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Cyphopods

Left: FemaleLissodesmus hamatus (Dalodesmidae), Tasmania
Right: FemaleTasmanopeltis grandis (Dalodesmidae), Tasmania
Posteroventral view of ring3

Thecyphopods (image above, right) are a pair of sacs inside ring3 in adult female Polydesmida. They are also sometimes calledvulvae (singularvulva). They store sperm aftermating and connect to the rest of the female reproductive system. The cyphopods are not visible externally*, and access to them is through a narrow ventral opening on ring3. The opening is between thesternite supporting legpair2, and a 'bridge' which completes the ring and is formed by the ring3pleurites. The anterior margin of the 'bridge' (= the posterior edge of the ventral opening), is called theepigyne (images above and below).

FemaleTasmaniosoma armatum (Dalodesmidae), Tasmania
Ventral view of ring3

The epigyne is often raised above the surface of ring3 (i.e., it extends ventrally) and its shape is variable. In the Dalodesmidae shown above and many other species, its centre extends as a rounded-triangular 'tooth'. The epigyne can also be 'two-toothed', rectangular or trapezoidal, with or without a sculptured edge.

Cyphopods have been carefully studied by Polydesmida specialists to see if they might be useful in identifying and classifying Polydesmida. The answer so far is 'not often'. A European study of 29 Polydesmida species in six genera (Tadler and Thaler1993) also found within-species variations in the epigyne:

Als ausserordentlich variabel erwies sich allerdings die Querleiste der Ventralspange vonP. [Polydesmus]subterraneus: diese war selbst innerhalb einer Population einteilig-tafelförmig bis zweigeteilt ausgebildet.

The transverse margin of the ventral bridge ofP. [Polydesmus]subterraneus certainly proved to be unusually variable: within a single population it took the form of a one-part or a two-part plate.

*When an adult female is killed and preserved in alcohol, or is distended after drowning in water, the cyphopods sometimes emerge from their cavity and extend ventrally.

Tadler, A. and Thaler, K. 1993. Genitalmorphologie, Taxonomie und geographische Verbreitung ostalpiner Polydesmida (Diplopoda: Helminthomorpha).Zoologische Jahrbücher, Abteilung für Systematik, Geographie und Biologie der Tiere 120: 71-128. 

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