44
THE ESSEX NATURALIST
NUCULANIDAE
Nuculana minuta (Muller)
Of rare occurrence only. Single shell valves have been found
in sand and fine shell from the middle of the Blackwater (1960)
and also from the Bench Head (1964). Some shells were in good
condition indicating that the species may still be living locally.
Order Filibranchia
Mytilidae
Mytilus edulis Linne Common Mussel
Very common and widespread on shores in all parts of the area,
on stones, shells, posts, etc. Sometimes forming clumps in areas
of stable shingle and quite dense growths on piers and ship
bottoms. This is mostly a littoral species but has also been com-
monly found on Sublittoral shell and stony grounds. Quite a
heavy spatfall occurred in 1963, but this did not produce a lasting
increase in the population. Specimens are often infected with the
parasite Mytilicola intestinalis.
Modiolus modiolus (Linne) Horse Mussel
Fairly common on stony bottoms. Specimens are seldom more
than four inches in length. Distribution is from the Thirslet down
the middle of the Blackwater and off-shore.
The Pea Crab, Pinnotheres, is sometimes found as a commensal.
Musculus discors (Linne)
Occasionally obtained from clean shelly and stony bottoms
particularly where the aggregations of sand tubes of the polychaete
Sabellaria are found to occur. Recorded from stations TL.2, C.3,
and N.2 in 1960, North Eagle in 1962, and station C.2 in 1965.
Order Pseudolamellibranchiata
Ostreidae
Ostrea edulis Linne Native Oyster
The distribution and abundance of oysters in the Blackwater
depends largely upon the activities of fishermen, but the species
can generally be found on most shelly bottoms from Northey
Island to the Cocum Hills area. There are concentrations of
oysters on the growing beds in creeks such as Strood Channel
and Tollesbury Fleet, and natural populations occur in the main
part of the Blackwater and on creek bottoms (e.g. in Bradwell
Creek). Oysters are dredged and relaid on the grounds as required.
The most utilised private and common grounds are usually areas
of muddy shell with an abundance of Crepidula, lying just below
low water mark, but oysters also occur on cleaner bottoms and in
deeper water. It was possible to obtain in excess of 150 per nr
of small oysters in grab samples from station C.3 (4.9.1962). The
larvae may be seen in the plankton from mid-June until mid-
August.