Omodeo on megadriles

[Geoff Read]

Hello Annelida listers,

I include the lengthy abstract to Pietro Omodeo's recent paper which may 
be of interest beyond the earthworm specialists. I've broken it into 
paragraphs (not in the original) for easier reading onscreen.  

Omodeo, P.* 2000. Evolution and biogeography of megadriles (Annelida, 
Clitellata). -  Italian Journal of Zoology 67:179-201.

[* Dipartimento di Biologia Evolutiva, Università di Siena, via P. A. Mattioli 
4, 1-53100 Siena (Italy)]

Abstract: The evolution of megadriles is analysed employing the 
traditional comparative method supplemented with palaeogeographic 
information drawn from plate tectonics. The origin of the group is 
considered in relation to special physiological and developmental 
strategies which evolved in response to life in compact soil and the 
acquisition of a larger body size. Further evolution, also related to the 
terricolous habits, implied differentiations of intestinal structures and 
modifications of the mating mechanics. The required modifications went 
on in divergent ways in the three superfamilies Lumbricoidea, 
Megascolecoidea, and Eudriloidea.   

The most primitive among the Lumbricoidea, which stemmed from some 
strain akin to the Haplotaxidae, are limicolous and are distributed over a 
broad territory corresponding to the northern and central regions of the 
Lower Triassic Pangaea. Based on ovarian structure, these megadriles 
may be divided into a northern strain, that originated in Laurasia, and a 
southern strain, that originated in Gondwana. The geographical range of 
the main families of Lumbricoidea suggests that they differentiated at a 
time when the continental masses were separated during the Cretaceous. 

The most primitive among the Megascolecoidea are the Ocnerodrilidae, 
which are mostly limnic. Some peculiarities of their sexual apparatus 
suggest that they might have derived from a strain akin to the 
Alluroididae. On account of their more advanced adaptations of the 
copulatory apparatus, the fully terrestrial families Acanthodrilidae and 
Octochaetidae appear to have derived from some ocnerodrilid ancestor. 
The geographical range of the Octochaetidae suggests that they evolved 
in the central region of Triassic Pangaea. The distribution of the 
Acanthodrilidae supports the hypothesis that they originated in southern 
and eastern Gondwana and then spread into the western and northern 
regions, but the taxon is possibly polyphyletic. 

The Megascolecidae, which are the most diverse family of the group, 
appear to have stemmed from some ancestor akin to the acanthodrilids 
following their acquisition of further anatomical and physiological 
modifications of the copulatory apparatus. Native to Australia and  New 
Zealand, they spread northwards to Indochina and the Asian Far East, as 
well as to the Pacific coast of North America - possibly during the 
Cenozoic era. 

The Eudriloidea, endemic to intertropical Africa, are characterized by the 
extreme variation of the sexual apparatus, particularly the female 
structures. They probably took origin from an alluroidid ancestor, but not 
the same one from which the Megascolecoidea originated. In this 
superfamily, evolutionary processes seem to have proceeded more 
rapidly. More generally, the evolution of megadriles is characterized by 
numerous instances of convergence and remarkably slow speed, but 
speciation events in Megascolecidae and Eudrilidae were apparently very 
frequent."

--
Geoff Read <g.read at niwa.cri.nz>


-- ANNELIDA 
Discuss   = annelida at net.bio.net      = talk to all members
Server    = biosci-server at net.bio.net = un/subscribes
Archives  = http://www.bio.net/hypermail/annelida/
Resources = http://biodiversity.uno.edu/~worms/annelid.html
--