The homolid spermatozoon, as
exemplified by Homola sp., Paromola sp. and
Paromola
petterdi, differs markedly from spermatozoa of crabs of the
Heterotremata-Thoracotremata assemblage but agrees with the sperm of
dromiids, in the
strongly anteroposteriorly depressed acrosome
(apomorphy?) and
the capitate form of the perforatorium (a major
synapomorphy seen
nowhere else in the Crustacea). These similarities
support inclusion
of the Dromiidae and Homolidae in a single grouping, the
Podotremata. The
homolid perforatorium differs from that of dromiids in
the autapomorphic
spiked-wheel form of the anterior expansion. Homolid
spermatozoa show
nuclear arms symplesiomorphic of all investigated crabs
(small or
questionably sometimes absent in Dromiidae), and corresponding
loss of purely
microtubular arms seen in other reptants. Homolid sperm
agree with those
of dromiids (synapomorphy?), raninids, higher
heterotremes and
thoracotremes (homoplasies?) but differ from lower
heterotremes, in
lacking microtubules in the nuclear arms. A posterior
median process of
the nucleus in homolids, not seen in dromiids, is shared
with anomurans and
lower heterotremes. No features in the ultrastructure
of homolid or
dromiid sperm have been detected which associate them
exclusively with
either the Raninidae or the heterotreme and thoracotreme
Brachyura.