Echiniscus testudo

(Doyère, 1840)

type species of Echiniscus

Echiniscus testudo is a tardigrade in the genus Echiniscus (Echiniscidae, Echiniscoidea), described by Doyère in 1840. The parentheses around the authority mean it was first described in another genus.

Where it has been recorded

What we have read about it

Facts we extracted from the literature into our knowledge graph, each with the source and page it came from.

• The clava and cirrus A of Echiniscus testudo, which lie dorsolaterally at the posterior margin of the head at the front of the scapular plate, are innervated by the outer cluster: an accumulation of 17 cells arranged in a smaller anterior lobe of 5 cells and a larger posterior lobe of 12, spatially separated from the central brain but keeping a direct connection to its lateral region through a narrow neurite bridge, where it joins the fibres of the outer connectives. Two neurite bundles serve the clava, one entering the anterior lobe and one the posterior lobe, and a single bundle serves cirrus A, entering the posterior lobe; each bundle ends at the base of its sensillum.Gross et al. 2021. Organization of the central nervous system and innervation of cephalic sensory structures in the water bear Echiniscus testudo (Tardigrada: Heterotardigrada) revisited. Journal of morphology. J Morphol 282, section 3.3, pp1302-1303; Figs 1a, 5b-e
• Tardigrades are scarce or absent in muddy or dusty mosses, in towns, industrial zones and along busy roads; in dusty moss or moss exposed to industrial and car fumes often only Milnesium tardigradum and Echiniscus testudo remain.Ramazzotti & Maucci 1983. Il Phylum Tardigrada, 3rd edition (English translation by C. W. Beasley, 1995: The Phylum Tardigrada). Memorie dell'Istituto Italiano di Idrobiologia 41; translation published by the translator, McMurry University, Abilene, Texas. p. 125 (PDF p. 125): "in powdery mosses, or those exposed to industrial and automobile fumes, there are often only two species to be found, which are: Milnesium tardigradum and Echiniscus testudo, which obviously resist this type of interference best"
• Total fibres in legs I–IV (ventral + lateral + dorsal groups): Milnesium cf. tardigradum 12, 13, 13, 4; Acutuncus antarcticus 14, 13, 13, 5; Bertolanius volubilis 11, 11, 12, 6; Paramacrobiotus richtersi and Dactylobiotus parthenogeneticus 10, 11, 12, 5; Echiniscus testudo 9, 10, 11, 4. Only the ventral group was resolved in Batillipes bullacaudatus (5, 6, 6, 3).Marchioro et al. 2013. Somatic musculature of Tardigrada: phylogenetic signal and metameric patterns. Zoological Journal of the Linnean Society. Table 3 pp. 595–596, rows 'Total fibres within each leg'
• Every hemiganglion of Echiniscus testudo gives off at least three neurites (n1-n3) running laterally, and in each hemiganglion one of them connects to an FMRFamide-immunoreactive soma in the corresponding leg, the leg ganglion (lgg1-lgg4). From each hemiganglion of the fourth ganglion a further FMRFamide-immunoreactive soma extends posteriorly, in line with its hemiganglion.Schulze & Schmidt-Rhaesa 2013. The architecture of the nervous system of Echiniscus testudo (Echiniscoidea, Heterotardigrada). Journal of Limnology. J Limnol 72(s1), p48 and Fig. 6b,d
• The longest reliably documented survival in anhydrobiosis is 20 years, in the heterotardigrade Echiniscus testudo (Jørgensen et al. 2007).Schill RO, Hengherr S 2018. Environmental Adaptations: Desiccation Tolerance. In: Schill RO (ed.) Water Bears: The Biology of Tardigrades. Zoological Monographs 2, pp. 273–294 p. 275 (PDF p. 278)
