LAUSR

Brooding is known for at least 57 species within Actiniaria, making it a rare phenomenon among the approximately 1100 described species in the order. Within the order, brooders are known from taxonomically disparate groups in both suborders (Anenthemonae and Enthemonae) and all superfamilies except for Actinernoidea. Two-thirds of brooders do so internally and have a pan-latitudinal distribution whereas external brooders show a disproportionate diversity in the poles, particularly in the Southern Ocean. Here, we describe Halcampulactidae fam. nov., a new family of burrowing sea anemones from Antarctica characterized by a novel combination of morphological features: twelve mesenteries (eight macrocnemes and four microcnemes) and invaginations of the oral disc similar to glandular sacs of Oractiidae Riemann-Zürneck (Polar Biol 23:604–608, 2000) hypothesized to brood offspring. Halcampulactidae fam. nov. is the first endemic family from Antarctica and Halcampulactis solimar sp. nov. is the 11th species of sea anemone with parental care recorded from Antarctica; it is also the first burrowing anemone with external brooding from the Southern Ocean, representing the second instance of external brooding on the oral disc within the order Actiniaria. In addition, we use molecular evidence to establish the phylogenetic position of the new family within the order; Halcampulactidae fam. nov. is the first burrowing family within the superfamily Actinostoloidea. We discuss the evolution of external brooding within the superfamily in light of these new findings.