In anterior segments of spionid polychaetes notochaetae are generally capil
laries arranged in three distinct groups or rows including an anterior and
a posterior row and a dorsal superior tuft; neurochaetae are also capillari
es arranged in anterior and posterior rows plus a ventral inferior tuft. In
succeeding segments, the notopodial capillaries are reduced in number with
the groups becoming indistinct, the neuropodial capillaries are usually re
placed by hooks in differing patterns. These patterns of replacement includ
e those with replacement only in the posterior row, in both anterior and po
sterior rows, or of all neuropodial capillaries. A pattern of alternating n
europodial capillaries alternating with the neuropodial hooks is described
for the first time. In most polydorid taxa the chaetal arrangement on segme
nt 5 is changed from a vertical to a diagonal or horizontal position, presu
mably associated with the elongation of the segment. The modified chaetae a
re usually arranged in two curved diagonal or horizontal rows corresponding
to the anterior and posterior rows of notochaetae in other spionids. Based
on positional criteria different kinds of spionid chaetae can be shown to
be homologous making it possible to code them consistently for a cladistic
analysis.