Hypechiniscus crassus, 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 : 10-15

Genus: Hypechiniscus Thulin, 1928 Hypechiniscus crassus sp. nov. ( Figs. 12–18 , Tables 6–9)

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Description: Females (i.e., from the third instar onwards; measurements and statistics in table 6): Body plump ( Figs. 12–13A , 14A ), opalescent white before mounting in Hoyer’s medium. Large black eyes present ( Fig. 12 ) but may dissolve during mounting ( Fig. 13A ). Dactyloid (elongated) clavae ( Figs. 12 , 15–16A ); cephalic cirri with large cirrophores ( Figs. 15–16A ). Cirrus dorsalis absent.

Dorsal plate sculpturing of the Pseudechiniscus type, consisting of endocuticular pillars, which can be connected by striae in some plate portions (visible only under ×1000 magnification, Figs. 15A , 16B ). Epicuticular matrix forms ornamented pattern in all plates, overlapping with pillars. Cephalic plate hexapartite, with dominant trapezoidal posterolateral portions and a central rhomboidal portion; cervical plate adjacent to it and weakly delineated ( Figs. 13A , 17A ). Scapular plate divided in two portions by a central epicuticular ridge ( Fig. 16B ). Three median plates: m1–2 bipartite and m3 unipartite; m1 divided in two roughly similar portions by a transverse suture, identical suture divides m2, but its posterior portion is much reduced compared to the anterior, rhomboidal portion. Paired segmental plates I–II large, with no sutures or incisions. Five pairs of lateral supplementary plates flanking the median plates ( Fig. 17A ). Caudal plate with two long, weakly sclerotised incisions ( Figs. 13A , 14A , 15A , 17A ).

Venter with evident species-specific sculpturing pattern ( Figs. 15B , 17B ) comprising overlapping belts of endocuticular pillars and epicuticular thickenings. Sexpartite gonopore placed between genital plates, and a trilobed anus between legs IV. Pedal plates in the form of aggregations of pillars in central leg portions ( Fig. 15 ). Pulvini poorly delineated. Lacking papilla on leg I. Papilla IV small, but visible in PCM ( Figs. 12 , 14A , 15A ). Curvature of claws typical for Hypechiniscus , with strongly bent spurs on internal branches. Pseudoaccessory points present ( Fig. 16C–D ).

Males (i.e., from the third instar onwards; measurements and statistics in table 7): Sexual dimorphism weakly marked. Males are only slightly slimmer ( Figs. 13 B, 14 B ) than large females. Qualitatively alike females, beside of the circular gonopore.

Juveniles (i.e., the second instar; measurements and statistics in table 8): Qualitatively similar to adults. Gonopore absent. A clear morphometric gap between juveniles and sexually mature individuals of both sexes.

Larvae (i.e., the first instar; measurements and statistics in table 9): Gonopore and anus absent. Twoclawed individuals smaller than juveniles, but with a fully developed dorsal sculpturing and papilla IV visible in PCM ( Fig. 18 ).

Eggs: Up to two pearly white eggs per exuvia were found.

Molecular markers and phylogenetic position: Single haplotype was found in 18S rRNA (OK048612– 3) and 28S rRNA (OK048630–1) for both populations. According to the updated phylogeny from Gąsiorek et al. (2021a), H. crassus sp. nov. is sister to the clade ( H. cataractus Gąsiorek et al., 2021 + the H. gladiator group) ( Fig. 19 ).

Type material: Holotype (adult female on the slide TW.006.04), allotype (adult male on slide TW.006.02), 23 paratypes: 13 adult females, 3 adult males, 4 juveniles, 3 larvae on slides TW.005.01–5, TW.006.01– 5, TW.008.08–10, 13. Four females and one male on SEM stub 21.08. Two specimens per samples TW.005–6 were used for DNA sequencing, including one retrieved as a hologenophore. Holotype ( ASIZ01000036 ) deposited in the Biodiversity Research Center of Academia Sinica , one paratype (NHMD-915767) deposited in the Natural History Museum of Denmark, and the remaining material stored at the Jagiellonian University .

Type locality: 24°23'18"N, 121°15'39"E, 3 200 m asl: Taiwan, Snow Mountain (Xueshan), East Peak. Mosses on rocks exposed to sun.

