change color at the same time as whole brittlestars and severed arms. His results
showed that the day-night color change involves a replacement of brown shades by
gray and black. Individuals of all four species change color in the late afternoon.
Experimental evidence demonstrated that transformation occurs over a period of
three to four hours and it is effected by chromatophores. Furthermore, as seen with
the separated body parts, they appear to respond to light independently of the
nervous central system.
During the day O. paucigranulata was brownish-black. At night the overall
color fades to dark gray. In O. echinata regions that are brown during the day turn
into gray at night. Ophiocoma pumila undergoes a comparatively subtle colorchange during the day from yellowish-brown to brownish-gray. At night, the
brown shades turn to gray and the gray ones turn black. The color-change of
O. wendtii is striking. During the day, specimens had a homogeneous brownishgray color-phase, including the spines that sometimes have brownish-orange tips.
At night, the disk turns grayish–brown and black and the dorsal side of the arm
develops conspicuous gray or white and black bands while the ventral side of the
arm remains unbanded. At night the arm spines often turn white basally, gray
along the shaft, and orange.
Hendler (1984b) demonstrated that the four species are not equally sensible to
light. Three species withdrew their arms into crevices in response to illumination,
while O. pumila showed little reaction to illumination. Hendler (1984b) tested
whether O. paucigranulata was more sensitive than O. echinata by measuring the
speed of reaction. Ophiocoma wendtii was the most sensitive species, reacting
rapidly to the lights even when the light was attenuated with two layers of red
cellophane. The other three species did not react to dim red light. Ophiocoma
wendtii reacts to lower levels of illumination at night more than during the day,
and exhibits negative phototaxis in moonlight as well as in sunlight. He argued that
color-change is either an endogenous rhythm, or a response to the light regime and
that the color-change may expose photosensitive tissues that control the ophiuroid’s detection of shaded places in the reef. Finally, he concluded that negative
phototaxis, coordinated with color-change, may facilitate the defensive shadowseeking response under varying illumination levels. Color change also confers
pigmentation patterns which may camouflage ophiuroids from predatory fish.
Hendler and Byrne (1987) described for the first time a presumed photoreceptor
system in the body wall of the ophiocomid brittlestar O. wendtii, and it was based
on examination of the fine structure of the dorsal arm plate (DAP). This led Cobb
and Hendler (1990) to test the photoreceptor hypothesis, that microscopic, transparent structures of the skeletal plates, and that their associated chromatophores
and nerve bundles comprise a photoreceptor system in O. wendtii as porposed by
Hendler and Byrne (1987).
In order to examine the functional, systematic, and paleontological importance
of their distinctive integument, Byrne and Hendler (1988) undertook a comparative examination of the arm structure of shallow water and bathyal ophiomyxid
brittlestars. Additionally, they used the behavior and arm morphology to evaluate
the specialization of Paleozoic ophiuroids. Specimens of Ophiomyxa flaccida,
3 Central America Echinoderms: Diversity, Ecology and Future Perspectives
91
showed that the day-night color change involves a replacement of brown shades by
gray and black. Individuals of all four species change color in the late afternoon.
Experimental evidence demonstrated that transformation occurs over a period of
three to four hours and it is effected by chromatophores. Furthermore, as seen with
the separated body parts, they appear to respond to light independently of the
nervous central system.
During the day O. paucigranulata was brownish-black. At night the overall
color fades to dark gray. In O. echinata regions that are brown during the day turn
into gray at night. Ophiocoma pumila undergoes a comparatively subtle colorchange during the day from yellowish-brown to brownish-gray. At night, the
brown shades turn to gray and the gray ones turn black. The color-change of
O. wendtii is striking. During the day, specimens had a homogeneous brownishgray color-phase, including the spines that sometimes have brownish-orange tips.
At night, the disk turns grayish–brown and black and the dorsal side of the arm
develops conspicuous gray or white and black bands while the ventral side of the
arm remains unbanded. At night the arm spines often turn white basally, gray
along the shaft, and orange.
Hendler (1984b) demonstrated that the four species are not equally sensible to
light. Three species withdrew their arms into crevices in response to illumination,
while O. pumila showed little reaction to illumination. Hendler (1984b) tested
whether O. paucigranulata was more sensitive than O. echinata by measuring the
speed of reaction. Ophiocoma wendtii was the most sensitive species, reacting
rapidly to the lights even when the light was attenuated with two layers of red
cellophane. The other three species did not react to dim red light. Ophiocoma
wendtii reacts to lower levels of illumination at night more than during the day,
and exhibits negative phototaxis in moonlight as well as in sunlight. He argued that
color-change is either an endogenous rhythm, or a response to the light regime and
that the color-change may expose photosensitive tissues that control the ophiuroid’s detection of shaded places in the reef. Finally, he concluded that negative
phototaxis, coordinated with color-change, may facilitate the defensive shadowseeking response under varying illumination levels. Color change also confers
pigmentation patterns which may camouflage ophiuroids from predatory fish.
Hendler and Byrne (1987) described for the first time a presumed photoreceptor
system in the body wall of the ophiocomid brittlestar O. wendtii, and it was based
on examination of the fine structure of the dorsal arm plate (DAP). This led Cobb
and Hendler (1990) to test the photoreceptor hypothesis, that microscopic, transparent structures of the skeletal plates, and that their associated chromatophores
and nerve bundles comprise a photoreceptor system in O. wendtii as porposed by
Hendler and Byrne (1987).
In order to examine the functional, systematic, and paleontological importance
of their distinctive integument, Byrne and Hendler (1988) undertook a comparative examination of the arm structure of shallow water and bathyal ophiomyxid
brittlestars. Additionally, they used the behavior and arm morphology to evaluate
the specialization of Paleozoic ophiuroids. Specimens of Ophiomyxa flaccida,
3 Central America Echinoderms: Diversity, Ecology and Future Perspectives
91