Angulorostrum monothrix Kornicker 1981

Angulorostrum monothrix

ETYMOLOGY.—The specific name from the Greek mono (one, single, alone) plus thrix (hair) in reference to the single bristle on the mandibular exopodite of the species.

HOLOTYPE.—(USNM 156960, ovigerous female in alcohol and on slide.

ALLOTYPE.—USNM 157814, 1 adult male in alcohol and on slide; from same sample as holotype.

PARATYPES.—USNM 156964A, adult female; USNM 156962, adult female; USNM 156963, juvenile (valves only); USNM 156964B, 41 specimens. All paratypes from same sample as holotype.

TYPE-LOCALITY.—R/V Atlantis II, cruise 31, sta 167, off Brazil.

DESCRIPTION OF ADULT FEMALE (Figures 1–3).—Carapace with pointed rostrum and prominent caudal process; greatest height anterior to valve middle; ventral margin broadly rounded (Figures 1, 2a,c,d).

Ornamentation: Surface smooth with numerous bristles, especially along anteroventral margin. Carapaces in collection weakly calcified but with numerous microconcretions.

Infold: Infold of rostrum with 2 bristles near dorsal margin (Figure 2c); anteroventral infold with small bristle just ventral to lower end of rostrum and striations paralleling anteroventral curvature (Figure 2a); infold of caudal process with 6 broad frondlike bristles forming row (Figure 2d).

Selvage: Wide lamellar prolongation with marginal fringe present along free margin of valves except possibly along posteroventral end of caudal process (Figure 2e).

Central Adductor Muscle Attachments (Figures 1, 2b): Consisting of about 14 to 19 ovoid scars.

Size: USNM 156960, right valve with specimen removed, length only, 1.56 mm; USNM 156962, length 1.67 mm, height 0.92 mm; USNM 156964A, length 1.63 mm, height 1.10 mm.

First Antenna (Figure 2f,g): Joints 1–5 spinous. 2nd joint with spinous dorsal bristle. 3rd joint with 3 spinous bristles, 1 ventral, 2 dorsal. 4th joint short, with 3 spinous bristles, 2 ventral, 1 dorsal. Sensory bristle of long 5th joint with 3 short dorsal filaments and 2 hairs at tip. Short medial bristle of minute 6th joint with long proximal and short distal spines. 7th joint: a-bristle with spines along dorsal margin; b-bristle almost twice length of a-bristle, with 2 small dorsal filaments near middle and 2 hairs at tip; c-bristle about 3 times length of a-bristle, with 3 short dorsal filaments near middle and 2 hairs at tip. 8th joint: d- and e-bristles slightly longer than c-bristle, bare with blunt tips; f-bristle about same length as c-bristle, with 3 short marginal filaments and 2 hairs at tip; g-bristle slightly longer than c-bristle, with 3 short marginal filaments and 2 hairs at tip.

Second Antenna (Figures 2h, 3g,h): Protopodite bare. Endopodite 2-jointed: 1st joint with 1 or 2 short anterior bristles; 2nd joint minute with 1 long spinous terminal bristle. Exopodite 9-jointed: long 1st joint with minute terminal tubular bristle; joints 2–9 decreasing in size distally along exopodite; joints 2–8 with long hairs along distal margins; bristles of joints 2–8 relatively short, with fairly stout ventral spines but no natatory hairs; 9th joint with 3 bristles, longer of these with ventral spines, remaining 2 shorter bristles with slender short hairlike spines along both margins.

Mandible (Figure 2i): Coxale endite consisting of large spinous bifurcate process without bristle near base. Basale: dorsal margin with 3 spinous bristles, 1 distal to middle, 2 terminal; ventral margin with 1 spinous subterminal bristle (this with base on medial side on some limbs); medial surface near ventral margin with 2 short spinous proximal bristles and 1 longer spinous bristle near middle; lateral surface near ventral margin with 3 spinous bristles near middle (these on ventral margin on some limbs); both medial and lateral surfaces with long hairs. Exopodite about one-third length of dorsal margin of 1st endopodial joint, with spines at tip, and with 1 long spinous terminal bristle. 1st endopodial joint with 2 long spinous terminal bristles on ventral margin and spines forming rows on medial surface. 2nd endopodial joint: dorsal margin with 4 long bristles forming cluster near middle; ventral margin with bristles forming 2 distal groups (1 bristle in proximal group, 2 in terminal group); medial surface with spines forming rows; end joint with 3 claws and 3 bristles.

