Nyxis rostrocularis, Willen, 2009

Willen, Elke, 2009, Nyxis rostrocularis, a new genus and species of Paranannopinae Por, 1986 (Copepoda, Harpacticoida) from the Southern Atlantic deep sea, Zootaxa 2096 (1), pp. 299-312 : 300-302

Nyxis rostrocularis gen. nov. sp. nov.

( Figures 1–8 )

Material: The female holotype of Nyxis rostrocularis was collected in the Weddell Sea during the ANDEEP expedition of RV Polarstern, PS 61/138, at 62°58.03'S and 27°54.08'W at a depth of 4541.3 m, on the 18.03.2002, using a multicorer .

Other examined material: 4 female specimens collected in the Angola Basin using a multicorer during the DIVA 1 campaign of the RV Meteor M 48/1 from 06.07.2000 to 08.08.2000 at the northern station 346 :

1 female specimen: 346-1: 16°17.005'S, 005°26.989'E, 27.07.2000, depth 5432m

3 female specimens: 346-5: 16°17.005'S, 005°26.989'E, 27.07.2000, depth 5433m

1 female specimen was collected in the Cape Basin during the DIVA 2 campaign of the RV Meteor M 63/ 2 using a multicorer at station 36 (Cape Basin, 28°6.7'S, 7°20.8'E, depth 5038m) sampled on 03.03.2005 .

The type material is stored in the collection of the Senckenberg research institute, Germany.

Female holotype: SNG 32235 on 12 slides

5 female paratypes: SNG 32236 -32241

Etymology. Nyx personifies the night in Greek mythology, the species name rostrocularis refers to the rostral pores looking like eyes.

Description of female (holotype). Body length 450 µm, furcal rami length 25 µm, Ro 48 µm.

Rostrum (figure 1B) demarcated from cephalothorax, longer than broad, margin hyaline, rounded, with one pair of longer sensilla apically and another one pair subapically, dorsal surface with a pair of large pores.

Body (figures 1A, B; 4A). No distinct separation between prosome and urosome. Cephalothorax longer than broad, cephalic shield with only a few sensilla visible. Posterior margin of each body somite (excluding penultimate somite) with sensilla. Urosomal somites with ventrolateral and dorsal spinule rows on distal margins (figures 1B, 4A); other somite surfaces dorsally without spinule ornamentation; genital doublesomite (free somites 5 and 6) dorsally fused, in ventral view with sclerotized ridge separating both genital somites, genital field as in figure 4A; P6 with 1 long seta. Anal somite completely divided, with two dorsal sensilla, anal operculum absent (figures 1B, 4A). Furcal rami (figures 1B, 4A) almost square, furcal seta I absent, II and III long and slender, II subapically near outer margin, III pinnate and inserting at outer edge, IV and V well developed, VI slender and naked, located on inner edge, VII triarticulated, subterminally on dorsal surface near inner margin.

Antennule (figures 1B; 2A, B). With six segments. Armature: I(1); II(9), setae of various shape and ornamentation: some setae biarticulated, some spine-like and ornamented with large spinules, 1 seta on posterior margin enlarged, biarticulated and ornamented with long spinules; III(8), 1 seta slightly enlarged and with irregular spinule ornamentation; IV(5+aes); V(5); VI(9 + aes).

Antenna (figures 3C, D). Allobasis with abexopodal pinnate seta in proximal half with basal spinule row; exp 3-segmented, with 1-1-(1+2) pinnate setae; enp with subapical row of long spinules, subapical armature consisting of two pinnate spines one of which is geniculate, 1 seta ornamented with long spinules and 1 tiny naked seta; apically with seven setae: one pinnate spine, 4 geniculate setae, the outermost of which fused at base with a tiny naked seta, and one additional small naked seta on abexopodal side.

Mandible (figure 5C). Gnathobase with 1 large and several smaller, fine and pointed teeth, becoming longer again near inner edge, with 1 slender naked seta on inner edge; basis with 3 pinnate setae and a few long spinules; enp and exp of nearly equal length, cylindrical, enp with 1 lateral and 3 apical setae, one of which is modified into a small mouthpart aesthetasc, exp with 1 lateral and 2 apical pinnate setae.

