Introduction to Polydesmida
(Jump to Polydesmida key)
To positively identify most of Tasmania's ca 130 Polydesmida to species, you need to examine a mature male. On a separate website I explain how to age and sex a polydesmidan, and the important difference between 'H+19' and 'H+20' species. Please read those webpages before using the key.
Always look first for gonopods. The illustrations above are simplified views of an adult female (top) and male (bottom). Note the red-coloured lines on the male. These represent the gonopods, which are leg-like structures used to transfer sperm during mating. In Polydesmida the gonopods are always on body ring 7, which is the third ring carrying two pairs of legs. Gonopods replace the anterior pair of legs on this ring in adult males. The gonopods are often translucent and yellowish in colour (see image below). If your specimen does not have gonopods (if it is not a mature male), it may not be possible to identify it to species, or even to genus.
You should look for the ozopores. These are openings to the chemical defence glands. In Polydesmida they open on the side of the body or on the paranota, one on each side of a ring, 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'. The size, shape, position and number of the ozopores can vary from genus to genus.