Scambicornus sewelli Humes 1975

Scambicornus sewelli

TYPE MATERIAL.—161 , 204 from 50 holothurians, Halodeima edulis (Lesson), in 3 m, near reef between Isle Ndié and Mt. Kumuru, northwest of Noumea, New Caledonia, 22°13′40″S, 166°24′18″E, 9 July 1971. Holotype 9, allotype, and 240 paratypes (100 , 140 ) deposited in the National Museum of Natural History, Smithsonian Institution, Washington, D.C.; 117 paratypes (57 , 60 ) in the Zoölogisch Museum, Amsterdam; the remaining paratypes (dissected) in the collection of the author.

OTHER SPECIMENS.—From Halodeima edulis: 4 ,1 from 1 host, in intertidal pool, Ricaudy Reef, Noumea, 22°19′00″S, 166°26′44″E, 9 June 1971; 3 , 5 from 1 host, in 2 m, western side of Isle Maître, near Noumea, 22°20′05″S, 166°24′05″E, 11 June; 7 ,1 from 6 hosts, in 1 m, western side of Isle Maître, 20 June; 3 ern side of Port Ngea, 2 kms north of Ricaudy Reef, 22°18′18″S, 166°26′47″E, 8 July.

From Halodeima coluber (Semper): 3 , 4 from 1 host, intertidal, southwestern side of Port Ngea, 2 kms north of Ricaudy Reef, 8 July 1971; 22 , 57 from 6 hosts, intertidal, eastern side of Isle Maître, near Noumea, 22°20′35″S, 166°25′10″E, 16 July; 14 from 6 hosts, intertidal, eastern side of Isle Maître, 31 July.

From Halodeima atra (Jaeger): 11 ,5 from 8 hosts, in 1.5 m, Rocher à la Voile, 22°18′24″S, 166°25′50″E, 2 June 1971; 56 , 18 from 10 hosts, intertidal, Ricaudy Reef, 9 June; 137 , 65 from 31 hosts, in 4-5 m, reef between Isle Ndié and Mt. Kumuru, northwest of Noumea, 22°13′40″S, 166°24′18″E, 29 July.

From Holothuria curiosa Ludwig: 16 , 10 from 1 host, in 1 m, Ricaudy Reef, 9 June 1971; 19 , 20 from 1 host, intertidal, eastern side of Isle Maître, 16 July; 14 , 9 from 1 host, intertidal pool, eastern side of Isle Maître, 16 July.

From Actinopyga echinites (Jaeger): 4 from 2 hosts, intertidal, Ricaudy Reef, near Noumea, 9 June 1971.

From Microthele nobilis (Selenka): 1 from 2 hosts, in 2 m, west of Isle Mando, 22°18′59″S, 166°09′30″E, 3 July 1971.

In all but one of these collections the new species was accompanied by S. subtilis (Humes and Cressey, 1961).

FEMALE.—Body (Figure 17a) with the prosome a little less widened than in S. tylotus. Length 1.14 mm (1.07–1.20 mm) and the greatest width 0.60 mm (0.57–0.63 mm), based on 10 specimens. Epimera of the segments of legs 1 and 2 angular, those of the segments of legs 3 and 4 rounded. Ratio of the length to the width of the prosome 1.33:1. Ratio of the length of the prosome to that of the urosome 2.21:1.

Segment of leg 5 (Figure 17b) 91 × 156. Between this segment and the genital segment no ventral sclerite. Genital segment 94 in midlength, 140 in greatest length, and 180 wide, posterolaterally expanded to the level of the second postgenital segment. Genital areas situated laterally in the posterior half of the segment. Each area (Figure 17c, d) with two unequal naked setae 50 and 21, and a small spiniform process. Margin of the segment medial to the genital area with a small inwardly turned flange. Three postgenital segments from anterior to posterior 39 × 75, 34 × 70, and 55 × 69. Anal segment with a row of small spinules on its posteroventral margin on each side.

