Abstract
Selected sea spider specimens of Antarctic Colossendeis species collected during the Italica XIX cruise and the Polarstern cruise ANT XXIII/8 were examined to provide new information about the external and internal anatomy of the basal parts of the palps and ovigers. The presence and insertion of the muscle bands, as well as the arthrodial membrane are illustrated and discussed. The results obtained in this study show that the basal parts of the palps and ovigers have a similar internal structure. This is in agreement with the currently established 10-articled status for the ovigers (the basal element is not considered an article). Despite the currently established 10-articled status for the palps, our results suggest that the palp should be considered as being 9-articled.
Highlights
The pycnogonids or sea spiders are a monophyletic group; they are defined by autapomorphies such as the prominent proboscis, an extremely reduced abdomen, and the presence of a ventral pair of appendages on the cephalon [1]
The material examined for this study was identified as Colossendeis megalonyx Hoek, 1881, C. australis Hodgson, 1907, C. tortipalpis Gordon, 1932, C. scotti Calman, 1915, and C. glacialis Hodgson, 1907
The cuticular gross structure of palpal and ovigeral basal parts examined for the present study is similar
Summary
The pycnogonids or sea spiders are a monophyletic group; they are defined by autapomorphies such as the prominent proboscis, an extremely reduced abdomen, and the presence of a ventral pair of appendages (ovigers) on the cephalon [1]. This group contains more than 1300 described species [2], of which more than 260 are Antarctic and Subantarctic species [3]. Some contributions based on molecular data suggested that the Austrodecidae (the only family included in Stiripasterida) is the basal-most group, being the sister group of the remaining extant families (all them in Eupantopodida) [2, 5]. Chelifores, palps, and ovigers, show a wide range of variation in number of articles and other external features, and this structural and ornamental variability seems to be valid even within some genera and among ontogenetic stages [6]
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