THE MARINE FAUNA OF THE BLACKWATER ESTUARY 39
Triphoridae
Triphora perversa (Linne)
One record only; a shell taken in a grab sample at station C.2
(2.1964).
Epitoniidae
Clathrus Clathrus (Linne)
One record only; a broken shell found on the shore at Bradwell
(10.7.1965).
Clathrus clathratulus (Kanmacher)
Shells occasionally taken in grab samples from clean shelly
bottoms in the middle of the Blackwater, off Mill Creek. One
living juvenile from station C.3 (29.11.1961).
Pyramidellidae
Odostomia eulimoides Hanley
Parasitic on Oysters. Reported to be common in some years
on oyster beds in the Colne estuary, but not recorded from the
Blackwater.
Turbonilla elegantissima (Montagu)
Shells common in bottom deposits and in shell sand on beaches
at the seaward end of the Blackwater. There are no records of
living animals.
Calyptraeidae
Crepidula fornicata (Linne) American Slipper Limpet
A sedentary species living individually on stones and shells
or in clusters, on the lower shore and sub-littorally. It was
introduced into Essex waters with imported American oysters in
about 1880-1890 (Cole, 1897) and was considered to be rare at
the beginning of the century. By 1915 the species became so
abundant as to be considered an oyster pest (Cole, 1915). The
spread of Crepidula to other parts of the British coast has been
recorded by Robson (1915). In recent years the species has been
abundant in the Blackwater seawards of Northey Island and also
in the Colne. The greatest density of population occurs along the
south side of the Blackwater between Thirslet and Pewet Island,
with numbers of up to 2,000 animals per m2 recorded from some
samples. Breeding takes place from April to September and shows
some lunar periodicity; the times of maximum spawning being at,
or immediately after, neap tides (Chipperfield, 1951). After about
36 days of planktonic larval life settlement and metamorphosis to
the adult form occurs. There have been good and poor spatfall
years, 1960 and 1964 being the best in recent years.
Naticidae
Natica catena (da Costa)
Shells are occasionally found on the shores at the seaward end
of the Blackwater. Freshly vacated shells and shells of bivalves,