Stegnaster inflatus
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| Stegnaster inflatus Hutton, 1872 |
Stegnaster inflatus, or the New Zealand cushion star, is a sea star of the family Echinasteridae, endemic to New Zealand. It is found under rocks around the low-tide mark, from Banks Peninsula northward. Armspread is up to 90 mm.
Stegnaster inflatus' shape is an almost perfect pentagon - the sides between the points of the arms are almost straight. Its colour is quite variable, from pale orange blotched with red and black, bright purple or cream daubed with red, blue, green or brown. This predator moves by using its rows of tube feet in the radiating grooves on the underside. Individual feet are extended, attached, and shortened, pulling the animal along. Although the feet step in one direction, there is no regular sequence of movement of adjacent feet.
Stegnaster inflatus' method of capturing prey is most interesting. It arches its body above the rock surface creating what appears to be a "cave" and when a small fish, crustacean or mollusc investigates the inviting crevice the sea star immediately flattens its body, trapping the prey. As soon as the prey is trapped the sea star's stomach is inverted, pressed against the soft parts of the victim and digestion starts. When the prey is reduced to a broth it is drawn into the body with the stomach. Any hard parts are disgorged later. Other common names for this species are ambush star and elevated cushion star, which both allude to its prey capture method.
[edit] References
- Miller M & Batt G, Reef and Beach Life of New Zealand, William Collins (New Zealand) Ltd, Auckland, New Zealand 1973
- NIWA
- SeaFriends
