Synasterope pseudomystax Chavtur & Keyser, 2016, sp. nov.

Synasterope pseudomystax sp. nov.

(Figs. 14–19)

Etymology. The species name refers to the similarity to S. mystax Kornicker, 1975.

Holotype. ZMH-K-45824, adult female, length 3.12 mm, appendages are mounted on slide (45824/1) and destroyed valves are preserved in 70 % ethanol (45824/2).

Type locality. R/V “Polarstern”, ANT XIX /3, PS 61, 2002: ZMH-K-45824—adult female (length 3.12 mm), Stat. 43-8-E, 60°26.48´S – 56°4.00´W to 60°27.18´S – 56°4.80´W, depth 3953.6-3962.4 m, 4 February 2002.

Paratype. R/V “Polarstern”, ANT XXII /3, PS 67, 2005:

Stat. 154-9-E: ZMH-K-41911—immature female (2.81 mm).

Material (Fig. 20). R/V “Polarstern”, ANT XIX /3, PS 61, 2002:

Stat. 41-3: ZMH-K-45817 possible—juvenile (1.9 mm);

Stat. 42-2: ZMH-K-41911 possible—juvenile (1.6 mm);

Stat. 46-7: ZMH-K-45818 immature female and juvenile;

RV “Polarstern”, ANT XXII /3, PS 67, 2005:

Stat. 154-9: ZMH-K-41911– immature female (2.81 mm).

Description of adult female.

Carapace (Figs. 14 and 15). Elongate with evenly rounded posterior margin. Length 3.12 mm. Greatest height in middle (44%). Infold behind rostrum with about 10 setae between list and outer margin; only 4 setae on rostral list; anterior infold with about 10 setae; posterior list with about 15 transparent setae and about 15 small setae between adjacent transparent setae. Infold between posterior list and posterior edge of carapace is poorly preserved.

First antenna (Fig. 16 C–H). 1st joint with lateral terminal sclerotized knob on both outer and inner sides (fig. 16 D, E); 2nd joint with dorsal spinous seta; 3rd joint with very short bare ventral seta and 6 long spinous dorsal setae; 4th joint with 1 short bare and 1 long spinous seta, and 1 long spinous dorsal seta; sensory seta of 5th joint with 6 filaments (Fig.16 C, I); seta of 6th joint somewhat longer than a-seta of 7th joint. 7th joint: c-seta with 3 long proximal and 1 short distal and 1 terminal filaments; b-, f-, and g-setae broken.

Second antenna (Fig. 17 A–E). Protopodite with short slender medial seta. Endopodite 3-jointed; 3rd joint with long terminal seta. Exopodite joints without obvious spines.

Mandible (Figs. 17 F–J, 18 A–D). Coxale endite broken and lost. Basale (Fig. 18 C, D): endite with 3 terminal spinous setae, 3 triaenid setae, 2 dwarf setae and glandular peg; U-shaped margin depression and short dwarf seta present on basale proximal endite; dorsal margin on right limb with 1 and on left limb without midseta. Exopodite (Fig. 17 F, H–J) reaching about one-half distance up dorsal margin of 1st endopodite joint, with hirsute tip and 2 short subterminal setae. Endopodite: 1st joint with 3 long spinous ventral setae; ventral margin of 2nd joint with 3 long spinous terminal setae, dorsal margin (Fig. 18 A, B) with 1–3 proximal setae and stout spinous a-, b-, c- and dsetae; 1 short seta between a- and b-setae; 2 medial setae at margin between b- and c-setae; 5 medial setae forming oblique row between b- and c-setae; 1 long seta between c- and d-setae; 1 long seta near margin distal to d-seta; 3rd joint with pointed dorsal claw and 5 setae (Fig. 17 G).

Maxilla (Figs. 18 E, 19A). Epipodial appendage relatively long. Proximal endite with 4 long spinous setae and distal endite with 3 long spinous setae. Dorsal margin of basale with 1 short proximal and 1–2 distal setae; ventral margin with 1 short proximal seta and 1 long terminal seta. Endopodite: 1st joint with short dorsal seta and long ventral seta; 2nd joint with long terminal seta.

Fifth limb (Fig. 19 B–D). Epipodial appendage with 74 plumose setae. Comb: with long exopodial seta, 3 setae near ventral margin and 6 terminal setae.

Sixth limb (Fig. 19 E–G). Antero-dorsal corner without seta on medial surface; anterior margin with 1 upper seta; anterior tip without setae, lateral flap with 4 seta; postero-ventral margin with about 20 setae.

Seventh limb. Limb with 20–21 setae, proximal group with 9+7(8) setae and distal group with 2+2 setae.

Caudal furca. Each lamella with 9 claws and setae (1st– 7th claws and 8th and 9th setae).

Medial and lateral eyes (Fig. 16 A). Medial eye bare, lateral eyes absent.

Rod-shaped organ (Fig. 16 A, B). 1-jointed with rounded tip.

Description of immature female. Carapace (Fig. 15 B). Length 2.80–2.81 mm. Similar to that of adult female except a somewhat higher? position of incisur and pattern of central adductor muscle scars.

First antenna, mandible (each limb with 1 midlength seta on dorsal margin on basale), maxilla etc. similar to that of female.

Caudal furca. Each lamella with 8 claws.

Comparison. This species is closely related to S. mystax Kornicker, 1975 but differs from it by size and structure of first and second antenna, mandible, maxilla, fifth and sixth limbs and rod-shaped organ (Table 7).

Distribution. S. pseudomystax was collected from Antarctic waters between 59°–62° S and 56°–64° W at a depth of 2879–3962 m (Fig. 20).

Composition. The genus Bathyleberis includes 8 species of which the following are known from the study area: B. monothrix Kornicker, 1975, B. oculata Kornicker, 1975, B. grossmani Kornicker, 1975, B. babax Kornicker, 1996 (in Kornicker & Poore 1996).

Distribution. Members of this genus live between 71° N (Kornicker, 1988) and 61° S (Kornicker, 1975) and a depth range of 2–4303 m.

1. Sensory seta of 1st antenna with 7 long terminal filaments, anterior margin of 6th limb with 6 or 7 setae....... B. grossmani

– Sensory seta of 1st antenna with 1 short proximal and 6 long terminal filaments, anterior margin of 6th limb with 1 or 2 setae.................................................................................................... 2

2. Lateral eye well developed with about 18 ommatidia; dorsal margin of mandibular basale with 3–4 midsetae...... B. oculata

– Lateral eye absent or, if present, without ommatidia; dorsal margin of mandibular basale with 1 midseta................. 3

3. Rod-shaped organ 1-jointed; anterior margin of 6th limb with 2 setae....................................... B. babax

– Rod-shaped organ 2-jointed; anterior margin of 6th limb with 1 setae.................................. B. monothrix