Canuellina pacifica Gómez, Yáñez-Rivera, García-Vázquez & Armenteros, 2024, sp. nov.

Canuellina pacifica sp. nov. urn:lsid:zoobank.org:act: 9077F344-BF1D-44B4-B9CD-37457A1549D0 (Figs. 12–23) Material examined. ♀ holotype preserved in alcohol (ICML-EMUCOP-020623-01), ♂ allotype partially dissected (habitus preserved in alcohol; right A1, right P1–P3, left P4 dissected and mounted on one slide each) (ICML-EMUCOP-020623-04), two ♀ paratypes (ICML-EMUCOP-020623-02–03), June 2, 2023, from the type locality (stn 2, see below); three ♀ paratypes dissected and mounted on eight, 11, and nine slides (ICML-EMUCOP-020223- 22–24), February 2, 2023, from stn 6 (see below); Leonardo García-Vázquez leg. Type locality. North-western Mexico, northern Sinaloa state, Ohuira Bay, stn 2 (25.6°N, 109.02°W); sand 79.59%, silt 14.20%, clay 6.21%, C org 0.60 %. Other sites: North-western Mexico, northern Sinaloa state, Ohuira Bay, stn 6 (25.56°N, 108.98°W); February 2, 2023; sand 27.34%, silt 49.06%, clay 23.6%, C org 2.37%. Etymology. The species name refers to the region where the material was collected. Differential diagnosis. Canuellidae. P5-bearing somite with dorsal pattern of chitinized plates. Caudal rami with seven setae of which six unmodified, one transformed into triangular blunt, hyaline spiniform dorsal element close to outer subdistal margin.Antennary basis with one seta. Distal inner seta on P3EXP3 nearly half as long as the distal outer seta; distal inner element on P3ENP3 shorter than distal outer seta; distal inner seta on P2EXP3 visibly shorter than distal outer element; P2ENP2 with long stiff inner seta parallel to inner margin of outer projection. Female P5 separated from somite, pair of legs fused medially, each with four setae. Male P6 with four elements of different lengths, three outermost ones sclerotized, innermost shortest. Description of female. Habitus (Fig. 12A) semicylindrical; total body length measured from anterior tip of rostrum to posterior margin of caudal rami ranging from 1120 µm to 1260 µm (mean= 1202.5 µm; n= 4), with maximum width at the posterior margin of cephalothorax. General body shape largely as in C. secunda. Rostrum (Fig. 15A) not fused to cephalothorax; large, broadly triangular, with rounded tip; with one subapical somewhat thickened sensilla on each side. First pedigerous somite fused to cephalosome. Urosome (Figs. 12A, 13B, D, 14A) tapering posteriad, hyaline posterior fringe of urosomites smooth, consisting of fifth pedigerous somite, genital double-somite, two free somites, and anal somite; dorsal and ventral surface of urosomites with sensilla and pores as shown. P5-bearing somite (Figs. 13B, 14B) with dorsal pattern of chitinized plates as shown. Genital somite and third urosomite fused dorsally and ventrally forming genital double-somite (Figs. 12A, 13B, D, 14A, C), with lateral internal cuticular band indicating former division between somites, slightly longer than wide, with genital area situated lateroventrally in the middle of genital double-somite, with one side covered with minute spinules as depicted. Fourth urosomite longer than fifth. Anal somite shorter than preceding somite, with caudal rami. Caudal rami (Figs. 13B–E, 14D) largely as in C. secunda, rami visibly longer than fifth and anal somites combined, about 2.3 times as long as wide, proximal margin wider and abruptly tapering posteriad; inner margin concave, outer margin nearly straight; distal margin extended ventrally into a rounded hyaline outgrowth; with pores as shown; homology of setae difficult to determine; setal complement as in C. secunda, with two inner plumose elements on distal fourth, one medial subdistal dorsal seta, one short distal inner seta, and two principal distal setae of which inner with fracture plane, and additionally with triangular blunt, hyaline spiniform dorsal element close to outer subdistal margin (Figs. 13B, C, 14D). With two uniseriate egg sacs with eight eggs each. Antennule (Fig. 15A) presumably with seven original segments. First to fifth segments imperfectly separated forming large first composite segment with two proximal spinular rows, with set of medial inner long setules, with 26 setae in all and two seemingly free aesthetascs; penultimate segment distinct, with four setae; last segment distinct, with 14 setae as shown of which proximal outer stout and plumose, three medial outer and two subdistal biarticulate. Antenna (Fig. 15B) biramous. Basis with spinular row medially, with short outer seta. Exopod seven-segmented; first-sixth segments with one, seventh segment with four pinnate elements. Endopod three-segmented; first segment with outer spinules as shown, with two medial setae; second segment seemingly unornamented, with one proximal and two distal elements; third segment with seven setae (six long of which two bare and four pinnate as depicted, and one short naked seta). Mandible (Fig. 16A, B) with well-developed gnathobase bearing multicuspidate teeth and several (five?) pinnate spines of which ventral