Senariellus latiseta Humes 1977

Senariellus latiseta

TYPE MATERIAL.—3 , 1 from one echinoid, Heterocentrotus mammillatus (Linnaeus), in 0.5 m, western side of Isle Maître, near Noumea, New Caledonia, 22°20′05″S, 166°24′05″E, 11 June 1971. Holotype , allotype (with the left maxilliped removed), and 2 paratypic deposited in the National Museum of Natural History, Smithsonian Institution, Washington, D.C.

OTHER SPECIMENS.—1 (dissected) from one echinoid, Tripneustes gratilla (Linnaeus), in 1 m, Rocher à la Voile, Noumea, 22°18′24″S, 166°25′50″ E, 3 June 1971.

FEMALE.—Body (Figure 4a) with the prosome moderately broad. Length 0.80 mm (0.77–0.84 mm) and the greatest width 0.37 mm (0.35–0.39 mm), based on 4 specimens. Ratio of the length to the width of the prosome 1.39:1. Ratio of the length of the prosome to that of the urosome 1.69:1.

Segment of leg 5 (Figure 4b) 60 × 112. Genital segment in dorsal view 117 × 107, with the sides nearly parallel. Genital areas located dorsolaterally posterior to the middle of the segment. Setae on the genital area 29 and 16, both naked. Three postgenital segments from anterior to posterior 39 × 78, 31 × 75, and 26 × 73.

Caudal ramus (Figure 4a) 47 × 34, ratio 1.38:1. Outer lateral seta 99 and smooth. Dorsal seta 57, outermost terminal seta 137, innermost terminal seta 143, and the two median terminal setae 115 (outer) and 160 (inner). All these setae with lateral spinules.

Egg sac (Figure 4c) 320 × 170, reaching to two-thirds of the length of the caudal setae, and containing 20–25 eggs about 55–62 in diameter.

Rostrum as in Senariellus diadematis.

First antenna 228 long, with the armature as in S. diadematis. Lengths of the seven segments: 17 (35 along the anterior margin), 69, 22, 41, 33, 15, and 13 respectively.

Second antenna (Figure 4d) slender and elongated, 250 long. Fourth segment 91 along the outer edge, 72 along the inner edge, and 14 wide, lacking the small spinules seen in S. diadematis. Two terminal claws about 35 long, with simple attenuated tips, and finely denticulated along their concave margin.

Labrum, mandible, paragnath, and first maxilla similar to those in S. diadematis. Second maxilla also as in that species except that the seta on the second segment is barbed. Maxilliped (Figure 4e) showing only minor differences from S. diadematis.

Legs 1–4 with the segmentation and armature as in S. diadematis. In leg 1 the proximal outer spine on the third exopod segment shorter than the adjacent spines, not subequal in length as in S. diadematis. All spines except those on the exopod of leg 1 with lamellate rather than barbed edges. Third segment of the endopod of leg 3 (Figure 4f) with the formula I, II, I, 2. Leg 4 (Figure 4g) with the inner coxal seta 8 and naked. Exopod 156 long. Distal outer spine on the third segment of the exopod distinctly smaller than the proximal outer spine. Endopod 78 × 34 with smooth margins. Two smooth terminal spines 39 (outer) and 81 (inner), ratio 2.08:1.

Leg 5 (Figure 4h) with three elements: a broad gladiolate seta 52 × 18 with a dentate inner margin and a striated outer margin, an adjacent smooth seta 40, and a dorsal seta (held erect and difficult to measure accurately).

Leg 6 represented by the two setae on the genital area.

Color of living specimens as in S. diadematis.

MALE.—Body (Figure 4i) with the prosome like that of the female. Length 0.62 mm and the greatest width 0.26 mm. Ratio of the length to the width of the prosome 1.42:1. Ratio of the length of the prosome to that of the urosome 1.57:1.

Genital segment 140 × 135.

Caudal ramus (Figure 4i) 34 × 26, ratio 1.31:1. Inner of the two terminal setae unusually small and naked (compare with Figure 4a).

Rostrum and appendages, as far as determinable without dissection, similar to those of the female except for the maxilliped. Maxilliped (Figure 4j) with the second segment bearing two setae and two rows of spines, one row straight, the other row in the form of a compressed loop. Claw 135 along its axis, with a small pointed process about midway on the concave surface at the level of the weak subdivision, and bearing proximally two unequal setae.

Legs 1–5 similar to those of the female.

Leg 6 resembling that of S. diadematis.

Color as in the female.

ETYMOLOGY.—The specific name latiseta (Latin, latus = broad) and seta, referring to the broad gladiolate seta on leg 5.

COMPARISON WITH Senariellus diadematis.—Senariellus latiseta has several easily recognizable features that distinguish it from S. diadematis: (1) the second antennal claws with simple rather than bifurcated tips and with their concave margins finely denticulated, (2) the shorter caudal ramus, with the outer median terminal seta shorter than the outermost terminal seta, and in the male with the inner median terminal seta reduced to a small naked seta, (3) the distal outer spine on the third exopod segment of leg 4 distinctly smaller than the adjacent proximal spine, (4) the broad gladiolate seta on leg 5, and (5) the small pointed process on the concave surface of the claw of the male maxilliped.