Rythabis asymmetrica, Markhaseva & Schulz, 2007

Markhaseva, Elena L. & Schulz, Knud, 2007, New species of Brodskius, Rythabis, and Omorius (Crustacea: Calanoida) from deep Antarctic waters, Journal of Natural History 41 (13 - 16), pp. 731-750 : 737-742

publication ID	https://doi.org/ 10.1080/00222930701297772
persistent identifier	https://treatment.plazi.org/id/444A8794-7B63-FFA7-FE73-FBF5FE2CF92C
treatment provided by	Felipe
scientific name	Rythabis asymmetrica
status	sp. nov.

Treatment

Rythabis asymmetrica sp. nov.

( Figures 4–7 View Figure 4 View Figure 5 View Figure 6 View Figure 7 )

Material examined

Holotype: adult female, dissected, body length 1.35 mm ( ZMH K-41168). Scotia Sea, 58 ° 24 9 S, 25 ° 01 9 W, station 141-10, supranet, 23 February 2002, above the sea bed at depths of 2258–2281 m GoogleMaps . Paratype: dissected, body length 1.28 mm ( ZMH K-41169), locality data as for holotype GoogleMaps .

Description

Adult female. Total length 1.28, 1.35 mm; prosome 3.0–3.4 times longer than urosome. Cephalosome and pediger 1, and pedigers 4 and 5, incompletely separate ( Figure 4A, B, D–G View Figure 4 ); posterior corners of prosome rounded, asymmetrical, right one shorter ( Figure 4B, D, F View Figure 4 ). Genital double-somite nearly symmetrical ( Figure 4D View Figure 4 ). Spermathecae elongate, in distal half frontally directed ( Figure 4E–H View Figure 4 ). Caudal rami with four terminal setae, one small dorsal seta; ventral seta apparently missing ( Figure 4D, E View Figure 4 ).

Antennule ( Figures 4A View Figure 4 , 5A View Figure 5 ) exceeding anterior margin of pedigerous somite 4; of 24 free segments, armature as follows: I—3s, II–IV—6s+1ae, V—2s+1 ae, VI—2s, VII—2s+1 ae, VIII—2s, IX—2s+1ae; X–XI—4s+1ae, XII–XIII—1s; XIV—2s+1ae, XV—1s, XVI— 2s+1ae, XVII–XIX—1s each, XX—2s, XXI—1s+1ae, XXII–XXIII—1s each, XXIV– XXVI—2s each, XXVII–XXVIII—4s+1 ae.

Antenna ( Figure 5B, C View Figure 5 ): coxa with one seta, basis with two setae, exopod sevensegmented, ca 2.5 times as long as endopod, with 0, 1, 1, 1, 1, 1, 3 setae; endopod segment 1 with two setae, segment 2 with seven and six setae.

Mandible ( Figure 5D–G View Figure 5 ): gnathobase with five large and three small teeth, one seta and a row of spinules along cutting edge; basis with two setae; exopod of five segments with 1, 1, 1, 1 and 2 setae; endopod segment 1 with two setae, endopod segment 2 with nine setae.

Maxillule ( Figure 5H View Figure 5 ): praecoxal endite with nine thick and one thin small terminal and four posterior setae; coxal endite with five setae; coxal epipodite with nine setae; proximal basal endite with four setae, distal basal endite with five setae fused to endopod, endopod with nine setae; exopod with four setae.

Maxilla ( Figure 6A, B View Figure 6 ): proximal praecoxal endite with four setae, distal with three setae; proximal and distal coxal endites with three setae each; proximal basal endite with four setae: one thick, one sensory and one poorly sclerotized; distal basal endite plus endopod with six worm-like (three longer than others) and two brush-like sensory setae with distal filaments longer than setae itself ( Figure 6B View Figure 6 ).

