Thulinius

Class : Eutardigrada

Order : Isohypsibioidea

Family : Doryphoribiidea

Genus : Thulinius

Genus Thulinius

Isohypsibioidea from Marley et al. 2011: “Parachela. Claws asymmetrical (2121); Isohypsibius-type claw pairs; AISM ridged.”

Isohypsibioidea from Bertolani et al. 2014: “Double claws asymmetrical with respect to the median plane of the leg (2121), normally with similar shape and size on each leg; double claws of the Isohypsibius type (secondary branch of the external claw inserted perpendicularly on the claw basal tract), or reduced from it: Hexapodibius type (very short, without common basal tract, with a base as large as the sum of the primary and secondary branch widths, and with an evident suture between primary and secondary branch); Haplomacrobiotus type (one branch only); completely absent (Apodibius). Buccal tube completely rigid (apart Paradiphascon; see below) and often relatively large, without (Dastychius, Eremobiotus, Halobiotus, Isohypsibius, Paradiphascon, Pseudobiotus, Thulinius) or with (Apodibius, Doryphoribius, Haplomacrobiotus, Haplohexapodibius, Hexapodibius, Parhexapodibius) ventral lamina. Eggs with smooth shell laid within the exuvium.”

Isohypsibiidae from Marley et al. 2011: “Isohypsibioidea. Claw pairs of similar size and shape. External and internal claws exhibiting articulation (the basal section and secondary branch form a solid unit while the primary branch and secondary branch articulate). Claws Isohypsibius-type, forming a right-angle between basal section and secondary branch. AISM ridge-like.”

Genus description from Bertolani 2003: “Mouth opening with 12 small, partially fused peribuccal lamellae surrounded by six peribuccal lobes, sometimes subdivided into a larger number of irregular sublobes; crest-shaped apophyses for the insertion of the stylet muscles on the buccal tube, claws of Isohypsibius-type
Remarks. The three species are characterized by a buccal armature with a posterior band of fine teeth, followed by a line of bigger round teeth, instead of transverse mucrones, as in several other genera of Hypsibiidae, Macrobiotdae and Eohypsibiidae, and by rows of macroplacoids, whose curvatures resemble a Grecian urn. The species differ together mainly for the shape of the cuticular structures of the legs. Thulinius ruffoi differs from T. stephaniae in having thinner claws with longer tapering basal tract, lunules evident and a less prominent cuticular bar below the claws of the first three pair of legs (other than for a more slender body). Thulinius augusti differs from the other two species by the presence of a particularly long and thin basal tract of the claw, especially in the external one, from T. stephaniae also by a weaker cuticular bar below the claws of the first three pair of legs, and from T. ruffoi also by the absence of lunules. The subdivision of the lobes into sub-lobes is another possible difference between T. augusti and the other two species.”

Key from Kaczmarek, Bertolani, & Nędzyńska-Stygar, 2010: “The genus Thulinius has a very conserved
morphology and its members are extremely similar to
one another. Specimens of this genus should be very
carefully examined, especially with regard to the
presence or absence of lunules, which are sometimes
barely visible especially in specimens in poor
condition or in specimens with unsuitable
orientation.”
1 Lunules under claws present……………………………………………………………………………………………………………………….2
– Lunules under claws absent………………………………………………………………………………………………………………………..4
2Lunules present only under the external (I–III) and posterior claws (IV), cuticular bars under claws divided ………… ………………………………………………………………………………………………………………………………. T. saltursus comb. nov.
– Lunules present under all claws, cuticular bars under claws not divided……………………………………………………………3
3 Buccal tube and macroplacoids short (buccal tube 28.6 long, macroplacoids: I placoid—3.7 [12.9], II—2.9 [10.1], III—3.7 [12.9] long in specimen 326.0 long), total body length up to 550 ……………………………………………… T ruffoi
– Buccal tube and macroplacoids long (buccal tube 42.2 long, macroplacoids: I placoid—5.5 [13.0], II—3.6 [8.5], III—5.2 [12.3] long in specimen 293.0 long), total body length up to 407 ………………………………………………… T. itoi
4 Basal claw very long and thin, cuticular bar under claws thin and short, evident subdivided lobes around the mouth …………………………………………………………………………………………………………………………………………………. T. augusti
– Basal claw short and robust, cuticular bar under claws long and wide, absence of subdivided lobes around the mouth……………………………………………………………………………………………………………………………………. T. stephaniae


Citations :

Thulinius image from Kaczmarek Ł, Bertolani R, Nędzyńska-Stygar M. 2010. Thulinius saltursus comb. nov.: a new systematic position for Isohypsibius saltursus Schuster, Toftner & Grigarick, 1978 (Eutardigrada: Hypsibiidae) and a key for the genus Thulinius. Zootaxa. 2483: 58-64.

“Parts” image from Bertolani R. 2003. Thulinius, new generic name substituting for Thulinia Bertolani, 1981 (Tardigrada, Eutardigrada). Zootaxa. 314: 1-4.

Bertolani R, Guidetti R, Marchioro T, Altiero T, Rebecchi L, Cesari M. 2014. Phylogeny of Eutardigrada: New molecular data and their morphological support lead to the identification of new evolutionary lineages. Molecular Phylogenetics and Evolution. 76: 110-126.

Marley NJ, McInnes SJ, Sands CJ. 2011. Phylum Tardigrada: A re-evaluation of the Parachela. Zootaxa. 2819: 51-64.

Claw Symmetry Relative To Median Plane Of Leg?

Image from Bingemer J, Hohberg K. 2017. An illustrated identification key to the eutardigrade species (Tardigrada, Eutardigrada) presently known from European soils. Soil Organisms. 89 (3): 127-149.

