Senariellus diadematis Humes 1977

Senariellus diadematis

TYPE MATERIAL.—125 , 184 , and 30 copepodids from 42 sea urchins, Diadema setosum (Leske), in 3 m, Anse Vata, Noumea, New Caledonia, 22°18′27″S, 166°26′30″E, 17 July 1971. Holotype female, allotype, and 250 paratypes (100 , 150 ) deposited in the National Museum of Natural History, Smithsonian Institution, Washington, D.C.; 51 paratypes (21 , 30 ) in the Zoölogisch Museum, Amsterdam; the remaining paratypes (dissected) in the collection of the author.

OTHER SPECIMENS.—18 , 22 , and 5 copepodids from 23 Diadema setosum, in 3 m, at the type-locality, 15 July 1971.

FEMALE.—Body (Figure 1a,b) moderately slender. Length 0.83 mm (0.79–0.86 mm) and the greatest width 0.32 mm (0.31–0.33 mm), based on 10 specimens. Ratio of the length to the width of the prosome 1.66:1. Ratio of the length of the prosome to that of the urosome 1.85:1. Segment of leg 1 separated from the head by a transverse furrow.

Segment of leg 5 (Figure 1c) 60 × 109. Genital segment in dorsal view 107 × 99, bulging slightly in its anterior third and tapering posteriorly. Genital areas located laterally behind the middle of the segment. Each genital area (Figure 1d,e) with two naked setae 22 and 11 and with an adjacent minute spiniform process. Three postgenital segments from anterior to posterior 36 × 73, 34 × 70, and 42 × 70. Anal segment with a smooth posteroventral margin.

Caudal ramus (Figure 1f) 51 × 33, ratio 1.55:1. Outer lateral seta 74 and the dorsal seta 42, both naked. Four terminal setae relatively short and stout, less than three times the length of the ramus. Outermost terminal seta 81, the innermost terminal seta 104, and the two median terminal setae 88 (outer) and 130 (inner). All terminal setae with lateral spinules as in Figure 1g.

Body surface with a few hairs (sensilla) as in Figure 1a,b.

Egg sac (Figure 1h) a loose cluster of 4×6 large eggs, each about 94 in diameter.

Rostrum (Figure 1i) broadly rounded, and in lateral view lobate (Figure 1b).

First antenna (Figure 1j) 195 long. Lengths of the seven segments: 19 (32 along the anterior margin), 66, 16, 39, 22, 9, and 11 respectively. Formula for the armature: 4, 13, 6, 3, 4 + 1 aesthete, 2 + 1 aesthete, and 7 + 1 aesthete. All setae naked. Third segment with the sclerotization of the posterior surface extended ventrally (Figure 2a).

Second antenna (Figure 2b) slender and elongated, 247 long, exceeding the length of the first antenna. Formula: 1, 1, 3, and II +5. Third segment with a sclerotized band on the posterior surface and a few outer spinules. Fourth segment very long and slender, 105 along the outer margin, 80 along the inner margin, and 10 wide, bearing terminally two jointed claws 39 with bifid tips (Figure 2c) and five small setules. Outer surface of the fourth segment with small spinules. All elements naked.

Labrum (Figure 2d) with two divergent posteroventral lobes. Mandible (Figure 2e) having on its convex margin a row of denticles diminishing in size distally; on its concave margin a row of longer slender spinules. Lash moderately long with short lateral spinules. Paragnath (Figure 2d) a small smooth lobe. First maxilla (Figure 2f) with four smooth elements. Second maxilla (Figure 2g) with a large first segment. Second segment slender and elongated, bearing a naked seta on its anterior surface and produced to form a long lash with graded spines along one edge and a few minute distal spinules along the outer edge. Maxilliped (Figure 2h) 3-segmented, the first segment unarmed, the second segment having on its inner surface two naked setae (the proximal seta with a blunt tip) and a row of spinules, and the small third segment bearing two barbed setae and having a barbed spiniform tip.

Ventral area between the maxillipeds and the first pair of legs (Figure 2i) slightly protuberant (Figure 1b).

Legs 1–4 (Figures 2j,k, 3a,b) with the formula for the armature as follows (the Roman numerals indicating spines, the Arabic numerals representing setae):


Setae on the rami relatively short, those on the third segment of the endopod of leg 1 almost spiniform (Figure 2j). Last segment of the endopod of leg 3 (Figure 3a) with an extra inner spine, so that the formula is I, II, I, 2, instead of I, II, 2 as in the related genus Pseudanthessius and many other lichomologoid genera. Leg 4 (Figure 3b) with the inner coxal seta 22 and naked, instead of plumose as in the preceding legs. Exopod of leg 4 120 long. Endopod 64 × 21, with the outer margin having a row of hairs and with two terminal spines, the slender outer spine 51 and smooth, the stouter inner spine 68 and barbed along the outer margin; ratio between the two spines 1.33:1.

Leg 5 (Figures 1d, 3c) with three naked setae 50, 28, and 23.

Leg 6 represented by the two setae on the genital area (Figure 1d,e).

Living specimens in transmitted light pale brown, the eye red.

MALE.—Body (Figure 3d) slender. Length 0.65 mm (0.62–0.68 mm) and the greatest width 0.25 mm (0.23–0.26 mm), based on 10 specimens. Ratio of the length to the width of the prosome 1.50:1. Ratio of the length of the prosome to that of the urosome 1.68:1.

Segment of leg 5 (Figure 3e) 40 × 85. Genital segment 130 × 130, the length including the posteriorly pointed extensions of leg 6. Four postgenital segments from anterior to posterior 22 × 54, 20 × 52, 18 × 57, and 30 × 59.

Caudal ramus resembling that of the female but smaller, 40 × 28; ratio 1.43:1.

Body surface ornamented as in the female.

Rostrum like that of the female. First antenna (Figure 3f) resembling that of the female, but the aesthete on the fifth segment much stouter. Second antenna, labrum, mandible, paragnath, first maxilla, and second maxilla like those of the female. Maxilliped (Figure 3g) slender and 4-segmented (assuming that the proximal part of the claw represents a fourth segment). First segment unarmed. Second segment bearing three rows of spines and two naked setae. Small third segment unarmed. Claw 121 along its axis (including the terminal lamella) showing a slight evidence of division about midway, with the concave margin slightly irregular proximal to the division, and bearing proximally two unequal naked setae.

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

Legs 1–4 resembling those of the female. Two spines on the endopod of leg 4 more unequal, 38 and 61, with the ratio 1.61:1.

Leg 5 similar to that in the female.

Leg 6 (Figure 3h) a posteroventral flap on the genital segment produced posteriorly and bearing two naked setae 17 and 36.

Spermatophore (Figure 3i) oval, 65 × 39, not including the neck.

Living specimens colored as in the female.

ETYMOLOGY.—The specific name diadematis is the genitive form of the generic name of the host.