Angulorostrum costatum Kornicker 1981

Angulorostrum costatum

ETYMOLOGY.—The specific name is from the Latin costatus (ribbed) in reference to the lateral ribs on the carapace of the species.

HOLOTYPE.—USNM 156778, adult female in alcohol and on slides.

PARATYPE.—USNM 157839, ovigerous female, in alcohol and on slide, from sta 0155–2 (2G), South Carolina continental slope.

TYPE-LOCALITY.—Beaufort Shelf Transect sta 60, North Carolina continental slope.

DESCRIPTION OF FEMALE (Figures 1–8).—Carapace elongate, widest near posterior end of lateral midrib (Figures 6, 7a,h). In medial view, rostrum triangular and with minute indentation representing incisur (Figure 7i); in lateral view, rostrum appearing subrectangular due to lateral overhang (Figure 6). Caudal process projecting posteriorly (Figures 6, 7a,j).

Ornamentation (Figures 6, 7a): Each valve with 3 lateral ribs connected near their posterior ends by weak vertical rib. Surface with shallow fossae and scattered bristles.

Infold: Rostral infold with 2 long spinous bristles in dorsal part and 2 minute bristles near incisur (Figure 7i); anteroventral infold with 1 bristle; ventral margin obscure but possibly with 3 bristles; infold of caudal process with 6 broad spinous bristles on ridge along anterior edge of pocket (Figure 7j); inner margin of infold in vicinity of caudal process with few small faint bristles.

Selvage: Broad lamellar prolongation present along free margin; fringed along ventral margin and possibly elsewhere.

Size: USNM 156778, length 1.18 mm, height 0.76 mm; USNM 157839, length 1.08 mm, height 0.67 mm.

Central Adductor Muscle Attachments (Figure 7a,b): Consisting of about 17 ovoid and elongate scars.

First Antenna (Figure 7k): 1st joint bare. 2nd joint with 1 spinous dorsal bristle, spines forming distal row on lateral surface, and spines forming short rows medially along ventral margin. 3rd joint short with 3 bristles, 2 dorsal, 1 ventral. 4th and 5th joints with faint ventral and dorsal spines. 4th joint elongate, with 3 bristles, 1 dorsal, 2 ventral. 5th joint elongate, with sensory bristle bearing 2 or 3 short proximal filaments. 6th joint minute, with spinous medial bristle. 7th joint: a-bristle longer than bristle of 6th joint, with short marginal spines; b-bristle almost twice length of a-bristle, with 1 filament near middle; c-bristle about same length as sensory bristle of 5th joint, with 1 or 2 proximal filaments. 8th joint: d- and e-bristles about same length as c-bristle, bare with blunt tips; f- and g-bristles with 2 or 3 filaments.

Second Antenna (Figure 7l): Protopodite bare. Endopodite 2-jointed: 1st joint with 1 short anterior bristle; 2nd joint small with 1 long spinous terminal bristle. Exopodite: 1st joint with small medial terminal bristle or spine; bristles of joints 2–8 fairly short, with long segments and stout ventral spines; 9th joint with 3 bristles (1 long with stout ventral spines, remaining shorter bristles bare or with few slender spines); joints 2–8 with minute spines forming row along distal margin.

Mandible (Figure 7c,m): Coxale endite bifurcate with proximal spines and distal teeth. Basale: dorsal margin with 3 bristles (1 distal to middle, 2 terminal); ventral margin with 1 terminal bristle; medial surface spinous, with 3 short bristles near ventral margin (2 proximal, 1 near middle); lateral surface with 2 or 3 spinous bristles (bases almost on ventral margin). Exopodite minute, with single spinous terminal bristle reaching past distal end of 1st endopodial joint. 1st endopodial joint with medial spines and 2 long spinous ventral bristles. 2nd endopodial joint: medial surface with spines forming rows; dorsal margin with 3 or 4 long bristles near middle; ventral margin spinous, with bristles forming 2 groups (1 bristle in proximal group, 2 in distal group). End joint with 2 long claws with teeth near middle, 1 short dorsal claw, and 3 bristles.

Maxilla (Figure 7n,o): Endite I broad with 6 terminal bristles; endite II narrow with 5 or 6 terminal bristles; endite III narrow with 4 terminal bristles and 1 proximal lateral bristle; all endite bristles spinous. Precoxale and coxale with transparent dorsal lamella with marginal fringe. Coxale with spinous dorsal bristle. Basale with 2 ventral bristles (1 medial, 1 lateral). Exopodite short, with 3 bristles (Figure 7o). Endopodite: 1st joint with 1 spinous alpha-bristle and 1 beta-bristle; end joint with 7 spinous bristles (2 clawlike).

Fifth Limb (Figure 7d,e,p,q): Endite I small with 1 bristle with long marginal hairs; endite II with 3 bristles with long marginal hairs; endite III with 7 bristles. Exopodite: 1st joint with 2 anterior bristles on distal edge; main tooth with 1 smooth anterior tooth followed by 2 larger pectinate teeth and 2 or 3 small teeth and then 1 short bristle; a large pectinate indistinct tooth present near main tooth (difficult to interpret); 2nd joint large, triangular, with 3 posterior bristles; 3rd joint with 2 or 3 bristles on inner lobe and 2 on outer lobe; 4th and 5th joints fused, with total of 4 or 5 bristles.

Sixth Limb (Figure 8a): Endite I small with 2 short spinous bristles; endite II narrow with 3 spinous terminal bristles; endites III and IV broad, each with 5 spinous terminal bristles. End joint narrow, with 4 anterior bristles with long proximal and short distal marginal spines, and 2 longer plumose posterior bristles. 1 short pulmose bristle in place of epipodial appendage.

Seventh Limb (Figure 8b): 2 bristles in proximal group, 1 on each side; 5 bristles in terminal group, 3 on one side, 2 on other; each proximal bristle with 1 bell, each terminal bristle with 1 to 4 bells; all bristles spinous distally. Terminus consisting of comb with 6 or 7 recurved teeth opposite 2 pegs.

Furca (Figure 8c): Each lamella with 7 or 8 claws decreasing in length and width posteriorly along lamella; hairs present following claws and medially at base of claws.

Bellonci Organ (Figures 7f, 8d,e): Elongate with 6 to 8 sutures and 1 or 2 minute spines at tip.

Eyes: Medial eye unpigmented (Figures 7f, 8d,e). Lateral eyes absent.

Upper Lip (Figures 7f, 8f): With rounded anterior projection, hirsute.

Genitalia (Figure 7g): Consisting of sclerotized ring on each side of body anterior to furca; ovoid? spermatophore attached to ring.

Eggs: USNM 156778 with small unextruded eggs; USNM 157839 with 4 eggs in marsupium.

VARIABILITY.—The specimen collected off South Carolina (USNM 157839) differs from the specimen collected off North Carolina (USNM 156778) in being more elongate, in having a narrower lateral overhang on the rostrum, and in having 7 or 8 rather than 7 furcal claws on each lamella. Because I could detect no other differences in either the carapaces or appendages, I have attributed the observed differences to intraspecific variability.

COMPARISONS.—The carapace of the new species A. costatum differs from the carapace of A. monothrix in having ribs and in having a lateral overlap on the rostrum.