Pseudechiniscus (Meridioniscus) dreyeri, Gąsiorek & Vončina & Kristensen & Michalczyk, 2021

Gąsiorek, Piotr, Vončina, Katarzyna, Kristensen, Reinhardt Møbjerg & Michalczyk, Łukasz, 2021, Fig. 7 in Fig. 4. A in Saphonecrus globosus Schweger and Tang 2015, Zoological Studies (Zool. Stud.) 60 (70), pp. 1-45 : 19-25

Genus: Pseudechiniscus Thulin, 1911 Subgenus: Meridioniscus Gąsiorek et al., 2021 Pseudechiniscus (Meridioniscus) dreyeri sp. nov. ( Figs. 24–25 , Tables 11–12)

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Description: Females (i.e., from the third instar onwards; measurements and statistics in table 11): Body small and cylindrical ( Fig. 24A ), light orange with tiny crystalline eyes; body colour and eyes dissolve in Hoyer’s medium. Clavae elongated (dactyloid); cirrophores of peribuccal cirri merged with flagellum, cirrophores A distinct ( Fig. 24A–B ).

Dorsal plate sculpturing of the Pseudechiniscus type, with rudimentary, faint striae present occasionally in central plate portions ( Fig. 24B ). Endocuticular pillars of similar diameters throughout the dorsum. Pentapartite cephalic plate adjacent to the scapular plate; lacking cervical plate ( Fig. 24A ). Scapular plate divided by two weakly marked sutures: central longitudinal suture and transversal suture, thus delineating four plate portions: two large anterior ones and two posterior, more narrow and with poorly visible lateralmost subportions ( Fig. 24B ). Median plates m1, m3 unipartite and large, a pair of lateral intersegmental plates flanking m1 and two pairs of such plates flanking m2; m2 bipartite, with narrow triangular posterior part. Paired segmental plates I–II and paired pseudosegmental plate IV’ present ( Fig. 24B ). Caudal plate with two slightly curved incisions ( Fig. 24A ).

Ventral sculpturing with well-developed and evident reticulum composed of endocuticular pillars solely ( Figs. 24C – 25). Single dense aggregation of pillars forming an aliform shape in the subcephalic region. Sexpartite gonopore placed between legs III– IV, and a trilobed anus between legs IV. Pedal plates formed as belts of pillars in central limb portions ( Fig. 24A ). Pulvini faint. Papillae or spines on legs I absent. Papilla IV small and tubby ( Fig. 24A ). Claws minute and isonych; internal claws with delicate primary spurs positioned at ca. 20% of the branch height and closely adjacent to it ( Fig. 24A , insert).

Males: Not found.

Juveniles (i.e., the second instar; measurements and statistics in table 12): Qualitatively identical to females, beside of the lack of gonopore. No morphometric gap with respect to adult females.

Larvae (i.e., the first instar): Cuticle sculpturing developed as in older instars. Gonopore and anus absent. Body length 94–100 μm, scapular plate length 14.4–14.7 μm; cephalic appendages lengths: cirri interni 3.8–6.0 μm, cephalic papillae 2.8–3.0 μm, cirri externi 4.7–6.4 μm, (primary) clavae 3.0–3.1 μm, cirrus A 15.3–15.9 μm. Papilla IV length 1.4–1.6 μm. Claw branches 4.6–5.0 μm, spurs 1.4–1.8 μm.

Eggs: Up to two orange eggs per exuvia were found.

Molecular markers and phylogenetic position: Single haplotypes were found in all markers: 18S rRNA (OK048615), 28S rRNA (OK048633), ITS- 1 (OK048646) and COI (OK047278). In the updated phylogeny from Gąsiorek et al. (2021c), the closest relative of P. (M.) dreyeri sp. nov. within the Meridioniscus clade is P. (M.) cf. saltensis from the Neotropics ( Fig. 30 ).

Type material: Holotype (adult female on the slide TW.008.12), 32 paratypes: 18 adult females, 12 juveniles, and two larvae on the slides TW.005.11, 13, 15–16, TW.008.10–13. Four specimens were preserved for molecular analyses. Holotype deposited in the Biodiversity Research Center of the Academia Sinica ( ASIZ01000039 ), the one paratype (NHMD-915766) deposited in the Natural History Museum of Denmark, and remaining material stored at the Jagiellonian University .

