Oniscoidea Dana, 1852

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Suggested Common Name: Typical Woodlice
Number of subordinate taxa: over 3000 species in an undetermined amount of families worldwide, 224 species in our area.
Etymology: after Oniscus Linnaeus, 1758, see that account for more information.
Taxonomic History: Extremely convuluted, with this name at times refering to all Oniscideans. It curently refers to a group of Crinochetans that are united by details in the antennae and sensory setae.
Description: Antenna 2 flagellum (1-)2-3-segmented, flagellomeres usually fairly bulky. Pereon tergal sensilla with sheath of epicuticalar scales, one(-several?) pair(s) per segment differentiated by a more protruding sensory hair (termed noduli laterali).
Type taxon: Oniscidae Latreille, 1802
Notes: The familial, generic and even species taxonomy in this superfamily is extremely disorganized, the result of 200 years of very simple descriptions and focus on details that are variable at a species or even individual basis. The knowlege of this group has effectively been set back 100 years by the poor contributions of oniscidologists from the first half of the 20th century, who were often made many errors and poor judgements in their work. Researchers in the later half of the 20th century and into the 21st century have made progress in correcting mistakes made in the past, although the work is far from complete and remains a daunting task to unravel. The key below reflects this, with many couplets being based off of seemingly dubious characters that appear inappropriate for distinguishing larger-scale taxa.

Subordinate Taxa: Agnaridae, Alloniscidae, Armadillidae, Armadillidiidae, Bathytropidae, Bisilvestriidae, Cylisticidae, Delatorreiidae, Dubioniscidae, Eubelidae, Globarmadillo, Haplarmadillo, Matazonellus, Oniscidae, Philoscomorph Woodlice, Porcellionidae, Rabdoniscus, Rhyscotidae, Scleropactidae, Stenoniscidae, Synuropus, Trachelipodidae, Trichorhinidae

Provisional key to families and isolate taxa
1 a Face with enormously enlargened swelling, creating a "cicada mask"; adults monoecious, with both ♂ pleopods and ♀ oostegites; N Gulf Coast S through tropics --> Rhyscotidae
b. Face not as above, usually flat or lobed; adults dioecious (in known species); widespread --> 2

2 (1) a. Flagellomeres 1 , large and conical; blind white ant-associates in temerate areas --> Oniscidae (Platyarthrus)
b. Flagellomeres 2-3 (1 in Haplarmadillo but then a spikey conglobulator); various morphologies and ecologies --> 3

3 (2) a. Uropods ventral to telson, hidden from dorsal view (or peeking over the tip of the telson); tropical (to S FL) --> 4
b. Uropods lateral to telson, visible in dorsal view; widespread --> 6

4 (3) a. Coxal plates distinct from pereonite tergites by grooves; body elongate cylindrical, non-conglobulating --> Stenoniscidae
b. Coxal plates not distinct; body domed, conglobulating --> 5

5 (4) a. Telson flat, semicircular to semielliptical; flagellum 3-segmented; littoral --> Buchnerillo*
b. Telson concave dorsally, rhomboidal; flagellum 2-segmented; Cuba --> Bisilvestriidae

*Buchnerillo is currently placed as incertae sedis in Oniscidea, but is placed in the Oniscoidea key for simplification

6 (3) a. Uropods with protopods or exopods flat, platelike, generally following the margin of body (projecting in Scleropactidae and Matazonellus, but then antennae flagellomeres 3 and body spikey respectively); body usually highly domed and conglobulating (endo- or exoantennal, flattened in some derived species) --> 7
b. Uropods not as above, generaly terete or subterete with rami projecting past margin of body; flagellomeres 2-3 (but never 3 if conglobulating); body various but usually not conglobulating (Cylisticidae with exoantennal conglobulation) or spikey --> 15

7 (6) a. Flagellomeres 1; currently only known from St. Vincent --> Haplarmadillo
b. Flagellomeres 2-3; widespread --> 8

8 (7) a. Flagellomeres 3; tropical to NE Mexico + Cuba --> Scleropactidae
b. Flagellomeres 2 --> 9

9 (8) a. Uropod exopod flattened, plate-like, forming the segment visible dorsally (best visible ventrally); widespread cold-temperate to tropical  --> Armadillidiidae
b. Uropod exopod conical, terete, protopod forming the segment visible dorsally; warm-temperate (to South Carolina and California) and tropical --> 10

10 (9) a. Telson hourglass-shaped; warm temperate and tropical --> Armadillidae
b. Telson triangular or truncate; Caribbean and Central America --> 11

11 (10)a. Uropod exopod distinctively lateral, endopod long and projecting; spiny conglobulator from Jamaica --> Acanthoniscus
b. Uropod exopod more medial; endopod not as above, not projecting; elsewhere --> 12

12 (11)a. Pereonite 1 coxal plate dorsally with a curved groove ("sulcus arcatus") --> Eubelidae
b. Pereonite 1 coxal plate dorsally flat --> 13

