New species of Brodskius, Rythabis, and Omorius (Crustacea: Calanoida) from deep Antarctic waters

Three new species of rare benthopelagic clausocalanoidean genera with sensory setae on the maxilla are described from female specimens collected during the German Antarctic expeditions ANDEEP I–III in 2002 and 2005, mainly from abyssal depths close to the sea bed. Brodskius abyssalis sp. nov. differs from congeners by the lack of rostral filaments, two setae on the second segment of antenna exopod, thread‐like tips of maxillary worm‐like sensory setae, and the length of spines of P5 exopod. Rythabis assymmetrica sp. nov. is distinguished from other species in the genus by asymmetrical posterior corners of the prosome, the shape of spermathecae, and setal numbers on the maxillulary distal basal endite plus endopod. Omorius curvispinus sp. nov. is characterized by strongly curved setae of the maxillipedal syncoxa, a comparatively long seta on the basis of antenna, a slightly swollen genital double‐somite, and the shape of spermathecae. The genera Brodskius, Omorius, and Rythabis are recorded for the first time from the southern hemisphere.


Introduction
The benthopelagic fauna encompasses species usually found exclusively in the vicinity of the sea bed. Up to now near-bottom calanoid copepods have been poorly known. However, recent studies show that benthopelagic copepods of the Southern Ocean are highly diverse and include a great number of species that proved of outstanding interest both in taxonomic and ecological view (Bradford & Wells 1983;Schulz 1996Schulz , 1998Schulz , 2002Schulz , 2005Schulz , 2006Ohtsuka et al. 1998;Schulz & Markhaseva 2000;Markhaseva & Dahms, 2004;Markhaseva & Schulz 2006).
Three new species of three rare benthopelagic genera were found in the samples collected during the German expeditions ANDEEP I-III in 2002 and 2005 in the Scotia and Weddell Seas of the Southern Ocean which incorporated a deep benthopelagic sampling programme using an epibenthic sledge (Brandt et al. 2004).
In this paper three new species of the rare benthopelagic genera Brodskius Markhaseva and Ferrari, 2005, Omorius Markhaseva and Ferrari, 2005, and Rythabis Schulz and Beckmann, 1995 are described from deep waters of the Southern Ocean.

