Pseudomesochra longiseta, Vasconcelos, Danielle Menor, George, Kai Horst & Santos, Paulo Jorge Parreira Dos, 2008

Vasconcelos, Danielle Menor, George, Kai Horst & Santos, Paulo Jorge Parreira Dos, 2008, First record of the genus Pseudomesochra T. Scott (Harpacticoida: Pseudotachidiidae) in the South Atlantic with description of a deep­sea species: Pseudomesochra longiseta sp. nov. *, Zootaxa 1866, pp. 337-348 : 338-341

Pseudomesochra longiseta sp. nov.

Material. The holotype (18835 MZUSP = 29 slides) is deposited in the Museum of the University of São Paulo ( MZUSP), Brazil. Female holotype was registered at station 6 ( 11°29'42"S 037°09'41"W), depth 492 m.

Etymology. The species name longiseta refers to the very long terminal “rat­tail” seta present on the second segment of the Exp A2.

Description of female Holotype. Habitus ( Fig. 1 ). Total body length measured from anterior tip of rostrum to posterior margin of telson: 0.63 mm. Including the furcal rami: 0.73 mm. There is a distinct separation between broad prosome and smaller urosome; spinules, sensilla and pores are distributed dorsally and laterally on cephalothorax and abdomen. Anal somite broken, with outer spinules and one pair of sensilla.

Rostrum ( Fig. 2 ) very large and broad; two pairs of sensilla located medially and subapically; pore on dorsal surface.

Antennule ( Fig. 2 ) 5­segmented. First segment broader than long, trapezoid in shape, with several spinules and 1 “rat­tail” seta. Second segment nearly square in shape, all setae of “rat­tail” shape. Third segment smallest, all setae of “rat­tail” shape. Fourth segment on its outer margin elongate, forming a protrusion which bears an aesthetasc accompanied by 2 “rat­tail” setae, and with 3 additional “rat­tail” setae. Fifth segment long, terminally with small aesthetasc, and with 13 setae, 7 of which “rat­tailed”. Setal formula: 1/1; 2/10; 3/8; 4/5 + aesthetasc; V (13 + aesthetasc).

Antenna ( Fig. 3 ) allobasis with spinules and 1 pinnate seta on outer margin. Exp 2­segmented. Exp1 basally with 1 pinnate seta and several spinules, terminally with 1 bare seta. Exp2 proximally with small tube pore and 1 small bare seta, terminally with 1 bare seta and 1 very long “rat­tail” seta bearing a long tube pore on its distal part. Enp2 with several rows of spinules, 3 “rat­tail” setae on outer margin, and terminally with 6 “rat­tail” setae (all broken).

Furcal rami ( Fig. 4 ) four times longer than broad. Setae I–V bipinnate. Seta I very small, located on the proximal half of the outer margin; II on distal half of outer margin; III subterminally on outer margin; IV and V well developed, “rat­tail” shaped, inserting terminally; seta VI bipinnate; seta VII triarticulate, bare. Spinules present on the outer, inner and terminal margin of the FR.

Mandible ( Fig. 5 ). Corpus large. Gnathobase with bi­ and tridentate slender teeth; 1 long, pinnate seta on the inner side. Palp biramous; basis with rows of spinules and 4 setae (1 pinnate and 3 bare); exp and enp 1­ segmented, enp long and slender, bigger than exp, with 3 lateral setae. Exp with spinules, 6 bare setae and 1 seta.

Maxillula ( Fig. 6 ). Praecoxal arthrite with 9 apical spines and 2 surface setae. Coxal endite with 5 bare setae. Basis armed with 7 slender bare setae. Exp with 2 bare and 1 pinnate setae; Enp with 2 bare setae.

Maxilla ( Fig. 7 ). Syncoxa with 2 rows of spinules and 3 endites. Proximal endite with few spinules, terminally with 3 setae. Middle endite with 1 uniplumose and 2 pinnate spines (one spine with terminal tube pore). Distal endite with 1 bare, 1 plumose, and 1 pinnate spine terminally. Enp not clearly defined at base, with 4 bare setae; syncoxa and basis fused, terminally with 1 strong spine, 1 small and 1 longer terminal seta.

