Neoechiniscoides, 2020

Møbjerg, Nadja, Jørgensen, Aslak & Kristensen, Reinhardt M., 2020, Ongoing revision of Echiniscoididae (Heterotardigrada: Echiniscoidea), with the description of a new interstitial species and genus with unique anal structures, Zoological Journal of the Linnean Society 188 (3), pp. 663-680 : 668-669

GENUS NEOECHINISCOIDES MØBJERG, JØRGENSEN & KRISTENSEN GEN. NOV.

( FIGS 2–7 )

urn:lsid:zoobank.org:act:8FA86B31-39B9-4523- AFAF-E0DB7DE91562:

Diagnosis: Primarily interstitial Echiniscoidinae , with seven to eight, occasionally six or nine, anisonych claws (generally more than six claws on each leg in adults). Epicuticular pillars absent. The dorsal cuticle is strongly sculptured. Cirri Aand Eare present and relatively short in both sexes. First and second leg sensory structures are small and dome shaped. The third leg sensory structure is a seta, and the fourth leg sensory structure is papillar, as is the primary clava. Secondary clavae (cephalic papilla) are more distinct and appear relatively larger in males than in females. Cephalic papillae may be subdivided into secondary and tertiary clavae. Seminal receptacles are lacking. The anal system appears large, with two wings associated with the lateral lobes. The distance between the anus and the gonopore is larger in females than in males. Asmall ventral cuticular plate is present in front of the female gonopore (not observed in N. pollocki ).

Etymology: From the Greek νέος, neos (new or young) combined with the generic name Echiniscoides .

Type species: Neoechiniscoides aski ; described below.

Other members of the genus: Neoechiniscoides horningi ( Miller & Kristensen, 1999) comb. nov. (basionym: Echinsicoides horningi Miller & Kristensen, 1999 ), sub-Antarctic (Macquarie Island), collected from the lichen Caloplaca sp. on rock in lower supralittoral zone. Neoechiniscoides pollocki ( Hallas & Kristensen, 1982) comb. nov. (basionym: Echiniscoides pollocki Hallas & Kristensen, 1982 ), Rhode Island, USA, found interstitially, from tidal sediments.

Differential diagnosis of the genus: Neoechiniscoides leg sense organs are of the Echiniscoides sigismundi type, i.e. p1 and p2 are dome shaped, p3 is a short setae, and p4 is similar to the primary clava, consisting of a small papilla with a spiny tip. Cirri (internal, external, Aand E) are shorter in Neoechiniscoides (range unadjusted for body size 3.0–8.7, 3.0–7.6, 10.0– 17.0 and 10.0–18.0 µm, respectively) compared with Isoechiniscoides (range unadjusted for body size 7.3– 12.0, 6.6–9.7, 14.5–21.0 and 24.0–33.0 µm, respectively), but generally longer than cirri of Echiniscoides . Specifically, cirri are longer in N. aski and N. pollocki than in Echiniscoides , but N. horningi falls within the range of Echiniscoides , which has an internal, external, Aand Ecirri length unadjusted for body length of 3.1– 4.8, 2.2–3.8, 8.3–13.0 and 7.5–12.0 µm, respectively, according to Kristensen & Hallas (1980). The anal system ( Fig. 6 ) of Neoechiniscoides differs from that of Echiniscoides and Isoechiniscoides , specifically in the paired wings associated with the lateral lobes of the anus (wl in Figs 2 , 4 ). Using light microscopy, the lateral anal lobes thus appear as a double structure. In scanning electron microscopy, these anal lobes appear as a double swollen structure, which can be observed when viewed dorsocaudally. Interestingly, during sampling we observed that the movements of the new interstitial Neoechiniscoides species were more similar to slowly moving eutardigrades than to other members of Echiniscoididae . Notably, specimens of the new species, N. aski , were highly responsive to freshwater shocking, which resulted in a fast gain of body water and associated swelling.

Generic discussion: The molecular phylogenetic investigation of Echiniscoididae reveals several possibly undescribed taxa. Here, we establish the new genus Neoechiniscoides , with its members morphologically clearly distinguishable from the other taxa in Echiniscoididae . The wing structure of the lateral anal lobes is not present in other heterotardigrades. We acknowledge that a cautious approach should be taken to morphological structures with regard to their significance at a specific taxonomic level at this early stage of echiniscoidid revision. Hence, characteristics of the anal system might, in the future, have significance at a higher taxonomic level.

