Deficient Merlia normani Kirkpatrick, 1908, from the Curaçao reefs, with a discussion on the phylogenetic interpretation of sclerosponges

A specimen of the sclerosponge Merlia lacking a basal skeleton of calcareous chambers (corresponding to the description of Merlia deficiens Vacelet, 1980) is reported from the underside of the coral Agaricia at a depth of 10 m on the reef of Curaçao, Netherlands Antilles. Its spiculation is identical to Merlia normani Kirkpatrick, 1908 specimens with the basal skeleton, from which it is concluded that M. deficiens and M. normani are probably conspecific. The phylogenetic significance of a sclerosponge with an unstable calcareous skeleton is discussed and in accordance with Vacelet (in press) it is postulated that sclerosponges are polyphyletic. It is suggested that sclerosponge skeletons are an ancestral character for a large part of the Demospongiae. The relationships of Demospongiae and Calcarea are discussed in the same light.