Leptotachidia senaria, Kim, Jong Guk, Yu, Ok Hwan & Lee, Jimin, 2019

Kim, Jong Guk, Yu, Ok Hwan & Lee, Jimin, 2019, Description of two deep-water copepods of the genus Leptotachidia Becker from the northwestern Pacific (Harpacticoida, Pseudotachidiidae), ZooKeys 873, pp. 133-153 : 135-137

Leptotachidia senaria sp. nov. Figs 2 , 3 , 4

Type locality.

Abyssal basin of the Northwest Pacific Ocean (31°58'42.9"N, 155°53'42.7"E), 5482 m depth ( Fig. 1 ).

Material examined.

Holotype: adult female dissected and mounted on 11 slides (cat. no. MABIK CR00246484) collected from the type locality on 1 November 2017.

Etymology.

The specific epithet is derived from the Latin senaria meaning 'consisting of six’ and refers to the female fifth leg with six elements in both rami, which is a unique characteristic within the genus Leptotachidia . It is in the nominative singular. Gender feminine.

Description of female.

Total body length about 710 μm measured from anterior tip of rostrum to posterior margin of caudal rami in lateral view; greatest width about 106 μm measured at the middle of cephalothorax. Habitus ( Fig. 2A, B ) elongate, cylindrical, with weak constriction between prosome and urosome; urosome slightly narrower than prosome. Prosome ( Fig. 2A, B ) composed of cephalothorax and three free pedigerous somites. Cephalothorax bell-shaped, slightly longer than wide in dorsal view, as long as 21% of total body length; surface ornamented with several small and large pores, and short and long sensilla; hyaline frill smooth; arthrodial membrane of first pedigerous somite visible posteriorly. Metasome gradually narrowing posteriorly; second pedigerous somite with two, third and fourth pedigerous somites with a single mid-dorsal pore, all free pedigerous somites with paired large pores and sensilla dorsally and laterally, with two lateral rows of minute spinules; pleural areas of second and third pedigerous somites distinctly produced posteriorly, weak in fourth one; hyaline frills of second and third pedigerous somites well developed and weakly serrate, smooth in fourth one. Dorsal surface ridges on third and fourth pedigerous somites partly modified with internal chitinous ribs ( Fig. 2A ).

Urosome ( Fig. 2 A–C ) gradually narrowing posteriorly, with large pores and paired sensilla dorsally and laterally; first urosomite with deeply incised and continuous hyaline frill, of genital double-somite interrupted ventrally by continuous row of strong spinules, of second abdominal somite interrupted ventrally by two short rows of strong spinules. Arthrodial membranes of all urosomites visible posteriorly. Original division between genital somite and third urosomite indicated by ventral and lateral subcuticular ridges, but dorsal aspect fused. Genital field with a transverse genital slit ( Fig. 2G ) covered by single plate with P6 represented by two vestigial setae and one row of minute spinules on both sides; copulatory pore located in a depression posterior to genital slit; seminal receptacles paired, placed inside genital aperture and connected with copulatory pore; one row of spinules and one large pore on ventrolateral surface; two pairs of large ventral pores on first abdominal somite. Second abdominal and penultimate somites with particular polygonal ribs along anteroventral surface ( Fig. 2C ). Penultimate somite with pseudoperculum, the latter with long spinules; posterior margin finely dentate dorsally and laterally, coarsely dentate ventrally, with two rows of stout spinules ventrolaterally. Anal somite short, with one pair of sensilla dorsally, one lateral pore, and one small and one large pores ventrally; dorsal surface depressed medially forming anal opening, with three rows of setules on inner margin.

Caudal rami ( Fig. 2 A–C, E, F ) divergent, slightly tapering towards posterior end, about 1.7 times as long as greatest basal width, with one dorsal and one ventrolateral large pore; rows of spinules present near base of setae III and V, and on inner distal corner; a small pore located at proximal forth of ventrolateral surface; with six caudal setae: seta I absent; seta II bare, small, at distal forth dorsolaterally; seta III pinnate, about three times as long as seta II, and inserted in lateral margin subdistally; principal setae IV and V well developed, distally pinnate and rat tail-like, seta V about twice as long as seta IV; seta VI minute, inserted at inner distal corner; seta VII tri-articulate at base, arising from distal third of inner-dorsal surface, with fine hairs distally.