longest. Basis large, with spinular rows as shown, with two inner subdistal setae. Exopod three-segmented, bent outwards; first segment with two setae (one medial, one subdistal); second segment with one proximal element; third segment with three setae; all endopodal setae plumose. Endopod two-segmented; first segment larger, with three pinnate inner setae, second segment with eight elements of which two outer plumose, two medial seemingly unornamented, the other setae pinnate. Maxillule (Fig. 16C, D) with praecoxa and coxa partially fused. Praecoxal arthrite narrow, seemingly unornamented; proximally with one thick seta with long slender pinnae, distally with seven spines and one seta, with two setae arising from short setophore. Coxal endite with row spinules and five setae; with three long plumose epipodal plumose setae. Exopod massive, bent outwards, one-segmented; with 11 setae of which ten inner and distal long and plumose, outermost shorter and bipinnate. Endopod three-segmented; first segment with four medial and four distal pinnate setae; second segment with five pinnate elements, third segment with six plumose setae. Maxilla (Fig. 17A) with praecoxa and coxa imperfectly separated forming large syncoxa, seemingly unornamented; with four endites, of which two praecoxal close-set (proximal with five, distal with two setae), and two coxal separated (each with three setae). Allobasis drawn out into strong pinnate claw accompanied by three setae and two spines. Endopod seemingly one-segmented, with nine setae. Maxilliped (Fig. 17B) phyllopodial. Praecoxa and coxa fused forming large syncoxa with one medial and one subdistal row of spinules, with one (praecoxal) proximal seta, and three sets (endites) of setae with two medial, four subdistal, and three distal elements. Basis with longitudinal row of outer long spinules; with three spinulose medial inner setae, and one spinulose inner element arising from distal long setophore. Endopod one-segmented, with ten setae arranged in four groups with two, two, three, and three setae, of which outermost seven plumose, the other pinnate. P1 (Fig. 18A) with intercoxal sclerite transversely elongate. Coxa and basis with spinular ornamentation and with pores as figured, the former with inner long bipinnate seta, the latter with reduced outer naked seta and inner pinnate spine. Exopod with three subequal segments, reaching tip of ENP2; EXP1 with few, EXP2 without outer spinules, the former with outer spine and without inner armature, the latter with outer spine and inner seta; EXP3 unornamented, with three outer spines, two distal elements (one distal outer spine, one distal inner plumose seta), and two inner plumose setae. Endopod three-segmented, first segment longest, third segment shortest; ENP1 with short longitudinal row of outer spinules and medial subdistal pore, with one inner plumose seta; ENP2 and ENP3 with anterior patch of spinules as shown, the former with one inner plumose seta, the latter with two outer spines, two distal elements (one distal outer spine, one distal inner plumose seta), and two inner plumose setae. P2 (Figs. 18B, 19A, B) with U-shaped intercoxal sclerite with two distal pointed tines, proximal part triangular. Coxa large, with spinular ornamentation as figured, with medial inner pore, unarmed. Basis as shown, with medial pointed projection distally between rami; with medial pore close to base of endopod; with reduced outer seta. Exopod three-segmented, inserted at a lower level than endopod and reaching distal third of ENP3; EXP1 shortest, EXP3 longest; exopodal segments with anterior patch of spinules as shown; EXP1 with outer spine, without inner armature; EXP2 with outer spine and inner seta; EXP3 with two outer spines, two apical elements (one distal outer spiniform element, one distal inner plumose seta), and two inner plumose setae. Endopod three-segmented, first segment shortest, third segment longest; ENP1 with outer pointed projection reaching tip of ENP2, unornamented, with long stiff inner seta parallel to inner margin of outer projection; ENP2 with outer and inner distal pointed projections, unornamented, with inner seta as shown; ENP3 with medial subdistal pore, with distal pointed outgrowths as depicted, with two outer naked spines, two distal elements (one distal outer spine with hook-like spinules, one distal inner seta), and one inner seta. P3 (Fig. 20A) with U-shaped intercoxal sclerite with two distal pointed tines, proximal part of sclerite attenuated. Coxa large, with spinular ornamentation as figured, with medial inner pore, with strong inner spiniform element. Basis largely as in P2; with medial inner pore close to base of endopod; with outer seta comparatively longer than in P2. Exopod three-segmented, inserted at a lower level than endopod and reaching middle of ENP3; EXP1 largest, EXP3 elongate; exopodal segments with anterior patch of spinules as shown; EXP1 with outer subdistal pore, with outer spine, without inner armature; EXP2 with outer subdis