Pseudotachidiidae Lang, 1936a

Family Pseudotachidiidae Lang, 1936a View in CoL .

3.1.1. Subfamily Pseudomesochrinae Willen, 1996

Genus Pseudomesochra Scott T., 1902 .

Type species: Pseudomesochra longifurcata Scott T., 1902 .

Other species: Pseudomesochra aberrans Bodin, 1968 ; P. abyssalis Becker and Schriever, 1979 ; P. affinis (Sars G.O., 1920a) ; P. axa sp. nov.; P. bathyalis sp. nov.; P. bathyhabitatrix sp. nov., P. bathysicola sp. nov.; P. beckeri Becker and Schriever, 1979 ; P. brucei (Scott T. and Scott A., 1901) ; P. crispata ( Brady, 1910) ; P. divaricata (Sars G.O., 1906a) ; P. gemina Coull, 1973a ; P. gertwilleni Willen, 1996 ; P. laptevensis Willen, 1996 ; P. latifurca (Sars G.O., 1911) ; P. media (Sars G.O., 1911) ; P. meridianensis Willen, 1996 ; P. minor Becker, 1974 ; P. perplexa Bodin, 1968 ; P. scheibeli Schriever, 1982 ; P. similis Lang, 1936b ; P. tatianae Drzycimski, 1968 .

3.1.1.1. Pseudomesochra bathyalis sp. nov. urn:lsid:zoobank.org:act:

Type material. Female holotype dissected and mounted on seven slides (ICML-EMUCOP-170616-02); June 17, 2016; Ivonne Martínez-Mendoza leg.

Type locality. Xiximi 5 cruise; stn A5, Gulf of Mexico, northern Sigsbee Deep ( 25.1168 ◦ N, 92.0002 ◦ W); 3513 m depth; clay 16 %, silt 66 %, sand 18 GoogleMaps %.

Etymology. The specific epithet comes from the ancient Greek Вαθύς (bathús, deep), and the Latin suffix -alis. It is an adjective in the nominative singular, gender feminine.

Description. Female. Total body length measured from tip of rostrum to posterior margin of caudal rami 390 μm. Habitus ( Fig. 2A View Fig ) semicylindrical, tapering posteriad, with clear division between pro- and urosome. Rostrum ( Figs. 2A View Fig and 4A View Fig ) large, broad, subrectangular, with two lateral sensilla subdistally and pores as shown. Prosome ( Fig. 2A View Fig ) composed of cephalothorax, and P2–P4-bearing somites, widest at the middle of cephalothorax; urosome ( Figs. 2B View Fig and 3A View Fig ) composed of P5- bearing somite, genital double-somite, two free urosomites, and anal somite with caudal rami. Prosomites with sensilla as shown, with smooth posterior fills. Urosomites with sensilla and pores as shown; P5- bearing somite without spinular ornamentation; genital double-somite formed by the complete fusion of genital and third urosomites, without spinular ornamentation; genital complex ( Fig. 3A View Fig ) medially on proximal half, with single copulatory duct and copulatory pore posterior to P6 medially, single dumpbell-shaped seminal receptacle slightly anterior to P6; fourth urosomite with short lateral row of spinules; fifth urosomite with dorsal posterior frill extended medially forming pseudoperculum, with lateral spinules smaller than in preceding somite and with stronger and larger lateroventral spinules close to posterior margin; anal somite cleft medially, dorsally with one medial sensilla and an oblique row of small setules on each side, laterally and ventrally with transverse row of small spinules close to insertion of caudal rami. The latter cylindrical, slightly twice as long as wide, divergent; with small spinules medially on lateroventral surface, and at bases of setae II, III, and VI, and with large pore between setae III and IV; with six setae as follows: lateral seta II slender, arising at distal third of ramus; seta III slender, issuing subdistally close to outer distal corner; setae IV and V well-developed, the former shorter, both setae with fracture planes, distal half rat-tail-like and furnished with minute pinules; seta VI issuing at distal inner corner; dorsal seta VII triarticulate at base, located on distal third of ramus close to inner margin.

Antennule ( Fig. 4B View Fig ) six-segmented; surface of segments smooth except first segment; relative length of segments as shown, sixth segment longest; all setae smooth except for the seta on first segment, one seta on fourth, and three setae on sixth segment. Armature formula as follows: 1 (1), 2(10), 3(9), 4(4+ae), 5(2), 6(12+ae).

Antenna ( Fig. 4C and D View Fig ) with allobasis, the latter as long as free endopodal segment, with few proximal spinules and one long slender abexopodal seta. Exopod two-segmented; first segment visibly shorter than second, unornamented, with two setae; second segment elongate, with transverse row of small spinules subdistally, with two lateral and two distal setae as shown. Free endopodal segment with proximal longitudinal row of small spinules and with curved row of longer ornaments subdistally; lateral armature consisting of one proximal slender seta and two median spiniform elements; distal armature consisting of six setae of which five rat-tail-like and outermost longest fused basally to slender short normal seta.

Mandible ( Fig. 5A–C View Fig ) with well-developed coxa; gnathobase with bicuspidate teeth as depicted, with two spines and one unipinnate seta. Palp biramous; basis large, with three setae; rami one-segmented; endopod with two inner and five distal setae; exopod with six setae in all.

