Pseudanthessius implanus Humes 1977

Pseudanthessius implanus

TYPE MATERIAL.—8 , 4 from 7 pencil urchins, Phyllacanthus imperialis (Lamarck), in 0.5–1 m, western side of Isle Maître, near Noumea, New Caledonia, 22°20′05″S, 166°24′05″E, 11 June 1971. Holotype , allotype, and 7 paratypes (5 , 2 ) 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 17a) with a moderately broad flattened prosome. Length 1.13 mm (1.11–1.16 mm) and the greatest width 0.61 mm (0.58–0.64 mm), based on 8 specimens. Ratio of the length to the width of the prosome 1.18:1. Ratio of the length of the prosome to that of the urosome 1.56:1. Segment of leg 1 separated from the head by a dorsal transverse furrow. Epimera of the segments of legs 1–4 rounded, those of leg 4 with a notched margin (Figure 17b).

Segment of leg 5 (Figure 17c) 60 × 159. Between this segment and the genital segment a weak ventral sclerite. Genital segment in dorsal view 140 × 143, broadened anteriorly. Genital areas situated dorsolaterally in the posterior half of the segment. Each genital area (Figure 17d) bearing two naked setae 6 and 8 and a minute spiniform process. Three postgenital segments from anterior to posterior 52 × 78, 44 × 79, and 86 × 82. Posterior margin of the anal segment ventrally with minute spinules and dorsally with small crenulations.

Caudal ramus (Figure 17e) elongated, 107 × 38 in greatest dimensions, ratio 2.82:1. Outer lateral seta 65 and the dorsal seta 24, both naked. Outermost terminal seta 68 and the innermost terminal seta 78, both with delicate lateral hairs. Two median terminal setae 148 (outer) and 265 (inner), both with lateral spinules. Inner margin of the ramus irregularly notched in its midregion.

Body surface with many hairs (sensilla) and refractile points.

Egg sac (Figure 17f) elongated oval, 263 × 148, reaching to the beginning of the caudal ramus. Eggs 52–57 in diameter.

Rostrum (Figure 17g) not well defined.

First antenna (Figure 17h) 312 long and slightly bent at the level of the third segment. Lengths of the seven segments: 28 (50 along the anterior margin), 114, 25, 46, 36, 21, and 20 respectively. Formula for the armature as in Pseudanthessius procurrens Humes, 1966. All setae naked.

Second antenna (Figure 17i) 280 long. Formula: 1, 1, 3, and II + 5. All setae naked. Two claws unequal, 39 and 54. Third segment with a sclerotized band across the posterior surface. Fourth segment 94 along the outer edge, 72 along the inner edge, and 24–27.5 wide.

Labrum (Figure 17j) with two widely divergent lobes crenated along the posterior margin. Mandible (Figure 17k), paragnath (Figure 17l), first maxilla (Figure 17m), second maxilla (Figure 17n), maxilliped (Figure 17o), and the ventral area between the maxillipeds and the first pair of legs (Figure 17p) similar in major respects to those of P. procurrens.

Legs 1–4 (Figures 18a–d) armed and ornamented as in P. procurrens. Leg 4 with the exopod 130 long. Endopod 45 × 16.5, its two terminal spines 14 and 38. Inner seta on the coxa of leg 4 very small, 8 long, and naked.

Leg 5 (Figure 18e) with a broad spine 33 finely dentate along its inner edge, a naked seta 24, and an adjacent dorsal naked seta 33.

Leg 6 probably represented by the two setae on the genital area (Figure 17d).

Living specimens in transmitted light pale brown, the eye red, the egg sacs opaque gray.

MALE.—Body (Figure 19a) resembling in general form that of the female. Length 0.89 mm (0.85–0.92 mm) and the greatest width 0.41 mm (0.32–0.44 mm), based on 5 specimens. Ratio of the length to the width of the prosome 1.19:1. Ratio of the length of the prosome to that of the urosome 1.38:1.

Segment of leg 5 (Figure 19b) 52 × 117. No ventral intersegmental sclerite. Genital segment 120 × 148. Four postgenital segments from anterior to posterior 39 × 61, 39 × 58, 27 × 60, and 60 × 83.

Caudal ramus (Figure 19b) resembling that of the female, but smaller and with different proportions, 88 × 43, ratio 2.05:1.

Body surface ornamented as in the female.

Rostrum, first antenna, second antenna, labrum, mandible, paragnath, first maxilla, and second maxilla as in the female. Maxilliped (Figure 19c) resembling that of P. procurrens. Distal concave surface of the claw with a crenated fringe. Claw 130 along its axis including the terminal lamella. Ventral area between the maxillipeds and leg 1 as in the female.

Legs 1–4 resembling those of the female except for slight sexual dimorphism in the third segment of the endopod of leg 2 (Figure 19d).

Leg 5 similar in general form to that of the female.

Leg 6 (Figure 19e) a posteroventral flap on the genital segment, bearing two slender naked setae 20 and 16.

Spermatophore not observed.

Living specimens colored as in the female.

ETYMOLOGY.—The specific name implanus (Latin, = uneven) alludes to the irregularly notched inner margin of the caudal ramus.

COMPARISON WITH RELATED SPECIES.—The irregularly notched inner margin of the caudal ramus is distinctive of this species. In all other Pseudanthessius this margin as far as known is smooth.

The new species is similar in certain respects to Pseudanthessius procurrens, associated with Phyllacanthus imperialis in Madagascar. Strong resemblances between the two species are to be found in the body form, the female genital segment, the second antenna, the labrum, the mouthparts, leg 1, leg 5, and the male maxilliped. Among the ways that P. implanus differs from the Madagascan species are the form of the female genital segment, the length of the caudal rami, the weak rostral area, the relative length of the third endopod segment of leg 3, and the form of the spine in leg 5.

Species of Pseudanthessius from Phyllacanthus imperialis have thus far been reported only from two widely separated areas (Madagascar and New Caledonia). Although the collections of P. procurrens and P. implanus are small in number, it would appear that these two related species have evolved from a common ancestral species on Phyllacanthus, with subsequent diverging into the two present-day species in distant parts of the range of the host.