Geoscience Reference
In-Depth Information
F
IG. 27
Pill millipede
Glomeris marginata
(Photograph J. Grant.)
The flat-backed millipedes in the family Polydesmidae form another major
side of each segment and which act as wedges in splitting apart compacted leaves.
One of the smallest British millipedes belongs to this family while rejoicing in one
of the longest names,
Macrosternodesmus palicola.
Fully grown individuals do not
exceed 4 x 0.4mm in size.
Millipedes have a life span extending over several years. Eggs hatch into six-
legged larvae which resemble insect larvae in many ways and suggest a common ori-
gin. The number of segments and legs increases with each moult until maturity is
reached. In some species the number of eyes also increases in a distinctive pattern
which allows one to determine the particular stage, or instar, and to distinguish other-
wise very similar species. Two distinct breeding strategies are found among the Jul-
idae: adult
Julus scandinavius
and
Ophiulus pilosus
breed only once and then die,
whereas the “black, swift-footed millipede”
Tachypodoiulus niger
and the handsome
orange-striped
Ommatoiulus sabulosus
breed and moult several times. The males of
these latter two species show a curious alternation of reproductive and non-reproduct-
ive stages termed periodomorphosis. This is thought to be an adaptation which allows
the dispersal of both mature males and females. Whereas all mature females are cap-
able of breeding, a male which has bred cannot normally moult directly into another
breeding male, presumably because of the physical difficulties of re-forming the mod-
