Asteropterygion setiferum (Kornicker & Caraion 1974)

Asteropteron setiferum

HOLOTYPE.—[USNM 141266], 1 adult female, length 2.70 mm. Specimen deposited in the Museum of Natural History “Grigore Antipa,” Bucharest (1 vial, 4 slides).

TYPE-LOCALITY.—Station X044.

ETYMOLOGY.—The specific name from the Latin setifer (bearing bristles), in reference to the many bristles on the mandibular basale.

DISTRIBUTION.—Known only from the type-locality off the coast of Mauritania at a depth of 1100 m on a mud bottom. No other species in the genus has been reported from water deeper than 100 m (Kornicker, in press).

DESCRIPTION.—Carapace ornate with small incisur and rostrum; single lateral protuberance projecting anteriorly beyond rostrum (Figures 37, 38, 41a–c); similar protuberance, but broader, projecting anteriorly beyond shell margin below incisur; 3 lateral posterior protuberances projecting posteriorly and reach to, or slightly beyond, posterior shell margin; ventral and posterior margins of shell slightly inset; process lateral to rostrum continuing posteriorly as lateral ridge above central muscle scar area and terminating posteriorly in short posterior process; middle part of ridge with 3 low nodes; a second lateral ridge with 3 or 4 low nodes present just within ventral margin and parallel to it; middle part of valve containing central muscle scars depressed; posterior ends of upper and lower lateral ridges connected by vertical ridge with node near middle; surface of carapace with numerous coarse punctae.

Infold (Figures 39c–l, 41b,c): Rostral infold with 6 short bristles near rostral tip, row of about 56 long and short bristles (35 long, 21 short) forming row parallel to anterior margin, about 21 short bristles between row of bristles and anterior margin of carapace, about 5 bristles between row of bristles and inner margin of infold; about 10 bristles forming row on anterodorsal infold (this row is continuation of anterior row of long and short bristles); 3 minute bristles present posterior to inner end of incisur; anteroventral infold with about 13 bristles between selvage and list; distinct list present near inner margin of infold extending from below incisur to posterior end of ventral infold; ventral infold with 7 widely spaced short bristles; posteroventral infold with 12 less widely spaced bristles (some with long marginal hairs) followed by 9 short closely spaced bristles and then about 12 minute bristles; posterior infold with outer row of 10 short bristles, middle row of 8 short bristles, and inner row of about 33 short and minute bristles (13 short, 20 minute); outer margin of posterior infold (edge of valve) forming right angle near valve middle.

Central muscle scars: Consisting of about 24 oval to slightly elongate individual scars (Figure 38a,e–g).

Selvage: Ventral and anteroventral margins with broad lamellar prolongation with distinct striations in proximal part and weak striations in distal part, edge smooth; anterodorsal margin including rostrum with lamellar prolongation similar to that on ventral margin except for being narrower and having marginal fringe (Figures 38c, 39d,e); posterior margin ventral to right angle with narrow selvage with marginal fringe.

Size: [USNM 141266], holotype, length 2.70 mm, height 1.98 mm.

Micromorphology of carapace based on scanning-electron photomicrographs (the valve was held about 10 seconds in a sonic vibrator which removed a thin covering film and exposed intricate microstructures): Surface of carapace with numerous fossae (Figure 38a–c); about 25 fossae containing 10–25 round bundles of tubes pointing inwards present in the central muscle scar area (each fossae appears to be placed over the end of a muscle strand) (Figure 38e–g); fossae with flat bottoms having a pebbly texture present between tubular fossae in area of the central muscle scars and elsewhere (Figure 38e–i,l); fossae on surface of valve outside central muscle scar area with about 70 long tubes having a more-or-less polygonal cross-section (Figure 38i,j); the long tubes point inwards from sides of fossae and are on bottom of fossae; fossae along anterodorsal margin of valve with short bundles of tubes on bottom, each tube polygonal in cross-section (Figure 38k–m); latter type fossae also present elsewhere on surface except in area of central muscle scars (Figure 38i); surface between fossae with closely spaced patches of short tubular structures (Figure 38f–l); bristles sparsely distributed on valve surface (see arrow on Figure 38l) and forming 2 rows along free margins (Figure 38k); some bristles emerge from closed pores (Figure 39a), and some from open lipped pores (Figure 39b); bristles have surface papillae (Figure 39a,b).

Posterior list: List with middle row of closed pores with bristles and inner and outer rows of open pores with bristles (Figure 39f–k); bristles in middle row include long bristles (Figure 39h), short bristles (Figure 39h), and medium bristles with pore at base (Figure 39h–j) (It is possible that the short and medium bristles are tubular with open ends, but this was not determined herein); many open pores in inner and outer rows have bristles missing (Figure 39g,h,k).

