Leiocanthus quinquenudus Cepeda & Sánchez & Sørensen & Landers 2022, sp. nov.
Creators: name: Cepeda, Diego
name: Sánchez, Nuria
name: Sørensen, Martin V.
name: Landers, Stephen C.
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Kinorhyncha
Allomalorhagida
Pycnophyidae
Leiocanthus
Leiocanthus quinquenudus

description: Leiocanthus quinquenudus sp. nov.
Zoobank code: urn:lsid:zoobank.org:act: 72EC0153-2637-449D-A08D-BDB8E997C413
(Figs. 2–4)
Synonymy
Leiocanthus sp. 2 —in Landers et al. 2020: p. 496, Table III.
Leiocanthus sp. 2 —in Hoffman et al. 2021: p.377, Table 4.
Material examined. Holotype, adult female, collected on March 17, 2018 at St. 13-2018 in the northern Gulf of Mexico continental shelf: 30.1463° N, 88.2583° W (Table 1) at 18 m depth; mounted in Fluoromount G ®, deposited at the NHMD under catalogue number: NHMD-915196. Paratypes, three adult males and two adult females, all of them collected at different stations than the holotype (Table 1), mounted in Fluoromount G ® and stored at NHMD under catalogue numbers: NHMD-915197–915201. One additional female mounted for SEM and deposited in the personal reference collection of SCL.
Diagnosis. Leiocanthus with middorsal cuticular elevations on segments 2–6. Unpaired paradorsal setae on segments 2, 4, 6 and 8; paired setae in laterodorsal position on segments 3, 5, 7 and 9, in lateroventral position on segments 2, 4, 6, 8 and 10 (two pairs in the latter), ventrolateral position on segment 5 and ventromedial position on segments 3–4 and 6–9 longitudinally aligned. Anterior margin of segment 1 tergal plate irregularly denticulated, posteriorly followed by a transverse band of minute, circular perforations. Males with sexually dimorphic ventromedial tubes on segment 2, females with ventrolateral setae instead. Lateral terminal spines present.
Etymology. The specific epithet of the species derives from the Latin quinque (meaning five) and nudus (meaning naked), referring to the unique lack of ventromedial setae on segment 5 of the species.
Description. See Table 2 for measurements and dimensions and Table 3 for summary of seta, spine, tube, glandular cell outlet and sensory spot positions.
Head. Only one specimen, which was mounted for LM, had the head everted, hence exact details on the morphology and arrangement of the mouth cone and introvert structures cannot be completely provided. Internal rings of mouth cone not observed. Ring 00 of mouth cone with nine, equally sized outer oral styles, each one composed of a single, flexible unit, wider at the base, bearing a fringed basal sheath, progressively tapering towards a distally pointed tip. Outer oral styles located anterior to each introvert sector, except in the middorsal sector 6 where a style is missing.
Introvert with six transverse rings of scalids and 10 longitudinal sectors defined by the position of the primary spinoscalids. Ring 01 of introvert with 10 primary spinoscalids; primary spinoscalids larger than scalids in remaining rings; each primary spinoscalid composed of a basal, rectangular, wide sheath and a distal, elongated, flexible, laterally compressed, distally rounded end-piece. Basal sheath of primary spinoscalids superficially fringed, bearing a rhomboid cuticular piece superficially fringed near the articulation point with the end-piece. Rings 02–06 of introvert with several regular-sized scalids, also composed of a basal, rectangular, superficially fringed, wide sheath and a distal, elongated, flexible, distally rounded end-piece. Exact arrangement of regular-sized scalids cannot be provided due to the collapsed condition of the only available introvert when mounted for LM. A ring of 14 trichoscalids posterior to the scalid rings, arranged as two in the odd-numbered sectors (except sector 1 with a single trichoscalid) and one in the even-numbered sectors of the introvert.
TABLE 2. Measurements (in μm) of six adult specimens of Leiocanthus quinquenudus sp. nov. (three females and three males) from the Gulf of Mexico. Abbreviations: LTS, lateral terminal spine length; MSW-5, maximum sternal width (measured at segment 5); n, number of measured specimens; S, segment length (followed by number of corresponding segment); SD, standard deviation; SSW, standard sternal width (measured at segment 10); TL, trunk length.
