TARDIGRADE KEY

Tag: Family Stygarctidae

Stygarctus

Genus description from Schulz 1951 in McKirdy et al. 1976: Stygarctidae with dorsal cuticle thickened to form three unpaired body plates between a one-piece cephalic plate and a caudal plate; prominent caudal spikes present; legs with four claws each, the central pair with long filamentous appendages; anterior clavae elongate.” Genus description from Bello & Grimaldi […]

Pseudostygarctus

Genus description from McKirdy et al. 1976: “Stygarctidae with dorsal cuticle thickened to form semi-circular head plate, three body plates, and a caudal plate devoid of spike-like posterior processes; cephalic appendages Stygarctus-like except for anterior clavae modified as semi-globular structures; each leg terminated by three claws, each with a minute dorsal accessory spine.” Genus description […]

Prostygarctus

Genus description from Rubal et al. 2013 in Fontoura et al. 2017: “Stygarctinae with dorsal cuticle strongly sculptured, forming five dorsal plates (one head plate; three body plates and one caudal plate). Intersegmental dorsal plates and ventral plates present. Head plate divided into five lobes; the frontal lobe subdivided into four smaller lobes. Three body […]

Parastygarctus

Genus description from Renaud-Debyser 1965: “Stygarctidé dont la tête est formée de deux parties : une plaque dorsale aplatie et découpée en quatre grandes expansions portant les appendices céphaliques, et un cône buccal portant les cirres médians internes. Cirre médian impair présent. Cirres céphaliques articulés avec hampe épaissie. Plaques I, II et III de la […]

Mesostygarctus

Genus description from Hansen et al. 2012: “Stygarctinae with head plate divided into three lobes: posterior part of the head with two lateral lobes bearing the primary clavae; anterior part of the head divided into three lobes by a pair of deep indentations with dorsal cuticular membranes. Three dorsal body plates extending laterally into two […]

Faroestygarctus

Genus description from Hansen et al. 2012: “Stygarctinae with perfectly semicircular head plate divided into three lobes: an anterior lobe bearing the median cirrus, internal cirri, external cirri and secondary clavae, and two posterolateral lobes bearing the primary clavae and lateral cirri. Three body plates, each with a pair of lateral processes tapering to flexible […]

Megastygarctides

Genus description from McKirdy et al. 1976: “Stygarctidae with typical dorsal plate pattern of the family (head plate, three body plates, caudal plate), modified by intercalated accessory plates resulting from accordion-like folds of the dorsal cuticle. Body more cylindrical than in other stygarctid genera. First three leg pairs each with four claws, fourth pair with […]

Megastygarctidinae

Megastygarctidinae from Bello & de Zio Grimaldi 1998, amended by Hansen & Kristensen 2006, in Degma 2018: “Four claws on the first three pairs of legs and two claws on the fourth pair; all claws with small dorsal spur; each claw originating from a short pedestal. Typical dorsal plate pattern of the family (head plate, […]

Hansenarctus

Genus description from Fujimoto & Ohtsuka 2019: “Stygarctinae with punctate cuticle; dorsally-plated cephalic region (head) divided into anterior medial lobe with pair of internal cirri, pair of medio-lateral lobes each with dorsal semi-globular secondary clava and ventral external cirrus, and pair of lateral lobes each subdivided into antero-lateral and postero-lateral lobes with anterior lateral cirrus […]

Stygarctinae

Stygarctinae from Bello & de Zio Grimaldi 1998 in Degma 2018: “Head divided into five lobe; intermetamerical doral plates; ventral plates sometimes present. In adults, all legs with the same number of claws: four, three, or two. Sense organs of the first three pair of legs present or absent. Bulb-shaped papilla on fourth leg.” Citations: […]

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