Janiroidea Sars, 1897

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Suggested Common Name: Witchers
Number of subordinate taxa: 1750 species in at least 25 families (see Notes) along with 9 incertae sedis genus worldwide, 328 species in 20 families and 4 incertae sedis genera in our area.
Etymology: after Janira Leach, 1814, see that account for more information. Common name is derived from "bewitching", refering to the bewitching diversity
Taxonomic History: Paraselloidea [undet.] [INCOMPLETE]
Description: Penes short, close-set. ♂ pleopod 1 protopods and endites fused into one elongate piece. ♂ pleopod 2 protopod large, usually forming an operculum with pleopod 1; exopod usually minute; endopod elongate. ♀ pleopod 2 protopods and endites fused into one piece, usually operculate. Pleopod 3 endopod uniarticulate, exopod 2-segmented.
Type taxon: Janiridae Sars, 1897
Notes: This enormous superfamily contains multiple radiations into the deepsea environments and reverse radiations into shallower waters. Janiroidea is most likely paraphyletic or even polyphyletic, with evidence pointing to some genera and families being closer to members of the other marine superfamilies than members traditionally placed in Janiroidea. The taxonomy of subordinate groups is also messy, with many genera either being stuffed in the wastebin family Janiridae or left at incertae sedis. A full revision of the entire superfamily may be needed in the future to sort out relationships among families and genera.

Subordinate taxa: Acanthaspidiidae, Angeliera, Dendrotionidae, Desmosomatidae, Echinothambematidae, Haplomunnidae, Haploniscidae, Ischnomesidae, Jaeraella, Janirellidae, Janiridae, Joeropsididae, Katianiridae, Lepidocharontidae, Macrostylidae, Mesosignidae, Munnidae, Munnopsidae, Nannoniscidae, Paramunnidae, Pleurocopidae, Rhacura, Tole, Santiidae

Key to families
1 a. Pereon conspicously divided into two sections: a less-robust section with ambulatory or digging legs (the ambulosome, generally pereonites 1-4) and a more robust section with natatory or somewhat natatory legs (the natatosome, generally pereonites 5-7); almost entirely deepsea (some Munnopsids can reach shallow waters) --> 2
b. Pereon not divided as above, if pereonites 5-7 differentiated from pereonites 1-4 then only a bit smaller and legs all subequal or equal in shape and size (asides from pereopod 1); shallow or deep --> 4

2 (1) a. Pereon split into an anterior digging section (fossosome) and an anterior walking section (ambulosome); pereopods 1-4 (fossopods) twisted, especially pereopod 4, which is twisted 180° around to face "backwards", pereopods 1-3 twisted to point upwards; pereopods 5-7 cylindrical; bizarre fossorial isopods --> Macrostylidae
b. Pereon split into an anterior ambulatory section (ambulosome) and a posterior swimmin section (natatosome); pereopods 5-7 carpus and merus usually expanded, fringed with setae; generally swimming or surface-benthic (some Munnopsids infaunal) --> 3

3 (2) a. Body generally slender; head lacking rostrum; antenna 1 peduncle segment 1 distally simple, scale absent or simple;  --> Desmosomatidae
b. Body generally ovate; head with rostrum; antenna 1 peduncle segment 1 distally 2-lobed, scale 2-segmented --> Munnopsidae

4 (1) a. Pereonite 5 very elongate, longer than others, combined with pereonite 4 resembling a humerous bone; head fused to pereonite 1; pereopod 1 strongly subchelate; very elongate deepsea isopods --> Ischnomesidae
b. Pereonites 4-5 not as above, similar to others; head free; pereopod 1 ambulatory to subchelate (chelate in Katianiridae); various ecologies --> 5

5 (4) a. Body extremely compact, ovate, often with long spidery legs (frequently longer than body); pereonites generally short, with pereonites 5-7 being shorter than pereonites 1-4 and curved backwards; pereopod 1 carposubchelate; deepsea species often spiny --> 6
b. Body not as above, generally more elongate and parallel-sided, legs generally shorter; pereopod 1 ambulatory or subchelate --> 11

6 (7) a. Body domed, generally spiny; head emarginate (frontal margin absent); pereopods 1-7 ischium and merus generally (but not always) subequal in length, shorter than basis; eyes absent (present in Acanthomunna); mostly deepsea --> 7
b. Body flattened, usually smooth (sometimes spiny or encrusted in symbiotic red algae); head frontal margin present; pereopods 1-7 ischium and merus; eyes present (sometimes absent); generally shallow (Spiderwitchers) --> 8

7 (6) a. Uropods long, dorsocaudal; telson bloated or not, not curled over body --> Dendrotionidae
b. Uropods minute, apical; telson bloated, often curled over body (esp. in Thylakogaster) --> Haplomunnidae

8 (6) a. Uropods elongate (in some Santiids often covered in symbiotic encrusting algae); generally shallow-water tropical species --> 9
b. Uropods minute, often with protopod absent; cold to tropical waters --> 10

9 (8) a. Eyes set on very long lateral stalks --> Pleurocopidae
b. Eyes set on short lateral stalks or dorsal protuberances --> Santiidae

