Metacyclops deserticus Mercado-Salas & Suárez-Morales 2013 ex Mercado-Sa

Female: Habitus as in Fig. 1A (dorsal view) and Fig. 4A (lateral view).Length of holotype 0.87 mm from anterior end of cephalothorax to posterior margin of caudal rami (range=0.72–0.87 mm; mean=0.80 mm; n=9). Body robust, cephalothorax relatively long, slightly expanded laterally at midlength of cephalosome in dorsal view; lateral margins of pedigers 3 and 4 straight, produced posteriorly. Cephalothorax length= 0.55 mm, representing 63% of total body length. Dorsal surface smooth, antennules not reaching distal margin of first pediger. Urosome (excluding caudal ramus) (Fig. 1B) representing 37% of body. Posterior margins of genital double-somite, free urosomites, and anal somite smooth both dorsally and ventrally. Relative length of each urosomite (proximal to distal) as: 65.4: 10.3: 10.3: 14.1=100. Genital double-somite (Fig. 5E) representing 17% of body length (excluding caudal rami), somite about 1.1 times longer than broad, with maximum width at proximal half; ventral and dorsal surfaces smooth. Anterior half of genital double-somite expanded laterally. Seminal receptacle with a reduced and narrow anterior part, posterior part rounded and expanding along the somite. Anal somite with distal rows of spines at insertion points of each caudal rami on ventral and dorsal margins. Anal operculum (Fig. 1I) slightly rounded and smooth. Caudal ramus (Fig. 1B, 5F): Ramus representing 8.2% of total body length and 0.3 times as long as urosome. Length/width ratio= 3.5–3.8. Inner and outer margins smooth. Lateral caudal seta (II) inserted at 53% of total length of caudal rami. Outermost terminal seta (III) without ornamentation at point of insertion and 0.6–0.7 times as long as caudal ramus. Dorsal seta (VII) relatively short, 0.4–0.5 times as long as caudal ramus. Innermost terminal seta (VI) about 0.5 times as long as caudal ramus. Innermost terminal seta (VI) about 0.8–0.84 times outermost terminal seta (III). All terminal caudal setae plumose. Antennule (Fig. 1C, 4A): 11-segmented in all specimens examined, armature per segment as follows (s=seta, sp= spine, ae=aesthetasc): 1(7s), 2(4s), 3(6s), 4(2s), 5(1s +1sp), 6(2s), 7(3s), 8(2s + 1ae), 9(2s), 10(3s), 11(7s). Antennule not reaching posterior margin of first thoracic somite. Antenna (Fig. 1D, 4C): Four-segmented, basis without cuticular ornamentation, armed with long exopodal seta and two basipodal setae of different size, outer seta 1.6 times longer than inner seta. First endopodal segment with single outer seta and inner group of spinules. Second segment with 6 setae; inner margin with longitudinal row of spinules. Third endopodal segment with 6 terminal setae; inner margin with row of spinules. Mandible (Fig. 1E): Gnathobase with 7 strongly chitinized teeth and dorsal seta armed with inner row of spinules. Palp reduced, with 2 long and 1 short setae, the later not reaching half-length of former two. Maxillule (Fig. 1F): Precoxal arthrite with 3 strong chitinized claws and 2 spiniform setae on frontal side. Palp 2-segmented, proximal segment armed with 3 inner setae and outer exopodal seta. Distal segment of palp armed with 3 setae. Maxilla (Fig. 1G): Precoxa and coxa not fused; precoxal endite armed with two strong biserially setulated setae. Coxal surface naked, proximal endite well developed, with two subequal apical setae. Claw-like distal endite well developed, with row of 6 spinules and basal seta. Endopodite 2-segmented, proximal segment with 2 robust setae, distal segment with single seta. Maxilliped (Figs. 1H, 4D): Four-segmented. Syncoxa with 3 spiniform setae along inner margin: proximal one without ornamentation at insertion, middle one longest, more than twice as long as the other setae. Basis with 2 spiniform setae and transverse row of spines. Endopod reduced, 2-segmented, first segment with single lightly spinulate seta. Second endopodal segment armed with spiniform proximal seta and 2 slender setae. Legs P1-P4: with naked intercoxal sclerites, distal margins with rounded projections. All endopodal and exopodal setae slender and plumose. Armature formula of all swimming legs as in Table 1. Leg 1(Fig. 2A, 5A): Coxa with inner