Maxillule ( Fig. 5D View Fig ) with well-developed praecoxa; arthrite of praecoxa with two surface setae, and eight spines and one ventral seta as depicted. Coxal endite with four setae of which three slender and bare, one spiniform and spinulose. Basis with few subdistal spinules, with four slender apical elements and one slender lateral seta. Rami one segmented; endopod elongate, with three distal setae; exopod shorter than endopod, with three elements.

Maxilla ( Fig. 6A) with large syncoxa ornamented with few strong outer spinules subdistally, with three elongate subequal endites armed with three setae each. Basis drawn out into strong claw accompanied by strong spine and one anterior and one posterior seta. Endopod incorporated into allobasis, represented by three slender setae.

Maxilliped ( Fig. 6B) robust. Syncoxa nearly as long as basis, unornamented, with one inner subdistal seta. Basis with few inner strong spinules as shown, with one subdistal seta. Endopod one-segmented, with distal spinulose claw.

P1 ( Fig. 7A View Fig ) with transversely elongate intercoxal sclerite. Coxa subrectangular, with few outer and some inner subdistal spinules. Basis with spinules at base of inner spiniform element, between rami, and at base of outer seta. Exopod three-segmented, inserted at a lower level than endopod; segments with outer and subdistal spinules as shown, EXP1 with inner setules and few distal minute spinules; EXP1 without, EXP2 with inner seta; EXP3 with two outer spines and two distal elements of which distal outer spiniform, distal inner setiform and rat-tail-like. Endopod two-segmented, longer than exopod; ENP1 slightly shorter than ENP2, with inner, subdistal, and outer spinules as depicted, unarmed; ENP2 with longitudinal row of outer spinules and some ornaments subdistally, with one inner seta, two distal elements of which innermost rat-tail-like and medial spiniform, and one outer spine.

P2 ( Fig. 7B View Fig ) with trapezoidal intercoxal sclerite ornamented with strong spinules distally on rounded distal tines. Praecoxa triangular, transversely elongate, with transverse row of distal spinules. Coxa subrectangular, with few outer short spinules. Basis with one proximal outer and one medial pore, with spinules at base of outer seta and between rami. Exopod inserted at a lower level than but reaching tip of endopod, three-segmented; EXP1 and EXP3 longest; EXP1 and EXP2 with outer spinules as shown; EXP1 without, EXP2 with subdistal outer pore; EXP1 and EXP2 with outer spine of which outer spine of EXP2 visibly longer; EXP1 without, EXP2 with inner seta; EXP3 with outer spinules at the base of outer and distal armature elements and with subdistal medial pore, with three outer spines, two distal spiniform elements, and two inner slender setae. Endopod three-segmented; segments with outer spinules as shown; ENP1 widest, with medial subdistal pore, with outer distal corner moderately produced, inner distal margin with produced pointed projection, inner element strong, spiniform, strongly spinulose; ENP2 largely as ENP1 but visibly narrower, with outer distal corner drawn out into long pointed outgrowth; ENP3 longest and narrowest, with medial pore, with two inner slender setae, two distal elements of which outer spiniform and inner setiform (rat-tail-like condition of the latter not evident), and one outer spine.

P3 ( Fig. 8A View Fig ) with intercoxal sclerite similar to that of P2 but with less-developed distal rounded outgrowths ornamented with comparatively shorter outer spinules, and with pointed distal outer tines slightly larger. Praecoxa (not shown), coxa and basis as in P2. Exopod largely as in P2 but EXP3 without pore, and with three inner setae. Endopod as in P2 but ENP2 with less-developed distal outer outgrowth, and inner armature of ENP1 and ENP2 comparatively longer.

P4 ( Fig. 8B View Fig ) with intercoxal sclerite ornamented with few distal outer spinules, without distal rounded outgrowths, but with outer distal pointed tines well-developed. Praecoxa as in P2. Coxa and basis as in P2 and P3. Exopod as in P3, but medial inner seta on EXP3 visibly longer. Endopod largely as in P3, but with one inner long seta.

Pair of P5 ( Figs. 2B View Fig and 3B View Fig ) not fused medially; baseoendopod and exopod fused; baseoendopodal and exopodal lobes subequal in length; baseoendopod with outer basal seta, endopodal lobe with two inner and two distal setae of which distal inner element longest. Exopodal lobe with one subdistal outer and one distal seta.

P6 ( Fig. 3A View Fig ) represented by two setae.

Male. Unknown.

Variability. The exopodal lobe of the left P5 ( Fig. 3B View Fig ) bears the typical long apical and the shorter outer seta, and an additional outer proximal small seta.

3.1.1.2. Pseudomesochra axa sp. nov. urn:lsid:zoobank.org:act:

Type material. Female holotype dissected and mounted on seven slides (ICML-EMUCOP-210817-01); August 21, 2017; Ivonne Martínez-Mendoza leg.

Type locality. Xiximi 5 cruise; stn B18, Gulf of Mexico, Campeche Escarpment ( 24.0501 ◦ N, 86.8835 ◦ W); 1150 m depth; clay 7.4 %, silt 55.8 %, sand 36.8 GoogleMaps %.

Etymology. The species is dedicated to Dr Axay´acatl Rocha-Olivares (Centro de Investigacion´Científica y de Educaci´on Superior de Ensenada, Baja California, Mexico) for providing us with the biological material from the Xiximi 5 cruises in the Gulf of Mexico). The speciesgroup name is to be treated as indeclinable and need not agree in gender with the genus name.

