Evolution of cave A xiokebuita and S peleobregma ( S calibregmatidae, A nnelida)

The evolutionary history of A xiokebuita and S peleobregma, two poorly known lineages of annelids exclusive from deep‐sea or marine caves but always from crevicular habitats, is explored here. S peleobregma lanzaroteum Bertelsen, 1986, and A xiokebuita cavernicola sp. n. are described from anchialine and marine caves of the C anary Islands using light and electron microscopy. S peleobregma lanzaroteum is previously known only from a single specimen from the water column of an anchialine cave in L anzarote. Emended diagnosis, details on the ciliary patterns and behavioural observations are provided based on newly collected material and in situ observations. A xiokebuita cavernicola sp. n. is found in Pleistocene gravel deposits in a shallow water marine cave in T enerife ( C anary I slands). The new species is characterized by the presence of dorsal ciliary bands and short knob‐like neuropodial cirri from segment two. The porosity and permeability of the gravelly environment of A .  cavernicola sp. n. are shown to be equivalent to the water column or crevices of S peleobregma and other A xiokebuita spp. P hylogenetic analyses of five gene fragments and 44 terminals using maximum‐likelihood and B ayesian methods support a derived position of A . cavernicola sp. n. within A xiokebuita and confirm a sister‐group relationship of A xiokebuita with S peleobregma with high nodal support. The A xiokebuita– S peleobregma clade is morphologically characterized by a globular pygidium with adhesive glands and ventral ungrooved ciliated palps. Our results support two independent cave colonization events, favoured by the preadaptation of the members of A xiokebuita– S peleobregma lineage to crevicular habitats.