Methods and terminology
Copepod specimens were collected during R/V Polarstern expeditions ANDEEP I-II in 2002 and ANDEEP III in 2005. Sampling was done close to the sea bed at bathyal and abyssal depths between 2258 and 4655 m in the Scotia Sea and the Weddell Sea of the Southern Ocean by a closing epibenthic sledge (Brandt & Barthel 1995), with both supranet (sampling layer ca 1.00-1.30 m above the bottom; mesh size 0.3 mm) and epinet subsamples (0.27-0.60 m above the bottom; mesh size 0.5 mm). Specimens were fixed in 96% ethanol and later stained by adding a solution of chlorazol black E dissolved in 70% ethanol/30% water. Oral parts and swimming legs were dissected in glycerin and figures were drawn using a camera lucida.
The following abbreviations are used in the descriptions: P1-P5, swimming legs 1-5. Free segments of the antennule are designated by arabic numerals, ancestral segments are designated by roman numerals. One seta and one aesthetasc on a segment of the antennule are designated: 1s+1ae; ''1?'' indicates that a setal element was broken so that its identity on the antennule could not be determined and only the scar at the location of its attachment was counted. Segmentation of the antenna is assumed as having an 11-segmented exopod (Schulz 2005). The maxilliped syncoxa is considered to consist of three praecoxal endites and one coxal endite (Ferrari & Markhaseva 2000a, 2000bFerrari & Ivanenko 2001). Type specimens are deposited at the Zoological Museum Hamburg (ZMH).
Maxillule ( Figure 3C): praecoxal endite with nine terminal and two posterior setae; coxal endite with two setae, coxal epipodite with six setae; proximal basal endite with four setae, one of them longer and thicker than others and heavily setulated; distal basal endite fused to endopod with 10 setae in total, two of them longer and thicker than others and heavily setulated; exopod with six setae.
Maxilla ( Figure 3D, E): 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 of them thicker than others, one poorly sclerotized; distal basal endite plus endopod with eight sensory setae: five worm-like and three brush-like. Tips of worm-like sensory setae thread-like, one of brush-like setae thicker than others ( Figure 3E).
Maxilliped ( Figure 2B): syncoxa without seta on proximal praecoxal endite, two setae on middle endite, and three setae on distal praecoxal endite; coxal endite with three setae. Basis with three medial, two distal setae and row of denticles proximally. Endopod of five segments with 4, 3, 2, 2+1 and 4 setae. P1 ( Figure 3F): basis with tiny distolateral seta and medial distal seta moderately curved; endopod one-segmented with three medial and two terminal setae and small denticles along lateral edge distally; lateral lobe poorly developed, triangular. Exopod threesegmented, segment 1 with lateral spine, segment 2 with lateral spine and medial seta, segment 3 with lateral spine, terminal spine and three medial setae. All lateral spines of comparatively great lengths, distal one slightly shorter. P2 ( Figure 2C): coxa with medial seta; endopod two-segmented, segment 1 with one medial seta, segment 2 with two medial, two terminal and one lateral setae and spinules on posterior surface. Exopod three-segmented, segments 1 and 2 with lateral spine and medial seta each, segment 3 with three lateral spines, terminal spine and four medial setae. P3 ( Figure 2D): coxa with medial seta; endopod three-segmented, segments 1 and 2 with one medial seta each, segment 3 with two medial, two terminal and one lateral setae; segments 2 and 3 with scattered spinules on posterior surface. Exopod three-segmented, segments 1 and 2 with lateral spine and medial seta each, segment 3 with three lateral spines, terminal spine as long as combined lengths of segments 2 and 3 and very finely serrate.
P5 ( Figure 1L): uniramous, three-segmented; coxae naked and fused by intercoxal sclerite; basis with small patch of denticles distolaterally; exopod with denticles on posterior surface, one short lateral, a moderately long subterminal spine, a long terminal unarticulated extension, and one long medial spine, all toothed; short lateral spine hardly reaching base of subterminal spine; subterminal spine exceeding mid-length of terminal unarticulated extension; medial spine extending nearly to tip of terminal extension.

Etymology
The specific name is derived from the Greek abyssos meaning bottomless, abyss, and refers to the type locality of the species. Markhaseva and Ferrari (2005) attributed four species to the genus Brodskius: B. benthopelagicus Markhaseva and Ferrari, 2005, B. confusus Markhaseva and Ferrari, 2005, B. paululus (Park, 1970), and B. robustipes (Grice and Hulsemann, 1965). The new species fits well the generic definition, but is distinguished from the above species by: (1) the lack of rostral filaments (present in other species); (2) presence of two setae on the second exopodal segment of the antenna (one seta in other species); (3) thread-like tips of maxillary worm-like sensory setae (not thread-like); and (4) the subterminal spine of P5 having moderate length surpassing mid-length of terminal unarticulated extension. The new species shares a long subterminal spine of P5 with B. confusus, however, it differs by a shorter lateral spine not reaching the base of the subterminal spine (exceeding the base in B. confusus); in other congeners the subterminal spine not reaching or hardly reaching midlength of terminal extension.

Remarks
An additional single female of an undescribed species of Brodskius was found in sample 042-2 at depths of 3680-3683 m (59u409S, 57u359W), collected on 27 January 2002, which could not be described due to poor condition. This specimen differs from congeners particularly by larger size (1.48 mm) and the presence of a well-developed rostrum furnished with two thick filaments.
Maxilla ( Figure 6A, B): 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). Maxilliped ( Figure 6C-E): 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), second and third rows (of short and long denticles) between distal group of setae on praecoxal endite and coxal endite ( Figure 6D) 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.  Figure 6F, G): 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): 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.