Type locality: 24°23'51"N, 121°14'04"E, 3 700 m asl: Taiwan, Snow Mountain (Xueshan), North Peak. Mosses from rocks exposed to sun.

Etymology: Patronym honouring Niklas Dreyer, a carcinologist and the collector of the Taiwanese moss samples used in this study. Noun in the genitive singular.

Differential diagnosis: There are few Meridioniscus species with a smooth posterior margin of the pseudosegmental plate IV’ (or with minute projections) and lacking lateral hemispherical projections. Pseudechiniscus (M.) dreyeri sp. nov. differs from:

P. (M.) angelusalas Roszkowska et al., 2020 , described from Madagascar, by relative lengths of some of the cephalic appendages (cirrus internus 22.0–33.0, cirrus A 96.8–126.8 in P. (M.) dreyeri sp. nov. vs cirrus internus 34.4–36.6, cirrus A 129.2–152.2 in P. (M.) angelusalas ).

P. (M.) dastychi Roszkowska et al., 2020 , known from the maritime Antarctic, by adult female body size (body length 121–152 μm and scapular plate length 18.9–23.7 μm in P. (M.) dreyeri sp. nov. vs 167–202 μm and sc 27.5–33.0 μm in P. (M.) dastychi ), lengths of cephalic appendages (cirrus internus 4.7–7.0 μm, cirrus externus 6.8–11.9 μm, cirrus A 21.0–27.0 μm [14–20% of the body length] in P. (M.) dreyeri sp. nov. vs cirrus internus 10.4–12.7 μm, cirrus externus 15.9–19.1 μm, cirrus A 40.0–45.0 μm [22–26% of the body length] in P. (M.) dastychi ), and claw heights (5.0–8.1 μm in P. (M.) dreyeri sp. nov. vs 8.7–12.2 μm in P. (M.) dastychi ).

P. (M.) indistinctus Roszkowska et al., 2020 , known from the Scandinavian Peninsula, by the morphology of dorsal pillars (homogeneous in size in P. (M.) dreyeri sp. nov. vs heterogeneous in size in P. (M.) indistinctus ) and relatively shorter peribuccal cirri (cirrus internus 22.0–33.0, cirrus externus 31.9–52.2 in P. (M.) dreyeri sp. nov. vs cirrus internus 34.1–38.5, cirrus externus 54.3–59.3 in P. (M.) indistinctus ).

P. (M.) mascarenensis Kiosya et al., 2021 , known from Mauritius, by having smaller adult females (121– 152 μm in P. (M.) dreyeri sp. nov. vs 151–177 μm in P. (M.) mascarenensis ) and a relatively longer cirrus A (14–20% of the body length in P. (M.) dreyeri sp. nov. vs 9–13% in P. (M.) mascarenensis ).

P. (M.) santomensis Fontoura et al., 2010 , a São Tomé endemic, by a relatively longer cirrus A (14–20% of the body length in P. (M.) dreyeri sp. nov. vs 9–14% in P. (M.) santomensis ) and dorsal plate sculpturing (striae rarely identifiable in P. (M.) dreyeri sp. nov. vs striae delicate and thin, but clear in all plates in P. (M.) santomensis ).

Moreover, P. (M.) dreyeri sp. nov. is distinguishable from all abovementioned species by the ventral sculpturing pattern.

Figures

Fig. 24. Morphology of Pseudechiniscus (Meridioniscus) dreyeri sp. nov. (PCM): A, holotypic female in dorsolateral view (insert shows claws II); B, dorsal sculpturing; C, ventral sculpturing. Scale bars in μm.

Fig. 30. Position of the Taiwanese species on the phylogenetic tree of the genus Pseudechiniscus based on the concatenated matrix (18S rRNA+28S rRNA+ITS-1). Values at nodes separated by forward slashes signify Bayesian posterior probability and bootstrap values (ML), respectively. Maximum supports, i.e., 1.00 for BI and 100 for ML, are indicated by asterisks (*), whereas nodes unsupported in either analysis are marked by hashtags (#). The scale refers to the Bayesian consensus tree and represents substitutions per site. Species numbering preserved from Gąsiorek et al. (2021c).