Caudal ramus (Figure 17e) elongated, 68 × 31 in greatest dimensions, about 2.19 times longer than wide. Outer lateral seta (situated dorsally on the ramus) 300 and naked. Dorsal seta 210 and naked. Outermost terminal seta 220 and naked, innermost terminal seta 150 with a few proximal inner spinules. Two long median terminal setae 540 (outer) and 870 (inner), both with a few delicate lateral spinules (easily broken off) in their midregions and both inserted between small dorsal (smooth) and ventral (with a marginal row of small spinules) flanges.

Body surface with a few small hairs (sensilla) as in Figure 17a.

Egg sac (Figure 17a) elongated oval, 570 × 250, with numerous eggs, each about 60 in diameter.

Rostral area (Figure 17f) not well defined.

First antenna (Figure 17g) 380 long. Lengths of its seven segments: 24 (57 along the anterior edge), 130, 34, 66, 41, 29, and 23 respectively. Formula for the armature as in S. tylotus. All setae naked.

Second antenna (Figure 17h) 286 long. Segmentation and armature as in S. tylotus. All setae naked. Claw 80 along its axis. Third and fourth segments without fine ornamentation.

Labrum (Figure 17i) similar to that in S. tylotus.

Mandible (Figure 18a) with a small conical process preceding the serrations on the convex margin and with unusually long proximal spinules on the concave margin; bifurcation at the tip unequal. Paragnath (Figure 17i) a small hairy lobe. First maxilla (Figure 18b) resembling that of S. tylotus but with a spiniform process adjacent to the longest terminal seta. Second maxilla (Figure 18c) armed as in S. tylotus. Second segment with the posterior surficial seta naked, the inner (dorsal) seta with prominent unilateral barbs (Figure 18d) and the second and third teeth on the lash longer than the rest. Maxilliped (Figure 18c) similar to that in S. tylotus. Tip of the third segment recurved.

Area between the maxillipeds and the first pair of legs (Figure 18f) slightly protuberant in lateral view (Figure 18g).

Legs 1–4 (Figures 18h–j; 19a) segmented and armed as in S. tylotus. Leg 4 with the inner coxal seta 11 and naked. Outer seta on the basis 130. Exopod 118. Endopod 109, with the inner element on segments 1 and 2 a plumose seta about 40. Five spines on the third segment from outer to inner 21, 28, 59, 61, and 31.

Leg 5 (Figure 19b) with a small free segment 22 × 16, ratio 1.37:1. Outer terminal seta 42 and smooth. Inner terminal seta 61, slightly swollen proximally and angular. Segment ornamented distally with a few small spinules. Seta on the body near the insertion of the free segment 65 and naked.

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

Color in life in transmitted light as in S. tylotus.

MALE.—Body (Figure 19c) with the prosome more slender than in the female. Length 0.71 m.m (0.66–0.75 mm) and the greatest width 0.31 mm (0.30–0.32 mm), based on 10 specimens. Ratio of the length to the width of the prosome 1.59:1. Ratio of the length of the prosome to that of the urosome 1.89:1.

Segment of leg 5 (Figure 19d) 31 × 76. No ventral intersegmental sclerite. Genital segment 109 × 117, slightly wider than long. In dorsal view the greatest width of the segment occurring in its posterior third. Four postgenital segments from anterior to posterior 26 × 49, 29 × 48, 26 × 47, and 23 × 45.

Caudal ramus (Figure 19d) similar to that of the female, but shorter, 29 × 21, or 1.38 times longer than wide.

Body surface ornamented with hairs as in the female.

Rostral area like that of the female.

First antenna 250 long, resembling that of the female but the second segment relatively a little shorter (Figure 19e). Lengths of the segments: 20 (39 along the anterior edge), 81, 21, 46, 26, 19, and 18 respectively.

Second antenna (Figure 19f) with two groups of small spinules on the second segment and a few spinules on the third segment; otherwise as in the female.

