Doridicola praelongipes (Humes 1975)

Metaxymolgus praelongipes

TYPE MATERIAL.—15 , from 6 colonies of Xenia membranacea Schenk, in 15 cm, on the reef about 5 km south of Yaté, southeastern New Caledonia, 22°11′00″S, 166°59′00″E, 23 June 1971. (These are the same colonies from which Noloxynus mundus was recovered.) Holotype , allotype, and 17 paratypes (11 , 6 ) deposited in the National Museum of Natural History, Smithsonian Institution, Washington, D.C. (under the catalog numbers of the former United States National Museum: USNM); the remaining paratypes (dissected) in the collection of the author.

FEMALE.—Body (Figure 3i) moderately elongated with the prosome not unusually thickened dorsoventrally. Length 2.14 mm (1.76–2.30 mm) and the greatest width 0.79 mm (0.67–0.86 mm), based on 10 specimens. First pedigerous segment separated dorsally from the cephalosome by a transverse suture. Ratio of the length to the width of the prosome 1.56:1. Ratio of the length of the prosome to that of the urosome 1.35:1.

Segment of leg 5 (Figure 3j) 122 × 363. Between this segment and the genital segment no ventral sclerite. Cenital segment in dorsal view elongated, 374 long, 286 in greatest width anteriorly and 197 wide posteriorly; in lateral view (Figure 3k) not swollen. Ratio of the length to the average width about 1.55:1. Cenital areas located dorsolaterally in the anterior half of the segment. Each area (Figure 3l) with two small naked setae 22 and 20 and a spiniform process. Three postgenital segments from anterior to posterior 125 × 159, 70 × 140, and 117 × 148. Anal segment bearing on each side a posteroventral row of minute spinules.

Caudal ramus (Figure 4a) elongated, 177 in greatest dorsal length, 187 in greatest ventral length, and 65 wide. Ratio of dorsal length to width 2.72:1. Outer lateral seta 160 and naked. Dorsal seta 44 and naked. Outermost terminal seta 230, innermost terminal seta 340, and the two median terminal setae 510 (outer) and 780 (inner), both inserted between dorsal (smooth) and ventral (with marginal denticles) flanges. All four terminal setae plumose.

Body surface with a few hairs (sensilla) and retractile points (Figure 3i,j).

Egg sac (Figure 3i) elongated oval, 780 × 415 in the specimen drawn, reaching to the middle of the caudal ramus and containing approximately 25 eggs about 125–140 in diameter though of irregular shape.

Rostrum (Figure 4b) subtriangular in ventral view.

First antenna (Figure 4c) 682 long. Lengths of the seven segments: 60 (130 along the anterior margin), 169, 42, 143, 112, 81, and 31 respectively. Formula for the armature: 4, 13, 6, 3, 4 + 1 aesthete, 2 + 1 aesthete, and 7 + 1 aesthete. All the setae naked.

Second antenna (Figure 4d) 429 long and 4-segmented, with the armature 1, 1, 3, and II + 5. Fourth segment 82 along the outer side, 46 along the inner side, and 36 wide. Two terminal claws very unequal, the larger 46 along its axis, the smaller 17. Five small subterminal setules.

Labrum (Figure 4e) with two broadly rounded posteroventral lobes. Mandible (Figure 4f) having a strongly constricted liase. Distal to the constriction on the convex margin a scalelike area with a row of blunt spinules followed by two small teeth or none (Figure 4g) and then a serrated fringe; on the convex margin a row of long slender spinules. Lash long and barbed. Paragnatli (Figure 4e) a small hairy lobe. First maxilla (Figure 4h) relatively large; terminally with two slender setae, a stout hyaline element, and subterminally having a small fingerlike process. Second maxilla (4i) with a large unarmed first segment. Second segment armed with a small setule on its proximal outer (ventral) surface, a surficial posterior seta barbed along one edge, and an inner (dorsal) distal spine bilaterally with spinules. This segment produced to form a lash whose proximal half is expanded on the outer (ventral) side, where it bears strong marginal teeth grading into small barbules distally. Maxilliped (Figure 4j) 3-segmented. First segment with an inner cluster of slender spinules. Second segment with two unequal finely barbed setae and a similar cluster of spinules. Third segment with a smooth spine, a small naked seta, and a stout terminal bilaterally barbed spiniform process (lacking a distinct articulation with the segment); in addition to the three elements a small but distinct adjacent marginal knob.

Area between the maxillipeds and the first pair of legs (Figure 4k) not protuberant.