Maxillule (figure 3B). Arthrite of praecoxa with 8 apical spines, 1 slender anterior seta and two juxtaposed setae on anterior surface; coxal endite with 5 setae; basis with two distinguishable endites, bearing 4 + 2 setae, respectively; proximal basal endite with 1 seta modified as a small mouthpart aesthetasc; exp and enp of nearly equal length, with 3 setae each.

Maxilla (figure 3A). Syncoxa with 3 endites; proximal endite bilobed, proximal lobe bulbous with 1 enlarged pinnate spine and another large pinnate spine, distal lobe with 1 slender pinnate spine, middle and distal endites each with 3 setae/spines; basal endite with 1 pinnate claw fused to basis, accompanied by 1 slender spine on posterior and 2 setae on anterior side; enp 1-segmented, bearing 4 setae, one of which is modified as a small mouthpart aesthetasc.

Maxilliped (figure 5B). Syncoxa with few spinule rows and 1 enlarged pinnate seta on distal margin; basis bearing 1 small naked seta medially on inner margin as well as 1 spinule row parallel to inner margin; enp well developed with fused slender claw, 1 small and slender seta inserting “below”.

P1 (figure 4B). Coxa large, of rectangular shape, with spinule rows on margins and anterior surface. Basis with large pinnate outer and pinnate inner spine; terminal margin and base of spines with spinule rows. Exp 3- segmented, outer and distal margins with spinules; exp1 and 2 each with one outer pinnate spine, exp2 with inner seta; exp3 with 3 outer pinnate spines and 2 pinnate terminal setae; enp 2-segmented, enp1 shorter than enp2 with spinules along outer and distal margins and 1 inner plumose seta inserting near terminal margin; enp2 with pinnate inner seta, short pinnate outer seta and 2 long pinnate terminal setae.

P2–P4 (figures 6A, 7A, 8A). Exps and enps slender and 3-segmented, of nearly equal length. Coxae of almost rectangular shape, with spinule rows on inner and outer margins and anterior surface. Basis with a slender pinnate outer seta and spinule rows at base of outer setae. Inner setae of enp3 slightly displaced distally, segment appearing slightly elongated, as well as terminal swimming and inner setae of exopods. The specimens of the Angola Basin show an inner seta on P2 enp1, whereas this seta is lacking in the holotype and the specimen from the Cape Basin.

Setal formulae (after Lang 1948):

P5 (figure 5A). Pair of legs not fused medially, basal part with well developed pinnate outer seta, endopodal lobe slightly flattened but with a rounded outer edge and marginal spinules, with 5 pinnate setae, innermost of which is long and pinnate, second innermost short and pinnate in distal half, middle one shorter and pinnate, and outer 2 setae long and pinnate; exp longer than broad, narrow, setation consisting of 1 shorter and unipinnate inner seta, 2 pinnate terminal setae and 1 pinnate outer seta.

Figures

FIGURE 1. Nyxis rostrocularis gen. nov., sp. nov., A, female habitus lateral, scale bar = 50 µm; B, female habitus dorsal, scale bar = 50 µm.

FIGURE 2. Nyxis rostrocularis gen. nov., sp. nov., A, female antennule, segments I–VI illustrated separately, scale bar = 20 µm; B, female antennule without setation, scale bar = 20 µm.

FIGURE 3. Nyxis rostrocularis gen. nov., sp. nov., A, maxilla, scale bar = 20 µm; B, maxillule, scale bar = 20 µm; C, antenna, scale bar = 20 µm; D, subterminal setation of antennal endopod, scale bar = 20 µm.

FIGURE 4. Nyxis rostrocularis gen. nov., sp. nov., A, female urosome and genital field from ventral view, scale bar = 50 µm; B, P1, scale bar = 30 µm.

FIGURE 5. Nyxis rostrocularis gen. nov., sp. nov., A, female P5, scale bar = 30 µm; B, maxilliped, scale bar = 20 µm; C, mandible, small arrow indicates aesthetasc, scale bar = 20 µm.

FIGURE 6. Nyxis rostrocularis gen. nov., sp. nov., A, female P2, scale bar = 30 µm.

FIGURE 7. Nyxis rostrocularis gen. nov., sp. nov., A, female P3, exopod and basis, scale bar = 30 µm, B, female P3, endopod, scale bar = 30 µm.

FIGURE 8. Nyxis rostrocularis gen. nov., sp. nov., A, female P4 scale bar = 30 µm.