Neck. Neck with four dorsal and two ventral sclerotized placids (Fig. 2A–B). Mesial dorsal placids subquadrangular, conspicuously higher than lateral ones (Fig. 2B), ca. 26–32 μm wide at the base; lateral dorsal placids rectangular (Fig. 2B), ca. 20–23 μm wide at the base. Mesial and lateral dorsal placids with saw-toothed anterior margin and longitudinal striation on the surface (Fig. 2B). Ventral placids even more rectangular, longitudinally compressed, with straight laterodistal margins (Fig. 2A), ca. 17–30 μm wide at the base.
Trunk. Trunk rectangular, stout, triangular in cross-section, composed of 11 segments (Figs. 2A–B, 3A, 4A). Segment 1 with one tergal, two episternal and one midsternal plates; remaining segments with one tergal and two sternal plates (Figs. 2A–D, 3A–J, 4A–H). Maximum sternal width at segment 5 (Table 2), almost constant in width throughout the trunk until segment 8, and progressively tapering along the last trunk segments (Figs. 2A–B, 3A, 4A). Sternal cuticular plates relatively narrow in relation to trunk length (MSW–5:TL interval ratio = 20.6–28.2%) (Table 2), giving the animal a relatively slender appearance (Figs. 2A–B, 3A, 4A). Segments 1–10 with rounded to slightly oval glandular cell outlets, each consisting of a single, round opening located in subdorsal and ventromedial positions, except ventral outlets of segment 1 shifting its position to ventrolateral (Figs. 2A–D, 3 B-J); intraspecific variation of this character was found in a single specimen that showed two round openings in some glandular outlets. Segments 2–10 with paired, small, not always conspicuous cuticular ridges in ventrolateral position, with adjacent, minute glandular cell outlets (Fig. 2A, C). Minute, acicular cuticular hairs widely covering the cuticular surface of segments 1–10, except in ventromedial position, denser at the tergosternal junctions (Fig. 4B–G). Muscular scars in laterodorsal and ventrolateral positions throughout segments 1–10 as rounded to oval, hairless cuticular areas, poorly conspicuous, even less visible on the sternal plates (Figs. 2A–C, 3B–J). Pachycycli and ball-and-socket joints well-developed and thick on segments 2–10 (Figs. 2A–D, 3A, F, H). Apodemes absent. Posterior margin of segments straight, with primary pectinate fringes showing weakly serrated free flaps (Figs. 2A–D, 3B–J, 4B–G). Secondary pectinate fringes as three (dorsal) to two (ventral) transverse rows, finely serrated, becoming slightly wavier at the sternal plates, extending posteriorly in triangular extensions in ventrolateral position (Figs. 2A–D, 3C, H, J).
Segment 1 without middorsal process or elevation. Anterolateral margins of tergal plate as low, distally rounded protuberances (Figs. 2 A-B, 3A, 4A). Anterior margin of tergal plate irregularly denticulated, posteriorly followed by a transverse band of minute, circular perforations (Fig. 2B). Anterior margin of sternal plates with several semicircular ridges and a few, scattered, minute, circular depressions (Fig. 2A). Midsternal plate slightly wider at the posterior edge (Figs. 2A, 3A). Sensory spots in subdorsal (two pairs), laterodorsal (one pair), ventrolateral (two pairs longitudinally arranged) and ventromedial (one pair) positions (Figs. 2A–B, 3B). Sensory spots on this and remaining segments rounded to oval, with a single posterior pore surrounded by several rings of micropapillae.
Segment 2 with middorsal elevation not projecting beyond the posterior margin of segment, with conspicuous paradorsal, butterfly-like atria of sensory spots (Figs. 2B, 3D). Unpaired seta in paradorsal position, and paired setae in lateroventral and ventrolateral positions, the latter only in females (sexually dimorphic) (Figs. 2A–C, 3C–E, 4B). Sensory spots in paradorsal, subdorsal, laterodorsal and ventromedial positions (Figs. 2A–C, 3C–E, 4B). Males with conspicuously large, sexually dimorphic tubes in ventromedial position (Figs. 2A, 3E).
