Short note on the occurrence of Cumacea in the surface plankton collected at "Texel" lightship in the Southern North Sea

From mid-January 1961 until the end of 1966 macroplankton was collected in the surface water of the North Sea around "Texel" lightship (position: 53°01'3o"N 04°22'E). As pointed out in a recent paper on decapod larvae (Van der Baan, Holthuis & Schrieken, 1972) the plankton nets were originally intended for collecting elvers and medusae, and the numbers of smaller species obtained, such as larvae and also Cumacea, was greatly influenced by incidental circumstances. Therefore no great significance can be attached to the actual numbers of these smaller animals. Cumacea are mostly bottom-dwelling species, and cannot regularly be expected in surface waters. Still, four species were found in our samples viz.: Diastylis bradyi Norman, 1879 Iphinoe trispinosa (Goodsir, 1843) Pseudocuma similis G.O. Sars, 1900 Bodotria scorpioides (Montagu, 1804) The last two species are very small. They were only held back by the nets in a very few cases, when the meshes got clogged by great quantities of algae or various animal species. According to Zimmer all the above species belong to those Cumacea which are found throughout the North Sea (Zimmer, 1933: 11o) and also to the species which, by vertical migration, can be found at the surface at night, especially during the reproductive periods. The only specimen of Bodotria scorpioides was caught in the evening, in a flood haul. Of the 15 hauls in which Pseudocuma similis occurred, 3 were made by day, the others completely or partly during the dark hours;