Limulus is a xiphosuran chelicerate, the sister group to arachnids.
Transcriptomes and genome assemblies were critical for identifying the full repertoire of Limulus opsins and for providing new information about opsin gene duplication and loss in the xiphosuran lineage.
Other paralogous pairs may be products of a whole-genome duplication that is proposed to have occurred early in the xiphosuran lineage (Nossa et al., 2014; Kenny et al., 2015).
This is consistent with the idea that a whole-genome duplication followed by opsin gene loss occurred early in the xiphosuran lineage before the species split from one another an estimated 130-150 million years ago (Obst et al., 2012).
It has subsequently been demonstrated that Maldybulakia most likely represents remains of an aquatic xiphosuran
(Anderson et al.
Currently, 96 xiphosuran species can be recognized, although revisions of Pennsylvanian genera (Anderson 1994, 1997) resulted in quite dramatic reductions in overall diversity.
The xiphosuran Liomesaspis from the Montceau-les-Mines Konservatt-Lagerstatte, Massif Central, France.
Chasmataspidida.--These little-known late Cambrian-mid Devonian marine euchelicerates are characterized by a long postabdomen of nine segments, but share prosomal features with both eurypterids and xiphosurans, rendering their monophyly and affinities uncertain.
Xiphosurans from the Westphalian D of the Radstock Basin, Somerset Coalfield, the South Wales Coalfield and Mazon Creek, Illinois.
(2016) data set already contained opsin sequences from several arachnids as well as those identified from the genomes of three xiphosuran horseshoe crabs for comparison.
Although opsin genes from this clade have been identified from several xiphosuran horseshoe crab species (Battelle et al., 2016), this is the first characterization of a middle-wavelength-sensitive (MWS) opsin from a spider.
Many groups of marine invertebrates (e.g., annelids, bryozoans, cnidarians, crustaceans, mollusks, polychaetes, poriferans etc.) are recognized as epizoans on a wide variety of other mobile and sessile invertebrates, mainly crustaceans, xiphosurans
and mollusks (see Mori & Manconi, 1990; Gili, Abello, & Villanueva, 1993; Key, Jeffries, Voris, & Yang, 1996; Villegas, Stotz, & Laudien, 2005; Fernandez-Leborans, 2010; Farrapeira & Calado, 2010; Lima, Queiroz, Bravo de Laguna, & Mioso, 2014; Lima, Queiroz, Oliveira, Christoffersen, & Guimaraes, 2016; Machado et al., 2013; Romero et al., 2013).