Legs 1–4 (Figures 4l, 5a–c) segmented and armed as in other species in the genus. Coxa of leg 1 with an outer prominence on the posterior surface (Figure 4l). Leg 4 (Figure 5c) with the inner coxal seta 50 and naked. Inner margin of the basis smooth. Exopod 290 long. First segment of the endopod 65 long without the spiniform processes and 68 wide, its distal inner seta plumose and 100. Second endopod segment 161 long without the processes (172 including the processes), 58 in greatest width, 43 in least width; outer terminal spine 57, inner spine 73 with a bifurcated tip; both spines barbed.

Leg 5 (Figure 5d) elongated, reaching to the first postgenital segment. Free segment in dorsal view 424 long, 95 in greatest width proximally at the slight expansion. In flat ventral view the free segment as in Figure 5e. Two naked terminal setae 40 and 117.

Leg 6 represented by the two setae on the genital area (Figure 3l).

Living specimens in transmitted light opaque, the eye red, the egg sacs grayish to opaque.

MALE.—Body (Figure 5f) more slender than in the female. Length 1.77 mm (1.66–1.86 mm) and the greatest width 0.54 mm (0.51–0.54 mm), based on 8 specimens. Ratio of the length to the width of the prosome 1.73:1. Ratio of the length of the prosome to that of the urosome 1.07:1.

Segment of leg 5 (Figure 5g) 73 × 187. No ventral intersegmental sclerite. Genital segment elongated, 363 × 297. Four postgenital segments from anterior to posterior 73 × 125, 75 × 110, 44 × 94, and 84 × 104.

Caudal ramus resembling that of the female, but smaller, 112 in greatest dorsal length, 122 in greatest ventral length, and 44 wide.

Body surface sparsely ornamented as in the female.

Rostrum as in the female. First antenna like that of the female but three long aesthetes added, two on segment 2 and one on segment 4. Second antenna similar to that of the female except for numerous short spines on the inner surface of the first and second segments (Figure 5h).

Labrum, mandible, and paragnath like those of the female. First maxilla (Figure 5i) with the stout terminal element less enlarged than in the female and relatively longer. Second maxilla similar to that in the female. Maxilliped (Figure 5j) with the first and third segments unarmed. Second segment ornamented with two rows of spines and bearing two setae, one smoothly tapered, the other with a hyaline inset distal portion. Claw 360 along its axis including the terminal lamella, showing a weak subdivision about midway, and bearing proximally two very unequal setae, the larger one with an obliquely striated tip.

Area between the maxillipeds and the first pair of legs like that of the female.

Legs 1–4 segmented as in the female and with the same spine and setal formula as in that sex except for the third segment of the endopod of leg 1 (Figure 6a) where the formula is I, I, 4 instead of I, 5 as in the female. Rest of leg 1, legs 2 and 3, and the exopod of leg 4 resembling the female. Second segment of the endopod of leg 4 (Figure 6b) a little shorter than in the female, 117 long including the processes, 43 in greatest width, 32 in least width. Two terminal spines more unequal than in the opposite sex, outer 34, inner 52.

Leg 5 (Figure 6c) with the free segment 70 × 18, the two terminal setae 28 and 17.

Leg 6 (Figure 6d) the usual posteroventral flap on the genital segment, bearing two naked setae 33 and 24.

Spermatophore not observed.

Color in living specimens like that of the female.

ETYMOLOGY.—The specific name prarlongiprs, from Latin praclongus (= very long) and pes (= foot), alludes to the elongated fifth leg.

COMPARISON WITH OTHER SPECIES IN THE GENUS.—The genus Metaxymolgus contains 25 species. Twenty-three of these were listed by Humes and Stock (1973). Two new species have since been described: M. echinasteris Humes, in press, from the asteroid Echinaster luzonicus (Gray) in New Caledonia, and M. micropus Humes, 1973a, from the ophiuroid Astroboa nuda (Lyman) in Madagascar.

Metaxymolgus praelongipes, a species whose large size is noteworthy, may be distinguished from all other members of the genus by a combination of three characters: (1) the elongated female genital segment with small anteriorly located expansions in dorsal view, (2) the long free segment of the female leg 5 (more than twice as long as any other previously described species) reaching to the first postgenital segment (in all other species it is clearly shorter than the genital segment), and (3) the very unequal claws on the second antenna in both sexes.

Sexual dimorphism in the first maxilla, evident in the new species, does not occur is other species of Metaxymolgus as far as known; however, the first maxilla in both sexes has not been described in several species.