Description. Female. Total body length measured from tip of rostrum to posterior margin of caudal rami 335 μm. Habitus ( Fig. 9A View Fig ) semicylindrical, tapering posteriad, with clear division between pro- and urosome. Rostrum ( Figs. 9A View Fig and 11A View Fig ) large, broad, subrectangular, with two lateral sensilla subdistally and pores as shown. Prosome ( Fig. 9A View Fig ) composed of cephalothorax, and P2–P4-bearing somites, widest at the middle of cephalothorax; urosome ( Figs. 9A and B View Fig , 10A View Fig ) composed of P5-bearing somite, genital double-somite, two free urosomites, and anal somite with caudal rami. Prosomites with sensilla as shown, with smooth posterior fills. Urosomites with sensilla and pores as shown; P5- bearing somite without spinular ornamentation; genital double-somite formed by the fusion of genital and third urosomites, with internal cuticular rib indicating former division between somites, without spinular ornamentation; genital complex ( Fig. 10A View Fig ) medially on proximal half, with single copulatory duct and copulatory pore slightly posterior to unarmed P6 medially, single dumpbell-shaped seminal receptacle slightly anterior to P6; fourth urosomite without spinular ornamentation; fifth urosomite seemingly without pseudoperculum, with lateral spinules; anal somite cleft medially, dorsally with one medial sensilla on each side, laterally and ventrally with transverse row of small spinules close to insertion of caudal rami. The latter cylindrical, slightly twice as long as wide, divergent; with small spinules medially on lateroventral surface, and at bases of setae II, III, and VII, and with large pore between setae III and IV; with six setae as follows: lateral seta II slender, arising at distal third of ramus; seta III slender, issuing subdistally close to outer distal corner; setae IV and V well-developed, the former shorter, both setae with fracture planes, distal half rat-tail-like and furnished with minute pinules; seta VI issuing at distal inner corner; dorsal seta VII triarticulate at base, located in the middle of the ramus close to inner margin.

Antennule ( Fig. 11B View Fig ) six-segmented; surface of segments smooth except for first segment; relative length of segments as shown, sixth segment longest; all setae seemingly smooth except for one seta on sixth segment. Armature formula as follows: 1(1), 2(10), 3(8), 4(4+ae), 5(2), 6(12+ae).

Antenna ( Fig. 11C View Fig ) with allobasis, the latter as long as free endopodal segment, with few proximal spinules and one long slender abexopodal seta. Exopod two-segmented; first segment visibly shorter than second, unornamented, with two setae; second segment elongate, with subtle notch midway outer margin aligned with insertion site of proximal seta (arrowed in figure), with transverse row of small spinules subdistally, with two lateral and two distal setae. Free endopodal segment with proximal longitudinal row of small spinules and with subdistal spinular ornaments; lateral armature consisting of one proximal slender seta and two median elements of which one spiniform and one setiform; distal armature consisting of six setae of which five rat-tail-like and outermost longest fused basally to slender short normal seta.

Mandible ( Fig. 12A View Fig ) with well-developed coxa; gnathobase with bicuspidate teeth as depicted, with three spines and one unipinnate seta (the latter missing in figure). Palp biramous; basis large, with three setae; rami one-segmented; endopod with two inner and five distal setae; exopod with six setae as shown.

Maxillule (not shown) lost during dissection.

Maxilla ( Fig. 12B View Fig ) with large syncoxa ornamented with two outer spinular patches as shown, with three endites of which proximal thicker, middle and distal endites elongate and subequal in length; proximal and middle endites with three, distal endite with two setae. Basis drawn out into strong claw accompanied by strong spine and one seta. Endopod seemingly one-segmented (?), with three setae.

Maxilliped ( Fig. 12C View Fig ) robust. Syncoxa visibly shorter than basis, unornamented, with one inner seta. Basis with hump-like inner protrusion proximally, ornamented with inner spinules as shown and with subdistal outer spinular ornaments, with one subdistal seta. Endopod one-segmented, with distal spinulose claw.

P1 ( Fig. 13A View Fig ) with transversely elongate intercoxal sclerite. Coxa rectangular, with few outer spinules close to outer distal corner. Basis with spinules at base of inner spiniform element and between rami, with outer pore close to outer basal seta. Exopod three-segmented, inserted at a lower level than endopod; segments with outer and subdistal spinules as shown, EXP1 and EXP2 with somewhat elongate outer spines, without inner armature; EXP3 with two outer spines and two distal elements of which distal outer spiniform, distal inner setiform and rat-tail-like. Endopod two-segmented, longer than exopod; ENP1 slightly shorter than ENP2, with inner, subdistal, and outer spinules as depicted, unarmed; ENP2 with longitudinal row of outer spinules, with two distal elements of which innermost rat-tail-like and medial spiniform, and one outer spine.

P2 ( Fig. 13B View Fig ) with trapezoidal intercoxal sclerite ornamented with spinules distally. Praecoxa triangular, transversely elongate, with transverse row of distal spinules. Coxa subrectangular, with few short spinules close to outer distal corner. Basis with small spinules between rami, with one outer pore, and short outer seta. Exopod inserted at a lower level than and not reaching tip of endopod, three-segmented; EXP1 and EXP3 longest; EXP1 and EXP2 with outer spinules as shown, with outer spines of which outer spine of EXP2 visibly longer; EXP1 without, EXP2 with inner seta; EXP3 with outer spinules at the base of outer armature elements and with subdistal medial pore, with three outer spines, and two distal spiniform elements. Endopod three-segmented; segments with outer spinules as shown; ENP1 widest, with outer distal corner moderately produced, inner distal margin with produced pointed projection, inner element strong, spiniform, spinulose; ENP2 largely as ENP1 but visibly narrower, with outer distal corner drawn out into pointed outgrowth; ENP3 longest and narrowest, with medial pore, with one inner slender seta, two distal elements of which innermost setiform (rat-tail-like condition of the latter not evident) and outer spiniform, and one outer spine.

