Alebion gracilis Wilson C. B. 1905

Alebion gracilis Wilson, 1905

MATERIAL.—A single collection containing 1 from body surface of Galeocerdo cuvieri 16 August 1965.

Alebion gracilis Wilson, 1905

Alebion gracile Wilson, 1905:128.—Rathbun, 1905:93

Alebion gracilis Wilson, 1907:704; 1932:420.—Vaissière, 1959:549.—Yamaguti, 1963:100.—Cressey, 1970:5.

MATERIAL EXAMINED.—Holotype female (USNM 8122), 9 collections identified as A. gracilis in the Smithsonian collections, and a single collection made by the author off Sarasota, Florida.

FEMALE.—Body form as in Figure 88. Total length 9.3 mm (9.0–9.6 mm) and greatest width 5.4 mm (4.95–5.55 mm) based on an average of 5 specimens. Genital segment (Figure 89) somewhat wider than long (3.68 × 3.23 mm), widest in posterior third, lateral margin with prominent spinules as in A. carchariae; posterior outer corners produced and extending well beyond caudal rami. Abdomen 2-segmented, first segment with lateral expansions much shorter than in A. carchariae. Spermatophores slender, posterior half only slightly wider than anterior, anterior portions lie between two sclerotized rings on ventral surface of genital segment. Caudal ramus (Figure 90) nearly twice as long as wide (370µ × 200µ), armed as in other members of the genus.

Cephalic appendages as in A. carchariae except as noted below. Tip of shorter flagellum of second maxilla with serrations as indicated in Figure 91. Adhesion pad lateral to mouth tube with canaliculations on surface as in Figure 92. Maxilliped (Figure 93) with short, stout claw and patch of fine scales on surface of basal segment.

Legs as in A. carchariae. Last exopod segment of leg 1 as in Figure 94.

MALE.—Body form as in Figure 95. Total length 5.7 mm (5.3–6.3 mm) and greatest width 3.4 mm (3.3–3.5 mm) based on an average of 5 specimens. Genital segment (Figure 96) longer than wide (1.5 × 1.1 mm), widest portion with a few spinules on lateral margin. Abdomen 2-segmented, each segment measures 0.44 and 0.55 mm respectively, second segment wider than first. Caudal ramus (Figure 97) longer than wide (230µ × 180µ) and armed as in other members of genus.

Cephalic appendages as in female except as noted below. Second antenna (Figure 98) with stout claw bearing well-developed accessory process, adhesion pads as indicated in the figure.

Legs 1–4 as in the female except for the presence of modified spines on the exopod of leg 2 (Figure 99). Legs 5 and 6 as in A. carchariae.

Alebion gracilis.—Shiino, 1959:316

MATERIAL EXAMINED.—Holotype female (USNM 139170), allotype (USNM 139171), and 4 paratypes females (USNM 139172) from the body surface of Carcharinus malpeloensis caught near Tres Madres Is. Four additional collections from C. azureus, C. galapagensis, and C. malpeloensis (2) from the eastern Pacific off Mexico and Lower California. An additional collection was found in the British Museum labeled A. gracilis from “sand shark” off Baija Honda, Panama.

FEMALE.—Body form as in Figure 111. Total length 9.6 mm (9.0–10.2 mm) and greatest width 4.5 mm (4.3–4.8 mm) based on an average of 5 specimens. Cephalon only slightly longer than wide 4.5 × 4.6 mm) and comprising nearly one-half total length. Thoracic segments bearing legs 1–3 fused. Thoracic segment bearing leg 4 with dorsal bilobed plate. Genital segment (Figure 112) about as long as wide (2.5 × 2.5 mm), a row of spinules along anterolateral edge; genital segment with slight lateral bulge, superficially resembling form produced in A. elegans and lobatus, posterior outer corners produced. Abdomen 2-segmented, segments incompletely divided; first segment with prominent lateral winglike expansions, second segment narrowed anteriorly. Spermatophores (Figure 113) each with anterior outwardly directed lobe, widest anteriorly, the two spermatophores joined along most of midline and lying nearly parallel with each other, central sinus between them similar to that seen in A. carchariae. Caudal ramus (Figure 114) longer than wide (630 μ × 410μ) and armed as in figure.

First antenna (Figure 115) as in other members of genus except for two terminal setae with blunt tips. Second antenna (Figure 116) in form of claw with small rugose areas as indicated in figure. Mandible and first maxilla as in A. carchariae. Second maxilla (Figure 117) having same general form as other members of genus with rows of setae near middle of terminal segment (Figure 118) and edge of shorter flagellum as in Figure 119. Postoral adhesion pad with canaliculations as indicated in Figure 120. Maxilliped (Figure 121) in form of stout claw, claw incompletely divided proximal to seta.

Legs 1–3 biramous. Leg 1 (Figure 122) exopod 2-segmented, basal segment with small spine on outer distal corner and row of hairs along inner edge, second segment (Figure 123) with three terminal spines, middle one modified as in other members of genus, and four inner setae, distalmost one short; endopod 2-segmented, first segment unarmed, second segment with three setae. Leg 2 (Figure 124) exopod 3-segmented, first segment with mantlelike membrane (not shown in figure) covering most of exopod; endopod 3-segmented; both rami armed as in A. carchariae. Leg 3 (Figure 125) rami 3-segmented and armed as in A. carchariae. Leg 4 as in A. carchariae. Leg 5 (Figure 126) produced as an extension of posterior outer corners of genital segment, tip armed with two short spines and three stout plumose setae. Leg 6 absent.

Egg strings uniseriate.

MALE.—Body form as in Figure 127. Total length 6.45 mm and greatest width 3.23 mm based on a single specimen. Cephalon slightly wider than long (3.23 × 3.10 mm). Genital segment (Figure 128) longer than wide (1.12 × 0.90 mm), widest in anterior third and bearing many small spinules laterally. Abdomen 2-segmented; first segment 0.45 mm long, second segment 0.64 mm long. Caudal ramus (Figure 129) about twice as long as wide (560 μ × 295 μ), and armed as in the figure.

Cephalic appendages as in female except as noted below. Second antenna (Figure 130) with stout claw bearing prominent accessory claw, inner surface of basal segment with prominent adhesion pad, outer edge with rugose area. Maxilliped (Figure 131) basal segment with raised area covered with blunt spinules as indicated in the figure.

Legs 1–4 as in female except for modified spines on exopod of leg 2 (Figure 132).

ETYMOLOGY.—The name pacificus refers to the geographic area to which this species is restricted.