New Zealand Common Cushion Star

Patiriella regularis is a spinulosan asterinid with a pentagonal shape. It typically has five short arms, however, 2% of the population is composed of individuals with 4, 6, 7 or 8 arms. It has an arm spread of up to 60 mm (2.4 in). The colour of Patiriella regularis differs greatly between individuals and includes blues, greens and browns as the more common colours, although oranges, reds and individuals with mottled forms have also been identified.

Two separate forms of Patiriella regularis have been identified. The most significant difference between the two is the plate arrangement along the ray crests. They typically grow up to 10 cm (3.9 in) across in diameter, although their sizes vary greatly within the species.

Although native to New Zealand, Patiriella regularis has also spread to Southern Australia and Tasmania. This spread is likely due to mussel exports in the 19th century. Establishing populations in Tasmania are bordering on becoming labelled an invasive species due to their effects on the native fauna in those habitats.

Patiriella regularis is an omnivore that predominantly feeds on crustose coralline algae and microorganisms. It can act as a detritivore and consume dead flesh of other organisms. Carrion is an important part of the diet of this asteroid and is linked to increased growth rates and reproduction. Common prey includes sponges, annelids, gastropods, bivalves, crustaceans and ascidians. Patiriella regularis regularly competes with other organisms such as whelk over shared resources, specifically mussel flesh. This starfish can prey on small organisms such as gastropods and can also feed on the Elminius modestus barnacle. Diet and energy intake is key to population survival, with a direct link between well fed populations and increased growth rate and gonad activity.

Patiriella regularis follows an annual reproductive cycle. They reproduce asexually by fission and also sexually, with males and females releasing eggs and sperm into the water for external fertilisation. Reproductive success in Patiriella regularis is dependent on environmental conditions that are the most favourable for success of the offspring, for example the abundance of food within the habitat. Where food abundances are low, the stored food reserves in the pyloric caeca of the asterinid will also be low, resulting in poor gonad development.