Polydesmida key

To identify Polydesmida to genus and species, it's necessary to understand their anatomy. I strongly recommend a visit to the External Anatomy of Polydesmida website. The site offers an illustrated guide to how Polydesmida are built and explains the anatomical terms used here.

The absolute basics are as follows:

H+20 vs H+19, and gonopods. Depending on species, adult Polydesmida have either 14 segments with two pairs of legs (H+20; segments 5-18), or 13 segments with two pairs of legs (H+19; segments 5-17). In both cases, a pair of specialised structures called gonopods replace the first pair of legs on segment 7, which in females carries the third set of "doubled" legs (see diagram). If you don't have an adult male with gonopods, it is often impossible to identify the specimen.

Paranota, ozopores and spiracles. Paranota (singular paranotum) are lateral extensions of the metatergite (see below). Spiracles are the holes through which a millipede breathes. On most segments there are two spiracles on each side, opening just above the leg bases. Ozopores are openings to the chemical defence glands. These open on the side of the body or on the paranota, one on each side and usually on rings 5, 7, 9, 10, 12, 13, and 15-18 (H+19) or 15-19 (H+20). This is called the "normal pore formula".

Note: For troglomorphic cave-dwelling millipedes, try Atalopharetra clarkei for Ida Bay, A. eberhardi for Precipitous Bluff and Noteremus infimus for the Junee-Florentine.

1a. Paranota broad and obvious (left-hand image) ..........go to 2 1a. Paranota greatly reduced or absent (right-hand image) ..........go to 10
2a. Rear corner of paranotum clearly projecting backwards (left-hand image) ..........go to 3 2b. Rear corner of paranotum square or slightly rounded (right-hand image) ..........go to 6
3a. Prominent long seta arising near rear corner of paranotum ("Lissodesmus group") ..........go to 4 3b. No long seta at posterior corner of paranotum ..........go to 5
4a. Spiracles large, seemingly swollen (top image; except Dasystigma tyleri), adult 20-25 mm long, pale brown or chestnut brown ..........Dasystigma species 4b. Spiracles large, seemingly swollen, close together; adult >30 mm long, reddish-brown, northeast only ..........Tasmanopeltis grandis 4c. Spiracles inconspicuous, not seemingly swollen, not close together (bottom image) ..........Lissodesmus species
5a. Adults at least 15 mm long, reddish-brown; metatergites flat; found in bush areas ..........Tasmanodesmus hardyi 5b. Adults no more than 10 mm long, pale brown; metatergites with rows of low swellings; mainly gardens (introduced species) ..........Brachydesmus superus
6a. Second tergite greatly expanded laterally (see image at right), metatergites covered with numerous tiny bumps, adults 5-7 mm long ..........Asphalidesmus species 6b. Second tergite not greatly expanded, metatergites not covered with numerous tiny bumps ..........Go to 7
7a. Metatergites in adults smooth with 3 transverse rows of low bumps; animal dark reddish-brown; gonopods as shown (right) ..........Dysmicodesmus jeekeli 7b. Metatergites in adults smooth or with 3 tranverse rows of low bumps; adults sometimes reddish in colour; gonopods not as shown ..........Tasmaniosoma species 7c. Metatergites in adults with 3 tranverse rows of small setae; sometimes coloured but never with reddish pigmentation ..........Go to 8
8a. Body usually well-pigmented (various colours); gonopods with large, rearwards-projecting "flange" (see image at right) ..........Atrophotergum species 8b. Body pale or faintly pigmented; mainly tiny species 4-7 mm long as adults ..........Go to 9
9a. Very long gonopods ending in 2-pronged fork (top image) ..........Setoisenoton pallidus 9b. Long gonopods bent or "hinged" in the middle (bottom image) ..........Ginglymodesmus species 9c. Gonopods otherwise ..........undescribed Polydesmida
10a. Paranota visible as reduced structures or slight lateral swellings ..........Go to 11 10b. No trace of paranota, or paranota only visible as fine line ..........Go to 18
11a. Paranota shaped as shown (head is to left) ..........Go to 12 11b. Paranota merely slight lateral swellings ..........Go to 14
12a. Body light brown with well-defined dark brown ring around each ring and light paranota (introduced species; see image at right) ..........Akamptogonus novarae 12b. Body light brown to black ..........Go to 13
13a. Gonopod as shown (head is to right); eastern and northern Tasmania ..........Aethalosoma solum
13b. Gonopod as shown (head is to right); eastern and northern Tasmania ..........Notodesmus scotius
13c. Gonopod similar to the one shown (head is towards top); western and northern Tasmania ..........Somethus species
14a. Adults to 12 mm long, pale red in colour; ozopores on rings 5 and 7-18 ..........Procophorella species 14b. Adults at least 15 mm long; variously coloured ..........Go to 15
15a. Adults reddish brown or black, gonopod as shown (left-hand image); far northeast Tasmania and eastern Bass Strait ..........Dicranogonus pix 15c. Adults reddish brown, gonopod as shown (right-hand image; introduced species) ..........Taxidiotisoma portabile 15c. Adults otherwise ..........Go to 16
16a. Adults reddish, ozopores on rings 5 and 7-18, far south only ..........Noteremus summus 16b. Adults with normal pore formula ..........Go to 17
17a. Gonopod long, with "fringed hood" at tip and long, needle-like solenomere (see image at right; dashed line through solenomere) ..........Bromodesmus species 17b. Gonopod short, curled over like a partly closed hand, solenomere stout, short, inconspicuous ..........Atalopharetra species
18a. Paranota reduced to a fine, just-visible line (see image on right) ..........Gasterogramma species 18b. No trace of paranota ..........Go to 19
19a. Adults 20-25 mm long, pale with 3 dark longitudinal stripes (see image on right) ..........Pogonosternum species 19b. Adults 10-12 mm long, without longitudinal stripes; ozopores on rings 5 and 7-18 ..........Paredrodesmus species 19c. Adults 17-20 mm long, without longitudinal stripes; normal pore formula ..........Kebodesmus zonarius