Segment 3 with middorsal elevation as on the preceding segment (Figs. 2B, 3D). Paired setae in laterodorsal and ventromedial positions (Figs. 2A–B, 3D, 4B). Sensory spots in paradorsal, subdorsal, laterodorsal and ventromedial positions, the latter more lateral than the ventromedial setae (Figs. 2A–B, 3D, 4B).
Segment 4 with middorsal elevation as on the preceding segments (Fig. 2B). Unpaired seta in paradorsal position, and paired setae in lateroventral and ventromedial positions, the latter longitudinally aligned with those of segment 3 (Figs. 2A–B, 4F). Sensory spots in paradorsal, subdorsal, laterodorsal and ventromedial positions (Figs. 2A–B, 4F).
Segment 5 with middorsal elevation as on the preceding segments (Fig. 2B). Paired setae in laterodorsal and ventrolateral positions (Figs. 2 A-–B, 3F, 4D, F). Sensory spots in paradorsal, subdorsal, laterodorsal and ventromedial positions (Figs. 2A–B, 3F, 4D, F).
Segment 6 similar to segment 4 in the arrangement of cuticular elevation, setae and sensory spots (Figs. 2A–B, 3F, 4D, G).
Segment 7 similar to segment 3 in the arrangement of setae and most sensory spots, but lacking the middorsal elevation and paradorsal sensory spots (Figs. 2A–B, 3H, 4C, G). Bilateral deviation was observed in two specimens, as the ventromedial seta was lacking on one of the sternal plates.
Segment 8 without middorsal process or elevation. Unpaired seta in paradorsal position, and paired setae in lateroventral and ventromedial positions, the latter longitudinally aligned with those of the preceding segments (Figs. 2A–B, 3G–H, 4C). Sensory spots in subdorsal (two pairs), laterodorsal (one pair) and ventromedial (one pair) positions (Figs. 2A–B, 3G–H, 4C). Bilateral deviation was observed in two specimens, as the ventromedial seta was lacking on one of the sternal plates.
Segment 9 without middorsal process or elevation. Paired setae in laterodorsal and ventromedial positions (Figs. 2A–B, 3G, J, 4E). Deviation was observed in a single male specimen, as the ventromedial pair of setae was absent. Sensory spots in subdorsal (two pairs), laterodorsal (one pair), ventrolateral (one pair) and ventromedial (one pair) positions (Figs. 2A–B, D, 3G, J, 4E). Nephridia externally opening as short cuticular tubes with fringed tips (Fig. 2A).
Segment 10 without middorsal process or elevation. Two pairs of setae in lateroventral position (Figs. 2A–B, D, 4E). Sensory spots in subdorsal, laterodorsal, ventrolateral and ventromedial positions (Figs. 2A–B, 3I, 4E).
Segment 11 with three pairs of type 3 sensory spots in subdorsal position (Fig. 2B). Males with two pairs of sexually dimorphic penile spines and genital pores (Figs. 2A, 3I). Lateral terminal spines (Figs. 2A–B, D, 3A, 4A) relatively long (LTS:TL interval = 19.7–33.0 %; LTS:TL mean = 27.2%; Table 2).
Remarks. The specimen mounted for SEM carried several epibiontic Ciliophora on the sternal plates of segments 1 and 5 (Fig. 4A, H–I).
description: Published as part of Cepeda, Diego, Sánchez, Nuria, Sørensen, Martin V. & Landers, Stephen C., 2022, Leiocanthus quinquenudus sp. nov. and L. satanicus sp. nov., two new species of pycnophyid Kinorhyncha (Allomalorhagida: Pycnophyidae) from the Gulf of Mexico, pp. 315-336 in Zootaxa 5093 (3) on pages 319-323, DOI: 10.11646/zootaxa.5093.3.3, http://zenodo.org/record/5909853