Dwarf brittle star

Amphipholis squamata

ORDER

Ophiurida

FAMILY

Amphiuridae

TAXONOMY

Amphipholis squamata Delle Chiaje, 1828, Mediterranean, Naples, Italy.

OTHER COMMON NAMES

English: Scaly brittle star, long-armed brittle star; French: Ophiure ecailleuse; German: Schuppiger Schlangenstern; Norwegian: Overgslangestjerne.

PHYSICAL CHARACTERISTICS

The disk is very small, attaining a maximum diameter of only 0.19 in (5 mm); it is bluish or gray in color, circular in shape, and covered with scales. The arms are relatively short and thin. The radial plates are half-moon shaped and conspicuous. Dwarf brittle stars come in a range of colors from orange, dark brown or beige to black and gray. Previously these color varieties were thought to belong to sibling species, but genetic analyses do not support this hypothesis.

DISTRIBUTION

Amphipholis squamata has a world-wide distribution; it is found in all oceans of the world, including subarctic and subantarctic waters. This pattern of distribution is interesting; one would expect the organism to be restricted to certain regions since it is a brooder and supposedly a poor disperser. Genetic analyses indicate, however, that sporadic long-distance dispersal does in fact occur, probably through passive transport (drifting or rafting on macroalgae).

HABITAT

Dwarf brittle stars are found in the mid- and lower littoral zones among algae, bryozoans, and similar organisms; and sub-littorally in waters several hundred meters deep. These brittle stars live mainly under stones but also on sandy surfaces.

BEHAVIOR

Amphipholis squamatais a good climber that also uses its tube feet when it moves. The arms are extremely flexible in a verti

cal direction. If the brittle star is dislodged from its substrate, it coils its arms over its disk and sinks rapidly to the bottom, probably to avoid being exposed to predators. When disturbed it produces light that appears as spots along each arm. Its bioluminescence is attributed to specific photocytes under the control of ganglia, or groups of nerve cells.

FEEDING ECOLOGY AND DIET

Amphipholis squamata feeds on deposits left on sediment and particles suspended in the water. It uses its tube feet to wipe off particles from its sticky spines. The stomach content includes a variety of such items as unicellular algae, small gastropods, foraminiferans and amphipod limbs. Amphipholis has sometimes been observed to feed on dead fish. It can absorb dissolved free amino acids from sea water, primarily through symbiosis with bacteria living under its cuticle.

REPRODUCTIVE BIOLOGY

The dwarf brittle star is a simultaneous hermaphroditic viviparous brooder that can brood several embryos at different stages of development in each bursa at the same time. The eggs are small (0.0039 in or 100 pm), which suggests that the larvae must obtain nutrition from the parent within the bursae. Breeding occurs throughout the year. It has also been shown in the laboratory that Amphipholis can reproduce in isolation. This finding suggests that it can reproduce by self-fertilization or possibly by parthenogenesis.

CONSERVATION STATUS Not listed by the IUCN.

SIGNIFICANCE TO HUMANS None known. ♦

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