P3 ( Fig. 14A View Fig ) with intercoxal sclerite similar to that of P2 but with larger distal tines, unornamented. Praecoxa transversely elongate, triangular, with transverse spinular row distally. Coxa and basis as in P2 except for spinular ornamentation of basis. Exopod largely as in P2. Endopod as in P2 but inner armature of ENP1 and ENP2 comparatively longer.

P4 ( Fig. 14B View Fig ) with unornamented intercoxal sclerite of which outer distal pointed tines well-developed. Praecoxa, coxa and basis as in P3. Exopod as in P3 except for outer spine of EXP2 not as elongate as in P3 EXP2. Endopod largely as in P3, but with inner elements comparatively longer.

Pair of P5 ( Fig. 10B View Fig ) not fused medially; baseoendopod and exopod completely fused making difficult to discern between endopodal and exopodal lobes; with six setae in all of which outermost basal.

P6 ( Fig. 10A View Fig ) seemingly unarmed.

Male. Unknown.

3.1.1.3. Pseudomesochra bathysicola sp. nov. urn:lsid:zoobank.org:act:

Type material. Female holotype dissected and mounted on six slides (ICML-EMUCOP-210817-02); August 21, 2017; Ivonne Martínez-Mendoza leg.

Type locality. Xiximi 5 cruise; stn B18, Gulf of Mexico, Campeche Escarpment ( 24.0501 ◦ N, 86.8835 ◦ W); 1150 m depth; clay 7.4 %, silt 55.8 %, sand 36.8 GoogleMaps %.

Etymology. The specific epithet comes from the ancient Greek Вαθύς (Bathús, deep), and the Latin suffix - cola (from colo ¯, -ere, dwell). It is a noun in the nominative singular, gender feminine.

Description. Female. Total body length measured from tip of rostrum to posterior margin of caudal rami 326 μm. Habitus ( Fig. 15A View Fig ) semicylindrical, tapering posteriad, with clear division between pro- and urosome. Rostrum ( Figs. 15A View Fig and 16A View Fig ) large, broad, subrectangular, with two lateral sensilla subdistally and pores as shown, tip slightly bilobate. Prosome ( Fig. 15A View Fig ) composed of cephalothorax, and P2–P4- bearing somites, widest at the middle of cephalothorax; urosome ( Fig. 15A and B View Fig ) composed of P5-bearing somite, genital double-somite, two free urosomites, and anal somite with caudal rami. Prosomites with sensilla as shown, with smooth posterior fills. Urosomites with sensilla and pores as shown; P5-bearing somite without spinular ornamentation; genital double-somite formed by the fusion of genital and third urosomites, with internal lateral cuticular rib indicating former division between somites, with two medial rows of tiny spinules dorsally; genital complex ( Fig. 15C View Fig ) medially on proximal half, with single copulatory duct and copulatory pore slightly posterior to P6 medially, single dumpbell-shaped seminal receptacle slightly anterior to P6; fourth urosomite without spinular ornamentation; fifth urosomite seemingly without pseudoperculum, with posterior ventrolateral spinules as shown; anal somite cleft medially, dorsally with one medial sensilla on each side, laterally and ventrally with transverse row of small spinules close to insertion of caudal rami, with two ventral pores. Caudal rami ( Fig. 15A–C View Fig ) cylindrical, about three times as long as wide, divergent; with small spinules medially on lateroventral surface, and at bases of setae II and VII, and with large pore between setae III and IV; with six setae as follows: lateral seta II short and slender, arising at distal fourth of ramus; seta III slender about three times as long as seta II, issuing subdistally close to outer distal corner; setae IV and V well-developed, the former shorter, both setae with fracture planes, distal half rat-tail-like; seta VI shorter than seta III, issuing at distal inner corner; dorsal seta VII triarticulate at base, located in the middle of the ramus close to inner margin.

Antennule ( Fig. 16A View Fig ) six-segmented; surface of segments seemingly smooth; relative length of segments as shown, sixth segment longest; all setae seemingly smooth. Armature formula as follows: 1(1), 2(9), 3(7), 4 (3+ae), 5(2), 6(10+ae).

Antenna ( Fig. 16B View Fig ) with allobasis, the latter as long as free endopodal segment, with few proximal spinules and one long slender abexopodal seta. Exopod two-segmented; first segment visibly shorter than second, unornamented, with two setae; second segment elongate, with transverse row of small spinules subdistally, with two lateral and two distal setae. Free endopodal segment with proximal longitudinal row of small spinules and with subdistal spinular ornaments; lateral armature consisting of one proximal slender small seta and two median setiform elements of which one spiniform, the other setiform; distal armature consisting of five rat-tail-like setae of which outermost longest and fused basally to slender short seta.

Mandible ( Fig. 17A View Fig ) with well-developed coxa; gnathobase with bicuspidate teeth as depicted, with two spines and one unipinnate seta. Palp biramous; basis large, with three setae; rami one-segmented; endopod with two inner and six distal setae; exopod with six setae as shown.

