Abstract
Ophiuroidea is the largest class among extant echinoderms, with over 2000 described species assigned to 33 families. Here, the first identification key to the recently revised classification was developed, and revised morphological descriptions were derived from it, expanding the previous short diagnoses. The key was built by analyzing internal and external skeletal characters of predominantly the type species of each family, including at least two mutually exclusive attributes per family. Various numeric and multistate characters were used to create a traditional as well as an interactive key using the DELTA and Xper software programs. Illustrations (SEM and digital photos) are included in the key to facilitate the assessment of character states by users. Not only is it the first identification key to the families, according to the recently proposed new classification and the examined species, but this interactive key also assists users in understanding the family level taxonomy of brittle stars. The interactive key allows new characters and states to be added, when more species will have been analyzed, without the need to reconfigure the complete key (as may be necessary with conventional keys).
Highlights
Ophiuroidea Gray, 1840 is one of the most diverse classes among extant echinoderms (Stöhr et al 2012), currently including 2096 species (Stöhr et al 2020)
Characters were collected by examining images in publications (Smith et al 1995; Pomory 2007; Gondim et al 2013), preserved specimens collected in the Persian Gulf and in the museum collections of the Royal Belgian Institute of Natural Sciences (RBINS), as well as examining scanning electron microscope images (SEM) and 3D images of museum specimens of the Swedish Museum of Natural History (SMNH) and RBINS
The interactive keys are available as a DELTA file package and as an Xper3 online application
Summary
Ophiuroidea Gray, 1840 is one of the most diverse classes among extant echinoderms (Stöhr et al 2012), currently including 2096 species (Stöhr et al 2020). Matsumoto (1915, 1917) suggested the first comprehensive classification for the whole class, separating it into two subclasses, Myophiuroida Matsumoto, 1915, which possesses ventral arm plates that cover the ambulacral groove, and Oeogophiuroida Matsumoto, 1915, which lacks ventral arm plates He divided the former into four different orders, Phrynophiurina Matsumoto, 1915, Laemophuirina Matsumoto, 1915, Chilophiurina Matsumoto, 1915, Gnathophiurina Matsumoto, 1915, and 13 families. Matsumoto’s (1915, 1917) classification was not universally accepted though, and Mortensen (1927) instead proposed two orders, Euryalae and Ophiurae, based on the articular structures of the vertebrae (streptospondylous vs zygospondylous) He provided the first traditional dichotomous identification key for 12 families but it was restricted to the British Isles. Interactive keys have been created for many other taxa though, e.g, for Australian aquatic invertebrates using the software LUCID (Lucidcentral 2012), and for various plants and animals using DELTA (Dallwitz 2019), but none includes echinoderms
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