Anteroventral and ventral list: List along anteroventral and ventral margin broad, flat; lamellar prolongation, if present, with smooth margin (Figure 39d–f,l).

Selvage: Broad lamellar prolongation present along free margins (Figures 38k, 39d–f,l); outer margin of prolongation serrate (Figure 38k).

First antenna (Figures 40a, 41d): 1st joint with long hairs along ventral margin; 2nd joint with spines along ventral and proximal dorsal margins and 5 dorsal bristles, 4 proximal, 1 distal (distal bristle missing on left limb of USNM 141266); 3rd joint with 1 short ventral bristle and 3–4 dorsal bristles (1 near middle, 2–3 terminal); 4th joint longer than 3rd, with 1 terminal spinous dorsal bristle and 3 ventral bristles (1 long spinous, 2 short bare, or with short spines); sensory bristle of 5th joint with 3 short proximal and 4 long terminal filaments; 6th limb with minute medial bristle. Seventh joint: a-claw longer than joints 5 to 8, ringed in distal part; b-bristle with about 6 short filaments including tip; c-bristle shorter than b-bristle, with 9 short filaments including tip. Eighth joint: d- and e-bristles bare, slightly shorter than c-bristle; f-bristle about same length as c-bristle, with 8 filaments including tip; g-bristle slightly shorter than f-bristle, about same length as c-bristle, with 8 filaments including tip; g-bristle slightly shorter than f-bristle, with 6 short filaments including tip.

Second antenna: Protopodite with short medial bristle, few long hairs on medial surface near endopodite and short hairs proximally on ventral margin (Figure 40b). Endopodite (Figures 40b, 41e): 3rd joint fused with 2nd and no suture evident between them; 1st joint with 9–11 bristles; 2nd joint bare; 3rd joint with 1 long bare terminal bristle. Exopodite: 1st joint with short distomedial bristle; bristle on 2nd joint with slender proximal spines along ventral margin and distal natatory hairs; 3rd to 8th joints with natatory bristles (some bristles with slender spines); 9th joint with 5 natatory bristles, 3 long, 1 medium, 1 short.

Mandible (right limb, [USNM 141266] ): Coxale endite (Figure 41h,i): ventral branch with spines forming 8 oblique rows on medial surface and stouter spines along ventral margin; tip with 3 small teeth (2 long, 1 short); minute bristle present on endite near base of ventral branch; ventral margin of dorsal branch with 3 small teeth proximal to 4 knobs; main spine with serrate margin; about 14 spines forming row on lateral side of branch proximal to main spine; dorsal corner of tip of dorsal branch with short spines forming cluster at base of hirsute bristle; tip of branch between base of hirsute bristle and main spine serrate. Basale (Figure 41f,g,f): endite with 7 terminal bristles (2 long, 4 medium, 1 short), 7 triaenid bristles (4th pair of spines from the proximal end much longer than others), and 5 dwarf bristles (distal of these about twice length of others); glandular opening with about 14 pores present near distal end of endite; ventral margin of basale with 5 triaenid bristles (one pair of spines much longer than others), 2 proximal short bristles (with bases on medial surface of basale), 1 very long bristle with long proximal and short distal spines, and 4 short spinous distal bristles; dorsal margin of basale with 7 short and 5 long distal spinous bristles; lateral surface with about 15 short spinous bristles proximally near dorsal margin and about 8 short spinous bristles distally, also near dorsal margin; medial surface near dorsal margin hirsute. Exopodite hirsute, slightly longer than dorsal margin of 1st endopodite joint, with 2 spinous subterminal bristles (proximal bristle longer than distal bristle) (Figure 41k). Endopodite: ventral margin of 1st joint with 2 long stout proximal bristles with long marginal spines and 1 shorter bristle near middle with short marginal spines; medial surface of 2nd joint with spines forming rows in distal half; ventral margin of joint with 3 spinous terminal bristles; dorsal margin with about 30 spinous bristles (some of these of triaenid type); end joint with 2 short spinous bristles on ventral corner, 1 long lateral terminal bristle with few marginal spines, 2 clawlike bristles (1 ventral, 1 dorsal) with few marginal spines along ventral margins, and 1 longer bare clawlike bristle medial to other claws.

Mandible (left limb, [USNM 141266] ) (Figure 40c): Endopodite differs from right limb described above in having 5 terminal bristles on ventral margin of 2nd joint and no short bristles on ventral corner of end joint.