Maxilliped ( Fig. 5 ). Syncoxa and basis each with several spinules and 1 bare seta. Enp fused with seta, forming a bipinnate claw, which bears 1 additional bare seta.

P1 ( Fig. 8 ). Coxa and basis with spinules on distal margins. Basis with 2 pores and 1 inner seta, outer seta broken. Exp 3­segmented, enp 2­segmented. Exp1 longer than exp2 and exp3 combined. Exp1 and exp2 with outer pinnate spine. Exps1–3 with outer spinules; exp1 additionally with inner spinules; exp2 with inner plumose seta; exp3 with 2 terminal and 2 outer “rat­tail” setae. Enp1 and enp2 with outer spinules. Inner seta of enp1 with asymmetrical ornamentation. Enp2 with 2 inner setae, terminally with 2 “rat­tail” setae.

P2–P4 ( Figs. 9 , 10 , 11 ). Swimming legs with pronounced intercoxal sclerite. Coxa of P4 broken at outer margin, with rows of spinules and with pore; intercoxal sclerite with “U” inverted in form and terminal spinules. Coxae and intercoxal sclerites of remaining swimming legs not drawn. Bases with 1 outer pinnate seta, spinules on margins, and 1 or 2 pores. Exps 3­segmented, enps 2­segmented; exps longer than enps, with pores on the segments. Exps1 and 2 with 1 inner asymmetric seta and 1 outer pinnate spine; P2 exp3 with 1 asymmetric and 1 naked inner seta, 1 asymmetric seta, 1 pinnate terminal seta, and 3 outer pinnate setae; P3 exp3 with 1 asymmetric and 1 pinnate inner setae, 2 asymmetric terminal setae and 3 outer pinnate setae; P4 exp3 with 2 pinnate inner setae, 1 “rat­tail”, 1 asymmetric terminal setae and 3 outer pinnate setae. Enps1 and 2 with spinules on the outer margin and between the segments. Enps1 with inner asymmetric seta; Enp2 with small spinules on the middle of the segment. Enps2 with 2 inner asymmetric setae, 1 small pinnate and 1 asymmetric terminal setae, and 1 outer pinnate seta. For comparison of ornamentation of swimming legs see Tab. 1

P5 ( Fig. 12 ) exp broken. Enp with 2 terminal and 2 inner pinnate setae.

Figures

FIGURE 1. Pseudomesochra longiseta sp. nov., holotype female from Sergipe, Brazil. Habitus, lateral and dorsal sides.

FIGURE 2. Pseudomesochra longiseta sp. nov., holotype female from Sergipe, Brazil. A 1 and rostrum.

FIGURE 3. Pseudomesochra longiseta sp. nov., holotype female from Sergipe, Brazil. A 2.

FIGURE 4. Pseudomesochra longiseta sp. nov., holotype female from Sergipe, Brazil. FR.

FIGURE 5. Pseudomesochra longiseta sp. nov., holotype female from Sergipe, Brazil. Md and mxp.

FIGURE 6. Pseudomesochra longiseta sp. nov., holotype female from Sergipe, Brazil. Mxl.

FIGURE 7. Pseudomesochra longiseta sp. nov., holotype female from Sergipe, Brazil. Mx.

FIGURE 8. Pseudomesochra longiseta sp. nov., holotype female from Sergipe, Brazil. P 1.

FIGURE 9. Pseudomesochra longiseta sp. nov., holotype female from Sergipe, Brazil. P 2.

FIGURE 10. Pseudomesochra longiseta sp. nov., holotype female from Sergipe, Brazil. P 3.

FIGURE 11. Pseudomesochra longiseta sp. nov., holotype female from Sergipe, Brazil. P 4.

FIGURE 12. Pseudomesochra longiseta sp. nov., holotype female from Sergipe, Brazil. P 5.