TARDIGRADE KEY

Tag: Family Styraconyxidae

Tholoarctus

Genus description from Kristensen & Renaud-Mornant 1983: “Epicuticule externe en forme de cloche, corps allongé, mince; tête avec assortiment complet d’appendices céphaliques. Clavas primaries ovoïdes, clavas secondaires élargies ventralement. Soies coxales seulement présentes sur P1; P4 avec papille. Cirres A et E avec cirrophore en entonnoir, dans lequel une partie du scapus peut se rétracter. […]

Tetrakentron

Genus description from Cuénot 1892, emended by van der Land 1975, in Fontoura et al. 2017: “Styraconyxidae with the body dorsoventrally flattened. Cephalic appendages (including cirrus medianus) very short; only the cephalic papillae are relatively large. Eyes lacking. Mouth opening on buccal cone and anus subterminal. Legs short, with short tibia and digits. Claws compound […]

Styraconyx

Genus description from Thulin 1942, emended by Kristensen & Higgins 1984: “Halechiniscidae with four digits. External digits always supported by peduncles; internal digits with proximal pads, peduncles present or absent. Claws with three exposed points (hooks), may be retracted within claw sheath. Dorsal cuticular plates absent although grid-like pattern of 18–23 folds sometimes present on […]

Rhomboarctus

Genus description from Renaud-Mornant 1984, emended by Hansen et al. 2003, in Fontoura et al. 2017: “Styraconyxidae with convex frontal edge; indistinct or lenticular secondary clavae; dorsal cuticle punctated; cuticular fins supported by medium sized pillars, extending on both sides of the body between primary clavae and the fourth pair of legs. More or less […]

Raiarctus

Genus description from Renaud-Mornant 1981, emended by Jørgensen et al. 2014, in Fontoura et al. 2017: “Styraconyxidae with the dorso-lateral epicuticular coat supported by long thin pillars 5–6 µm regularly arranged in close parallel lines. With 3-pointed claws, with or without heart shaped pads on the internal digits. With or without peduncles on every tarsus. […]

Pleocola

Genus description from Cantacuzène 1951, following Renaud-Mornant 1979, translated from French by Fontoura et al. 2017: “Styraconyxidae with strongly convex conical head; Cirri A and clavae implanted in a posterior plan relative to median cirrus. Simple claws. Remark: The original description does not exactly give a diagnosis of the genus: A subsequent incomplete diagnosis has […]

Paratanarctus

Genus description from D’Addabbo Gallo et al. 1992: “Styraconyxinae with a complete set of cephalic sense organs. Cephalic cirri short and thin, primary clavae tubular, P4 coxal, cirrus E articulated with an elementary accordion-plated portion. Lance-shaped tarsus with pretarsus. Basal pads on all the digits. All the claws with external dorsal calcars. Peduncles not present.” […]

Lepoarctus

Genus description from Kristensen & Renaud-Mornant 1983: “Epicuticule très développée formant une cloche autour du tronc, mais non dans la partie céphalique. Appendices céphaliques complets avec scapus [cylindrique], clavas secondaires indistinctes. Clavas primaires rétractables dans une gaine épicuticulaire et cirre E localisé dans un entonnoir épicuticulaire. Soies coxales présentes sur P1, de taille réduite sur […]

Bathyechiniscus

Genus description from Steiner 1926: “Marine Tardigraden mit glatter Haut, mit 4 Zehen an den Parapodien, die in einer quergestellten gezähnelten Leiste enden, mit einer medialen und je zwei lateralen, einfachen Kopfsinnesborsten, mit je einem gestielten Sinneskegl und basal eingesetzter Sinnesborste weiter hinten am Kopfende, mit je einer einfachen Sinnesborste auf dem Rücken der 3 […]

Angursa

Genus description from Pollock 1979, emended by Bussau 1992, in Fontoura et al. 2017: “Styraconyxidae with four digits. External digits supported by peduncles, internal digits with proximal pads. Claws with two divergent points (hooks), primary hook stronger than secondary hook. Claws retractable into membranous sheath. Dorsal cuticular plates absent. Complete set of cephalic cirri present, […]

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