Maxillule ( Fig. 17B View Fig ) with well-developed praecoxa ornamented with few spinules as shown; praecoxal arthrite armed with two surface setae, eight spines as shown, and one ventral seta. Coxal endite with four setae. Basis elongate, with one lateral and three distal setae. Exopod and endopod one-segmented, with three setae each.

Maxilla ( Fig. 17C View Fig ) with large syncoxa ornamented with outer spinular rows as shown, with three endites of which proximal thicker, middle endite shortest, distal endite elongate, each with three setae. Basis drawn out into strong claw accompanied by strong spine and two setae. Endopod represented by three setae.

Maxilliped ( Fig. 17D View Fig ) robust. Syncoxa visibly shorter than basis, unornamented, seemingly unarmed. Basis with hump-like inner protrusion proximally, ornamented with spinules as shown, with one subdistal seta. Endopod one-segmented, with distal spinulose claw.

P1 ( Fig. 18A View Fig ) with transversely elongate intercoxal sclerite. Coxa rectangular, with few distal spinules close to inner distal corner. Basis with spinules at base of inner spiniform element and between rami. Exopod three-segmented, inserted at a lower level than endopod; segments with outer and subdistal spinules as shown; EXP1 and EXP2 with outer spine, EXP1 without EXP2 with inner small seta; EXP3 with two outer spines and two distal elements of which distal outer spiniform, distal inner setiform and rat-tail-like. Endopod two-segmented, longer than exopod; ENP1 shorter than ENP2, with inner, subdistal, and outer spinules as depicted, unarmed; ENP2 with longitudinal row of outer spinules, with one inner element (the latter missing in figure), two distal elements of which distal inner setiform and rat-tail-like and distal outer spiniform, and one outer spine.

P2 ( Fig. 18B View Fig ) with trapezoidal intercoxal sclerite ornamented with subdistal spinules on distal pointed tines. Praecoxa triangular, transversely elongate, with transverse row of distal spinules. Coxa subrectangular. Basis with small spinules between rami, with one outer pore, and short outer seta. Exopod inserted at a lower level than and not reaching tip of endopod, three-segmented; EXP1 and EXP3 longest; EXP1 and EXP2 with outer spinules as shown, with outer spines of which outer spine of EXP2 visibly longer; EXP1 without, EXP2 with inner seta; EXP3 with outer spinules at the base of outer armature elements and with subdistal medial pore, with three outer spines, two distal spiniform elements, and two inner slender setae. Endopod three-segmented; segments with outer spinules as shown; ENP1 widest, with outer distal corner moderately produced, inner distal margin with produced pointed projection, with outer pore, unarmed; ENP2 largely as ENP1 but visibly narrower, with outer distal corner drawn out into pointed outgrowth, with outer pore and inner short element; ENP3 longest and narrowest, with outer spinules as shown, with medial pore, with one (or two?) inner slender seta, two distal elements of which outer spiniform and inner setiform (rat-tail-like condition of the latter not evident), and one outer spine.

P3 ( Fig. 19A View Fig ) with intercoxal sclerite similar to that of P2 but broader and with larger distal tines, unornamented. Coxa and basis largely as in P2. Exopod largely as in P2, but EXP3 with three inner slender setae. Endopod largely as in P2 but ENP1 and ENP2 without outer pore, ENP1 with strong inner element, and inner element of ENP2 visibly stronger; ENP3 as in P2 but with one inner seta only.

P4 ( Fig. 19B View Fig ) with unornamented intercoxal sclerite with outer distal pointed tines well-developed. Praecoxa, coxa and basis as in P3. Exopod largely as in P3. Endopod largely as in P3, but barely reaching tip of EXP, ENP1 narrower and unarmed, ENP2 with insertion site of inner element separated from segment by deep groove; ENP3 largely as in P2, with one inner seta.

Pair of P5 ( Fig. 19C View Fig ) not fused medially; baseoendopod and exopod completely fused; with three setae in all of which outermost basal.

P6 ( Fig. 15C View Fig ) with one small seta.

Male. Unknown.

Variability. Left P4 malformed (not shown), with basis bearing one inner element, endopodal segments abnormally thin, ENP2 without inner armature, ENP3 with two posterior setae.

3.1.1.4. Pseudomesochra bathyhabitatrix sp. nov. urn:lsid:zoobank.org:act:

Type material. Male holotype dissected and mounted on eight slides (ICML-EMUCOP-230800-03); August 23, 2000; Samuel Gomez´leg.

Type locality. Talud IV cruise; stn 5, Eastern Tropical Pacific , off Nayarit state, north-western Mexico ( 22.0172 ◦ N, 106.6672 ◦ W); 1540 m depth GoogleMaps .

Etymology. The specific epithet comes from the ancient Greek Вαθύς (Bathús, deep), and Latin habit¯atr¯ıx, dweller. It is a noun in the nominative singular, gender feminine.

