Members of the genus are characterised by having long arms with pointed tips fringed with spines. Their upper surfaces are covered with
paxillae, pillar-like spines with flattened summits covered with minute spinules. The upper marginal plates are replaced by paxillae, but the lower marginal plates are large and covered with paxillae. The
tube feet do not have suckers, but have two swollen regions. A mouth, oesophagus, and cardiac stomach are seen, but no pyloric stomach or anus is present. The
gonads are underneath the sides of each arm. The early
larval stages of starfish are known as
bipinnarial larvae, and members of this genus do not continue their development after this stage into a brachiolar stage before undergoing
metamorphosis. However, they are capable of larval
cloning, with
asexual reproduction taking place while they are larvae. This has been shown to take place both in the field and in laboratory cultures and has been studied by molecular analysis of
sequences of mitochondrial
tRNA to identify the
taxa involved. ==Species==