Mesocletodes brevisetosus sp. n.

Gomez, Samuel, 2018, New species of the genus Mesocletodes Sars, 1909 from the deep Gulf of California (Copepoda, Harpacticoida), ZooKeys 751, pp. 75-112 : 77-78

Mesocletodes brevisetosus sp. n.

Material examined.

One female holotype as follows: habitus, left antennule and right antenna left intact and preserved in alcohol (ICML-EMUCOP-270800-02), right antennule, left antenna, mandibles, maxillules, maxillae and maxillipeds dissected and mounted onto four slides (ICML-EMUCOP-270800-01); Talud IV cruise; August 27, 2000; coll. S. Gómez.

Type locality.

Southern Carmen Basin, Gulf of California, México (25°54.7'N, 110°11'W), 2018 m depth (see Fig. 1); coll. S. Gómez.

Diagnosis (based on female only).

Body subcylindrical. Cuticula of body surface reticulated. Free thoracic somites and urosomites, except for anal somite, with posterior margin coarsely serrated. Cephalothorax with dorsal process curved posteriorly. P3-P5-bearing somites and second half of genital-double somite with bifid cuticular processes dorsally. Genital somite and third urosomite incompletely fused dorsolaterally. Anal somite with upward bifid cuticular process dorsally. Caudal rami 17 times as long as wide in lateral view, with seven setae. Antennule octa-segmented; second segment with strong protrusion bearing one strong element. Antenna with basis, with uni-segmented exopod bearing two setae subequal in length. Gnathobase of mandible with grinding face, palp uni-segmented, endopodal lobe with four setae. P2-P4ENP1 with inner seta. P1-P4ENP2 with 3, 3, 2, 2, setae respectively. P5 endopodal lobe represented by two setae; inner seta of the P5EXP very small, issuing subapically.

Description of female.

Body: total length 1420 µm measured from anterior margin of rostrum to posterior margin of caudal rami, subcylindrical, tapering slightly posteriorly, without clear demarcation between prosome and urosome, cuticula of body surface reticulated (Fig. 2A); P2-P5-bearing somites (Fig. 2D), both halves of genital double-somite and fourth and fifth urosomites (Fig. 2E) with posterior margin coarsely serrated; lateral margin of cephalothorax less coarsely serrated (Fig. 2B). Rostrum (Figs 2 A–B, 3A) fused to cephalothorax, with two sensilla. Cephalothorax (Fig. 2 A–B) 0.2 times as long as entire body length; with small sensilla as shown, and with exceedingly long lateral sensilla (Fig. 2B); with dorsal process curved posteriorly (Fig. 2A, B), the latter with sensilla as shown (Fig. 2C). Body somites with posterior transverse longitudinal row of spinules (Fig. 2A, D, E). P2-bearing somite without, P3-P5-bearing somites with bifid cuticular processes dorsally, of P4-bearing somite smallest, of P3- and P5-bearing somites subequal (Fig. 2D). Genital somite and third urosomite (genital double-somite) incompletely fused dorsolaterally (Fig. 2E), posterior margin of genital somite indicated by suture with few spinules and sensilla, and serrated posterior margin, completely fused ventrally (Fig. 3B); first half of genital double-somite without cuticular process dorsally (Fig. 2A, E), with few lateral spinules close to posterior margin (Fig. 2E), ventrally with medial genital field (Fig. 3B) and with some spinules close to lateral margins, second half with bifid cuticular process dorsally (Fig. 2A, E), with lateral spinules along posterior margin, serrated posterior margin between pair of ventral sensilla less pronounced (Figs 2E, 3B). Dorsal and lateral surface of fourth urosomite with short row of small spinules, with few sensilla, posterior margin serrated (Fig. 2A, E), ventrally with posterior serrated margin slightly less pronounced between pair of ventral sensilla, with minute spinules as shown (Fig. 3B). Fifth urosomite (Fig. 2E) with less spinules than in preceding somite, without sensilla, posterior margin equally serrated along entire margin, ventrally (Fig. 3B) with continuous spinular row close to posterior margin, with minute spinules as shown.

Anal somite (Figs 2A, E, 3B) quadrate, as long as two preceding somites combined; with lateral (Fig. 2A, E) and ventral (Fig. 3B) spinules, with upward bifid cuticular process dorsally, flanked by pair of sensilla, posterior tip of cuticular process longer than anterior (Fig. 2A, E).

Caudal rami slender, exceedingly elongated, 17 times as long as wide in lateral view, as long as P4-bearing somite and entire urosome combined, gently curved upwards from lateral view, covered with small spinules (Fig. 2A, F); with seven elements as follows: seta I and II in distal part of first third of ramus, the former ventral to and smaller than the latter (Fig. 2F); seta III situated subdistally on dorsal surface (Fig. 2G); seta IV and VI small, subequal in length, arising at outer and inner distal corners, respectively; seta V longest; dorsal seta VII tri-articulated, situated on anterior part of second third of ramus.

Antennule (Fig. 4A, B) octa-segmented; all segments with small slender spinules; first segment without armature, with one medial and one distal row of strong spinules; second segment with strong protrusion bearing one strong element (arrowed in Fig. 4B), and two strong spinules; third segment elongated, as long as fourth–seventh segments combined; eighth segment smallest. Armature formula as follows: 1-[0], 2-[5sp+3se], 3-[5sp], 4-[1sp+(1se+ae)], 5-[1sp], 6[3sp], 7-[2sp+2se], 8-[5se+acro]. Spinulose, spiniform elements (sp) with STE.

