TARDIGRADE KEY

Schusterius

Kaczmarek, Ł. & Michalczyk, Ł. (2006) Redescription of Macrobiotus tridigitus Schuster, 1983 and the erection of a new genus of Tardigrada (Eutardigrada, Macrobiotidae). Journal of Natural History, 40(19-20), 1223-1229.

Class: Eutardigrada

Order: Parachela

Superfamily: Macrobiotoidea

Family: Macrobiotidae

Click taxa for descriptions

Genus description from Kaczmarek & Michalczyk 2006: “Holotype (paratype): body length 235.0 (295.0). Body colourless, eyes absent. Cuticle smooth, without granulation or pores. Mouth terminal, probably with 10 peribuccal lamellae. Bucco-pharyngeal apparatus of Macrobiotus type with ventral lamina 16.0 [59.3] (19.0 [57.6]) long and with one bend in anterior part. Buccal tube 27.0 (33.0) long and 3.5 [13.0] (4.0 [12.1]) wide. Stylet supports inserted on buccal tube walls at 21.0 [77.8] (26.0 [78.8]) of its length. Oral cavity armature poorly developed. On dorsal side all teeth absent. On ventral side first two bands of teeth absent and only one median tooth (in shape of transversal ridge) present in third band. Pharyngeal bulb oval with three oval macroplacoids without constrictions, similar in length, and microplacoid. First macroplacoid 4.0 [14.8] (4.5 [13.6]) long, second 3.0 [11.1] (4.0 [12.1]), third 3.0 [11.1] (4.0 [12.1]). Microplacoid 2.0 [7.4] (2.3 [7.0]) long. Macroplacoid row 12.0 [44.4] (15.0 [45.5]) long, placoid row 14.0 [51.9] (18.0 [54.5]) long.

Claws similar to Calcarobiotus type claws (primary branches very similar in length) with 2-1-1-2 configuration, Y-shaped but with extremely developed, very long and thin accessory points connected to primary branch by flexible light-refracting portion. Measurements of external claws in paratype: accessory points of I pair 11.0 [33.3]; primary branch of II pair of legs 8.0 [24.2]; secondary branch of II pair of legs 7.5 [22.7]; accessory points of II pair 11 [33.3]; primary branch of III pair of legs 9.0 [27.3]; secondary branch of III pair of legs 8.0 [24.2]; accessory points of III pair 12.5 [37.9]; primary branch of IV pair of legs 7.0 [21.2]; secondary branch of IV pair of legs 7.0 [21.2]; accessory points of IV pair 10 [30.3]. Smooth lunules present on all legs. Cuticular bars and other cuticular
structures on legs absent. Eggs unknown.”

Kaczmarek, Ł. & Michalczyk, Ł. (2006) Redescription of Macrobiotus tridigitus Schuster, 1983 and the erection of a new genus of Tardigrada (Eutardigrada, Macrobiotidae). Journal of Natural History, 40(19-20), 1223-1229.
Kaczmarek, Ł. & Michalczyk, Ł. (2006) Redescription of Macrobiotus tridigitus Schuster, 1983 and the erection of a new genus of Tardigrada (Eutardigrada, Macrobiotidae). Journal of Natural History, 40(19-20), 1223-1229.

Citations:

Kaczmarek, Ł. & Michalczyk, Ł. (2006) Redescription of Macrobiotus tridigitus Schuster, 1983 and the erection of a new genus of Tardigrada (Eutardigrada, Macrobiotidae). Journal of Natural History, 40(19-20), 1223-1229.

Restart Search

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