Valvifera Sars, 1882

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Suggested Common Name: Valvetails
Number of subordinate taxa: 608 species in 12 families worldwide, 101 species in 7 families worldwide
Etymology: Valve + -fer = bearing [multilingual], refering to the valve-like uropods. Common name is a somewhat direct transliteration of the scientific name.
Taxonomic History: Valvifera Sars, 1882.
Description: (modified from Bruce & Poore, 2003) Antenna 1 without scale. Mandible lacinia present; molar cylindrical, occasionally reduced, tip flat, grinding; palp absent (except extralimital Holognathus karamea). Maxilla 2 triramous (exopod with 2 endites) (biramous in extralimital Engidotea lobata) Pereopods 1-7 coxae fused to tergites into coxal plates. Pereonite 7 dorsal coxal plate similar to others (rarely narrower). Pleon with 0-5 pleonites fused to telson. Pleonite 1 similar to others (rarely reduced). Pleopod 3 endopod roughly triangular, at least with inner angle sharper than outer. Telson underside vaulted with lateral ridges, defining a branchial chamber. Uropods lateral, folded under and enclosing branchial chamber; rami short.
Type taxon: Idoteidae Samouelle, 1819
Notes: Valvifera is one the more distinctive suborders in Isopoda, with its unusual "double-door" uropods encasing the pleopods. While it has been recognized as distinctive for a very long time, more recent studies involving both morphology (Brandt & Poore, 2003) and genetics place it near the former Flabelliferan suborder Sphaeromatidea. The uniting features include a domed underside of the telson with lateral ridges creating a branchial chamber, something apparently taken even further in Valvifera with the uropods also contributing to the chamber.
Valvifera is often split into two different groups: the Idoteoids, with their pereonite 1 free from their heads, and the Arcturoids, with their pereonite 1 fused to their head. Recent studies have found that while the Arcturoids are monophyletic, the Idoteoids are a paraphyletic basal grade leading up to the Arcturoids.

Subordinate taxa: Antarcturidae, Arcturidae, Austrarcturellidae, Chaetiliidae, Holognathidae, Idoteidae, Thermoarcturidae

Key to families
1 a. Pereonite 1 free from head; pereopod 1 similar to pereopod 2, if not a bigger; pleopod 1 protopod not elongate; penes free or fused only at the base (Idoteoids) --> 2
b. Pereonite 1 fused with head; pereopod 1 very different from pereopod 2, usually much smaller; pleopod 1 protopod elongate; penes fused nearly to the tip (Arcturoids) --> 4

2 (1) a. Head with large lateral lobes (eyes placed dorsally on head); pereopods 2-6 frequently prehensile (sometimes ambulatory); uropods biramous --> Chaetiliidae
b. Head lacking lateral lobes (eyes placed laterally on head); pereopods 2-6 ambulatory; uropods uniramous or biramous --> 3

3 (2) a. Body conspicously cylindrical; telson cylindrical with rounded slanted tip; pereopod 4 shorter than others, distal segments spiny; odd isopods that almost exclusively live in hollow tubes --> Holognathidae
b. Body not cylindrical; telson mostly flat or domed with a usually acute tip; pereopod 4 similar to others; ecology otherwise --> Idoteidae

4 (1) a. Pereonite 1 margins expanded ventrally, enclosing pereopod 1; pereopod 1 gnathopod-like; ♂ pleopod 1 endite laminar with either a lateral notch, a tuft of fine setae, 2-3 long plumose setae or a combination of these features --> Arcturidae
b. Pereonite 1 margins not expanded ventrally; pereopod 1 prehensile; ♂ pleopod 1 endite thickened with a groove --> 5

5 (4) a. Telson with dorsolateral ridges usually ending in a central spine; pleonite 1 weakly or not jointed with telson; pereopods 2-4 with dactyl shortened, claw seta-like, longer than dactyl; pereopod usually smaller and less setose than pereopods 2-3; ♂ pleopod 1 endite groove opening distolaterally or with a prominent basally-derived lateral lobe --> Austrarcturellidae
b. Telson various but never with a central spine; pereopods 2-4 with strong dactyl, claw short, rarely seta-like; pereopods 2-4 similar; ♂ pleopod 1 endite groove opening distolaterally or laterally --> 6

6 (5) a. Body covered in a dense layer of fuzz; uropod rami triangular, similar in lengths, with a terminal robust seta --> Thermoarcturidae
b. Body not covered in a dense layer of fuzz; uropod exopod rectangular, shorter than endopod, with distal seta --> Antarcturidae


Brandt, A., & Poore, G. C. (2003). Higher classification of the flabelliferan and related Isopoda based on a reappraisal of relationships. Invertebrate Systematics, 17(6):893-923.

Poore, G. C. (2001). Isopoda Valvifera: diagnoses and relationships of the families. Journal of Crustacean Biology, 21(1):205-230.

Poore, G. C. (2015). Thermoarcturidae, a new crustacean family of three genera (Isopoda: Valvifera). Zootaxa, 4007(3):409-418.

Published: Jan 1, 2023