This book is the first in a series of 4 volumes in the Handbook of Zoology series about
morphology anatomy reproduction development ecology phylogeny and systematics of Annelida.
This first volume covers members of the so-called basal radiation and the first part of
Sedentaria. It is supplemented by chapters on the history of annelid research their fossil
record and an introduction to the phylogeny of annelids and their position in the tree of
life. In the latter chapter the history of their systematic is reviewed giving an almost
complete picture of systematic-scientific progress especially in the past years which changed
our view on annelid phylogeny dramatically. The most basal annelids lately united as
Palaeoannelida represent two families of aberrant polychaetes formerly often suggested to be
highly derived which now give us a fresh look on how the ancestral annelid may have looked
like. These lack certain key characters such as nuchal organs and possess rather simple nervous
systems which now likely represent primitive character states. In this basal radiation the
first taxon of apparently unsegmented and achaetigerous animals is positioned the Sipuncula.
Most likely another group of platyhelminth-like and unsegmented and even chaeta-lees annelids
Lobatocerebridae falls into this basal radiation. The section of Sedentaria starts with
Orbiniida a taxon characterized by elongated thread-like worms which do not have anterior
appendages like palps and comprises several families representing members of the Meiofauna.
These minute worms often inhabiting the interstitial spaces in marine sands are suggested to
have evolved by progenesis. The second higher taxon is represented by Cirratuliformia
comprising nine families of typical sedentary polychaetes each of which showing a remarkable
variation of the annelid body plan. Members of this taxon usually exhibit many annelid
characters but certain also lack the most typical prostomialappendages the palps.
