125.
Jamieson, B.G.M., Guinot, D. and Richer de Forges, B. 1993h. The spermatozoon
of Calocarcinus africanus (Heterotremata, Brachyura, Crustacea):
ultrastructural synapomorphies with xanthid sperm. Invertebrate Reproduction
and Development 24, 189-196.
Features of the spermatozoon of Calocarcinus
africanus which are general for heterotremes and endorse its inclusion in
the Heterotrematsa are: extension of the subacrosomal chamber almost to the
anterior apex of the sperm, presence of an acrosome ray zone, and presence of a
thickened ring where the capsule surrounds the base of the subacrosomal
chamber. A feature shared with "higher" heterotremes is the
restriction of cytoplasm to the periacrosomal region, the arms being nuclear
only, in contrast with invasion of their chromatin with cytoplasm and
microtubules in majids; and loss of a posterior median process, containing
chromatin, which is present in majids as in raninids and homolids. The
relationship of Calocarcinus with xanthids is unequivocally supported by
(1) presence of a posterior circumperforatorial zone, the xanthid ring; (2) the
precise form of the acrosome ray zone which is wide anteriorly and sends
a long slender extension posteriorly to meet the ring; (3) the irregular
external margin of the outer acrosome zone; (4) division of the operculum
complex into a distinct upper zone and a lower, subopercular zone of lesser
diameter; and (5) presence of an accessory ring around the operculum.
Modification of the xanthid ring is typical of thoraotremes and partial
modification in Calocarcinus may indicate origin of thoracotremes
from a related xanthoid stock. A difference of Calocarcinus sperm
from those of xanthids is the (plesiomorphic) presence of centrioles, also seen
in some heterotremes and thoracotremes. No synapomorphies which are not common
to other heterotremes are shared between Calocarcinus and trapeziid
sperm. Trapeziid sperm (plesiomorphically?) lack the xanthid ring, the
posterior extension of the acrosome my zone and the irregular margin of the
outer acrosome zone of Calocarcinus and xanthids. Apomorphic features of
the Calocarcinus africanus sperm include a spiral configuration
of the contents of the outer acrosome zone (autapomorphy?), as seen in cross-section,
and presence of a periopercular rim. A well developed periopercular rim is
known elsewhere only in Potamonautes (family Potamidae), but a rudiment
occurs in some xanthids (e.g., Etisus). The periopercular rim is
probably a true synapomorphy indicative of relationship of potamids to xanthoids (represented by Calocarcinus)
which has been postulated elsewhere on morphological grounds.