Labrum, mandible, paragnath, first maxilla, and second maxilla like those in the female. Maxilliped (Figure 19g) with a somewhat enlarged first segment. Second segment more slender with two inner naked setae and ornamented with a patch of slender spines and a distal group of minute spinules. Small third segment unarmed. Claw (Figure 19h) 145 along its axis (including the hyaline terminal lamella), bearing proximally two unequal setae, the longer with minute barbules along one side, the other naked. Convex margin of the claw with the sclerotization interrupted at five points where, in a favorable view, the margin is seen to protrude on a slight knob. Near the tip of the claw on the anterior surface a row of minute spinules (Figure 19i).

Legs 1–4 segmented as in S. tylotus, with the spine and setal formula as in that species. Leg 1 (Figure 20a) with the exopod 65 and the 2-segmented endopod 82 long. Terminal spiniform element on the endopod with lateral hairs proximally but with a barbed fringe distally (Figure 20b). Endopod of leg 2 (Figure 20c) also 2-segmented and relatively longer (99) than the exopod (73). Legs 3 and 4 with the outer seta on the basis much shorter than in the female, only about half as long as the exopod. Endopod of leg 3 (Figure 20d) longer (104) than the exopod (87). Outer terminal spine on the third segment with an attenuated rather than a blunt tip and deflected slightly toward the more proximal spine on the outer side of the segment. Leg 4 as in the female.

Leg 5 (Figure 20e) with a minute free segment 10 × 7.5 armed as in the female.

Leg 6 (Figure 20f) a posteroventral flap on the genital segment bearing two naked setae about 25, a small spiniform process, and a ventral row of slender spinules.

Spermatophore (Figure 20g) oval, 78 × 44, not including the neck.

Color as in S. tylotus.

ETYMOLOGY.—This species is named for the late Colonel R. B. Seymour Sewell, who described several species of Scambicornus (under the name Preherrmannella) from the Indian Ocean.

COMPARISON WITH RELATED SPECIES.—On the grounds mentioned above in connection with S. tylotus, the new species from Halodeima may be separated from S. propinquus, S. armoricanus, S. finmarchicus, S. tenuicauda, S. brevicauda, S. poculiferus, S. nicobaricus, S. idoneus, S. petiti, S. prehensilis, and S. serendibicus.

Eight of the eleven other species in the genus may be distinguished from S. sewelli by selected characters as follows: In S. campanulipes the female has a bell-shaped fifth leg. In S. subtilis, S. modestus, S. subgrandis, and S. lobulatus the female genital segment has laterally expanded wings. In S. hamatus the second antenna is stouter and more robust and the female caudal ramus is about 3:1. In S. tuberatus leg 5 in the female is much smaller (28 × 18) and the claw of the male maxilliped has a proximal inner digitiform process. In S. tylotus the female leg 5 is much larger, both alsolutely and in relation to the genital segment, and the claw of the male maxilliped has three inner knoblike processes.

The three species that remain are less well known and therefore more difficult to compare with the new species. In S. robustus, of which only the female is known, the genital segment has evenly rounded sides instead of being posterolaterally expanded. In S. brachysetosus both sexes are much smaller than in S. sewelli, the female genital segment has evenly rounded sides, and the concave side of the claw of the male maxilliped has a spiniform projection.

The two females and two males described as Preherrmannella adduensis by Sewell (1949) may comprise two species. His females represent a species close to S. subtilis, but distinguished from that species by the longer fourth segment on the second antenna and by the longer caudal ramus (nearly 3:1, instead of 1.67:1 as in S. subtilis). Sewell’s males show an irregular convex margin on the claw of the maxilliped (his fig. 21D) suggesting the unusual nature of the maxillipedal claw of S. sewelli. Although it is impossible to be certain from Sewell’s meager description and figures, the possibility exists that Sewell’s males of Preherrmannella adduensis may actually represent Scambicornus sewelli.

Examination of type material of Preherrmannella adduensis has not been possible. The specimens on which the original description was based, collected by Sewell while on board the Investigator in the Indian Ocean, no longer exist. Colonel Sewell informed me by letter of 26 April 1963 that the specimens from the Investigator were deposited in the collections of the Zoological Survey of India. During World War II the collections of the Indian Museum (containing the specimens from the Investigator) were transferred to Benares. There they were exposed to a severe flood, with the result that the labels were washed off.