Figures

Figure 2. Light microscopy of Neoechiniscoides aski. A–C, images of live, moving specimens. A, ventral view of a live adult female, showing the anal system with lateral wings. In live animals, the conspicuous anal complex moves from side to side when the animal walks/runs. Scale bar: 50 µm. B, dorsal view of live adult female used for DNA extraction (28S GenBank accession number KX363645; COI GenBank accession number KX363656). Note the eight to nine mature oocytes. Scale bar: 50 µm. C, dorsal view of live adult male. Scale bar: 50 µm. D, holotype of N. aski (female). Scale bar: 50 µm. E, paratypic allotype of N. aski (male). Scale bar: 50 µm. F, ventrocaudal view of holotypic female showing anal system and the gonopore, which is raised on an elevation (note that seminal receptacles are lacking). Scale bar: 20 µm. G, ventral view of paratypic

Figure 3. Scanning electron microscopy of Neoechiniscoides aski. A–C, female. A, habitus of mature female. Scale bar: 10 µm. B, close-up of gonopore with associated cuticular plate and anus. Note muscle attachment sites located lateral to the female gonopore. Scale bar: 10 µm. C, close-up of head region. Note the cuticular sculpture of the head. Scale bar: 10 µm. D–H, male. D, second leg, with dome-shaped sense organ (p2). Scale bar: 1 µm. E, habitus of adult male. Scale bar: 10 µm. F, prominent dorsal cuticular attachment sites of the caudal segment. Scale bar: 1 µm. G, posterioventral part of a male, showing the fourth leg pair, anal system and gonopore. Anterior is to the left. Scale bar: 10 µm. H, close-up of head region of male. Note the relatively large secondary clavae. Scale bar: 1 µm. Abbreviations: an, anus; cE, cirrus E; cl, claw; ec, external

Figure 4. Neoechiniscoides aski.Drawing of holotypicfemale (NHMD-230293),ventral view.Scale bar:50 µm.Abbreviations: an, anus; bt, buccal tube; cE, cirrus E; cm, claw membrane; ec, external cirrus; ey, eye; go, gonopore; ic, internal cirrus; lc, lateral cirrus (cirrus A); ma, lateral attachment sites associated with the female gonopore; mg, midgut; nc, new claws forming inside claw gland; oo, oocyte; ov, ovary; p1–p3, sensory structures of legs I–III, respectively; pa, ventral cuticular plate; pb, pharyngeal bulb; pc, primary clava; pl, placoid; sc, secondary clava; wl, lateral wing of the anal structure.

Figure 5. Neoechiniscoides aski. Drawing of allotypic male (NHMD-230297), dorsal view. Scale bar: 50 µm. Abbreviations: as, anal system; cE, cirrus E; cl, claw; ds, dorsal cuticular attachment sites; ec, external cirrus; fu, furca of the stylet; ic, internal cirrus; lc, lateral cirrus (cirrus A); mg, midgut; p1–p4, sensory structures of legs I–IV, respectively; pc, primary clava; sc, secondary clava; sp, spermatozoa; sv, seminal vesicle; te, testicle.

Figure 6. Drawing of anal system in Isoechiniscoides, Echiniscoides and Neoechiniscoides based on investigations of live animals and preparations on slides for light microscopy. In all three genera, a three-lobed anal system is present and consists of two lateral lobes and a terminal lobe of variable size. The anal opening is indicated in black. In Neoechiniscoides, two wings are present on the lateral lobes. These wings are easily visualized in live animals and using light microscopic preparations, whereas this double structure of the lateral lobes is difficult to visualize in specimens prepared for scanning electron microscopy. Scale bar: 10 µm.

Figure 7. Phylogenetic position of Neoechiniscoides aski inferred by Bayesian inference of COI. The figure represents the smallest supported clade informative with regard to the phylogenetic relationships of Neoechiniscoides. Posterior probabilities (first) are shown as percentages, and bootstrap values are indicated.