Maxilliped ( Figure 6C–E View Figure 6 ): syncoxa with groups of setae on praecoxal endites not well separated, one sensory worm-like on proximal praecoxal endite, two setae (one sclerotized and one sensory worm-like) on middle, and two setae (one sclerotized and one sensory brush-like with long filaments) on distal praecoxal endite. Syncoxa with four rows of denticles: first row on proximal praecoxal endite ( Figure 6C View Figure 6 ), second and third rows (of short and long denticles) between distal group of setae on praecoxal endite and coxal endite ( Figure 6D View Figure 6 ) and fourth row on coxal endite along distolateral edge. Basis with three medial setae, two distal setae and row of small denticles proximally; endopod five-segmented with 4, 4, 3, 3+1, and 4 setae.

P1 ( Figure 6F, G View Figure 6 ): basis with curved mediodistal seta; endopod one-segmented with poorly developed lateral lobe; three medial and two terminal setae present; endopod with denticles along proximal lateral edge and lateral corner distally. Exopod segment 1 with lateral spine and a row of small denticles along distal edge, segment 2 with lateral spine, one medial seta and row of small denticles along distal edge; segment 3 with lateral spine, one terminal and three medial setae. Lateral spines subequal in length, that of segment 1 extending well beyond base of lateral spine of segment 2, that of segment 2 well beyond base of lateral spine of segment 3.

P2 ( Figure 7A View Figure 7 ): coxa with medial seta; denticles on inner posterior surface of coxa and basis; endopod two-segmented, segment 1 with one medial seta, segment 2 with two medial, two terminal and one lateral setae; both segments with denticles on posterior surface. Exopod segments 1 and 2 with one medial seta and one lateral spine each, segment 3 with four medial setae, one terminal and three lateral spines; terminal spine slightly shorter than segment 3; segments 2 and 3 with posterior denticles.

P3–P4 ( Figure 7B, C View Figure 7 ): coxa with medial seta; coxa and basis with denticles on inner posterior surface; rami three-segmented; endopod segments 1 and 2 with one medial seta each, segment 3 with one lateral, two terminal and two medial setae; all segments with denticles on posterior surface. Exopod segments 1 and 2 with one medial seta and one lateral spine each, segment 3 with four medial setae, one terminal and three lateral spines, length of terminal spine subequal to that of segment 3; segments 2 and 3 of P3 and all segments of P4 ornamented with posterior denticles.

P5 ( Figure 5I View Figure 5 ) uniramous, three-segmented, coxa slightly smaller than basis, both with denticles on posterior surface medially and distally; exopod armed with four spines, one toothed medial, of greater length than others, one short lateral and two strong toothed spines distally; subterminal lateral spine slightly longer than terminal.

Etymology

The specific name asymmetrica refers to the asymmetrical shape of the prosomal posterior corners.

Remarks

Schulz and Beckmann (1995) placed the genus Rythabis in the family Tharybidae . This affiliation was supported by Bradford-Grieve (2001) and Vyshkvartzeva (2005) but was not accepted by Ohtsuka et al. (2003) and Boxshall and Halsey (2004), who included the genus in the Scolecitrichidae . Markhaseva and Ferrari (2005) considered the family placement as incompletely resolved. Rythabis accommodates R. atlantica Schulz, 1995 , R. schulzi Markhaseva and Ferrari, 2005 , and R. heptneri Markhaseva and Ferrari, 2005 . Rythabis asymmetrica differs from congeners by: (1) posterior corners of prosome asymmetrical (symmetrical in other species of Rythabis ); (2) elongate spermathecae, which are frontally directed in distal half (not directed frontally, or moderately frontally directed); (3) presence of 14 setae on the distal basal endite plus endopod of maxillule (17 setae in R. atlantica , 11 in R. heptneri , 13 in R. schulzi ). The new species shares with R. atlantica an articulated terminal spine on P5 exopod (unarticulated in other species of Rythabis ) and two setae on the antenna endopod segment 1 (one seta) and thus appears more closely related to this species than to any other.