Stegnaster inflatus
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| ( Hutton , 1872) |
Stegnaster inflatus is a starfish from the family Asterinidae in the order of the valve stars (Valvatida), whichis nativeto the coasts of New Zealand . He forms a kind of tent with his arms, into which some animals crawl in search of shelter. At the right moment the starfish drops and devours the prey, mostly small crabs .
features
Stegnaster inflatus has the shape of an almost "ideal" pentagon with only very few concave lines between the five arm tips. The edge of the starfish is thin, the center and the radial center lines running from here to the tips of the arms are raised. The radius to the tips of the arms is approximately 3.6 cm to 5.7 cm, and to the areas between the arms it is approximately 2.8 cm to 5.0 cm. The top is dull cream to light brown in color, with red, orange, pink, yellow or olive green coloring also occurring. The lime slabs on the top are arranged like roof tiles. They are heavily lobed and notched along the radial center lines. The suction feet on the underside are in two rows.
Reproduction
Stegnaster inflatus has relatively large eggs, about 0.4 mm to 1 mm in size, which are released into the open water through gonopores on the upper side of the female and are fertilized there. In contrast to species in the genus Asterina , there is apparently a development via a free-swimming Bipinnaria larva that later metamorphosed into a starfish in the Brachiolaria stage .
Distribution and occurrence
Stegnaster inflatus is only found on the coasts of New Zealand . Here it is mainly to be found in relatively shallow water down to a depth of about 35 m. During the day he prefers to stay under rock ledges and in crevices below the intertidal zone.
nutrition
Stegnaster inflatus feeds mainly on amphipods and decapods , with porcelain crabs ( Petrolisthes elongatus ) being the main prey. It has also been observed catching and eating small shrimp ( Leander affinis ) and fish (about 3 cm large Rhombosolea plebeia ). The starfish holds itself in a "waiting position" in which only the five tips of its arms touch the ground and the rest of the pentagon is raised like a tent. If a small animal - often looking for shelter - gets under the starfish, it lowers its edge in less than a second and presses it onto the ground. The cavity under the starfish is getting smaller and smaller, pushing the victim towards the mouth opening. About 10 minutes after catching, the stomach is everted. Smaller prey is immediately drawn into the starfish's stomach with the stomach, while larger prey is digested extraintestinally and only then sucked in.
literature
- Helen ES Clark, Donald George McKnight: The marine fauna of New Zealand. Echinodermata, Asteroidea (sea stars), Order Valvatida . National Institute of Water and Atmospheric Research (NIWA), New Zealand, 2001. Stegnaster inflatus (Hutton 1872), p. 162.
- Roger V. Grace: Feeding behavior of Stegnaster inflatus Hutton (Class: Asteroidea, Familiy: Asterinidae) . Tane 20, 1974.
- Maria Byrne: Life history diversity and evolution in the Asterinidae . In: Integrative and Comparative Biology . 2006, pp. 1-12. doi : 10.1093 / icb / icj033 .
Web links
- Roger V. Grace: Critter of the Week: Stegnaster inflatus . NIWA, New Zealand.