Biogeography of East African montane forest millipedes - Biogeography and Ecology of the Rain Forests of Eastern Africa - page 110

lringa', which is presumably in the Ruaha Gorge;
. r. kisarawensis Hoffman & Howell occurs n the
Pugu Forest near Dar es Salaam, . enghoffi Hoff-
man and . orestes Hoffman represent the genus in
the eastenmost Uzungwas, /. minimus Hoffman
at the westemost, and /. unwe Hofman is
endemic to the Rungwe area. . rossi may be found
in the southern Ulugurus, and probably several
addiional species in the Uzungwa and Rubeho
ranges. In gonopod characters, Iringius resembles
Ceratodesmus, from which it may be derived. As
regards peripheral features, the species of lringius
are certainly much more specialised, having a
strongly modified hypoproct as well as such items
as reduced pore formulas, areolated metaterga,
and spinose metazonal sides.
The pinnacle of localised oxydesmid speciaion
occurs in Ceratoesmus which has nine species in
and around the Usambaras (see Table 6.1). Only
one species, . cistatus Cook, is a lowland form
(widespread in Tanga Region) but it too ascends
to 100 m in the East Usambaras. Interesingly, its
closest relaive appears to be . gracilior Hoffman,
known only from Kanga Mountain in the Ngurus
and separated by about 100 m from the nearest
locality for ristatus. Perhaps this situaion reflects
more extensive distributions in some earlier
pluvial stage. Otherwise, the East Usambaras har-
bour the nominate subspecies of Ceratodesmus
ansatus Cook, which has the closely related . a.
hesperius in the West Usambaras and . a.
nguruensis in the Ngurus. The nucleus of this
genus is clearly the West Usambaras, where seven
taxa are known to occur, two of them subspecies
in different forest isolates ( . c. co riarius and . c.
angustilavius). Three species are known at
Mazumbai: . coiaius, . fraterulus, and .
mazumbai, all strikingly disinct in various
extenal characters of size, coloraion and
onamentaion. One excepionally interesing
relaionship is that between . msuyai Hoffman of
the West Usambaras (Ambangulu) and its
apparent sister species . eburatus, localised on
the relaively minute Pongwe Mountain 100 m to
the south. The inference that I draw from the
distribuions of this species pair, plus cristatus and
gracilior and the subspecies of ansatus, is that some
coninuity of rain forest habitat must have eisted

between the Usambaras, Pongwe, and Ngurus up
to some ime after the differeniaion of the taxa
menioned. The eising disjuncion of habitat
(assuming it to be real and not illusory) may be a
relaively recent episode, perhaps from the late
Pleistocene.
Almost certainly other members of this com-
plex genus will be found when other forest iso-
lates in the Usambaras (and perhaps Pares) have
been sampled. The interacions of syntopic
ceratodesmids would appear to be a specially
interesing problem. The presence of so many
taxa in such a limited area suggests a kind of
intense insular speciaion process may be in
operaion as well.
The postulaion has been made (Hoffman,
1990) that Lyodesmus may represent the ancesral
ctenodesmoid stock from which the various more
local and specialised ctenodesmine genera have
evolved by isolaion within the condensing rain
forest areas of the block-fault and other massifs in
Tanzania. Such genera may be characterised as
neoendemics in the sense of Braun-Blanquet
(1923).

Summay of mountain aunas
In so far as diplopods are concened, only three
areas can be considered as reasonably well
known: the East Usambaras around Amani, the
northen Ulugurus, and the easternmost end of
the Uzungwas at Mwanihana. Of these three,
perhaps only half of the resident faunas have been
discovered so far. Many of the taxa already col-
lected are sill either undescribed or belong in
very poorly understood families. A major diffi-
culy remains in deciding which species are really
confined to montane forests or simply have been
overlooked at lower elevaions and diferent bio-
topes. Such a disincion is sill a problem for the
much better known bird faunas, lending appreci-
aion to its relaive magnitude as regards
millipedes.
The Usambaras have been fairly well studied
around Amani, especially through the efforts of
Henrik Enghoff, the only diplopodologist to have
worked in East Africa so far. The westen sub-
group has been sampled especially around