Antenna (Fig. 4C). Basis elongated, covered with small spinules. Exopod uni-segmented, with two apical setae. Endopod bi-segmented; first segment with strong inner spinules, covered with smaller spinules, shorter than basis; second segment covered with small spinules, inner margin with stronger spinules and with two thin subdistal spines with STE, and six apical elements (one inner strong spinulose spine, one spinulose spine, two geniculate spinulose elements, and two outer elements fused basally of which innermost longer and with STE).

Mandible (Fig. 5A). Mandibular gnathobase with some surface spinules, with two distal blunt teeth, and with broad grinding face. Palp uni-segmented (exopod and endopod fused to basis), with one basal, one exopodal, and one subdistal and three apical endopodal setae.

Maxillule (Fig. 5B, C). Praecoxal arthrite with some very long spinules, two surface setae, and eight apical spines (Fig. 5C). Coxa with five elements, strongest fused to coxa. Basis with subapical row of spinules and five setae.

Maxilla (Fig. 5D). Syncoxa with outer and inner spinules, with smaller spinules close to allobasis; with two endites; proximal endite with one slender seta, distal endite with one strong spinulose element, one pinnate and one bare seta. Allobasis with longitudinal row of outer spinules, with one strong spinulose spine fused to allobasis, one slender seta and one spinulose spine. Endopod uni-segmented, very small, with two setae.

Maxilliped (Fig. 5E) subchelate, strong. Syncoxa with inner long and outer small spinules as shown, with two setae, one of which strong and longer than syncoxa. Basis unarmed, with inner long and outer small spinules. Endopod uni-segmented, fused to strong spinulose claw.

P1 (Fig. 6A). Coxa with outer and inner slender spinules, with stronger spinules medially. Basis seemingly without spinular ornamentation, with outer and inner spine, the former longer. Exopod tri-segmented; EXP1 as long as following segments combined; with spinules as depicted; EXP1 and EXP2 without inner armature; EXP3 with four elements, of which outer and apical elements with STE, inner seta slender and reduced. Endopod bi-segmented, small; ENP1 with few inner spinules and one inner seta; ENP2 with few inner spinules, two apical and one outer seta.

P2-P4 (Figs 6B, 7 A–B). Praecoxa as in P3 and P4, small (see Fig. 7A, B). Coxa with few strong spinules close to outer distal corner. Basis seemingly without spinules (but two small spinules were observed at the base of the basal setophore of P3); outer basal seta of P2 spiniform, without setophore (Fig. 6B), of P3 and P4 setiform, long, with well-developed setophore (Fig. 7A, B). Exopod tri-segmented; EXP1 and EXP3 elongated, subequal in length, EXP2 shortest; EXP1 without, EXP2 with inner seta; P2EXP3 and P3EXP3 with two outer spines, two apical elements, and two inner setae (Fig. 6 A–B), P4EXP3 with two outer spines, two apical elements and one inner seta (Fig. 7B). Endopod bi-segmented; first segment with one inner seta; second segment of P2 with one inner and two apical setae (Fig. 6B), of P3 (Fig. 7A) and P4 (Fig. 7B) with one inner and one apical seta.

P 5 (Fig. 8 A–C) with some spinules on baseoendopodal setophore. Endopodal lobe poorly developed, with two setae (innermost lost during dissection), of which outermost very small (Fig. 8A, B). Exopod distinct, long, slender, 7.8 times as long as wide (maximum width measured at its base), with spinules as figured, with three outer, one apical and one inner seta, and one subdistal tube pore (arrowed in Fig. 8C).

Armature formula as follows:

Description of male.

Unknown.

Etymology.

The specific epithet is derived from the Latin adjective brevis, meaning short, and the Latin noun seta, meaning hair, and refers to the reduced innermost seta of the female P5EXP. The name is a noun in the nominative singular.

Remarks.

Mesocletodes brevisetosus sp. n. seems to be more closely related to M. dorsiprocessus than to M. bicornis , both from the Angola Basin, by the combination of several characters: 1) serrated posterior margin of the cephalothorax and P2-bearing somite to penultimate urosomite (serrated posterior margin on cephalothorax, P2-bearing somite to first half of genital double-somite in M. bicornis ), 2) relative length of the setae of the antennary exopod (subequal in M. dorsiprocessus and in M. brevisetosus sp. n., but one of them noticeably reduced in M. bicornis ), 3) presence of an inner seta on P2-P4ENP1 in M. dorsiprocessus and M. brevisetosus sp. n., but absent in M. bicornis , 4) number of setal complements on P1-P4ENP2 (3, 3, 2, 2 in M. dorsiprocessus and M. brevisetosus sp. n., but 2, 4, 4, 4 in M. bicornis ), 5) number of setae on the female P5 endopodal lobe (two setae in M. dorsiprocessus and M. brevisetosus sp. n., but three in M. bicornis ), 6) position of the inner seta of the female P5EXP (issuing subapically in M. dorsiprocessus and M. brevisetosus sp. n., but situated in distal third of inner margin of ramus in M. bicornis ), and 7) degree of development of the endopodal lobe of the female P5 (without any trace of endopodal lobe in M. dorsiprocessus and M. brevisetosus sp. n., but endopodal lobe discernible in M. bicornis ). Mesocletodes dorsiprocessus and M. brevisetosus sp. n. can be separated based on the number of setae on the endopodal lobe of the mandibular palp (one seta in M. dorsiprocessus , but four elements in M. brevisetosus sp. n.), the relative length of the innermost seta of the female P5EXP (well-developed in M. dorsiprocessus , but very reduced in M. brevisetosus sp. n.), appearance of the cuticula (plain in M. dorsiprocessus , but reticulated in M. brevisetosus sp. n.), armature complement of the seventh antennular segment (six in M. dorsiprocessus , but four in M. brevisetosus sp. n.), and number of setae on the syncoxa of the maxilliped (one in M. dorsiprocessus , but two in M. brevisetosus sp. n.).