Rostrum ( Fig. 2D ) large, bell-shaped, with one median pore, one pair of medial sensilla, and one pair of subdistal sensilla modified into aesthetascs-like structures.

Antennule ( Fig. 3A ) short, five-segmented; segment I with one long distal pinnate seta and two rows of stout outer spinules; segment II largest, about 1.2 times as long as wide, with one plumose and eight pinnate setae; segment III with eight pinnate setae; segment IV smallest, with three long bare and three pinnate setae, and one aesthetasc fused basally to adjacent one long bare seta; segment V with one pinnate, six spinulose and seven bare setae, one aesthetasc fused basally to adjacent two spinulose setae, and one densely opaque bulbous appendage (Brodskaya organ). Segment V with apical acrothek. Armature formula as follows: 1-[1], 2-[9], 3-[8], 4-[5 + (ae + 1)], 5-[12 + Brodskaya organ + acrothek].

Antenna ( Fig. 3B ). Coxa distinct, unornamented. Allobasis with one long pinnate seta and one group of long spinules on abexopodal margin. Exopod three-segmented; proximal segment elongate, 4.5 times as long as wide, with one bipinnate and one minute bare setae; middle segment small, with one spinulose seta; distal segment with two spinulose setae and one seta with distal part uniserrate. Free endopod with two rows of stout spinules laterally; lateral armature comprising one bare, one geniculate and two bipinnate setae; distal armature composed of two bipinnate and four geniculate setae, one of which bears spinules medially; distal margin with one row of stout spinules and one subdistal surface frill.

Mandible ( Fig. 3C ). Coxa with one medial protuberance ventrally and one row of setules near base of palp; gnathobase with one large uni-cuspidate and four multi-cuspidate teeth, and one unipinnate ventral seta. Palp uniramus, two-segmented; basis elongate, with three rows of spinules and one plumose seta; endopod small, one-segmented, with one small unipinnate seta and a claviform aesthetasc with peduncle partially bipinnate distally, and one rudimentary seta (indicated by arrowhead in Fig. 3C ) on lateral margin.

Maxillule ( Fig. 4A ). Praecoxa with two rows of outer spinules; arthrite with nine distal elements and two surface setae anteriorly. Coxal endite with one anterior row of spinules, one lateral row of setules, and one bare, one plumose and three unispinulose distal setae. Basis with two endites; distal endite largest, with one bare, one plumose and one pinnate setae, and a claviform aesthetasc with peduncle partially bipinnate distally, and one row of anterior spinules; subdistal endite with one long and one small bipinnate setae. Exopod broad, one-segmented, with three spinulose apical setae and one row of inner setules. Endopod one-segmented, with three bipinnate setae and one row of outer spinules.

Maxilla ( Fig. 3D ). Syncoxa with one transverse row of stout outer spinules and one row of minute surface spinules; with three endites: proximal endite bilobate, with one stout spinulose seta on proximal lobe, and one bipinnate and one spinulose setae on distal lobe; medial and distal endites with one bare, one bipinnate and one spinulose setae each. Allobasis with one long bare seta near base of endopod, drawn into a weakly pinnate claw bearing one bare seta, one pinnate element with an accessory spinule, and one weakly plumose seta. Endopod small, one-segmented, with one bare and one bipinnate setae, and a claviform aesthetasc with peduncle partially bipinnate.

Maxilliped ( Fig. 4B ). Praecoxa small, unornamented. Coxa elongate, with two pinnate geniculate setae subdistally, with two inner rows of stout spinules and one row of minute spinules proximally. Basis elongate, ovoid, with one row of stout inner spinules and one subdistal setulose seta. Endopod one-segmented, represented by a dentate claw bearing one vestigial accessory seta.

