TARDIGRADE KEY

Arctodiphascon

Modified from: Tumanov DV, Tsvetkova AY. 2023. Some have drops and some do not, but can we rely on that? Re-investigation of Diphascon tenue (Tardigrada: Eutardigrada) with discussion of the phylogeny and taxonomy of the superfamily Hypsibioidea. Zoosystematica Rossica. 32 (1): 50–74. DOI 10.31610/zsr/2023.32.1.50

Class: Eutardigrada

Order: Parachela

Superfamily: Hypsibioidea

Family: Itaquasconidae

Click taxa for descriptions

Description from: Tumanov DV, Tsvetkova AY. 2023. Some have drops and some do not, but can we rely on that? Re-investigation of Diphascon tenue (Tardigrada: Eutardigrada) with discussion of the phylogeny and taxonomy of the superfamily Hypsibioidea. Zoosystematica Rossica. 32 (1): 50–74. DOI 10.31610/zsr/2023.32.1.50

“Peribuccal structures consisted of six peribuccal lobes. AISM in shape of “semilu­nar hooks” asymmetrical with respect to fron­tal plane with dorsal apophyses being distinctly higher, shorter and thicker than ventral ones, caudal processes of both apophyses pointing posteriorly and laterally. Buccal tube followed by a flexible annulated pharyngeal tube, with drop­-like apodeme, bearing annulation between them. Pharynx oval with three bar­-like, elongate macroplacoids. Microplacoids or septula absent. Claws of Hypsibius­ type. Lunules and cuticular bars on limbs absent. Eggs laid within exuviae, with numerous minute pillars­-like processes on chorion surface.
Comparison. Arctodiphascon gen. nov. is most similar to Bindius (Pilato, 2009) in having an asymmetrical AISM, a long thin bucco­pharyn­geal tube and three rod­like macroplacoids, but differs clearly from the latter in having the drop­-like apodeme of the bucco­pharyngeal tube, which is completely absent in Bindius. Arctodiphascon gen. nov. is also similar to Guidettion in having a long thin bucco­pharyngeal tube and three rod­-like macroplacoids without microplacoids or sep­tula, but differs clearly from it in having a drop­-like apodeme of the bucco­pharyngeal tube and an asymmetrical AISM. Arctodiphascon gen. nov. is similar to Diphascon in having a drop­-like apo­deme of the bucco­pharyngeal tube and three macroplacoids, but clearly differs from it in hav­ing no microplacoid or septula. The only species lacking both microplacoids and septula currently assigned to Diphascon is D. speciosum (Mihel­čič, 1971) (nomen dubium according to Dastych, 2015), but this species has a granulated body cu­ticle, while the body surface in Arctodiphascon gen. nov. lacks granulation.

Key to the species of the genus Arctodiphascon gen. nov. (from Tumanov DV, Tsvetkova AY. 2023. Some have drops and some do not, but can we rely on that? Re-investigation of Diphascon tenue (Tardigrada: Eutardigrada) with discussion of the phylogeny and taxonomy of the superfamily Hypsibioidea. Zoosystematica Rossica. 32 (1): 50–74. DOI 10.31610/zsr/2023.32.1.50)

1. Pharyngeal tube longer (buccal/pharyngeal tube length ratio 33–46%), pharyngeal apophyses ex­tremely poorly developed, usually indiscernible with LM, second macroplacoid shorter relative to first macroplacoid (second/first macroplacoid ratio 0.87–1.30) . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. tenue

– Pharyngeal tube shorter (buccal/pharyngeal tube length ratio 84–98%), pharyngeal apophyses nor­mally developed, discernible with LM, second mac­roplacoid longer relative to first macroplacoid (se­cond/first macroplacoid ratio 1.37–1.59) . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. wuyingensis

Tumanov DV, Tsvetkova AY. 2023. Some have drops and some do not, but can we rely on that? Re-investigation of <i>Diphascon tenue</i> (Tardigrada: Eutardigrada) with discussion of the phylogeny and taxonomy of the superfamily Hypsibioidea. Zoosystematica Rossica. 32 (1): 50–74. DOI 10.31610/zsr/2023.32.1.50
Tumanov DV, Tsvetkova AY. 2023. Some have drops and some do not, but can we rely on that? Re-investigation of Diphascon tenue (Tardigrada: Eutardigrada) with discussion of the phylogeny and taxonomy of the superfamily Hypsibioidea. Zoosystematica Rossica. 32 (1): 50–74. DOI 10.31610/zsr/2023.32.1.50
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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?

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, focus on other characters first!

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?

Modified from Lindahl K, Balser S.  1999. Key to tardigrade genera [Internet]. Available from: https://sun.iwu.edu/~tardisdp/Keypage33.html