Figure24.Ventral axial skeleton of representatives ofAcipenserandScaphirhynchus: Ontogeny of the haemal arch is shown inA.
brevirostrum(a) with a small juvenile (left) possessing only slight extension of the basiventrals (bv) comparedtothe nearly complete
haemal arch of an adult (right).Thisadult specimen possessed a complete haemal arch more anteriorly similar to that ofA. oxyrinchus(b)
with contralateral sealing of the basiventrals and interventrals (iv). Scaphirhynchines never possess a haemal arch and lack ventral
expansion of the basiventrals even in large adults (c; Character 52).
branchials in the tongue pad (see Character 21), but
they lack a posterior wedge contacting hypobran-
chial two (Figure 13b). Connective tissue ridges are
restricted to hypobranchial one in HusoandAci-
penser,but overlap hypobranchial two in scaphi-
rhynchines. Juvenile Pseudoscaphirhynchus pos-
sess a tooth plate on hypobranchial two (Berg
1948a), suggesting that the functional palate is ex-
panded generally in scaphirhynchines.
Character 52. Loss of a haemal arch- Scaphirhynchini
Ventral edges of basiventrals of scaphirhynchines
end flatly with a slight ventral lip (Figure 24c). The
basiventrals are open ventrally, lacking a haemal ca-
nal until reaching the caudal fin supported by hae-
mal spines (see Character 38). In the peduncle, the
basiventrals extend more ventrally to form a ven-
tral groove, but never converge toward the midline.