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New Zealand Coelenterates Ctenophores from Cook Strait

Order Cestida

Order Cestida

Cestum veneris Lesueur, 1813.

On five occasions during prolonged calm weather, specimens of this ctenophore were seen. Specimens were taken on March 9th from water 15.5°C. and on May 13th from water 12.25°C. and on this later date the species was plentiful, page 10 almost sufficient to be called a swarm. They were mostly between 100 and 200 mm. long. The specimens taken were sketched in the living condition and were found on comparison with figures given by Mayer (1912) and Chun (1880) to be identical with C. veneris. All specimens were colourless and were smaller than those recorded by Mayer. The largest New Zealand specimen taken was about 350 mm. long and the smallest 10 mm., whereas Mayer records a size range between 800 and 1500 mm.

Discussion

Cestum is predominantly a warm water ctenophore, (Mayer, 1912) although it has been recorded from the White Sea (Wagner, 1885). Mayer and Mortensen (1912) consider that the specimens described by Wagner were swept northward along the Norwegian coast by the Gulf Stream Drift. The South Equatorial current may have been responsible for the presence of C. veneris in New Zealand waters, but it has no reputation like the Gulf Stream in this respect. Moreover in latitude 41° S., a water temperature of 12.25°C. does not indicate a warm current. We suggest that they have not been reported from the temperate regions for two reasons, viz: the necessary calm periods with brilliant sunshine for collection are not of sufficient duration; and secondly, that C. veneris is not readily netted but must be sighted and then collected by a method of dipping.