Stylet Support Insertion Point As Percentage Of Buccal Tube Length

Stylet support insertion point = ss divided by Buccal tube length, as %. Note anterior measurements begin at anterior margin of stylet sheaths, ss is centred where stylet supports reach buccal tube (this requires a good dorsal or lateral view for proper measurement)


Image from Tumanov DV. 2006. Five new species of the genus Milnesium (Tardigrada, Eutardigrada, Milnesiidae). Zootaxa. 1122: 1-23.

Buccal Tube Long, Mouth At Anterior Of A Protrusible Snout

Images from Pilato G, Binda MG. 2010. Definition of families, subfamilies, genera, and subgenera of the Eutardigrada, and keys to their identification. Zootaxa. 2404: 1-54.

Pharyngeal Tube With Spiral Reinforcement

Images from Pilato G, Binda MG. 2010. Definition of families, subfamilies, genera, and subgenera of the Eutardigrada, and keys to their identification. Zootaxa. 2404: 1-54.

Peribuccal papillae?

Note: in a tardigrade with snout extended, the flex of the pharyngeal tube may not be obvious.


Images from Pilato G, Binda MG. 2010. Definition of families, subfamilies, genera, and subgenera of the Eutardigrada, and keys to their identification. Zootaxa. 2404: 1-54.

(Lateral) cephalic papillae, peribuccal papillae, Milnesiidae - type claws, exceptionally wide (and usually short) buccal tube?

Cephalic image modified from Nelson DR, Guidetti R, Rebecchi L. 2009. Tardigrada. Ch. 14 in Ecology and Classification of North American Freshwater Invertebrates, Thorp JH, Covich AP (eds.), 3rd ed.

Claw image modified from Pilato G, Binda MG. 2010. Definition of families, subfamilies, genera, and subgenera of the Eutardigrada, and keys to their identification. Zootaxa. 2404: 1-54.

Pharyngeal tube flexible?

Note: in a tardigrade with snout extended, the flex of the pharyngeal tube may not be obvious.


Images from Pilato G, Binda MG. 2010. Definition of families, subfamilies, genera, and subgenera of the Eutardigrada, and keys to their identification. Zootaxa. 2404: 1-54.

Serrated / dentate cuff / collar on legs IV

Left image from Kristensen RM. 1987. Generic revision of the Echiniscidae (Heterotardigrada), with a discussion of the origin of the family. pp. 261-335 in Bertolani R (ed). Biology of Tardigrades: Selected symposia and monographs.

Right Image from Richters F. 1926. Tardigrada. in Krumbach T. 1927. Handbuch der Zoologie, 3rd band, Walter de Gruyter & Co.

Leg sensory structures

Typically papilla on leg IV (se4 in image) and variable shape on leg I


Image from Kristensen RM. 1987. Generic revision of the Echiniscidae (Heterotardigrada), with a discussion of the origin of the family. pp. 261-335 in Bertolani R (ed). Biology of Tardigrades: Selected symposia and monographs.

Trunk appendages

Appendages (after Cirrus A) labeled according to plate … B (Scapular plate), C (First segmental plate), D (Second segmental plate), E (terminal plate). “B” is lateral, “Bd” is dorsal

Be careful! There can be great variability within a population, with individuals (especially juveniles) lacking some appendages. When in doubt, choose “Unclear” to ignore this character!


Left image from Ramazzotti G, Maucci W. 1983. Il phylum Tardigrada(III edizione riveduta e aggiornata). English translation by C. W. Beasley, 1995. Memorie dell’ Istituto Italiano di Idrobiologia 41: 1-1012.

Right image cropped from Kristensen RM. 1987. Generic revision of the Echiniscidae (Heterotardigrada), with a discussion of the origin of the family. pp. 261-335 in Bertolani R (ed). Biology of Tardigrades: Selected symposia and monographs.

Cirrus A form

Images modified from Kristensen RM. 1987. Generic revision of the Echiniscidae (Heterotardigrada), with a discussion of the origin of the family. pp. 261-335 in Bertolani R (ed). Biology of Tardigrades: Selected symposia and monographs.

Lower image (Mopsechiniscus) modified from du Bois-Reymond Marcus E. 1944. Sobre tardigrados brasileiros. Communicaciones Zoologicas del Museo de Historia Natural de Montevideo. 1(13): 1-19 plus plates.

Terminal / caudal plate with two notches?

Images modified from Kristensen RM. 1987. Generic revision of the Echiniscidae (Heterotardigrada), with a discussion of the origin of the family. pp. 261-335 in Bertolani R (ed). Biology of Tardigrades: Selected symposia and monographs.

First image (Echiniscus) modified from Richters F. 1926. Tardigrada. in Krumbach T. 1927. Handbuch der Zoologie, 3rd band, Walter de Gruyter & Co.

Inner & outer buccal cirri present

Image modified from Nelson DR, Guidetti R, Rebecchi L. 2009. Tardigrada. Ch. 14 in Ecology and Classification of North American Freshwater Invertebrates, Thorp JH, Covich AP (eds.), 3rd ed.

Pseudosegmental plate between last medial plate & terminal plate?

Note on 2nd image, what you see before the terminal plate is either no plate, or a full-width medial plate; don’t confuse the latter with a pseudosegmental plate!
Also, sometimes the pseudosegmental plate is paired, like segmental plates II & III. It’s still pseudosegmental!

Images from Clifford HF. 1991. Aquatic invertebrates of Alberta. University of Alberta Press, Alberta, Canada.

Segmental plates larger than intersegmental?

Image modified from Lindahl & Balser (1999), http://www.iwu.edu/~tardisdp/Keypage35.html

Any Paired Plates?

Images from Kristensen RM. 1987. Generic revision of the Echiniscidae (Heterotardigrada), with a discussion of the origin of the family. pp. 261-335