• Searches of genomes and transcriptomes found two putative pdfr homologues in the eutardigrade Paramacrobiotus metropolitanus and one each in the heterotardigrades Echiniscus testudo, Echiniscoides sigismundi and an unpublished Batillipes sp. genome; a maximum-likelihood tree of about 1,000 class B GPCRs places all of them, and both H. exemplaris splice variants, inside the protostome PDF receptor clade, sister to the corticotropin-releasing hormone receptors.Dutta et al. 2025. Pigment-dispersing factor neuropeptides act as multifunctional hormones and modulators in tardigrades. Open biology. Open Biology 15:240242 section 2.2, p4; figure 1c; electronic supplementary material figure S2 and table S2
• Ventral commissures within the trunk ganglia are present in both heterotardigrade and eutardigrade species, including Mesobiotus cf. harmsworthi and H. dujardini, and are therefore ancestral for Tardigrada; their absence in Macrobiotus hufelandi (Zantke et al. 2008) is the exception rather than the rule. Extra-ganglionic interpedal commissures are likewise present in H. dujardini, M. cf. harmsworthi, Paramacrobiotus richtersi and Echiniscus testudo, taxa spanning the basal split of Tardigrada, so they too are ancestral components of the tardigrade nervous system.Smith & Jockusch 2014. The metameric pattern of Hypsibius dujardini(Eutardigrada) and its relationship to that of other panarthropods. Frontiers in Zoology. Frontiers in Zoology 11:66, p12, Discussion
• Interpedal commissures lie anterior to trunk ganglia 2, 3 and 4 of Echiniscus testudo. The one in front of ganglion 2 has no neuronal somata anywhere near it, which indicates that the interpedal commissures may be no more than crossing points for contralateral commissures running between ganglia.Gross et al. 2021. Organization of the central nervous system and innervation of cephalic sensory structures in the water bear Echiniscus testudo (Tardigrada: Heterotardigrada) revisited. Journal of morphology. J Morphol 282, section 3.5, p1305; Fig. 6e,f
• Within one Echiniscus population adults vary in lateral filament length and in the presence (even unilateral) of dorsal and lateral appendages; young animals lack some appendages, which appear with successive moults. Maucci (1954) ranked variability: sculpture type, internal-claw spur on leg IV, cirrus A and median plates nearly constant; lateral appendages most variable, in the order B, D, C, A. Species must be described from many specimens.Ramazzotti & Maucci 1983. Il Phylum Tardigrada, 3rd edition (English translation by C. W. Beasley, 1995: The Phylum Tardigrada). Memorie dell'Istituto Italiano di Idrobiologia 41; translation published by the translator, McMurry University, Abilene, Texas. pp. 37–38 (PDF pp. 37–38): "The most changeable details are those concerning the lateral appendages, in the following order: B, D, C, A."
• The dorsal region of each leg receives fibres only from the dorsal group, the ventral region from all three groups. Legs I–III have similar fibre numbers (e.g. Bertolanius volubilis: three ventral, two lateral, six or seven dorsal per leg). Leg IV has only two attachment points, P1 and P2, reached by two or three fibres: one or two dorsal (to P2) and one lateral (to P1).Marchioro et al. 2013. Somatic musculature of Tardigrada: phylogenetic signal and metameric patterns. Zoological Journal of the Linnean Society. pp. 592–596, 'General remarks on leg musculature'; Table 3
• Echiniscus testudo has four ventral ganglia, each associated with one pair of legs and positioned slightly anterior to them. The hemiganglia of each ganglion are joined by ganglion commissures and chained longitudinally by connectives. Three further commissures that belong to no ganglion lie anterior to ventral ganglia II, III and IV. The hemiganglia of ganglia I and IV lie closer together than those of II and III, visible both in the arrangement of nuclei and in the lengths of the commissures.Schulze & Schmidt-Rhaesa 2013. The architecture of the nervous system of Echiniscus testudo (Echiniscoidea, Heterotardigrada). Journal of Limnology. J Limnol 72(s1), p48, Results 'The ventral ganglia'; Figs 1c, 6a-d
