52 THE ESSEX NATURALIST
times occurring on the lower shore. Cole (1888) records Solaster
from the Blackwater, and Walne (1956) gives records of its pres-
ence from Osea Island to St. Lawrence Bay and in areas offshore.
During the period 1960 to 1965 there seems to have been a steady
decline in numbers both in the Blackwater and immediately off-
shore. Spawning takes place in the spring and juveniles can be
seen in the benthos in late summer.
ECHINASTERIDAE
Henricia sanguinolenta (O. F. Muller)
Recorded as Cribella sanguinolenta during the Essex Field Club
excursion of September 1888 (Cole, 1888).
Order Forcipulata
ASTERIIDAE
Asterias rubens Linne Common Starfish or Five-finger
Common and widely distributed in the Blackwater and Colne
and offshore, on most types of bottom except mud. Previously
recorded in the Blackwater by the Essex Field Club (Cole, 1888)
and in offshore waters by Walne (1956). In the period 1960-1965,
A. rubens was recorded as far up river as Thirslet but it may
extend further than this. Spawn has been collected from April
to June and juveniles seen from about May onwards each year.
Sampling has shown an increase in the population from 1960 to
1961, but a marked decrease from then until 1965. The species is
regarded as a serious oyster pest in the Blackwater and other
Essex oyster grounds, but Hancock (1955) has shown experiment-
ally that A. rubens will actually feed on Urosalpinx and Crepidula
in preference to oysters.
A caprellid, Podalirius typicus, is often found as a commensal
with A. rubens in the Blackwater.
Class OPHIUROIDEA
Order Oplliurae
Ophiotrichidae
Ophiothrix fragilis (Abildgaard)
Locally common on clean shell or stony bottoms and often
associated with the mussel Modiolus modiolus and sponge
Halichondria panicea. From 1960 to 1962 the species was most
commonly obtained on stations TL.2, TL.3, C.3, N.3, S.21, HB.l,
HB.4 and N.6. As a result of the severe winter of 1962-63 the
population decreased to an undetectable level, but by the summer
of 1964 numbers had begun to build up again. Newly settled
juveniles recorded from the benthos in June (1961) indicate an
early summer spawning.