264
THE ESSEX NATURALIST
observed (fig. 4). In 1960, after 10 days two ancestrula each
began to produce a single distal bud, but then became moribund,
as did all the remaining individuals. The larval valves remained
attached to some ancestrulae throughout their entire develop-
ment, in others they had become detached six days after settle-
ment. None of the ancestrulae was observed to have developed
a proximal spine.
Figure 4. E. crustulenta, ancestrula with polypide.
Scale equals 100μ.
The number of tentacles observed in the living polypide of
the ancestrulae was generally 8, although two individuals with
7 tentacles were seen. The polypides in fully grown colonies
have an average of 11 tentacles. The transition to this number
was not seen in E. crustulenta, but a comparable condition was
observed in E. pilosa (Linn.), collected alive from the south bank
of the River Crouch on 14th March 1960. Here the number of
tentacles of polypides in the fully grown colony was 12, that of the
ancestrula 9. The number of tentacles increased as follows: —
A 9, Z1 9, Z2 10, Z3 10, Z4 11, Z5 (not observed), Z6 12.
Membranipora seurati (Canu). All the adult Polyzoa recorded
from the Creek by Howes were referred to E. crustulenta. In