Description. Male. Total body length measured from tip of rostrum to posterior margin of caudal rami 324 μm. Habitus ( Fig. 20A View Fig ) semicylindrical, tapering posteriad, with clear division between pro- and urosome. Rostrum ( Figs. 20A View Fig and 21A View Fig ) large, broad, triangular, with two lateral sensilla subdistally. Prosome ( Fig. 20A View Fig ) composed of cephalothorax, and P2–P4-bearing somites, widest at the posterior margin of cephalothorax; urosome ( Fig. 20A–C View Fig ) composed of P5-bearing somite, genital somite, three free urosomites, and anal somite with caudal rami. Cephalothorax with pores and sensilla as shown; P2–P4-bearing somites with smooth posterior hyaline frill, with sensilla and pores as depicted; P2 and P3-bearing somites without, P4-bearing somite with medially interrupted row of small spinules close to posterior margin; P5-bearing somite and genital somite as P4-bearing somite dorsally, laterally with row of comparatively stronger spinules close to P5 and P6, ventrally without spinular ornamentation; first and second free urosomites as previous somite dorsally, with ventral row of strong spinules; penultimate somite as preceding somite but without sensilla; anal somite cleft medially, with two dorsal pores, anal operculum not detected, with strong lateral spinules and comparatively smaller ornaments ventrally. Caudal rami ( Fig. 20A–C View Fig ) cylindrical, about three times as long as wide, slightly divergent; with small spinules medially on lateral surface, and at base of setae II and V; with six setae as follows: lateral setae II and III arising (sub)distally, seta III longer and ventral to seta II; setae IV and V broken off; seta VI very short, issuing at distal inner corner; dorsal seta VII triarticulate at base, located in the middle of the ramus close to inner margin.

Antennule ( Fig. 21A View Fig ) subchirocer, eight-segmented; surface of segments smooth except for few spinules on first and sixth segments; fifth segment shortest, sixth segment longest; all setae seemingly smooth; with exceedingly long aesthetasc on segments six and eight. Armature formula as follows: 1(1), 2(1), 3(8), 4(6), 5(1), 6(10+ae), 7(0), 8(5+ae).

Antenna ( Fig. 21B View Fig ) with allobasis, the latter as long as free endopodal segment, unornamented, unarmed. Without exopod. Free endopodal segment with two sets of long spinules proximally and medially; lateral armature consisting of two spiniform elements; distal armature consisting of five setae as shown of which two outermost rat-tail-like, medial and two inner spiniform (rat-tail-like condition of the three latter not conclusive).

Mandible ( Fig. 21C View Fig ) very reduced with non-functional gnathobase. Palp biramous; basis large, unornamented; rami one-segmented, elongate, each with two setae.

Maxillule and maxilla not observed, most probably very reduced.

Maxilliped ( Fig. 21D View Fig ) very reduced, non-functional; syncoxa and basis subquadrate, slightly wider than long, unarmed and unornamented; endopod globose, seemingly fused to vestigial endopodal claw.

P1 ( Fig. 22A View Fig ) with basis ornamented with spinules between rami, and with inner spiniform, and outer setiform element. Exopod three-segmented, inserted at a lower level than endopod; segments with outer and subdistal spinules as shown; EXP1 and EXP2 with outer spine, that of EXP1 visibly longer, EXP1 without EXP2 with inner seta; EXP3 with two outer spines and two distal setae seemingly rat-tail-like. Endopod two-segmented, longer than exopod; ENP1 shorter than ENP2, with outer and subdistal spinules, unarmed; ENP2 with longitudinal row of outer spinules, with one inner seta and three distal elements of which inner setiform and rat-tail-like, medial spiniform, and outer a bipinnate spine.

P2 ( Fig. 22B View Fig ) with triangular unornamented praecoxa. Coxa rectangular, with short row of small spinules close to outer distal corner. Basis with spinules between rami, with spiniform outer element. Exopod three-segmented, inserted at a lower level than and barely reaching tip of ENP3; EXP1 and EXP2 shortest, with outer spinules as shown, outer spines not elongate; EXP1 without, EXP2 with inner seta and outer pore; EXP3 with outer spinules as depicted, with three outer spines, two distal setae (rat-tail-like condition of the innermost not evident), and two inner elements. Endopod three-segmented; segments with outer and inner spinular ornamentation and pores as shown; ENP1 widest and shortest, ENP3 longest; ENP1 and ENP2 with inner short setae; ENP3 with two inner setae, and one seta and one recurved apophysis distally.

P3 ( Fig. 23A View Fig ) with coxa and basis largely as in P2, but with outer slender seta. Exopod largely as in P2 but longer than endopod, and with three inner setae. Endopod three-segmented, barely reaching middle of EXP3; ENP1 shortest, largely as in P2; ENP2 with outer and inner distal corners expanded, the former with pointed tip, the latter rounded, with one inner seta; ENP3 longest, with two inner, two distal setae of which distal inner visibly shorter and not rat-tail-like, and one outer spine.

P4 ( Fig. 23B View Fig ) with coxa and basis as in P3 but basis without spinular ornamentation and with large outer pore. Exopod as in P3. Endopod three-segmented, barely reaching proximal third of EXP3, segments with outer spinules as shown; ENP1 shortest, ENP3 longest; ENP1 and ENP2 with inner seta; ENP3 with one inner seta, two distal elements of which distal inner shorter and not rat-tail-like, and one outer spiniform element.

Pair of P5 ( Fig. 20B and C View Fig ) not fused medially; baseoendopod and exopod completely fused, unornamented; baseoendopod with outer basal seta, without endopodal lobe. Exopod represented by two setae.

P6 ( Fig. 20B and C View Fig ) with one small seta.

Female. Unknown.