• Paramacrobiotus and Macrobiotus tuns show a glass transition (DSC) at about 80 °C, above which survival drops sharply; Milnesium tardigradum, Echiniscus granulatus and E. testudo, with little or no trehalose, showed no vitrification and tolerated heat better.Schill RO, Hengherr S 2018. Environmental Adaptations: Desiccation Tolerance. In: Schill RO (ed.) Water Bears: The Biology of Tardigrades. Zoological Monographs 2, pp. 273–294 p. 283 (PDF p. 286), Fig. 10.3 and section 10.4.2
• Comparing their result with published descriptions, Smith & Jockusch conclude that a differentiated fourth ganglion is ancestral for Eutardigrada and probably for Tardigrada: the fourth ganglion is the most distinct in Halobiotus crispae (one transverse commissure against two in ganglia 1-3), the smallest and least populous in Macrobiotus hufelandi and Mesobiotus cf. harmsworthi, and in the heterotardigrade Echiniscus testudo the first and fourth ganglia are narrower than the second and third, which raises the possibility that the first was also differentiated ancestrally. RFamide immunostaining in M. cf. harmsworthi shows consistent morphological differences between all four ganglia.Smith & Jockusch 2014. The metameric pattern of Hypsibius dujardini(Eutardigrada) and its relationship to that of other panarthropods. Frontiers in Zoology. Frontiers in Zoology 11:66, p12, Discussion
• Anti-synapsin labelling of Echiniscus testudo reveals five major immunoreactive domains along the body: one large unitary horseshoe-shaped neuropil in the head and one neuropil in each of the four trunk ganglia. Gross et al. take this as support for the dorsal brain neuropil being serially homologous with the neuropil of the trunk ganglia.Gross et al. 2021. Organization of the central nervous system and innervation of cephalic sensory structures in the water bear Echiniscus testudo (Tardigrada: Heterotardigrada) revisited. Journal of morphology. J Morphol 282, Abstract p1298 and section 3.1 pp1300-1301; Figs 2a,b, 6a-d
• Species can be classed by habitat wetness: xerophilous (dry mosses IV–V: most Echiniscus including E. testudo, Adorybiotus coronifer, Macrobiotus islandicus, Hypsibius oberhaeuseri, Milnesium tardigradum); eurytopic (all categories: Macrobiotus areolatus, M. hufelandi, M. richtersi, M. harmsworthi and others); hygrophilous (moist mosses II–III: Hypsibius dujardini, H. convergens, most Diphascon); hydrophilous (wet mosses and water: all Dactylobiotus and Pseudobiotus). Physiological races of one species may occupy different habitats. About 80% of known species and varieties are found in moss.Ramazzotti & Maucci 1983. Il Phylum Tardigrada, 3rd edition (English translation by C. W. Beasley, 1995: The Phylum Tardigrada). Memorie dell'Istituto Italiano di Idrobiologia 41; translation published by the translator, McMurry University, Abilene, Texas. pp. 109–111 (PDF pp. 109–111): "Hygrophilous species: - Macrobiotus hibernicus, M. intermedius. - Hypsibius pallidus, H. convergens, H. microps, H. dujardini."
• Eutardigrade muscle architecture is more complex than heterotardigrade: eutardigrade attachment points mostly serve four to nine fibres (generally more than three), whereas those of Echiniscus testudo serve one or two; E. testudo has fewer but the thickest fibres seen in tardigrades, its two dorsal strands merged for most of their length and no interlongitudinal muscles.Marchioro et al. 2013. Somatic musculature of Tardigrada: phylogenetic signal and metameric patterns. Zoological Journal of the Linnean Society. p. 584 'Tardigrade musculature'; p. 593 'Dorsal muscle group'; p. 600 Discussion

