Comprehensive Description

    provided by NMNH Antarctic Invertebrates

    "HOLOTYPE—USNM 128503, N-l male, length 2.98 mm. Some appendages on slides, remaining appendages and carapace in alcohol.

    TYPE-LOCALITY—Eltanin Cruise 5, station 216.

    ETYMOLOGY—The specific name, derived from the Latin "frons" [ = leafy branch], refers to the spiny leaflike teeth in the comb of the 7th limb.

    PARATYPES—USNM 128504, N-l male; USNM 128505, N-l male. Both specimens from Eltanin Cruise 5, station 208.

    DIAGNOSIS (based on N-l males).—Shape and ornamentation of carapace similar to that of S. appelloefi and S. gallardoi; length of N-l male 2.23 to 2.98 mm.

    Seventh limb: Each limb with 10 bristles, 4 proximal, 6 distal; terminal comb with 7 or 8

    teeth, each tooth with about 4 extremely long lateral spines along each side; 1 peg with single pair of spines present opposite comb.

    Lateral eye: Large, about same size as medial eye, but pigment or ommatidia not observed.

    DESCRIPTION OF N-l MALE—Shape and ornamentation similar to Scleroconcha appelloefi (Skogsberg) (see Skogsberg, 1920:420, fig. 77) and Scleroconcha gallardoi Kornicker.

    Infold: Infold on rostrum with 14-17 bristles, mostly with spines; small bristle present below inner end of broad incisur followed forming row on list of anteroventral infold parallel to valve edge; anteroventral infold with about 12 striations; ventral infold bare; posteroventral and posterior list with numerous bristles in groups of up to 6 bristles; ridge with 8 or 9 bristles present between posterior list and outer edge of valve, upper bristle longer than others; 1 bristle present between ridge and posterior valve edge; several bristles present between ridge and list.

    Selvage: Striate lamellar prolongation with short fringe present; lamellar prolongation discontinuous in area of incisur (in this location on holotype, the upper lamellar prolongation is lateral to lower prolongation on right valve, but medial to lower prolongation on left valve).

    Size: USNM 128503, length 2.98 mm, height 2.04 mm; USNM 128504, length 2.23 mm, height 1.32 mm; USNM 128505, length only about 2.18 mm.

    First antenna: Lateral surface of 1st joint with spines forming clusters near dorsal margin; 2nd joint spinous and with 3 bristles, 1 ventral, 1 dorsal, 1 lateral, all with long proximal and short distal spines; 3rd joint spinous and with 3 bristles, 1 ventral, 2 dorsal, all with long proximal and short distal spines; 4th joint spinous and with 5 bristles, 3 ventral, 2 dorsal, all with long proximal and short distal spines; sensory bristle of 5th joint spinous, with 6 proximal and 4 terminal filaments including tip of stem; medial bristle of 6th joint with long proximal and short distal spines. Seventh joint: a-bristle similar to bristle on 6th joint but longer; b-bristle with 1 proximal and 4 distal filaments, including tip; c-bristle with 7 proximal and 5 distal filaments, including tip of stem. Eighth joint: d- and e-bristles long, bare, about same length as c-bristle; f-bristle stout, with 5 proximal and 4 distal filaments including stem; g-bristle with 5 proximal and 5 distal filaments including tip of stem.

    Second antenna: Protopodite bare. Endopodite 3-jointed: 1st joint with 5 bare bristles, 4 proximal and 1 distal, distal bristle longer than proximal bristles; 2nd joint elongate with 3 ventral bristles, all with long proximal and short distal spines, proximal bristle about 3 times longer than 2 distal bristles; 3rd joint with 1 bare proximal bristle (bristle fairly long on holotype, but short on paratype) and 2 short spinous terminal bristles. Exopodite: 1st joint with 1 small medial spine on distal margin; joints 2 to 8 with minute spines forming row along distal margin; small basal spine present at base of bristle on joints 4 to 7; bristles of joints 2-8 bare except for 2 or 3 short spines at tip; 9th joint with 6 bristles, most with short marginal spines.

    Mandible: Coxale endite with small spinous bristle at base. Basale: medial surface spinous and with 6 bristles near ventral margin, 5 proximal, 1 near middle (5 proximal bristles consisting of 3 pectinate and 2 spinous bristles); lateral surface with 3 spinous bristles near ventral margin (proximal of 3 practically on margin); ventral margin with 3 distal bristles, all with long proximal and short distal spines; dorsal margin with 3 or 4 bristles, 1 or 2 distal to middle, 2 terminal, all with long proximal and short distal spines. Exopodite about three-fourths length of dorsal margin of 1st endopodite joint, hirsute near tip and with 2 bristles, both with long proximal and short distal spines (inner proximal bristle longer than outer distal bristle). Endopodite: 1st joint with spines forming clusters on medial surface and 4 ventral bristles, all with long proximal and short distal spines; medial surface and margins of 2nd endopodite joint with spines forming clusters; ventral margin with bristles forming 2 distal groups, of these, proximal group with 4 bristles, terminal group with 3, all bristles with short marginal spines; dorsal margin with bristles forming 2 groups just proximal to middle of margin, proximal group with 4 bristles (1 with long proximal and short distal spines, 3 with short spines), distal group with 5 bristles, all with long proximal and short distal spines; 1 short pectinate bristle present on medial side of joint near dorsal margin between the 2 groups of bristles; end joint with 3 claws and about 3 bristles, all claws with teeth along middle part of concave margin (dorsal claw shorter than others but reaching past middle of longest claw).

