First observation of the marine tardigrades Batillipes mirus and Batillipes noerrevangi (Arthrotardigrada, Batillipedidae) from a strongly brackish part of the Polish Baltic Sea coast

Abstract

The tardigrade fauna of Poland is one of the better known in Europe. However, almost all studies have been carried out on the limno-terrestrial species, while marine Tardigrada have been neglected. To the best of our knowledge only one report on marine Tardigrada for Polish waters has been published up to now. In the present study the first records of two marine arthrotardigrade species, Batillipes mirus and Batillipes noerrevangi, from Puck Bay (Baltic Sea) are reported. The lowest salinity value in the study area was 3–4 PSU, and B. noerrevangi should be considered the most brackish water-tolerant arthrotardigrade. Samples were collected from the vegetated seabed (seagrass and macrophytes) and the bare sandy bottom in different seasons. A single specimen of B. mirus was found only during the autumn campaign. Specimens (adults and larval stages) of B. noerrevangi were found in all samples during spring, summer and autumn campaigns. Additionally, morphometric data with detailed microphotographs of B. noerrevangi (PCM, DIC) and B. mirus (PCM) as well as a discussion of the new records are presented. The validity of the occurrence of B. dicrocercus in Poland, which was determined based on a single larva from the Międzyzdroje area by Hummon, is also discussed. The larva from Międzyzdroje should be regarded as an undetermined species; thus, the marine tardigrade fauna from Poland consists of only the two newly recorded species.