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THE ESSEX NATURALIST
OITHONIDAE
Oithona helgolandica Clavis
Rare. Recorded from a plankton sample taken at the Barrier
Wall in December 1962.
LICHOMOLGIDAE
Mytilicola intestinalis Steuer
A common intestinal parasite of Mytilus edulis but also infect-
ing oysters. An investigation carried out on the shores of the
Blackwater and Colne Estuaries in 1964 showed the parasite to
be common and widespread in the Mytilus population.
NOTODELPHYIDAE
Notodelphys allmani Thorell
Frequently found as a commensal with the ascidians,
Ascidiella and Ascidia, mostly being attached to the walls of the
pharynx.
Doropygidae
Ascidicola rosea Thorell
Found with the last mentioned as a commensal with Ascidiella
and Ascidia.
Lernaeidae
Lernaeenicus sprattae (Sowerby)
An external parasite of the Sprat; mostly found attached to
the eye. Commonly occurring in Sprat shoals in the winters of
1963 and 1964. See also Harding & Wheeler (1958).
Lernaeenicus encrasicola (Turton)
Another external parasite of the Sprat but found on parts of
the body other than the eyes. Commonly occurring in 1963 and
1964 with the last mentioned. See also Harding & Wheeler (1958).
Class CIRRIPEDIA
Order Thoracica
Balanidae
Balanus crenatus Brugiere
Very common in the Blackwater and Colne estuaries and off-
shore. Mostly occurring below low water mark on shelly and
stony bottoms but also on the lower shore. Highest population
density recorded from a shelly bottom was 6,000/m2 at station
TL.4 (11.5.1960). The species is also recorded as a fouling
organisms on anchored ships and in Bradwell Power Station water
intake culverts.
Balanus perforatus Brugiere
Of rare occurrence in the bottom fauna.