Echiniscus brunus Dey & Gąsiorek & Michalczyk 2024, sp.nov.
Creators: name: Dey, Pritam K.
name: Gąsiorek, Piotr
name: Michalczyk, Łukasz
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Tardigrada
Heterotardigrada
Echiniscoidea
Echiniscidae
Echiniscus
Echiniscus brunus

description: Echiniscus brunus sp.nov.
ZooBank registration: urn:lsid:zoobank.org:act: A3069A8C-45BD-4901-B106-DBD8EF7157E8
(Figs 3, 5, 7B, 8B, 9A, 10, 11; Tables 2–4; Supporting Information, SM. 04)
Type locality and type series: 11°24ʹ55″N, 76°47ʹ35″E, 2110 m a.s.l.; India, Tamil Nadu, Nilgiris, Kothagiri. Holotype (adult female) on slide IN.391.02; 26 paratypes (13 adult females, nine juveniles, one exuvia and three larvae) on slides IN.391.01–IN.391.13; 20 paratypes on SEM stub no. 22.05; three hologenophores preserved on slides IN.391.01–IN.391.3, all deposited in the Department of Invertebrate Evolution of the Jagiellonian University.
Etymology: An epithet, in Latin brunus = brown, referring to the caramel/brown colour of the new species, the first formally described representative of the complex of brown echiniscids. An adjective in the nominative singular.
Adult females (i.e. from the third instar onwards; measurements and statistics are in Table 2). Body medium in size and plump (Figs 3, 5, 10A, F, 11A, B); dark orange pigments dominant in the ventral portion and limbs, but brown pigments prevalent within dorsal plates in living animals and specimens freshly mounted in Hoyer’s medium (Fig. 5A, D). Immediately asser the mount, specimen appears orange to crimson red with caramel–brown dorsal plates under PCM, while under BFM the body appears slightly greenish in colour, with orange pigment inside the body cavity (Fig. 5A, D). Several hours asser mounting, the body cavity becomes transparent, with a few droplets of yellowish orange pigments remaining inside the body cavity, but the dorsal and pedal plates appear more brown than caramel under PCM, while body cavity appears transparent with brown dorsal and pedal plates (Fig. 5B, E). Asser several days when all the yellow and orange pigmentation dissolve, the body cavity appears transparent, with brown dorsal plates and pedal plates (Figs 5C, F, 10). Large red granular eye spots are present in all individuals and vanish asser mounting. Buccal apparatus is short, rigid, with large cochlear stylet furcae and no stylet supports. Peribuccal cirri with cirrophores, cephalic papilla (secondary clava) elongated and conical (Figs 5D–F, 10, 11). Primary clava small and tightly adjacent to the cirrophore of cirrus A (Figs 5D–F, 9A, 10A, F, 11A, B), which is extremely short, in some specimens even shorter than cirrus externus (Fig. 10F).
Sculpturing of body plates comprises two types of pores: (i) more sparsely arranged and circular in shape with thick borders, dominant in most plate portions (Figs 10, 11); and (ii) tightly arranged and polygonal in shape, usually with thin borders, present only in anterior portions of paired segmental plates, lateralmost portions of the scapular, paired segmental, intersegmental and caudal (terminal) plates and pedal platelets (Figs 10, 11). Pores without dark intraporal rings. Cephalic plate small, with a clearly marked anterior chalice-like incision (Figs 5, 7B, 10A, E, F, 11A); cervical plate usually not identifiable, only sometimes a weak rectangular belt visible in LM (Figs 5, 7B, 10A, F). Scapular plate large, with the central poreless suture that can reach as far as to 80% of the plate (Figs 3E, 5, 7B, 9A, 10A, F, 11A); lateralmost plate portions demarcated by straight or slightly V-shaped sutures/incisions at the level of cirrus A (Figs 5, 7B, 10A, F). Always only two unipartite, triangular median plates, m1 and m2, with m2 being slightly larger. Posterior margins of median plates ossen with more sparsely distributed pores (Fig. 11A, B). Paired segmental plates I and II with posterior portions three to four times broader than anterior ones; a poreless belt separates anterior and posterior plate portions (Figs 5, 10A, B, F, 11B, C). Two pairs of large triangular intersegmental plates: the first positioned between the scapular plate and paired segmental plates I, and the second between plates I and II; a single pair between plate II and the caudal plate (Figs 5, 10A, B, F, 11B, C). The caudal plate is the largest element of the armour. In most specimens, a crescent-shaped thickening on the caudal plate is present, usually with fewer pores present in its central part compared with the remainder of the caudal plate (Figs 5, 10A, F, 11A, B). Venter densely granulated with minute endocuticular pillars, as typical for Echiniscus; a pair of subcephalic plates with large pores present (Fig. 13D).
Pulvini thin, but identifiable; pedal plates very large and intensely sculptured (Figs 5, 10A, D–F, 11B, D). First leg pair with a minute spine embedded on a pedal platelet (Figs 5, 10A, E, 11B, D). Fourth leg pair with a small papilla and a fringe composed of many tiny, separate teeth (Figs 5, 10A, F, 11B). Claws large and massive; internal ones with typical spurs divergent from main branches and positioned at ~20%–25% of the branch.
Juveniles (i.e. the second instar; measurements and statistics are in Table 3). ºualitatively similar to sexually mature females. Gonopore lacking.
Larvae (i.e. the first instar; measurements and statistics are in Table 4). ºualitatively similar to later life stages, already with two pronounced types of pores (Fig. 10E). Two claws per leg, each with divergent and evident spurs (Fig. 10E). Gonopore and anus lacking.
DNA sequences: A set of five markers was obtained: 18S rRNA (OR520116–7), 28S rRNA (OR520110–1), ITS-1 (OR520101–3), ITS-2 (OR520122–4) and COI (OR506701– 3). Uncorrected pairwise distances between the new species and the two candidate species within the complex were as follows: 18S rRNA, 0.2% (both E. aff. brunus sp. can. 1 and E. aff. brunus sp. can. 2); 28S rRNA, 0.1%–0.3% (E. aff. brunus sp. can. 2 and E. aff. brunus sp. can. 1, respectively); ITS-1, 3.1%–4.4% (E. aff. brunus sp. can. 1 and E. aff. brunus sp. can. 2, respectively); ITS-2, 3.4%–4.9% (E. aff. brunus sp. can. 2 and E. aff. brunus sp. can. 1, respectively); and COI, 2.0%–3.7% (E. aff. brunus sp. can. 2 and E. aff. brunus sp. can. 1, respectively). See Supporting Information, SM.03 for matrices with genetic distances.
Remarks: Found with Milnesium sp., Ramazzottius sp. and Macrobiotus sp. in the sample. In several specimens, developmental malformations were observed, in which various dorsal plates merged into a single large plate (for an example, see Fig. 10F).
Differential diagnosis: Because of the distinct brown, UV-absorbing cuticular pigmentation (also clearly visible in specimens mounted in Hoyer’s medium) and the presence of an anterior suture in the scapular plate, the new species cannot be mistaken for any other formally described echiniscid.
description: Published as part of Dey, Pritam K., Gąsiorek, Piotr & Michalczyk, Łukasz, 2024, Convergent evolution of dark, ultraviolet-absorbing cuticular pigmentation in a new Afro-Oriental Echiniscus brunus species complex (Heterotardigrada: Echiniscidae), pp. 34-59 in Zoological Journal of the Linnean Society 200 (1) on pages 40-46, DOI: 10.1093/zoolinnean/zlad132, http://zenodo.org/record/10470646