Amphiura filiformis Müller, 1776, Scandinavia, probably southern Norway.
OTHER COMMON NAMES None known.
Disk up to 0.39 in (10 mm) in diameter, reddish gray in color, with very long fine arms. The dorsal side is covered with fine scales but the underside is bare.
Northeastern Atlantic from Iceland and western Norway to the Iberian peninsula; Mediterranean.
Buries itself in fine muddy silt or sand at depths of 15-3,600 ft (5-1,200 m). Very common in the North Sea; populations may be as dense as 4,000 individuals per 10.8 ft2(1 m2).
When Amphiura is burrowing, it uses its tube feet to move material away from itself and virtually sinks into the substrate.
The animal then uses wavelike movements of its arms and digging movements of the tube feet to hollow out a burrow lined with mucus and equipped with channels to the surface of the sediment. For ventilation, it waves one or more of its arms to allow oxygen-rich water to enter the burrow. Amphiura filiformis is selectively pursued by some flatfishes like dab (Li-manda limanda) and frequently sheds its arms when attacked. It is able to sense the presence of predators attacking other members of its species in the surrounding water and will then pull its arms back into the burrow.
Amphiura filiformis is primarily a passive suspension feeder that collects small organic particles on its long sticky tube feet, which are covered with numerous papillae. In moving water, it raises its arms about an inch (2.5 cm) above the seafloor. The particles that it collects are packed together with mucus into a bolus (soft rounded mass) and carried along its arm to its mouth beneath the sediment surface. This species may also collect particles from the surface of the sediment or feed on larger dead organisms.
Amphiura filiformis has separate sexes and a seasonal developmental pattern with a spawning period that extends from late spring to late summer. When spawning, it emerges from its burrow and uses its arms to lift its disk about 0.39 in (1 cm) above the bottom. Its life history includes an ophiopluteus larva.
CONSERVATION STATUS Not listed by the IUCN.
SIGNIFICANCE TO HUMANS None known. ♦
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