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Abstract. In the first decisive study of color-change in brittlestars, four Caribbean species, Ophiocoma echinata, 0. paucigranulata, O. pumila, and O. wendti are reported to change color from day to night. Color-change is most striking in O. wendti, which is dark brown during the day, and is banded gray and black from dusk to dawn. The transformation occurs over a 3 to 4 hour period and is effected by chromatorphores which appear to respond to illumination, independently of the central nervous system. Color-change may also be mediated by an endogenous rhythm. Ophiocoma wendti is more responsive to light than the other 3 species tested. It reacts to lower levels of illumination at night than during the day, exhibiting negative phototaxis in moonlight as well as in sunlight. I suggest that color-change may expose (or shield) photosensitive tissues that control the brittlestar's detection of shaded fissures in the reef. Thereby, chromatophore activity may be connected with the brittlestar's chief defense from predators, the ability to detect shadow and escape into darkened crevices. Although experiments to date with predacious fish are equivocal. the color patterns of Ophiocoma species mav provide protective camouflage. 相似文献
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Abstract. The relationship between a sponge, Callyspongia vaginalis, and an associated brittlestar, Ophiothrix lineata, was examined for mutualistic symbiotic interaction. Cinematography, feeding experiments, and analyses of stomach contents reveal that O. lineata (unlike other Ophiothrix species) is a non-selective deposit feeder. Its diet consists of detrital particles adhering to the sponge, which are too large to be utilized by the sponge as food. Thus, the brittlestar cleans the inhalent surface of the sponge as it feeds. Since siltation interferes with sponge pumping-activity, it is suggested that the cleaning behavior of O. lineata may enhance the filtration capability of C. vaginalis. In situ elapsed-time films show that brittlestars expose their arms when they feed, suggesting that they feed only at night because of a need to avoid diurnal predators. Manipulative experiments show that residence in C. vaginalis protects O. lineata from predatory fish. A comparison of the incidence of arm regeneration for brittlestars residing on C. vaginalis, and on a toxic sponge, Neofibularia nolitangere, indicates that factors other than sponge toxicity are involved in protecting sponge-dwelling brittlestars. 相似文献
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