High Mountain Echiniscid (Heterotardigrada) Fauna of Taiwan

Abstract

Taiwan lies at the transitional zone between the East Palaearctic and Oriental regions, which translates into both Palaearctic and Indomalayan taxa being present on the island. Furthermore, large habitat heterogeneity and high mountains contributed to the rise of conditions favouring allopatric speciation and the emergence of endemic species. The tardigrade fauna of Taiwan is poorly studied, and the aim of this contribution is to provide new data on the members of the family Echiniscidae, the largest limno-terrestrial group of the class Heterotardigrada, found at high elevations in central Taiwan. We report 11 species grouped in 5 genera: Claxtonia (1 species), Echiniscus (3 species), Hypechiniscus (1 species), Nebularmis (2 species), and Pseudechiniscus (4 species). All are new to Taiwan, including 5 species that are new to science, 4 or which are described herein by means of integrative taxonomy: Hypechiniscus crassus sp. nov. (the exarmatus morphogroup), Pseudechiniscus (Meridioniscus) dreyeri sp. nov., Pseudechiniscus (Pseudechiniscus) formosus sp. nov., and Pseudechiniscus (Pseudechiniscus) totoro sp. nov. The new findings also help to clarify the description of Echiniscus clevelandi Beasley, 1999, and supplement the phylogenies of the Echiniscus virginicus complex and of the genera Hypechiniscus, Nebularmis and Pseudechiniscus.

Keywords: Biogeography; Endemism; Integrative taxonomy; Oriental; Palaearctic; Phylogeny.

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. 5.

Habitus of Echiniscus clevelandi (SEM): A, female with atypical sculpturing (dorsal view); B, male with poorly developed sculpturing (lateral view). Scale bars in μm.

Fig. 6.

Dorsal plate sculpturing of Echiniscus clevelandi (females, PCM). Scale bars in μm.

Fig. 7.

Dorsal plate sculpturing of Echiniscus clevelandi (males, PCM). Empty arrowheads indicate pulvini, whereas white arrowheads –pedal plates. Scale bars in μm.

Fig. 8.

Morphological details of Echiniscus clevelandi (SEM): A–C, varying levels of the sculpturing development of the scapular plate; D, cephalic region with peribuccal appendages and marked subcephalic swellings; E, claws II; F, claws IV. Scale bars in μm.

Fig. 9.

Claws of Echiniscus clevelandi (PCM): A, claws I (female); B, claws III (female). Scale bars in μm.

Fig. 10.

Habitus of Echiniscus hoonsooi (PCM) from Japan: A, female (dorsolateral view, insert shows claws II); B, dorsal sculpturing in close-up. Scale bars in μm.

Fig. 11.

Phylogenetic relationships within the Echiniscus virginicus complex based on concatenated ITS-1, ITS-2 and COI sequences as inferred in the Bayesian approach. Echiniscus succineus was used as an outgroup. Scale bar represents substitutions per site.

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. 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.

Fig. 20.

Habitus of a female of Nebularmis crebraclava (PCM). Scale bar in μm.

Fig. 21.

Sculpturing of a female of Nebularmis crebraclava (PCM): A, cephalic region; B, central body portion; C, caudal region. Scale bars in μm.

Fig. 22.

Morphological details of females of Nebularmis crebraclava (PCM): A, cephalic region with peribuccal appendages; B, subcephalic plates and spines I; C, claws I; D, claws IV. Scale bars in μm.

Fig. 23.

Historical biogeography of the genus Nebularmis as inferred in the S-DIVA on the Bayesian phylogenetic tree under the random local clock with the speciation: Yule process as the tree prior. B1–B5 denote subsequent nodes, all but B2 (0.85) had maximal (1.00) support. Echiniscus testudo and Diploechiniscus oihonnae were used as outgroups.

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. 25.

Schematic depiction of female ventral morphology of Pseudechiniscus (M.) dreyeri sp. nov.

Fig. 26.

Morphology of Pseudechiniscus (Pseudechiniscus) formosus sp. nov. (PCM): A, holotypic female in dorsal view; B, dorsal sculpturing (arrowheads indicate large capituli of pillars); C, ventral sculpturing. Scale bars in μm.

Fig. 27.

Schematic depiction of female ventral morphology of Pseudechiniscus (P.) formosus sp. nov.

Fig. 28.

Morphology of Pseudechiniscus (Pseudechiniscus) totoro sp. nov. (PCM): A, holotypic female in dorsolateral view (insert shows claws III); B, allotypic male in dorsolateral view; C, dorsal sculpturing; D, ventral sculpturing. Scale bars in μm.

Fig. 29.

Schematic depiction of female ventral morphology of Pseudechiniscus (P.) totoro sp. nov.

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).

Fig. 31.

Distributions of Echiniscus and Nebularmis species addressed in the present study.