brush-like sensory seta at mid-length; other four setae disposed as ®gured. Basis as long as syncoxa, with submarginal row of minute spinules and three setae along inner margin; ®rst endopodal segment almost incorporated into basis, with two setae; setal formula of second to sixth endopodal segments 4,4,3,31 1,4.

Seta and spine formula of legs 1±4 as shown in table 2. Leg 1 (®gure 6A±C) with uni-segmented endopod and three-segmented exopod; endopod bearing middle outer knob with patch of minute spinules, and patch of ®ne setules terminally (®gure 6B); ®rst exopodal segment with inner margin expanded (®gure 6C); ®rst and second exopodal segments each with naked outer spine; third exopodal segment bearing serrate outer spine and spiniform terminal seta. Leg 2 (®gure 6D, E) with twosegmented endopod and three-segmented exopod; coxa and basis each with sharply pointed prominence on lamellar outer margin; ®rst endopodal segment without prominences, second segment with one anterior and six posterior acute prominences; second exopodal segment with posterior row of prominences, third segment with two posterior patches of prominences. Leg 3 (®gure 6F±H) with three-segmented rami; inner distal corner of basis produced into pointed process; second and third endopodal segments with one minute anterior and four posterior prominences (®gure 6H); second exopodal segment bearing posterior row of prominences along distal margin, third segment with minute prominences on posterior surface. Leg 4 (®gure 6I, J) with three-segmented rami; coxal outer margin bearing proximally directed process; second and third exopodal segments with longitudinal row of stout prominences on posterior surface.

Leg 5 of holotype (®gure 2I, J) rudimentary, two-segmented with common base; second segment of left leg separate from base; that of right leg fused to it; each segment with spine and pointed process terminally; those of paratypes variable, second segment separate from common base on both rami, variable in size, with two or three minute elements terminally (®gures 2K, L, 4A, C±E).

Male: Body (®gure 7A) more slender than female. Rostrum (®gure 7B) bifurcate, with pair of ®laments as in female; cuticular median lens present at base of rostrum as in female. Cephalosome completely coalescent with ®rst pediger; ®fth pediger fused to fourth pediger with suture visible laterally; ®fth pediger slightly asymmetrical, with right dorsolateral process directed slightly outward and left one posteriorly directed (®gure 7C±E). Urosome (®gure 7F) approximately one-third as long as prosome; genital somite asymmetrical, with two round dorsolateral and one dorsal knobs on right side; second to fourth urosomites with striated posterior margin; second urosomite slightly asymmetrical viewed dorsally; anal somite small; caudal rami symmetrical, small; caudal seta II located dorsally at base of seta III; seta VII located ventrally at base of seta VI.

Antennule (®gure 7G±I) consisting of 19 and 18 free segments on left and right side, respectively. Armature elements and fusion pattern of left antennule as follows: I-11 ae, II-IV-61 4ae (II-21 ae, III-21 2ae, IV-21 ae), V-21 2ae, VI-21 ae, VII- 21 2ae, VIII-21 ae, IX-21 2ae, X±XV-71 6ae (X-21 ae, XI-21 2ae, XII-ae, XIIIae, XIV-21 ae, XV-11 ae), XVI±XVII-31 2ae (XVI-21 ae, XVII-11 ae), XVIII- 11 ae, XIX-11 ae, XX-11 ae, XXI-11 ae, XXII-unarmed, XXIII-1, XXIV-11 1, XXV-11 11 ae, XXVI-11 1, XXVII±XXVIII-51 ae (including two rudimentary setae). Right antennule with segments XXII and XXIII completely coalescent.

Mouthparts and legs 1±4 similar to those of female except: antennary endopod with shorter seta on proximal segment more reduced than in female (®gure 7K, arrowed); antennary exopod with proximal-most seta longer than in female, reaching to exopod tip (®gure 7J, arrowed); mandible palp with distal seta on basis and proximal seta on ®rst endopodal segment shorter than those in female (®gure 7L, arrowed); maxilliped (®gure 8A, B) with basis bearing row of ®ne setules along proximal one-third; outer setae on ®fth and sixth endopodal segments thicker and longer than those in female. Terminal two endopodal segments fused, with only three terminal setae on one side (®gure 8A), which is considered to be aberrant, but separate, with 31 1 and four setae on ®fth and sixth segments on other side (®gure 8B). Distribution of prominences on surfaces of legs similar to those in female except for lack of large prominences on posterior surface of leg 4 (®gure 8C±E).

Leg 5 elongate, about half length of prosome (®gure 7A). Right leg (®gure 8G) chelate; coxa with triangular swelling proximally; basis expanded laterally; ®rst exopodal segment with three processes along inner margin, proximal directed distally, middle irregular and distal triangular; second exopodal segment short, with three protuberances along inner margin, proximal process largest, truncate at tip; third exopodal segment lamellar, as long as preceding segment, curved inward distally; endopod uni-segmented, smoothly curved outward and recurved at tip, bearing one large proximal and one short middle process along outer margin. Left leg 5 (®gure 8F, H±J) with coxa as long as basis; basis with longitudinal keel-like structure along proximal half; exopod two-segmented, second segment with lamellar plate (`a’ in ®gures 8J, 9A, B), and three elements (`b’,`c’,`d’ in ®gures 8J, 9A, B) terminally; endopod uni-segmented, shorter than exopod, bearing inner serrated margin and one small seta terminally.

Variation. The dorsolateral projections of the ®fth pediger of the female more or less vary in shape, size and serration (®gure 2D±G). The ®fth leg of the female is also variable in fusion between the ®rst and the second segments, the size of the second segment, and the number and development of elements on the second segment (®gure 2J, K, L). The terminal serration on the left endopod of the male leg 5 also varies (®gure 8H, I).

Remarks. The new species is closely related to Macandrewella cochinensis Gopalakrishnan, 1973 from oOE Cochin, Indian Ocean, on the basis of the structure of the male leg 5. However, it is readily distinguishable from the latter in the following characters: (1) the dorsolateral processes on the prosomal ends of the female are serrated along the margin in M. stygiana (smooth in M. cochinensis ); (2) the right ventrolateral process of the prosomal end of the female reaches nearly to the posterior margin of the genital double-somite in M. stygiana (only to midlength of the compound somite in M. cochinensis ); (3) the female leg 5 is present in M. stygiana (absent in M. cochinensis ); (4) the outer middle process of the right endopod of the male leg 5 is smaller in M. stygiana than in M. cochinensis ; (5) the inner distal process of the penultimate exopodal segment of the male right leg 5 is present in M. stygiana (absent in M. cochinensis ); (6) the distal exopodal segment of the male right leg 5 is relatively larger in M. stygiana than in M. cochinensis , compared with the inner proximal process of its penultimate segment.

The female of the present new species is also similar to that of M. joanae , but distinguished from it by: (1) the ventrolateral processes of the prosomal end reaching nearly to the posterior margin of the genital double-somite; (2) the absence of a linguiform genital operculum; (3) elements on the terminal segment of leg 5 are variable, but tend to become more reduced than in M. joanae .

Distribution. The new species is so far known only from oOE Tokashiki Shima Is., southern Japan (see ®gure 21).

Feeding habits. Gut contents of three adult males were examined with SEM.

Small crustacean, mainly copepod, fragments were most frequently detected. Some fragments were evidently identi®ed as Oncaeidae and calanoids (®gure 10A, B). Tintinnids (®gure 10C), radiolarians (®gure 10D) and diatoms (®gure 10E) were less frequently found in the guts.

Etymology. The speci®c name, stygiana (Latin stygianus, meaning underworld) alludes to the hyperbenthic habitat of the new species.