P1 (
P3-P4 ( Figure 7B, C): 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) 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. 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 andFerrari, 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.
Mandible ( Figure 9E-G): gnathobase with tooth-like knob on posterior face and wide cutting edge, with eight blunt teeth and one seta; basis with three setae; exopod of five segments with 1, 1, 1, 1 and terminal setae broken; endopod segment 1 with two setae, endopod segment 2 with nine setae.
Maxilla ( Figure 10A, B): proximal praecoxal endite with four setae and short triangular attenuation; distal endite with three setae; proximal coxal endite with three setae, distal coxal endite with three setae, one long, thick and spine-like; proximal basal endite with four setae, one thick, spine-like and one worm-like sensory seta; all endites with small spinules distally; distal basal endite plus endopod with eight sensory setae, of these five worm-like and three brush-like.
Maxilliped ( Figure 10C, D): syncoxa with one seta on praecoxal endite, two setae on middle endite (one heavily sclerotized, spine-like and strongly curved), and one seta slightly curved in proximal third on distal praecoxal endite; coxal endite with three setae; four rows of spinules present: proximally; between medial and distal praecoxal endites; adjacent to coxal endite proximally; along distal edge of coxal endite. Basis with row of spinules proximally and three medial and two distal setae. Endopod five-segmented with 4, 4, 3, 3+1 and 4 setae. P1 ( Figure 10E): coxa with row of small denticles along distal outer edge; basis with tiny distolateral seta and mediodistal seta on anterior face; endopod one-segmented, comparatively long and extending to anterior margin of exopod segment 2, with three medial and two terminal setae; lateral lobe small and triangular lacking denticles, spinules present along distolateral edge of endopod. Exopod three-segmented, segment 1 with lateral spine, segment 2 with lateral spine and medial seta, segment 3 with lateral spine, terminal spine and three medial setae; lateral spines of exopod segments 1 and 2 covered with denticles, spine of segment 3 longest. P2 ( Figure 11A): coxa with medial seta; basis with group of small denticles on posterior surface near base of endopod; endopod two-segmented, segment 1 with one medial seta, segment 2 with two medial, two terminal and one lateral setae and ornamented with denticles on posterior surface; exopod segments 2 and 3 detached, segment 1 with one medial and one lateral seta. P3 ( Figure 11B): coxa with medial seta; basis with row of denticles distally; endopod segment 1 with one medial seta; exopod segment 1 with one medial and one lateral seta; exopod and endopod segments 2 and 3 detached. P4 ( Figure 11C): coxa with medial seta; coxa and basis with large patches of denticles on posterior surface; endopod segment 1 with one medial seta and with posterior denticles; exopod segment 1 with one medial, one lateral seta and sparse posterior denticles, exopod and endopod segments 2 and 3 broken. P5 ( Figure 9I): three-segmented, all segments with denticles on posterior surface; exopod (distal segment) with one medial spine (broken), one lateral, one short subterminal and one terminal attenuation (broken).

Etymology
The specific name is derived from the Latin curvus meaning curved and spinus meaning spine and relates to the strongly sclerotized, spine-like curved setae of the maxillipedal syncoxa.

Geographical distribution and bathymetry
Each of the genera Brodskius, Rythabis, and Omorius is recorded here for the first time in the southern hemisphere (Table I). Other congeners of Brodskius have been reported from the North Atlantic, namely B. paululus, B. robustipes, and B. confusus. Brodskius benthopelagicus was described from the tropical Pacific Ocean. The genus Rythabis was established for R. atlantica Schulz, 1995 from the North Atlantic but R. heptneri and R. schulzi were collected in the Pacific Ocean. The type species of Omorius, O. atypicus, has been recorded from the tropical Pacific Ocean (Grice & Hulsemann 1965;Park 1970;Schulz & Beckmann 1995;Markhaseva & Ferrari 2005). All three genera, Brodskius, Rythabis, and Omorius, are deep-water genera collected mostly at abyssal depths immediately above the sea bed. There are several records of Brodskius paululus between depths of 1900 and 509 m (Park 1970) and from the 800-1250 m layer (Roe 1975, as 'Xanthocalanus paululus'), all other records of this genus originate from depths below 1900 m (Table I). Up to now, species of Rythabis have been collected at depths between 2258 and 3100 m, except for R. heptneri recorded at mesopelagic depth (600 m) ca 30 m from the bottom. Both known species of Omorius were captured between 2889 and 3100 m.