Maxilla (Figure 2j): 3 endites present: endite I with 6 bristles; endite II with long slender lateral lobe with 3 bristles and shorter wider medial lobe with 2 bristles (medial lobe could be part of endite I); endite III narrow with 4 bristles. Precoxale and coxale with dorsal fringe of long hairs. Coxale with long slender lateral bristle with short marginal spines. Basale with 1 medial bristle near middle (this bristle could be a proximal bristle on endite I) and 2 bristles near ventral margin. Exopodite consisting of small lobe near ventral margin of basale with 2 long spinous bristles and 1 shorter slender bare bristle. Endopodite: 1st joint with 1 spinous alpha-bristle and 1 beta-bristle; end joint with 2 proximal spinous lateral bristles, 3 slender proximal medial bristles, 1 anterior spinous bristle, and 2 stout terminal claws.

Fifth Limb (Figures 2k, 3a): 3 endites present: endite I with 1 spinous bristle; endite II with 3 spinous bristles; endite III with 7 spinous bristles. Exopodite: 1st joint with 2 anterior bristles (1 with short spines and 1 with long hairs); main tooth consisting of smooth tooth followed by 2 stout pectinate teeth and a slender spinelike pectinate tooth; spinous bristle present proximal to slender tooth; an indistinct lobe with 2 distal minute teeth present near main tooth; 2nd joint consisting of large squarish tooth; a long and short bristle present on posterior side of 2nd joint just distal to a long bristle; 3rd joint with 3 spinous bristles on inner lobe (2 long and 1 short) and 2 short bristles on outer lobe; 4th and 5th joints fused, with total of 5 bristles. Epipodial appendage with 39 spinous bristles.

Sixth Limb (Figure 3b,c): Endite I with 2 spinous terminal bristles; endite II with 3 spinous terminal bristles; endite III and IV each with 5 spinous terminal bristles. End joint narrow, with 5 spinous anterior bristles followed by short space and then 2 long hirsute bristles; 1 short hirsute bristle present in place of epipodial appendage; limb hirsute.

Seventh Limb (Figure 3d): Each limb with 2 proximal bristles (1 on each side) and 5 terminal bristles (3 on one side, 2 on other) each bristle with distal marginal spines and 2 to 4 bells. Terminus with comb of about 6 alate teeth opposite 2 small bare pegs.

Furca (Figure 3e): Each lamella with 8 claws decreasing in length distally along lamella; all claws with teeth along posterior margins; claw 1 with stout small teeth forming groups between larger teeth; hairs at base of claws and following claws.

Bellonci Organ (Figure 3i,j): Elongate with about 3 or 4 faint sutures in proximal half, tip pointed.

Eyes: Medial eye small, unpigmented (Figure 3i,j). Lateral eyes absent.

Upper Lip (Figure 3f,k): Projecting anteriorly, with small anterior processes and abundant hairs.

Genitalia (Figure 3e): Consisting of oval cup with attached spermatophore.

Eggs: USNM 156960, 4 eggs; USNM 156964A, 1 egg; USNM 156962, 2 eggs.

DESCRIPTION OF ADULT MALE (Figures 4, 5a,e).—Carapace similar to that of adult female except for having greater slope of posterodorsal margin (Figure 4a-c).

Ornamentation (Figure 4b,c): Similar to that of adult female.

Infold:: Similar to that of adult female.

Size: USNM 157814, length 1.63 mm, height 0.90 mm.

First Antenna (Figure 4d): 1st joint with faint lateral and medial spines. 2nd joint spinous, with 1 spinous dorsal bristle. 3rd joint short, spinous, with 1 or 2 hirsute dorsal bristles. 4th joint elongate, spinous, with 1 spinous dorsal bristle. 5th joint small, wedged ventrally between 4th and 6th joints; sensory bristle with filamentous proximal bulb (proximal edge of bulb projecting backward) and stem with about 4 short filaments. 6th joint long, with spinous medial bristle. 7th joint: a-bristle spinous, about same length as bristle of 6th joint; b-bristle about twice length of a-bristle, with 4 marginal filaments; c-bristle long, with about 8 marginal filaments. 8th joint: d- and e-bristles bare, with blunt tips reaching past tip of sensory bristle of 5th joint, but not reaching tip of c-bristle; f- and g-bristles about same length as d- and e-bristles, each with about 6 marginal filaments.