P1 ( Fig. 4C ). Praecoxa small, with one row of minute spinules distally. Intercoxal sclerite wide, slightly arched and unornamented. Coxa large, medially with three rows of minute spinules and one row of long spinules anteriorly; distally with one row of minute spinules and one row of stout spinules anteriorly; with two rows of spinules near outer distal corner; with one row of posterior spinules. Basis with one row of inner setules; with one row of stout spinules on distal pedestal of endopod; with one large pore near outer seta anteriorly; outer seta long, spinulose and arising from peduncle with three minute spinules; inner spine stout, spinulose and arising from peduncle bearing one row of spinules. Exopod three-segmented, reaching middle of enp-2; each segment with strong outer and distal spinules; exp-1 with one bipinnate outer spine; exp-2 with one bipinnate outer spine and one plumose inner seta; exp-3 with three bipinnate outer spines, and two rat tail-like setae with outer spinules and inner setules. Endopod longer than exopod, two-segmented; each segment with outer and distal spinules; enp-1 broad, with one plumose inner seta, with one large anterior pore, one row of posterior spinules, and one row of inner distal setules; enp-2 elongate, about 2.7 times as long as wide, with one pinnate distal outer spine, and two setae with pinnate outer and setulose inner margins.

P2-P4 ( Fig. 4 D–F ). Praecoxa small, as wide as coxa, with one row of stout distal spinules. Intercoxal sclerite developed, concave distally, with two distal pointed projections. Coxa broad, with three rows of minute medial spinules, one row of longer spinules and one large pore anteriorly; one row of stout outer distal spinules; with one row of outer spinules and one row of distal spinules posteriorly; with one row of stout (P2) or minute (P3-P4) inner distal spinules anteriorly. Basis with one large anterior pore, one row of distal spinules on pedestal of endopod, and one row of spinules near base of outer seta; the latter unipinnate (P2) or uniplumose (P3-P4); outer setae of P3-P4 with internal fracture plane; inner distal corner produced. Exopod slightly longer than endopod, three-segmented; each segment with outer and distal spinules; exp-1 and exp-2 with inner distal frills; P4 exp-3 with one row of inner setules; anterior pores on all exopodal segments of P2, and exp-2 and exp-3 of P3-P4; exp-1 with one serrate outer spine and one uniplumose inner seta; exp-2 with one serrate outer spine; exp-3 with two (P3-P4) or three (P2) serrate outer spines, two rat tail-like distal setae with outer marine spinulose, and inner margin setulose, and with one plumose inner proximal seta (P2-P3), or without inner armature (P4). Endopod tapering distally, three-segmented; each segmented with outer, inner and distal spinules; with distal posterior spinules in P2-P3 enp-1; with anterior pores on P2-P3 enp-1 and P2 enp-3; all endopodal segments without inner element; P2 enp-3 with one pinnate, rat tail-like and one plumose setae; P3-P4 enp-3 with one pinnate, rat tail-like seta; inner margin of P3 enp-3 modified and dented (indicated by arrowhead in Fig. 4E ). P1-P4 armature formulae:

P5 ( Figs 2C , 4H ). Small sclerite present between both members. Exopod and baseoendopod fused, forming a single plate, with five coarsely serrate and one finely serrate distal spines; with two large anterior pores; outer seta plumose, arising from small peduncle and with internal fracture plane.

Male.

Unknown.

Variability.

Left P4 of the female holotype normal, right endopod of P4 with two segments ( Fig. 4G ).

Figures

Figure 1. Map showing the sampling station.

Figure 2. Leptotachidia senaria sp. nov., female A habitus, dorsal B habitus, lateral C urosome, ventral D rostrum, dorsal E caudal ramus, dorsal F caudal ramus, ventral G genital field, ventral.

Figure 3. Leptotachidia senaria sp. nov., female A antennule B antenna C mandible (arrowhead indicates a rudimental lateral seta) D maxilla.

Figure 4. Leptotachidia senaria sp. nov., female A maxillule B maxilliped C P 1, anterior D P 2, anterior E P 3, anterior (arrowhead showing the modified and dented inner margin) F P 4, anterior G abnormality of P 4 endopod, anterior H P 5, anterior.