The genus setaphyes (kinorhyncha, pycnophyidae) in european waters: Redescription of Setaphyes dentatus ( ) and Setaphyes kielensis ( ), including notes on morphometrics, sexually dimorphic features and reproduction of the genus

Abstract

Six of the eight species of the genus Setaphyes have been described from Europe. In the present contribution, the European Setaphyes species are revised and two of them, S. dentatus (Reinhard, 1881) and S. kielensis (Zelinka, 1928), are redescribed following the current approaches of Kinorhyncha taxonomy. For this purpose, material from 17 localities throughout the Atlantic Ocean and the Mediterranean and Black Seas was investigated. The redescriptions of two of the most common pycnophyid species in Europe include detailed information on intraspecific variation among populations. Setaphyes dentatus is characterized by the presence of middorsal elevations on segments 2–6, and middorsal processes on segments 1, 7–9, unpaired paradorsal setae on segments 2–9; laterodorsal setae on segments 3, 5 and 7; ventromedial setae on segments 4–5, 7–8 in males and 3–5, 7–9 in females; anterior cuticular, reticulate ridges on the tergal plate of segment 1 and conspicuous patch of laterodorsal and ventrolateral longitudinal, cuticular ridges on segment 10. Setaphyes kielensis is characterized by middorsal elevations on segments 1–9; paired paradorsal setae on segments 2–9 (unpaired on segment 8); laterodorsal setae on segments 2–9; ventromedial setae on segments 3–9. Furthermore, morphometric features of the European Setaphyes are analysed. Specifically, the morphometric analyses revealed sex-specific variability in the LTS/TL proportion, with females of all the European species of Setaphyes showing smaller LTS/TL. Thus, the LTS/TL ratio unveils a conspicuous sexual dimorphism in the genus.