Second Antenna (Figure 4e,f): Prodopodite bare. Endopodite 3-jointed: 1st joint short with 3 small anterior bristles; 2nd joint elongate with 2 proximal ventral bristles; 3rd joint elongate with unridged, pointed, sclerotized tip, and 2 small subterminal bristles. Exopodite: 1st joint elongate, with hairs forming clusters along ventral margin, and small, terminal, medial bristle with open tip; joints 2–9 progressively decreasing in size; bristles of joints 2–9 with natatory hairs but no ventral spines; bristle of 2nd joint about same length as exopodite, bristles of joints 3–8 much longer; 9th joint with 3 bristles (long ventral bristle with natatory hairs, short middle and dorsal bristles with short marginal spines); joints 2–8 with fairly long spines forming row along distal margin, but no basal spines.

Mandible (Figure 4g,h): Coxale endite represented by 2 minute subequal spines. Basale: medial surface spinous, with 3 short bristles near ventral margin (2 proximal, 1 near middle); ventral margin with 4 long spinous bristles (bases of some of these are on medial or lateral surface of joint); dorsal margin with 1 long spinous bristle distal to middle and 2 long spinous subterminal bristles. Exopodite about one-fourth length of 1st endopodial joint, with 1 long spinous terminal bristle. 1st endopodial joint with medial spines, and 2 long spinous ventral bristles. 2nd endopodial joint: ventral margin spinous, with bristles forming 2 groups (1 bristle in proximal group and 2 in distal group); dorsal margin spinous, with 4 long bristles near middle; medial surface spinous. 3rd endopodial joint with 3 claws (2 long, 1 short) with teeth near middle, and 3 bristles.

Maxilla (Figure 4i,j): 3 endites with weakly developed bristles, some spinous. Precoxale and coxale with fringe of long hairs. Coxale with stout spinous dorsal bristle. Basale with long hairs and 1 long ventral bristle. Exopodite small, with 3 bristles, 2 long, 1 short. Endopodite: 1st joint with 1 alpha- and 1 beta-bristle; 2nd joint with 8 bristles.

Fifth Limb (Figure 5a): Reduced with weakly developed bristles.

Sixth Limb (Figure 5b): Endite I with 1 small spinous medial bristle and 1 stout hirsute terminal bristle; endite II with 3 terminal bristles (2 hirsute, 1 with long proximal and short distal spines); endite III with 5 terminal bristles (3 hirsute, 2 with long proximal and short distal spines): endite IV with 5 stout terminal bristles (some hirsute, some spinous); end joint narrow, with 6 bristles (posterior 2 of these long, hirsute and separated by space from anterior bristles); 1 hirsute bristle in place of epipodial appendage.

Seventh Limb (Figure 5c): Each limb with 4 terminal bristles, each with distal marginal spines and 4 bells. Terminus consisting of comb with about 4 spinous teeth opposite single elongate peg.

Furca (Figure 5d): Right lamella with 8 claws, left with 9; claws decreasing in length and width posteriorly along lamella; each claw with teeth along posterior margin (small teeth forming groups between larger teeth); posterior 4 or 5 claws with few proximal teeth along anterior margin; few hairs present at base of claw 1 and following claws.

Bellonci Organ (Figure 5e): Elongate but fairly short, with 3 or 4 weak sutures proximally, tip pointed.

Eyes: Medial eye unpigmented, bare (Figure 5e): Lateral eyes absent.

Upper Lip (Figure 5e): Similar to that of female.

Genitalia (Figure 5d): Each limb consisting of 3 lobes, one of these with sclerotized tip, others with bristles.

DESCRIPTION OF JUVENILE VALVES (Figure 5f, Plates 1, 2).—Carapace similar in outline to that of adult female.

Ornamentation: Surface appearing smooth but scanning electron microscope used at high magnifications (above X 1000) revealing minute scattered pustules with central pore and abundant smaller pustules between them (Plates 1, 2). Surface with numerous bristles (Plate 1).

Size: USNM 156963, length 1.41 mm, height 0.87 mm.