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DescriptionLeptasterias muelleri is a small spiny starfish commonly 6 cm in diameter but may reach up to 20 cm. It has five medium length arms that are broad at the base, taper towards the tip and are clearly marked from the small disc. This species has four rows of tube feet with sucking discs. It may be pink, violet or green in colouration with pale arm tips. Green morphs obtain they're colour through the presence of single-celled algae within the starfish upper tissues. Green individuals are invariably found on the shore and shallow sublittoral.
The upper surface is covered by regular, longitudinally arranged spines, which increase in irregularity in larger specimens. The spines are distinctly knob-shaped, especially on the mid-dorsal line (Mortensen, 1927). The spaces between the spines are occupied by single papulae (soft projections of respiratory function). Small pedicellariae cluster around the spines and are straight around the ambulacral furrows. This species may have one or two rows of ambulacral spines present on its ventral surface and two regular rows of spines along the side of the arms.
Leptasterias muelleri breeds during March-April and the mother does not feed during this time. She puts her arms together and raises her back which provides a protective space to place her eggs. There is no larval stage as the embryos develop and leave the mother after the first 3 pairs of tube feet have appeared.
This speceis may be mistaken for small individuals of Marthasterias glacialis or Asterias rubens. However, it is distinguished from Asterias rubens by densely packed spines and a single papulae, in the spaces between the spines, on its upper surface.