10 (8) a. Antenna 1 peduncle segment 3 normal; head large, usually not sunken into pereonite 1; pleopod 4 exopod with lateral setae; anus not covered by uropods --> Munnidae
b. Antenna 1 peduncle segment 3 elongate; head usually smaller, sunken into pereonite 1; pleopod 4 exopod without lateral setae; anus covered by opercular pleopods --> Paramunnidae

11 (5) a. Eyes present (although frequently reduced); usually in shallow waters --> 12
b. Eyes absent (or reduced to dots without ocelli); usually in deeper waters or intersitial environments --> 15

12 (11)a. Pereopod 1 subchelate (grasping), usually with palm on carpus --> Janiridae and "associated" genera (Jaeraella, Rhacura and Tole, see Janiridae page)
b. Pereopod 1 ambulatory --> 13

13 (12)a. Uropods minute, embeded in a notch in the telson; mandible molar elongate, pointed, often with accessory teeth, mandible overall adapted to carnivory; body usually boldly patterned --> Joeropsididae
b. Uropods not as above, if minute then not neatly fiting into telson; mandible molar truncate or pointed, overall not adapted to carnivory; body variously colored --> 14

14 (13)a. Eyes on short lateral stalks with a short spine next to the eye; ♂ pleopods 1-2 complex, pleopod 1 with complex stylet guide and pleopod 2 stylet extremely long and coiled; tropical --> Acanthaspidiidae (Mexicope)
b. Eyes sessile, usually dorsal or dorsolateral; ♂ pleopods 1-2 not as above; arctic to tropical --> Janiridae (in part)

15 (11)a. Body elongate, flat or cylindrical; uropods usually long; deepsea or intersitial --> 16
b. Body ovate, flat or domed; deepsea (Caecijaera shallow-commensial) but not intersitial --> 19

16 (15)a. Pereopod 1 subchelate; cylindrical deepsea isopods --> Echinothambematidae
b. Pereopod 1 ambulatory (♂ pereopod 5 subchelate in Angeliera); shallow-intersitial --> 17

17 (16)a. Maxilliped palp 4-segmented, terminal segment sickle-shaped; pereopods 1-7 dactyli 3-clawed; ♂ pereopod 5 subchelate, palm on carpus; pleopod 3 (when present) uniramous; antenna 2 lacking scale; currently only known from the Caribbean (although could be found in other tropical areas) --> Angeliera (see Janiridae page)
b. Maxilliped palp 5-segmented, terminal segment usually narrow; pereopod 5 ambulatory; pereopods 1-7 2-clawed; pleopod 3 biramous; antenna 2 with scale (minute in Caecianiropsis); temperate Pacific and Caribbean --> 18

18 (17)a.  Head with a rounded non-projecting rostrum; mandible molar truncate; currently only known from California --> Janiridae (Caecianiropsis)
b.  Head lacking a rostrum; mandible molar conical; currently only known from the Caribbean --> Lepidocharontidae

19 (15)a. Uropods biramous; shallow or deep --> 20
b. Uropods uniramous, often tiny; all deep --> 22

20 (19)a. Antenna 1 terminal segment bulbous (absent in Nannoniscoides and Hebefustis); pereonites 6-7 and telson usually fused to one another in various ways (not at all in Exiliniscus and Thaumastosoma) --> Nannoniscidae
b. Antenna 1 terminal segments not as above; pereonites 6-7 and telson all free --> 21

21 (20)a. Pereonites 2-4(-7) epimera lobes bifid; ♂ pleopods 1-2 complex, with stylet on pleopod 2 long-coiling --> Acanthaspidiidae (in part)
b. Pereonites 2-7 epimera lobes all rounded or at least not lobed; ♂ pleopods 1-2 much simpler, generally "typical" for Janiroidea --> Janiridae (in part)

22 (19)a. Body generally smooth, lacking conspicous lateral lappets; posterior pereonites often fused with telson; pereopod 1 ambulatory; oddly Oniscidean-like deepsea isopods, often conglobulating --> Haploniscidae
b. Body generally spiny or tubercled, almost always with conspicous lappets, posterior pereonites almost always free; pereopod 1 ambulatory or grasping (subchelate or chelate); bizarre isopods not resembling Oniscideans --> 23

23 (22)a. Pereopod 1 ambulatory --> Mesosignidae
b. Pereopod 1 subchelate or chelate --> 24

24 (23)a. Antenna 2 shorter than antenna 1; pereopod 1 chelate; mandible molar pointed or reduced; maxilliped palp 4-segmented --> Katianiridae
b. Antenna 2 longer than antenna 2; pereopod 1 subchelate; mandible molar truncate, grinding; maxilliped palp 5-segmented --> Janirellidae


Kensley, B., & Schotte, M. (1989). Guide to the marine isopod crustaceans of the Caribbean. Smithsonian Institution Press.

Wilson, G. D. F. (1987). The road to the Janiroidea: Comparative morphology and evolution of the  asellote isopod crustaceans. Journal of Zoological Systematics and Evolutionary Research, 25(4), 257-280.

Published: Jan 1, 2023