SBV nucleocapsids with average dimensions of 24 x 205 nm are similar to or smaller than other crab gut-infecting baculoviruses (see Table 1). Baculo-A virions are 60 x 260-300 nm and have apical and unilateral envelope expansions similar to SBV (Johnson, 1976, 1983). The baculovirus Tau which infects Carcims mediterraneus also has these envelope expansions (Pappalardo and Bonami, 1979). While the dimensions do differ, the similarities among SBV, Tau, and Baculo-A suggest that a range of subtypes of a single branchyuran crab baculovirus exists.
When baculovirus nucleocapsids are enveloped in the nucleus it is thought the envelopes are assembledde nouo in the nucleus. It has been postulated these de nouo nuclear enveloped nucleocapsids are then released following rupture of the nuclear membrane (Adams et al., 1977). However electronmicroscopy of S. serrata hepatopancreas in this study has shown that enveloped
nucleocapsids can bud from the nucleus and acquire a second envelope from the nuclear membrane.
It could be postulated that SBV virions move to the cell membrane enclosed in the additional nuclearmembrane derived envelope which fuses with the cell membrane to release a nucleocapsid with a single envelope.
detection of CBV and SBV has widened the
known host range of the Baculoviridae. Investigations
of other decapod crustaceans will probably result in
detection of further baculoviruses. The development of
crustacean cell lines is urgently needed to permit comparisons
among the baculoviruses described from an
increasing number of geographic locations and host
species.