The first modern solitary Agariciidae (Anthozoa, Scleractinia) revealed by molecular and microstructural analysis

Dactylotrochus cervicornis (= Tridacophyllia cervicornisMoseley, 1881), which occurs in Indo-Pacific waters between 73 and 852m,was originally described as an astraeid butwas later transferred to theCaryophylliidae.Assumed to be solitary, this species has no stolons and only one elongated fossa, and is unique among azooxanthellate scleractinians in often displaying extremely long thecal extensions that are septate and digitiform. Based on both molecular phylogenetic analyses (partialmitochondrial CO1and16S rDNA, andpartial nuclear 28S rDNA) andmorphological characteristics,wepropose the transfer of D. cervicornis from the Caryophylliidae to the Agariciidae, making it the first extant representative of the latter family that is solitary and from deep water (azooxanthellate). The basal position of D. cervicornis within the agariciids implied by our analyses strengthens the case for inclusion of fossil species that were solitary, such as Trochoseris, in this family and suggests that the ancestor of this scleractinian family, extant members of which are predominantly colonial and zooxanthellate, may have been solitary and azooxanthellate. Received 21 December 2011, accepted 30 April 2012, published online 21 September 2012