Pseudanthessius vinnulus Humes 1977

Pseudanthessius vinnulus

TYPE MATERIAL.—14 , 11 from 4 sea urchins, Echinothrix diadema (Linnaeus), intertidal on reef at Yaté, southeastern New Caledonia, 22°11′00″S, 166°59′00″E, 23 June 1971. Holotype , allotype, and 18 paratypes (10 , 8 ) deposited in the National Museum of Natural History, Smithsonian Institution, Washington, D.C.; the remaining paratypes (dissected) in the collection of the author.

FEMALE.—Body (Figure 23a) with the prosome moderately broadened and flattened. Length 0.96 mm (0.92–1.01 mm) and the greatest width 0.42 mm (0.40–0.44 mm), based on 10 specimens. Ratio of the length to the width of the prosome 1.45:1. Ratio of the length of the prosome to that of the urosome 1.56:1. Segment of leg 4 much narrower than the preceding segments, its tergum partly concealed beneath the segment of leg 3. Segment of leg 1 separated from the head by a well-developed transverse furrow.

Segment of leg 5 (Figure 23b) 55 × 117. Between this segment and the genital segment a well-formed ventral sclerite. Genital segment in dorsal view subquadrate, 109 × 117. Genital areas located dorsolaterally at the midde of the segment. Each genital area (Figure 23c) with two naked setae 22 and 17. Three postgenital segments from anterior to posterior 49 × 99, 42 × 91, and 55 × 81. Anal segment with a row of minute spinules on the posteroventral margin on both sides.

Caudal ramus (Figure 23d) elongate, 109 × 29, with relatively short setae. Ratio 3.76:1. Outer lateral seta 22, the dorsal seta 24, the outermost terminal seta 43, the innermost terminal seta 48, and the two median terminal setae 83 (outer) and 125 (inner). All setae naked.

Body surface with numerous hairs (sensilla) as in Figure 23a.

Egg sac (Figure 23a) in the single ovigerous specimen seen a group of three large slightly oval eggs 99–120 in diameter.

Rostrum (Figure 23a) not developed.

First antenna (Figure 23f) short, 180 long. Lengths of the seven segments: 36 (30 along the anterior margin), 50, 25, 30, 13, 11, and 10 respectively. Formula for the armature as in Pseudanthessius procurrens Humes, 1966. All setae naked.

Second antenna (Figure 23g) 213 long, longer than the first antenna. Formula: 1, 1, 3, and II + 5. Fourth segment 75 along the outer margin, 48 along the inner margin, and 17 wide. Two terminal claws 21 and 27. All elements naked.

Labrum (Figure 23h) with two outwardly flaring lobes. Mandible (Figure 23i) with a slender basal part bearing on the convex side a row of hyaline teeth and on the inner side a transverse row of spinules and more distally a row of spinules; lash moderately long. Paragnath (Figure 23h) a small lobe. First maxilla (Figure 23j) with three small setae. Second maxilla (Figure 23k) with a few refractile points on the outer surface of the large first segment. Second segment bearing a smooth seta on the inner surface and prolonged to form a long lash with graduated teeth along one side. Maxilliped (Figures 23l, 24a) 3-segmented, the first segment unarmed, the second segment slender and bearing two small naked setae, and the very small third segment inset on the postero-outer surface of the second segment and bearing a finely barbed spine and two very small setae.

Ventral area between the maxillipeds and the first pair of legs (Figure 24b) not protuberant.

Legs 1–4 (Figure 24c–f) segmented and armed as in Pseudanthessius procurrens. Endopod of leg 1 directed medially. Outer spines on the exopod of leg 1 (Figure 24c) slender, the spine on the first segment unusually long. Outer spines on the exopod of leg 2 (Figure 24d) stouter than in leg 1, the spine on the first segment very long, about three times longer than the spine on the second segment. Inner terminal spine on the endopod slenderer than the outer spine. Spines on leg 3 (Figure 24e) similar to those in leg 2. Exopod of leg 4 (Figure 24f) 123 long. Outer spines on the exopod elongated. Endopod of same leg 54 × 13, its outer margin with hairs proximal to a small thornlike process. Two terminal spines 47 (outer) and 27.5 (inner). Ratio between the two spines 1.7:1. Inner coxal seta very small, 4 long.

Leg 5 (Figure 24g) with three setae, one very long, 146, finely barbed, and extending to the middle of the first postgenital segment. Other two setae short and naked, about 20 and 35.

Leg 6 represented by the two setae on the genital area (Figure 23c).

Living specimens in transmitted light pale brown, with narrow brown bands along the posterior borders of the head and the four metasomal segments. Eye red, the eggs lightly opaque.

MALE.—Body (Figure 25a) more slender than in the female. Length 0.86 mm (0.83–0.89 mm) and the greatest width 0.29 mm (0.28–0.30 mm), based on 10 specimens. 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 1.09:1.

Segment of leg 5 (Figure 25b) 31 × 133. No ventral intersegmental sclerite. Genital segment 156 × 169. Four postgenital segments from anterior to posterior 49 × 87, 39 × 74, 34 × 65, and 43 × 64.

Caudal ramus (Figure 25b) 91 × 29, shorter than in the female. Ratio 3.14:1.

Body surface ornamented as in the female.

Rostrum, first antenna, second antenna, and labrum similar to those in the female. Sclerotization of the postlabral area (Figure 25c) different from that of the female (Figure 23h). Mandible, paragnath, first maxilla, and second maxilla like those in the female. Maxilliped (Figure 25d) slender, with two small setae and two groups of small spinules on the second segment. Claw 120 along its axis, including the terminal lamella, bearing proximally two unequal setae. Near the base of the convex side of the claw a small proximally directed thornlike process. Tip of the claw opposite the lamella with an irregular hyaline flange.

Ventral area between the maxillipeds and the first pair of legs as in Figure 25e.

Legs 1 and 2 like those of the female. Leg 3 similar to that of the female but the outer spine on the first segment of the exopod not elongated (Figure 25f). Leg 4 (Figure 25g) also resembling that of the female but the exopod spines shorter. Endopod 46 × 11, the two spines 19 and 33.

Leg 5 resembling that of the female but the long seta shorter, 70 long.

Leg 6 (Figure 25h) a posteroventral flap on the genital segment, bearing two small setae about 5.5 and a spine 10. Two median sclerotized internal rods below the edge of the flap in ventral view.

Spermatophore not observed outside the body of the male.

Living specimens colored as in the female.

ETYMOLOGY.—The specific name vinnulus (Latin, = delightful or charming) alludes to the graceful nature of the long seta on leg 5.

COMPARISON WITH RELATED SPECIES.—Pseudanthessius vinnulus may be readily distinguished from the majority of species of Pseudanthessius where the caudal ramus in the female is clearly much shorter or much longer. Four species have the caudal ramus between 3:1 and 4:1, thus approaching the condition in the new species. These may be separated from P. vinnulus on the basis of other characters, however. In P. tortuosus Stock, Humes, and Gooding, 1963, the outer spine on the first exopod segment of leg 1 is not much longer than the next distal spine. In P. assimilis G. O. Sars, 1917, the female genital segment is much longer than wide. In P. obscurus A. Scott, 1909, the second antenna has three slender claws. In P. mucronatus Gurney, 1927, the second antenna has six curved setae, none of them clawlike. In all four of these species the longest element of leg 5 is relatively short, not longer than the genital segment as in P. vinnulus.