Showing 16 of 43, taking the best-supported facts from each source in turn.

Open questions

• How widespread are the opsin duplications found in single tardigrade genera: is the Echiniscus ciliary-opsin duplication shared by Echiniscoidea or Heterotardigrada, are the Batillipes duplications shared by Arthrotardigrada, and what do the independently duplicated arthropsins do?Posed by Fleming et al. 2021. New Tardigrade Opsins and Differential Expression Analyses Show Ontogenic Variation in Light Perception. Genome biology and evolution. PDF p 4: "Further studies will help elucidate whether this duplication is specific to the genus, or to Heterotardigrada or Echiniscoidea as a group." … "Further study of the independent duplications of arthropsin within both Tardigrada and Daphnia could advance our understanding of the function of this recently discovered homolog." … "Whether the duplications in Batillipes are shared among other members of the Arthrotardigrada is unclear"
• Do the abundant heat-soluble proteins of Echiniscus testudo (EtAHS) contribute to its desiccation tolerance?Posed by Murai et al. 2021. Multiomics study of a heterotardigrade, Echinisicus testudo, suggests the possibility of convergent evolution of abundant heat-soluble proteins in Tardigrada. BMC genomics. PDF p 9: "Functional experiments would be required as a future work to fully confirm the contribution of EtAHS in the desiccation tolerance of heterotardigrada."
• Why do the four trunk ganglia differ in size (narrower first and fourth), and is a differentiated first and fourth ganglion ancestral for Tardigrada?Posed by Smith & Jockusch 2014. The metameric pattern of Hypsibius dujardini(Eutardigrada) and its relationship to that of other panarthropods. Frontiers in Zoology. PDF p 12: "The functional significance, if any, for different sizes among ganglia remains unclear."
• Are the ventrolateral clusters of the tardigrade head serially homologous to the soma-containing, synapsin-free regions of the trunk ganglia?Posed by Gross et al. 2021. Organization of the central nervous system and innervation of cephalic sensory structures in the water bear Echiniscus testudo (Tardigrada: Heterotardigrada) revisited. Journal of morphology. J Morphol 282:1309: "we cannot exclude the possibility that part of the ventrolateral cluster may correspond to parts of the trunk ganglion, as previously suggested by Smith et al. (2017)... Additional experiments with the goal of localizing potentially serially homologous cells by using neuronal markers such as serotonin or dopamine... may be more informative"
• Do the cephalic sensory structures of the apochelan eutardigrade Milnesium, which has both sensory fields and a pair of cephalic papillae, settle the homologies between heterotardigrade sensilla and eutardigrade sensory fields?Posed by Gross et al. 2021. Organization of the central nervous system and innervation of cephalic sensory structures in the water bear Echiniscus testudo (Tardigrada: Heterotardigrada) revisited. Journal of morphology. J Morphol 282:1310: "Future immunohistochemical studies on the apochelan eutardigrade Milnesium tardigradum, which exhibits sensory fields in addition to a pair of cephalic papillae, may help clarify putative homologies of the cephalic sensory structures between heterotardigrades and eutardigrades"
• Do the cells of the posterior (outer) cluster of Echiniscus testudo innervate both cirrus A and the clavae, or only one of them?Posed by Schulze & Schmidt-Rhaesa 2013. The architecture of the nervous system of Echiniscus testudo (Echiniscoidea, Heterotardigrada). Journal of Limnology. J Limnol 72(s1):48: "It cannot be decided whether the cells of the posterior clusters innervate both, the cirri A and the clavae, or just one of these cephalic structures" answered
• What are the dorsally running neurite loops that leave the connectives between ventral ganglia II-III and III-IV of Echiniscus testudo in some specimens only, and does their presence depend on age or on the moult cycle?Posed by Schulze & Schmidt-Rhaesa 2013. The architecture of the nervous system of Echiniscus testudo (Echiniscoidea, Heterotardigrada). Journal of Limnology. J Limnol 72(s1):51: "These loops could not be detected in every examined individual. Whether this might be linked to age or maybe to molting cannot be decided because none of these parameters were recorded for this study"

Genomes and sequencing

Mitochondrial genomes

• LC385650.1, 15,817 bp: Echiniscus testudo mitochondrial DNA, complete genome

Raw sequencing data

27 runs (369.7 Gb) in 4 projects: 23 RNA-Seq, 2 Hi-C, 1 WGS, 1 EST. Browse them in the SRA.