Maxilla (Figures 40d, 42a,b): Epipodite long, tapering to point, tip hirsute; endite 1 with 5 bristles with spinous tips; endite II with 1 long bristle with spinous tip, 1 medium and 8 short slender bristles. Basale: dorsal margin with 15–19 proximal bristles of varying length and 9 short and 6 long distal bristles; medial side with 3 distal bristles, 2 near middle, 1 near ventral margin; ventral margin with about 13 bristles along margin, 1 long bristle present on lateral side at distal end of baleen-comb; medial surface of basale hirsute. Endopodite: medial side of 1st joint hirsute; dorsal margin with 7 short bristles; ventral margin with 1 long spinous -bristle; end joint with 5 spinous bristles. Exopodite with 3 bristles, 1 long, 2 short, not on lobe.

Fifth limb: Epipodial appendage with 80–82 bristles (Figure 40g). Comb: dorsal margin hirsute, with 7 slender bristles on left limb (Figures 40e, 42c) of [USNM 141266], 5 on right (Figure 40f); lateral surface with stout spinous epipodial bristle reaching end of comb and 4 short proximal bristles near ventral margin.

Sixth limb (left limb, [USNM 141266]) (Figures 40h, 42d): Anterior margin with 2 sutures; margin above upper suture with about 30 short spinous bristles; margin between sutures with 7 short spinous bristles (some of the bristles between sutures have bases on medial side of limb); anterior margin below lower suture with 4 short bristles; lateral anteroventral flap (sole) with 14 bristles; 11 spinous bristles present on limb medial to lateral flap (these bristles could be considered to be on anterior part of ventral margin); ventral margin posterior to lateral flap with 8 bristles; hirsute posterior tapering to rounded tip; 1 short spinous epipodial bristle present on posterior margin near middle; medial surface of end joint with about 26 minute bristles forming double row near ventral margin.

Sixth limb (right limb, [USNM 141266]) (Figure 42e,f): Differs from left limb described above in not having upper suture on anterior margin; ventral margin above single suture with 24 bristles; 15 bristles forming row present on medial side close to anterior margin; 7 bristles present on ventral margin posterior to lateral flap.

Seventh limb (Figures 40i, 42g): Each limb with 52–56 bristles, 23–30 bristles on each side; some distal rings near tip with 2 bristles on 1 side and I or 2 bristles on other; each bristle with up to 8 bells. Terminus: each opposing comb with 19 spinous teeth.

Furca (Figures 40j, 43a): Each lamella with 3 long stout claws followed by 7 or 8 short secondary claws; main claws with medial and lateral teeth along concave margins, secondary claws with slender teeth along posterior margins and minute teeth or hairs distally along anterior margins; anterior and ventral margins of lamellae hirsute; anterior margin also with some spines.

Rod-shaped organ: Broadening near middle, with indistinct proximal suture; tip rounded, bare (Figure 43b).

Eyes: Medial eye (Figure 43b) large, pigmented, bare. Lateral eye (Figure 43c) pigmented, about same size as medial eye, with about 14 ommatidia; each eye connected to head region by stalk.

Posterior (Figure 43d): Posterior hirsute; dorsal process finger-like, with spines at tip (terminal lobe may be present, but, if so, is folded over).

Upper lip (Figure 43e): Consisting of 2 hirsute lateral lobes on each side of low saddle; saddle with 4 slender anterior spines; each lobe with 4 spines on small node; a hirsute flap present posterolateral to each lobe.

Brushlike organ: Consisting of small lobe with about 9 minute bristles posterodorsal to genitalia (Figure 43f).

Genitalia: Consisting of oval sclerotized ring (Figure 43f).

Y-sclerite: Almost linear (Figure 43g).

COMPARISONS.—The large number of proximal bristles (15) and distal bristles (8) on the lateral surface of the mandibular basale near the dorsal margin distinguishes A. setiferum from previously described species. The carapace of A. setiferum differs from that of Asteropteron nodulosum Poulsen, 1965, in having fewer coarse punctae and in not having a U-shaped ridge in the posterodorsal part. The carapace of the new species does not have the elongate posterior process present on Asteropteron skogsbergi Poulsen, 1965.

Asteropteron species indeterminate

MATERIAL.—1 juvenile, probably instar III, length 1.49 mm, height 1.13 mm, USNM 143797, from Station X052; in collection of National Museum of Natural History (the shell of this specimen is similar to that of Asteropteron setiferum, new species, but the ventral margin and lateral surface of the mandibular basale have few bristles.

DISTRIBUTION.—From only one locality off the coast of Spanish Sahara at a depth of 53 m on a sand bottom.