3.1.2. Subfamily Danielsseniinae Huys and Gee , in Huys, Gee, Moore and Hamond, 1996

3.1.2.1. Genus Nuriaella gen. nov. urn:lsid:zoobank.org:act:

Type species: Nuriaella mendezae gen. et sp. nov., by monotypy

Diagnosis (based on the female of N. mendezae gen. et sp. nov.). Pseudotachidiidae : Danielsseniinae . Habitus semicylindrical. Rostrum not fused to cephalothorax, large, broad, subrectangular. Pro- and urosomites with large cup-shaped pores, except for P5-bearing somite. Second (genital) and third urosomites completely fused dorsally forming genital double-somite, with lateroventral internal cuticular rib. Fifth

Etymology. The genus name comes from the combination of the Basque proper noun Nuria and the Latin diminutive suffix -ella. It is in the nominative singular, gender feminine. The genus is dedicated to the fond memory of our friend and colleague María Nuria Mendez-Ubach ´† (Instituto de Ciencias del Mar y Limnología, UNAM).

3.1.2.1.1. Nuriaella mendezae gen. et sp. nov. urn:lsid:zoobank.org:act:

Type material. Female holotype dissected and mounted on seven slides (ICML-EMUCOP-210817-03); August 21, 2017; Ivonne Martínez-Mendoza leg.

Type locality. Xiximi 5 cruise; stn B18, Gulf of Mexico, Campeche Escarpment ( 24.0501 ◦ N, 86.8835 ◦ W); 1150 m depth; clay 7.4 %, silt 55.8 %, sand 36.8 GoogleMaps %.

Etymology. The specific name comes from the family name of Dr María Nuria M´endez-Ubach. It is a noun in the genitive case. It is dedicated to the late Dr María Nuria Mendez-Ubach ´† (Instituto de Ciencias del Mar y Limnología, UNAM).

Description. Female. Total body length measured from tip of rostrum to posterior margin of caudal rami 293 μm. Habitus ( Fig. 24A and B View Fig ) semicylindrical, tapering posteriad, with clear division between pro- and urosome. Rostrum ( Figs. 24A and B View Fig , 26A) large, broad, subrectangular, with two lateral sensilla subdistally, tip slightly bilobate. Prosome ( Fig. 24A and B View Fig ) composed of cephalothorax, and P2–P4- bearing somites, widest at the posterior margin of cephalothorax; urosome ( Figs. 24A and B View Fig , 25A View Fig ) composed of P5-bearing somite, genital double-somite, two free urosomites, and anal somite with caudal rami. Cephalothorax with cup-shaped pores and few posterior sensilla dorsally urosomite with posterior hyaline frill expanded dorsally forming pseudoperculum. Caudal rami cylindrical, about two times as long as wide, divergent, with six setae of which seta IV (and most probably seta V) well-developed, with fracture plane, distal part not rat-tail-like. Antennule six-segmented. Antenna with allobasis, the latter with long slender abexopodal seta; exopod three-segmented, with armature formula 1,1,120; free endopodal segment with three lateral setae of which one geniculate, and distal armature consisting of four geniculate setae of which outermost spinulose and fused basally to short slender seta, and one spinulose spine and one subdistal smooth seta. Mandibular basis with two setae; endopod one-segmented with three lateral inner and five distal setae; exopod two segmented, slightly longer than endopod, ENP1 with one medial and one subdistal seta, ENP2 with three distal elements. Maxillule with four coxal setae; basis with four setae; rami one-segmented, exopod with two, endopod with three setae. Maxilla with three endites of which proximal with two, middle and distal endites with three setae each; endopod one-segmented, with four setae. Maxilliped subchelate, slender; syncoxa with one seta; basis with one seta. Outer spines of P1–P4 EXP elongate and thin. Armature of swimming legs as in Table 1.

Table 1. Armature formula of swimming legs of Nuriaella gen. et sp. nov. (based on the female of its only and type species, N. mendezae sp. nov.).

P1 P2 P3 P4

EXP 0,1,022 0,1,123 0,1,122 0,1,222 ENP 1111 1,1,121 1,1,121 1,0,121

Both P5 not fused medially; EXP and BENP separate; EXP small, with five setae; endopodal lobe well-developed, with five setae.

and laterally as shown; P2–P4-bearing somites with smooth posterior hyaline frill, and with dorsal and lateral cup-shaped pores and sensilla as depicted; P5-bearing somite with smooth posterior hyaline frill, without cup-shaped pores, with two dorsolateral surface pores and posterior sensilla as shown, and with posterolateral row of small spinules interrupted medially; genital double-somite with finely serrated hyaline frill, anterior (second urosomite) and posterior (third urosomite) halves completely fused dorsally, with lateroventral internal cuticular rib, with dorsal and lateral cup-shaped pores as shown, with one median and one posterior dorsolateral row of small spinules interrupted medially; genital complex ( Fig. 25A View Fig ) ventrally on the middle of anterior half of composite somite, with single copulatory duct and copulatory pore slightly posterior to P6 medially, anterior part of genital double-somite damaged during dissection and seminal receptacle not discernible; fourth urosomite largely as posterior half of genital double-somite dorsally, with finely serrated posterior hyaline frill, ventrally with one cup-shaped pore on each side, and with four short crescentic spinular rows and few sensilla; fifth urosomite with posterior hyaline frill finely serrated and expanded dorsally forming pseudoperculum, with one dorsal and one lateral cup-shaped pore dorsally, ventrally as preceding somite; anal somite cleft medially, with two dorsal and two ventral cup-shaped pores, with lateroventral row of small spinules close to caudal rami, ventrally with pair of surface pores as depicted. Caudal rami ( Figs. 24A and B View Fig , 25A View Fig ) cylindrical, about two times as long as wide, divergent; with small spinules medially on lateral surface, and at base of setae II and V, dorsally with medial pore, ventrally with inner proximal surface pore and median cup-shaped pore; with six setae as follows: lateral setae II and III arising distally, seta III longer and ventral to seta II; setae IV well-developed, with fracture plane, distal part seemingly not rat-tail-like; seta V broken, presumably with fracture plane and longer than seta IV; seta VI very shorter, issuing at distal inner corner; dorsal seta VII triarticulate at base, located in the middle of the ramus close to inner margin.