Papers

45 works in our corpus of 5,137 tardigrade papers name it in the title or abstract (13 in the title), from 1987. This is by exact name match, so it misses papers that use an older name or only the genus.

• A molecular study of the tardigrade Echiniscus testudo (Echiniscidae) reveals low DNA sequence diversity over a large geographical area (2007, Journal of Limnology) doi
• An integrative redescription of Echiniscus testudo (Doyère, 1840), the nominal taxon for the class Heterotardigrada (Ecdysozoa: Panarthropoda: Tardigrada) (2017, Zoologischer Anzeiger) doi
• Echiniscus testudo (Doyère, 1840) in New Zealand: anthropogenic dispersal or evidence for the ‘Everything is Everywhere’ hypothesis? (2018, New Zealand Journal of Zoology) doi
• Organization of the central nervous system and innervation of cephalic sensory structures in the water bear Echiniscus testudo (Tardigrada: Heterotardigrada) revisited (2021, Journal of Morphology) doi
• Genetic diversity in the parthenogenetic reproducing tardigrade Echiniscus testudo (Heterotardigrada: Echiniscoidea) (2013, Journal of Limnology) doi
• The architecture of the nervous system of Echiniscus testudo (Echiniscoidea, Heterotardigrada) (2013, Journal of Limnology) doi

Classification

Synonyms: Echiniscus bellermanni C.A.S. Schultze, 1840; Echiniscus inermis Richters, 1902; Echiniscus trifilis Rahm, 1924; Echiniscus testudo quadrifilis according to Gąsiorek et al. 2017b; Echiniscus filamentosus Plate, 1888 according to Gąsiorek et al. 2017b; Echiniscus glaber Bartoš, 1937 according to Gąsiorek et al. 2017b; Echiniscus peruvianus Binda & Pilato, 1994 according to Gąsiorek et al. 2021f.

Changes: Redescribed and neotype (from original type locality Paris, France) designated by Gąsiorek et al. 2017b.

Other species of Echiniscus: E. africanus, E. angolensis, E. aonikenk, E. apuanus, E. arcangelii, E. arctomys, E. arthuri, E. attenboroughi, E. azoricus, E. baius, E. baloghi, E. becki, E. belloporus, E. bisculptus, E. blumi, E. brunus, E. calcaratus, E. calvus, E. canadensis, E. canedoi, E. capensis, E. cavagnaroi, E. cervicornis, E. cheonyoungi, E. clevelandi, E. crassispinosus, E. curiosus, E. darienae, E. dentatus, E. dikenli, E. diploglyptus, E. divergens, E. draconis, E. dreyfusi, E. duboisi, E. ehrenbergi, E. elaeinae, E. evelinae, E. gemmatus, E. gracilis, and 78 more.

Look it up

GBIF · NCBI Taxonomy · GenBank sequences · iNaturalist · Google Scholar

Classification, authority and notes: Degma & Guidetti 2026, Actual checklist of Tardigrada species, 45th edition (CC BY 4.0), which asks users also to cite Guidetti & Bertolani 2005 (Zootaxa 845: 1–46) and Degma & Guidetti 2007 (Zootaxa 1579: 41–53).
Records: GBIF.org, accessed 2026-09-20 through the GBIF API; each record belongs to the dataset that published it. The map shows only records released under CC0 or CC BY, with coordinates and no geospatial issue flag.
Sequence data: NCBI Assembly, Nucleotide and SRA, searched September 2026.
Papers: our corpus of tardigrade literature from OpenAlex.