seta and transverse row of 6 spinules on distal outer margin. Basis with inner row of short setae and long slender basipodal seta, reaching middle margin of second endopodal segment, row of hair-like setules along inner margin, row of 5 spines adjacent to insertion of endopodal ramus. Endopod slightly shorter than exopodite. Apical spine of second endopodal segment strong, slightly longer than segment, with spinules at insertion point. Leg 2 (Fig. 2B): Coxa with inner seta . Basis with short slender seta on outer margin. Surface of coxa and basis smooth. Endopod slightly shorter than exopodite. Leg 3 (Fig. 2C): Coxa with inner seta. Basis with outer seta. Surface of coxa and basis naked. Exopodite slightly longer than endopod. Leg 4 (Figs. 2D, 5B): Coxa and basis as in legs 2-3. Endopod shorter than exopodite. Second endopod about two times longer than wide (1.9), with apical spine shorter than bearing segment(0.8 times as long as segment). Spinules at insertion of all elements of second endopodal segment. Second exopodal segment with 2 outer spines and 1 apical spine with small spinules at insertion point. Leg 5 (Figs. 1B, 2E, 5C): Basal segment completely fused to somite, dorsal seta stout and plumose, about 1.4 times longer than outer seta of free segment. Free segment subrectangular, 1.2 times longer than wide, inner spine slightly shorter than bearing segment. Outer seta about 4 times longer than inner spine. Inner spine strong and smooth; outer seta plumose on distal half. Leg 6 (Figs 1B, 5D): Represented by small, low plate near lateral margin of genital double somite. Leg armed with relatively long plumose seta, and with 2 short, subequal smooth spines. Male:Length of allotype 0.58 mm (excluding caudal ramus) (range=0.58–0.64 mm; mean= 0.61mm; n =2). Body slender than in female, cephalothorax relatively long, slightly expanded laterally at midlength of cephalosome in dorsal view; lateral margins of pedigers 3 and 4 straight, produced posteriorly. Cephalothorax length= 0.40 mm, representing 68% of total body length, dorsal surface smooth. Posterior margins of genital somite, free urosomites, and anal somite smooth ventrally (Fig. 3D) and dorsally. Ventral surface of anal somite smooth; distal ventral margin with rows of 13–15 spines at insertion point of caudal rami. Anal operculum (Fig. 3G) slightly rounded, smooth. Caudal ramus (Fig. 3D): Length of ramus 0.07 mm. Length/width ratio= 3.1–3.2. Inner and outer margins smooth, unornamented. Lateral apical seta (II) inserted al 52.3% of total length of caudal ramus. Outermost terminal (III) seta with small spinules at insertion and 0.7–0.8 times as long as caudal ramus. Dorsal seta (VII) longer than in females; about 0.7 times as long as caudal ramus. Innermost terminal seta (VI) 0.5 times as long as caudal ramus and. Innermost terminal seta (III) slightly shorter than outermost terminal seta (VI), III/VI ratio 0.78–0.9. All terminal caudal setae plumose. Antennule (Fig. 3A–B): 14-segmented, geniculate, armature of segments 12, 13 and 14 not seen clearly (they could have more setae). Armature per segment as follows (s=seta; sp= spine ae= aesthetasc): 1(7s+1ae), 2(4s), 3(1s), 4(2s+1ae), 5(1s), 6(1s), 7(1s), 8(1s+ 1sp), 9(2s), 10(1sp), 11(0), 12(1sp), 13(1s), 14(4s). Antenna, mouthparts and legs 1–3 as in female. Leg 4 (Fig. 3C): as in female except for relatively longer exopodite. Leg 5 (Fig. 3E): Basal segment completely fused to somite, dorsal seta stout, as long as outer seta of free segment. Free segment subrectangular, 1.5 times longer than wide, spine as long as segment, outer seta about 5 times longer than inner spine. Inner spine strong, smooth; outer seta plumose on distal half. Leg 6 (Fig. 3F): Represented by small, low plate near lateral margin of genital somite with relatively strong and long inner spine, two outer setae about the half of length of inner spine. Spine and setae smooth. Armature of swimming legs 1–4 (spines in Roman numerals, setae in Arabic) of Metacyclops deserticus sp. n. Sequence follows external to internal positions.
coxa basis endopodite exopodite leg 1 0-1 1-1 0-1;1-I-4 I-1;III-5 leg 2 0-1 1-0 0-1;1-I-5 I-1;IV-5 leg 3 0-1 1-0 0-1;1-I-5 I-1;IV-5 leg 4 0-1 1-0 0-1;1-I-3 I-1; III-5