Antennule ( Fig. 26B and C) six-segmented; surface of segments smooth except for few spinules on first segment; first and second segments nearly subequal in length, third segment longest, fourth, fifth and sixth segments combined as long as third segment; all setae seemingly smooth except for one seta on third, two on fifth and one seta on sixth segments. Armature formula as follows: 1(1), 2(9), 3(11+ae), 4(5), 5(3), 6(6+ae).

Antenna ( Fig. 26D) with allobasis, the latter as long as free endopodal segment, seemingly unornamented, with long slender abexopodal seta. Exopod with three distinct segments of which third segment longest, middle segment shortest, all segments seemingly unornamented; first and second segments with one seta each; third segment with one lateral and two distal elements. Free endopodal segment with two sets of long spinules medially and subdistally; lateral armature consisting of three setae of which one geniculate; distal armature consisting of four geniculate setae of which outermost spinulose and fused basally to short slender seta, and one spinulose spine and one subdistal smooth seta.

Mandible ( Fig. 27A View Fig ) with well-developed coxa; gnathobase with elongate bicuspidate teeth as depicted, with one spine and one unipinnate seta. Palp biramous; basis elongate, with row of slender spinules medially, with two setae; endopod one-segmented, elongate, with three lateral inner and five distal setae; exopod two segmented, slightly longer than endopod, ENP1 with one medial and one subdistal seta, ENP2 with three distal elements.

Maxillule ( Fig. 27B View Fig ) with well-developed praecoxa ornamented with few spinules as shown; praecoxal arthrite armed with two surface setae, eight spines, and one ventral seta. Coxal endite with four setae. Basis with four setae. Exopod and endopod one-segmented, the former with two the latter with three setae.

Maxilla ( Fig. 27C View Fig ) with large seemingly unornamented syncoxa, with three endites of which proximal thicker with two, middle and distal endites elongate with three setae each. Basis drawn out into strong claw accompanied by spine and two setae. Endopod one-segmented, with four setae.

Maxilliped ( Fig. 27D View Fig ) rather slender. Syncoxa visibly shorter than basis, with few spinules as shown, with one subdistal seta. Basis with inner and outer spinules as shown, with one seta. Endopod with distal spinulose claw.

P1 ( Fig. 28A) with rectangular coxa ornamented with outer spinules, with subdistal inner pore. Basis with spinules at base of inner spiniform element and at base of endopod, with outer pinnate element. Exopod three-segmented, inserted at a lower level than endopod; segments with outer and subdistal spinules as shown; EXP1 and EXP2 with outer spine, that of EXP1 visibly longer, EXP1 without EXP2 with inner seta; EXP3 with two outer spines and two distal elements. Endopod two-segmented, longer than exopod; ENP1 shorter than ENP2, with outer and subdistal spinules and one medial pore, with one inner seta; ENP2 with longitudinal row of outer spinules and one medial subdistal pore, with one inner seta and three distal elements of which medial longest and inner shortest.

P2 ( Fig. 28B) with triangular praecoxa ornamented with row of distal spinules. Coxa rectangular, with outer, medial, and inner spinules and one inner pore. Basis with spinules at base of spiniform outer element. Exopod three-segmented, inserted at a lower level than and barely reaching proximal fifth of ENP3; EXP1 and EXP2 shortest; EXP1 and EXP2 with outer spinules as shown, with elongate outer spines of which outer spine of EXP2 visibly longer; EXP1 without, EXP2 with inner seta and outer pore; EXP3 with outer spinules as depicted, with three outer spines, two distal setae, and one inner slender element. Endopod three-segmented; segments with outer and inner spinular ornamentation as shown; ENP1 widest and as long as ENP2, ENP3 longest; ENP1 and ENP2 with outer subdistal pore and one inner short seta; ENP3 with subdistal pore, one inner seta, two distal elements of which distal inner reduced and distal outer very long, and one outer spiniform element.

P3 ( Fig. 29A View Fig ) with coxa and basis largely as in P2, but with outer slender seta. Exopod largely as in P2 but reaching proximal third of ENP3. Endopod largely as in P2 but ENP1 and ENP2 with comparatively longer inner setae.

P4 ( Fig. 29B View Fig ) with coxa and basis as in P3. Exopod three-segmented, visibly longer than ENP, with few outer spinules; EXP1 and EXP2 shortest, EXP3 longest; EXP1 and EXP2 with outer spine of which that of EXP2 visibly longer, EXP1 without, EXP2 with inner seta; EXP3 with two outer spines, two distal setae, and two inner elements of which proximal longest. Endopod relatively shorter than in P2 and P3, reaching proximal fourth of EXP3, segments with few outer spinules as shown; ENP1 with, ENP2 without inner armature; ENP3 with one inner seta, two distal elements of which distal inner shorter, and one outer spiniform element.

Pair of P5 ( Fig. 25B View Fig ) not fused medially; baseoendopod and exopod separated, ornamented with pores as shown, with long outer seta; endopodal lobe with five setae as figured. Exopod small, reaching about the middle of endopodal lobe, with five setae in all.

P6 ( Fig. 25A View Fig ) with one small seta.

Male. Unknown.