4. Priapulida

The oldest known priapulid‐like scalidophoran animal and its implications for the early evolution of cycloneuralians and ecdysozoans

“…Similarities with adult priapulids include an annulated trunk with a spacious body cavity, a heavily armed introvert with regularly arranged scalids, circlet(s) of anteriorly directed coronal scalid, and an inversible pharynx with circlets of teeth. Structures similar to and probably homologous with anteriorly directed coronal scalids on an everted introvert are present in extant loriciferans (known as clavoscalids) and many priapulids including Maccabeus and Meiopriapulus (Por and Bromley 1974;Morse 1981;Wills et al 2012;Schmidt-Rhaesa 2013). Thus, the E. sphinx specimen described here likely represents a post-embryonic animal capable of locomotion and possibly predation.…”

“…Scalids and pharyngeal teeth of living priapulids are arranged in a pentaradial pattern: scalids are arranged in 25 longitudinal rows and teeth in nested pentagons (Adrianov and Malakhov 2001;Schmidt-Rhaesa 2013). Interestingly, a hexaradial armature arrangement is also apparent in the introvert of nematomorph larvae and the nematode Kinonchulus (Nielsen 2001;Maas et al 2007b;Schmidt-Rhaesa 2013). E. sphinx, however, has a hexaradial symmetry, with 18 longitudinal rows of introvert scalids, an estimated 12 coronal scalids (arranged in one or two circlets), and a basal row of 18 pharyngeal teeth.…”

“…This pattern has been used to guide the interpretation of many Cambrian scalidophorans, although it has been confirmed in very few taxa (Donoghue et al 2006b;Maas et al 2007b). Even in kinorhynchs and loriciferans, there is a component of hexaradiality superimposed on the overall pentaradial pattern: the mouth cone has nine outer oral styles in kinorhynchs and six eversible styles in some loriciferans (Gad 2005a(Gad , 2005b(Gad , 2005cSørensen et al 2012;Schmidt-Rhaesa 2013). Interestingly, a hexaradial armature arrangement is also apparent in the introvert of nematomorph larvae and the nematode Kinonchulus (Nielsen 2001;Maas et al 2007b;Schmidt-Rhaesa 2013).…”

“…It is possible that some of the features E. sphinx shares with scalidophorans are cycloneuralian plesiomorphies. For example, an armed introvert may be an apomorphy of the cycloneuralians (but see Schmidt-Rhaesa 1998), as the parasitic larvae of nematomorphs have an armed introvert although their adults do not, and the nematode Kinonchulus has an armed introvert although most nematodes do not (Nielsen 2001;Maas et al 2007b;Schmidt-Rhaesa 2013). Indeed, Conway Morris and Peel (2010) hinted at the interesting possibility that a priapulan introvert might be plesiomorphic to the ecdysozoan clade.…”

“…With fewer than 20 known species, extant priapulids (penis worms) represent a relatively small phylum within the clade of ecdysozoans Rota-Stabelli et al 2013). They are worm-like animals with a proboscis, a trunk, sometimes a neck in between, and a pair of caudal appendages in some taxa (Schmidt-Rhaesa 2013). Phylogenetic analyses based on morphological characters have shown that priapulids are members of the scalidophorans, which together with nematoids form the cycloneuralians and a sister group to the panarthropods (Ahlrichs 1995;Schmidt-Rhaesa et al 1998;Lemburg 1999;Ax 2001;Nielsen 2001;Dong et al 2004Dong et al , 2005Dong et al , 2010Maas et al 2007a;Harvey et al 2010), although several molecular phylogenetic analyses place panarthropods within paraphyletic cycloneuralians (Garey 2001;Mallatt and Giribet 2006;Park et al 2006;Sørensen et al 2008;Rota-Stabelli et al 2011.…”