13 (12)a. Front of head "armadillidiid" in structure, with a distinct frontal lobe and antennal lobes; uropod endopod flattened, rectangular; Cuba and Andros --> Delatorreiidae
b. Front of head flattened or with a central or lateral lobe, never with antennal lobes; uropod endopod conical; distribution otherwise --> 14

14 (13)a. Front of head slightly excavate; Guatemala --> Globarmadillo
b. Front of head with a pointed lobe; Cuba --> Matazonellus

15 (6) a. Flagellomeres 3 --> 16
b. Flagellomeres 2 --> 20*

*the poorly known genus Rabdoniscus should key out to here, the one known specimen is too poorly preserved to place anywhere lower in the key. It is known from caves in eastern Cuba and has a unique ♂ pleopod 1 morphology.

16 (15)a. Pleonal epimera flat to weakly pointed, abruptly stepping down from pereonal margin; body barrel-shaped; isopods generally fast-moving --> Philoscomorph Woodlice (including Oniscidae in part and Halophilosciidae), poorly known basal assembalage of isopods, Philoscomorph key coming soon
b. Pleonal epimera pointed, usually continuing pereonal margin; body flatter to somewhat domed; isopods slow, clinging --> 17

17 (16)a. Body with shell-shaped scale-setae; currently only known from Cuba in the region --> Dubioniscidae
b. Body lacking setae or with setae not shell-setae; widespread --> 18

18 (17)a. Pleopodal respiratory fields on dorsal face of pleopods; Pacific coast and S Caribbean seashore isopods with smooth domed bodies --> Alloniscidae
b. Pleopodal respiratory fields on ventral face of pleopods; widespread, body not as above --> 19

19 (18)a. Uropod protopods large, angling endopods in a way that they are pressed together into one unit; Puerto Rico --> Synuropus
b. Uropods not as above; cold temperate and tropical --> Oniscidae (Oniscus + Phalloniscus)

20 (15)a. Lungs (visible as white patches on the rim of the pleopods on living individuals) absent; scale setae shell-shaped --> Trichorhinidae and Bathytropidae (functionally identical)
b. 2-5 sets of lungs present; scale setae not shell-shaped --> 21

21 (20)a. 2 sets of lungs present --> Porcellionidae
b. 5 sets of lungs present --> 22

22 (21)a. Body domed, able to conglobulate --> Cylisticidae
b. Body flattened, not able to conglobulate --> 23

23 (22)a. Lung spiracles near lateral margins, perispiricular area small; only known from the S Caribbean in our area --> Agnaridae
b. Lung spiracles not near lateral margins, perispiricular area large; cold-temperate (Trachelipus) and widespread tropical (Nagurus) --> Trachelipodidae

Sources

Arcangeli, A. (1929): Isopodi terrestri raccolti in Cuba dal Prof. F. Silvestri. Bollettino del Laboratorio di Zoologia generale e agraria della R. Scuola superiore d'Agricoltura in Portici, 23:129-148.

Armas, L. F., & Juarrero de Varona, A. J. (1999). Sistematica de la familia Delatorreidae (Isopoda: Oniscidea) en Cuba [Systematic of the family Delatorreidae (Isopoda: Oniscidea) in Cuba]. Avicennia,
10/11:1-42.

Garcia, L., & Robla, J. (2022). Buchnerillo atlanticus sp. nov., a new halophilic woodlouse (Isopoda: Oniscidea: incertae sedis) from the Atlantic coast of the Iberian Peninsula, with ecological remarks. European Journal of Taxonomy, 821:1-15.

Richardson, H. (1901). Key to the isopods of the Atlantic coast of North America with descriptions of new and little known species. Proceedings of the United States National Museum, 23(1222):493-579.

Schmidt, C. (2003). Contribution to the phylogenetic system of the Crinocheta (Crustacea, Isopoda). Part 2.(Oniscoidea to Armadillidiidae). Zoosystematics and Evolution, 79(1), 3-179.

Schmidt, C. (2007). Revision of the Neotropical Scleropactidae (Crustacea: Oniscidea). Zoological Journal of the Linnean Society, 151(1):1-339.

Schmidt, C. (2008). Phylogeny of the terrestrial Isopoda (Oniscidea): a review. Arthropod Systematics Phylogeny, 66(2), 191-226.

Van Name, W. G. (1936). The American land and fresh-water isopod Crustacea. Bulletin of the American Museum of Natural History, 71:1-523.

Vandel, A. (1973). Les isopodes terrestres et cavernicoles de l’île de Cuba. Résultats des expéditions biospéologiques cubano-roumaines à Cuba: 1:153-188.

Vandel, A. (1981). Les isopodes terrestres et cavernicoles de l’île de Cuba (second mémoire). Résultats des Expéditions biospéologiques cubano-roumaines à Cuba, 3:35-76.

Published: Jan 1, 2023