Alebion lobatus Cressey 1970

Alebion lobatus

MATERIAL.—Thirty collections from body surface of Carcharinus milberti. Holotype (USNM 128492) and 7 paratype (USNM 128493) collected from above host 25 February 1967 at Sarasota, Florida.

FEMALE.—Body form as in Figure 16. Total length 9.45 mm (9.30–9.90 mm) and greatest width 4.37 mm (4.20–4.50 mm) based on an average of 5 type specimens. Cephalon slightly longer than wide (4.50 × 4.95 mm, holotype), about one-half total length. Thoracic segments bearing legs 1–3 fused, articulating with cephalon. Thoracic segment bearing leg 4 free and bearing prominent dorsal bilobed plate, characteristic of other species in genus. Genital segment (Figure 17) only slightly longer than wide, measured from anterior border to abdomen (2.25 × 2.52 mm); genital segment 4.20 mm long when leg 5 is included (posterior processes). Row of small spines along anterolateral edge and another lateral row of small spines along posterior edge (segment bulges slightly at this part). Spermatophores attached ventrally near attachment of abdomen. Spermatophore of 2 forms. In the most common form encountered in the collection reported here, each spermatophore bears 2 prominent anterior lobes (Figure 18); inner surface of each with pilose area at about midmargin; anterior halves divergent, posterior halves parallel. Alternate form of spermatophore (Figure 19) without lobes and generally smaller but still exhibiting divergent nature (see Remarks). Abdomen (Figure 19) 1-segmented and 1.62 mm long; anterior segment with prominent lateral winglike processes. Caudal rami (Figure 19) bear 4 plumose terminal setae and 2 smaller subterminal setae, each ramus somewhat longer than wide (652 μ × 420 μ).

First antenna (Figure 20) 2-segmented, basal segment with several small plumose setae, terminal segment with 13 setae (2 in form of aesthetes and 2 fused at base), 4 setae plumose as indicated in figure. Oral area as in Figure 21. Second antenna in form of claw, first 2 segments each with rugose area, terminal claw with small seta near midpoint. Mandible of usual caligoid type with 11 teeth. First maxilla represented by group of 3 small setae lateral to mouth tube and anterior to prominent flangelike process. Second maxilla as in other species of genus, second segment with patch of hairs near distal end; terminal processes with lateral rows of spinules, spinules on longest process in incomplete spiral rows. Maxilliped in form of stout claw; tip of claw (Figure 22) thicker than in other species of genus, bearing seta near midpoint.

Legs 1–3 biramous. Leg 1 (Figure 23) exopod 2-segmented, basal segment with small spine on outer distal corner, terminal segment with 3 spines and 4 setae, terminal spine in form of broad blade directed toward mid-axis of body; terminal seta much shorter than other 3 and all setae plumose; endopod 2-segmented, terminal segment with 3 inwardly directed plumose setae. Leg 2 (Figure 24) exopod 3-segmented, basal segment with membranous outer sheet enveloping outer margin, last 2 segments each bear an inwardly directed modified spine (as in leg 1) and setae as indicated in figure; endopod 3-seg-mented, outer margins of first 2 segments pilose and each with inner setae as indicated in figure, terminal segment with 6 setae. Leg 3 (Figure 25) basipod in form of broad flange; exopod (Figure 26) 3-segmented, basal segment with few small spinules on outer edge and spine on outer distal corner, second segment with modified spine, terminal segment with 2 modified spines, each segment with setae as in figure; endopod first 2 segments with outer edges pilose, terminal segment small and bearing 4 setae; rami closely appressed and one overlapping the other (broad fringe on basipod lies over rami, not shown in Figure 25). Leg 4 (Figure 27) small, 2-segmented; basal segment with outer plumose spine, terminal segment with 3 spines (plumosities seen on outermost only). Leg 5 represented by 2 long processes on outer distal corner of genital segment, each tipped with several short spines (Figure 28) and row of short spines on dorsal surface. Leg 6 absent.

Egg strings uniseriate.

MALE.—Unknown. Because of the lack of understanding of the diagnostic features of males of Alebion coupled with the fact that this species commonly occurs in the same collections as A. carchariae, I have deferred description of the male until I have completed a comprehensive revision of the genus with a better understanding of the male distinguishing characters.

ETYMOLOGY.—The name lobatus refers to lobes present on spermatophore.

Alebion lobatus Cressey, 1970:7

MATERIAL EXAMINED.—Thirty collections (including types) from off west coast of Florida as previously reported (Cressey, 1970).

FEMALE.—A description of the female of this species will not be repeated here since it has been recently provided elsewhere (Cressey, 1970). Some illustrations are provided, however, to enable the reader to identify females of this species without consulting the previous work. The only feature here added to the original description of the female is the nature of the canaliculations on the surface of the postoral adhesion pad (see Figure 104).

MALE.—Body form as in Figure 105. Total length 6.2 mm (6.1–6.4 mm) and greatest width 3.2 mm (3.1–3.4 mm) based on an average of five specimens. Genital segment (Figure 106) longer than wide (1.50 × 1.16 mm); few scattered spinules on anterior lateral edge, widest anteriorly. Abdomen 2-segmented, segments measuring 0.54 and 0.70 mm long respectively. Caudal ramus (Figure 107) nearly twice as long as wide (940 μ × 580 μ), armed as in other members of genus.

Cephalic appendages as in female except as noted below. Second antenna (Figure 108) with stout terminal claw bearing small accessory spine near middle of inner curved margin; prominent adhesion pads as indicated in figure. Maxilliped (Figure 109) with stout claw; inner margin of basal segment with raised scale-covered areas opposing claw.

Legs 1–4 as in female except for modified spines on exopod of leg 2 (Figure 110); proximal spine stout and bearing several heavy spinules, distal spine narrowed in basal fourth and continuing same width to tip. Leg 5 represented by small podomere bearing three setae near midlateral margin of genital segment. Leg 6 represented by three setae at posterior outer corners of genital segment.