    Maxilla: 1st endite with 11 distal bristles; 2nd endite with 6 distal bristles, 3rd endite with about 8 distal bristles; coxale with 1 stout plumose dorsal bristle; basale with 1 short proximal bristle with few short marginal spines present near suture of 3rd endite, and 3 distal bristles, 1 short bare, 2 long with wreaths of long spines and short distal spines; exopodite with 3 bristles, proximal bristle short with short marginal spines, terminal bristles long with long wreaths of spines plus short distal spines. Endopodite: 1st joint with 1 a-bristle with long proximal and short distal spines and 4 spinous 6-bristles; end joint with 3 spinous a-bristles; 1 of the b- and 2 of the d-bristles clawlike, pectinate.

    Fifth limb: Epipodial appendage with 57 to 61 bristles; endite I with 6 spinous bristles, anterior and posterior of these quite short, others long; endite II with 6 long spinous

    bristles; endite III with 9 or 10 spinous bristles. Exopodite: anterior side of 1st joint with 2 spinous bristles near triangular anterior tooth of main tooth and 1 short spinous bristle closer to outer margin (on Figure 207h, part of 1st joint is folded so that short bristle appears proximal to 2 longer bristles); main tooth of 1st joint consisting of 4 constituent teeth, all pectinate; anterior part of main tooth triangular; 1 bristle with stout marginal spines present proximal to teeth of main tooth; anterior side of 2nd joint with small d-bristle with few spines on anterior projection near outer corner of large quadrate tooth; posterior side with usually groups of 3 a- and b-bristles, all with spines, and long spinous c-bristle proximal to a- and b-bristles; margin of inner curvature of large tooth of 2nd joint with 1 small pointed node; outer lobe of 3rd joint with 1 or 2 spinous bristles, inner lobe with 3; 4th + 5th joint hirsute and with 6 spinous bristles.

    Sixth limb: 3 bristles present in place of epipodial appendage; endite I with 3 spinous bristles, 2 medial, 1 terminal; endite II with 4 spinous bristles, 1 medial, 3 terminal; endites III and IV each with 9 spinous bristles, 1 medial, 8 terminal; end joint moderately prolonged posteriorly and with 26-28 spinous and plumose bristles; endites and end joint with clusters of long hairs on medial and lateral surfaces.

    Seventh limb: Each limb with 10 bristles, 4 proximal (2 on each side) and 6 distal (3 on each side); all bristles spindle shaped (a juvenile character) and with 1 to 3 bells; bristles with distal marginal spines; terminal comb with 7 or 8 teeth, each tooth with about 4 extremely long lateral spines along each side; 1 peg with single pair of spines present opposite comb.

    Furca: Holotype with 12 claws on right lamella, 13 on left; claw 3 about same length as 4th but about half its width; claw 5 with teeth forming lateral and medial row; claws 2 to 4 with teeth forming row along posterior margin and with few teeth along anterior margin; remaining smaller claws mostly with slender spines along both anterior and posterior margins; hairs present at base of claws and on lamella following claws; marginal spines more equally distributed on anterior and posterior sides of claws on posteriorly placed claws.

    Rod-shaped organ: Elongate with about 13 segments at middle; tip rounded with minute hairs; small hairs present along margins.

    Eyes: Medial and lateral eyes about same size; neither black pigment nor ommatidia observed in lateral eyes of holotype; 4 weakly defined Pommatidia observed in lateral eyes of USNM 128504.

    Upper lip
    : Lip hirsute with anterior projection; large rounded single process present between upper lip and medial eye.

    Posterior: Hairs present forming clusters on upper and lower parts.

    Copulatory organ: Organ not evident. Brushlike bristles not observed.

    REMARKS—The paratypes from Eltanin station 208 may have been dried at one time because their carapaces were considerably distorted. They were restored with the help of a chemical (Aerosol-OT). These paratypes have smaller carapaces than the holotype. Other differences between the paratypes and holotype occur in the length of the proximal bristle on the 3rd joint of the endopodite of the 2nd antenna, which extends beyond the end of the joint on the holotype, but is quite short on the paratypes; also, the dorsal margin of the mandibular basale bears 4 bristles on the holotype but only 3 on the paratypes. The anteroventral infold of the carapace bears a row with 19 bristles on the holotype, but only about half this number on the paratypes. These differences have been interpreted as the result of individual variation. The 7th limbs and the distribution of bristles on the 2nd joint of the endopodites of the 2nd antennae are similar on the holotype and paratypes. The maxillae, 5th and 6th limbs of the paratypes were not examined in detail. Most claws of the furcae on the paratypes are missing.

    COMPARISONS—The comb teeth on the 7th limb of the new species bear long marginal spines. The comb teeth of S. appelloefi Skogsberg, 1920, S. flexilis (Brady, 1898) (in Poulsen, 1962), and S. arcnata Poulsen, 1962, have short spines, and S. gallardoi Kornicker, 1970, has no spines. The endopodites of the 2nd antennae of the N-l & of S. appelloefi (Skogsberg, 1920:421, fig. 78-7) and S. trituberculatiis (Lucas, 1931:4, fig. ID) have been described. The 2nd joint of both species bears 1 long proximal bristle and a group of shorter bristles on the distal half of the joint; S. appelloefi has 5 bristles in this group and S. trituberculatus has 3. The new species also bears a long proximal bristle on the 2nd joint, but does not have the small distal bristles; instead, it has 2 rather stout bristles in the middle of the ventral margin. The furca on the N-l juvenile male of S. trituberculatus (Lucas, p. 411, fig. 1C) bears 16 claws compared to 12 or 13 on the furca of S. frons.

    DISTRIBUTION—This species has been collected at only two stations west of Chile in the Subantarctic and Subantarctic-to-35Eltanin Cruise 5, station 216S regions at depths of 957 to 1226 m." (Kornicker 1975, p.329-335)

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