Etymology: From Latin crassus = stout, plump; referring to the body proportions of both sexes. Adjective in the nominative singular.

Differential diagnosis: The new species differs from all representatives of the gladiator complex by the lack of cirrus dorsalis . It is also distinguishable from all members of the exarmatus morphogroup based on the presence of striae in some plate portions (typically absent in Hypechiniscus , see Gąsiorek et al. 2021a) and in additional characters from:

H. cataractus , a Southeast Asian species, by the dorsal plate sculpturing (plates smooth in PCM in H. cataractus vs clear sculpturing in H. crassus sp. nov.) and ventral cuticle sculpturing (no epicuticular thickenings in H. cataractus vs epicuticular thickenings present and overlapping with belts of endocuticular pillars in H. crassus sp. nov.).

H. exarmatus ( Murray, 1907) , a probable West Palaearctic element, exhibits no epicuticular ornamentation on dorsum and epicuticular thickenings on venter that do not overlap with belts of endocuticular pillars (both character states present in H. crassus sp. nov.).

H. flavus Gąsiorek et al., 2021 , a likely Japanese endemic, by body colour (yellow in H. flavus vs opalescent white in H. crassus sp. nov.) and by the dorsal plate sculpturing (epicuticular thickenings in dorsal plates absent in H. flavus vs present in H. crassus sp. nov.).

Remarks: The presence of pseudoaccessory points on claws of H. crassus sp. nov. falsifies the hypothesis from Gąsiorek et al. (2021a) that these structures could constitute a synapomorphy of the gladiator clade.

Figures

Fig. 12. Holotypic female of Hypechiniscus crassus sp. nov. (dorsolateral view, PCM). White arrowhead indicates papilla IV. Scale bar in μm.

Fig. 13. Habitus of Hypechiniscus crassus sp. nov. (PCM): A, female (dorsal view); B, allotypic male (dorsolateral view). Arrowhead indicates papilla IV. Scale bars in μm.

Fig. 14. Habitus of Hypechiniscus crassus sp. nov. (dorsal view, SEM): A, female; B, male. Arrowheads indicate papilla IV. Scale bars in μm.

Fig. 15. Sculpturing of Hypechiniscus crassus sp. nov. (PCM): A, dorsal (female); B, ventral (female). Arrowhead indicates papilla IV. Scale bars in μm.

Fig. 16. Morphological details of Hypechiniscus crassus sp. nov. (SEM): A, cephalic region with peribuccal appendages; B, sculpturing of the scapular plate in close-up (empty incised arrowheads indicate rudimentary striae); C, claws I; D, claws IV. White arrowheads point out pseudoaccessory points, and empty arrowhead – aberrant secondary spur on external claw. Scale bars in μm.

Fig. 17. Schematic depiction of female morphology of Hypechiniscus crassus sp. nov.: A, dorsum; B, venter.

Fig. 18. Larva of Hypechiniscus crassus sp. nov. Scale bar in μm. Arrowhead indicates papilla IV.

Fig. 1. Habitus of a male of a new, undescribed species of Claxtonia (PCM, dorsal view). Scale bar in μm.

Fig. 2. Habitus of females of Echiniscus clevelandi (PCM): A, fully developed sculpturing and chaetotaxy (dorsal view); B, typical sculpturing and asymmetric lack of spine C (dorsolateral view); C, atypical sculpturing with poorly developed pores and full chaetotaxy (dorsal view). Scale bars in μm.

Fig. 3. Habitus of males of Echiniscus clevelandi (PCM): A, typical sculpturing (dorsolateral view); B, atypical sculpturing with poorly developed pores and asymmetric lack of spine B (dorsolateral view). Scale bars in μm.

Fig. 4. Habitus of females of Echiniscus clevelandi with fully developed sculpturing (dorsal view, SEM). Scale bars in μm.

Fig. 19. The concatenated 18S rRNA+28S rRNA+ITS1 consensus Bayesian phylogenetic tree of Hypechiniscus, with Acanthechiniscus islandicus as the outgroup. Branch support is given as BI posterior probability values above branches and ML bootstrap values below branches. Maximum supports, i.e., 1.00 for BI and 100 for ML, are indicated by asterisks (*). The ML and the BI tree had the same topology. Scale bar represents substitutions per site.