Picture Of Starfish Download
Evelin Mceachron
The first thing I did to improve the image was to open it with Photoshop Elements 8.0 and adjust the contrast. I also increased the colour saturation (by + 10). These tweaks greatly improved the impact of the picture and the result is more like the original slide. However, the original slide had a significant problem: the line of crud on the inside of the glass, in the lower part of the image. I remember how disappointed I was when I got the slide back from the developer and saw that flaw. Now of course with Photoshop I was able to make it go away with a few clicks of the Clone Tool!
Something Old - This retired High Tide Designer Series Paper has lots of nautical and sealife patterns and I remembered this one featuring a coral starfish. The panels on this sketch lend themselves to co-ordinating DSP and I knew this card would give me the perfect opportunity to use up some of my old papers.
Something New - The starfish is the only image in the 'Picture Perfect' stamp set I've yet to use, so that was naturally my image of choice today. I stamped my starfish first in Blushing Bride, then overlaid the second image in Calypso Coral to tie it in with the coral starfish on my chosen DSP. I then cropped my image using my Circles Framelits.
In the constellation of Aquila (the Eagle), lies a star nearing the end of its life that is surrounded by a starfish-shaped cloud of gas and dust. A striking image of this object, known as IRAS 19024+0044 has been captured by the NASA/ESA Hubble Space Telescope.
Protoplanetary nebulae are relatively rare and short-lived objects that provide astronomers with clues into how the often strangely asymmetric planetary nebulae are formed. Clearly visible in this image are five blue lobes that extend away from the central star and give the nebula its asymmetric starfish shape. While astronomers have come up with theories for the origin of these structures, such as direction-changing jets or explosive ejections of matter from the star, their formation is not entirely understood.
Photoreceptors have evolved numerous times giving organisms the ability to detect light and respond to specific visual stimuli. Studies into the visual abilities of the Asteroidea (Echinodermata) have recently shown that species within this class have a more developed visual sense than previously thought and it has been demonstrated that starfish use visual information for orientation within their habitat. Whereas image forming eyes have been suggested for starfish, direct experimental proof of true spatial vision has not yet been obtained.
For crown-of-thorns starfish, visual cues are essential for close range orientation towards objects, such as coral boulders, in the wild. These visually guided behaviours can be replicated in aquarium conditions. Our observation that crown-of-thorns starfish respond to black-and-white shapes on a mid-intensity grey background is the first direct proof of true spatial vision in starfish and in the phylum Echinodermata.
Light sensitivity can be found in echinoderms like sea urchins (Echinoidea), sea cucumbers (Holothuroidea), starfish (Asteroidea) and brittle stars (Ophiuroidea) [1]. Sea urchins respond to shadows with movements of their spines [2, 3]. In addition, some sea urchins will cover themselves with objects in response to light [4], or display negative phototaxis. Even though sea urchins do not have eyes, species such as Echinometra lucunter L., Echinometra viridis and Strongylocentrotus purpuratus nevertheless orient towards visual targets and have been suggested to have a limited form of spatial vision, possibly by means of combining a dermal light sensitivity with shading by the spines [5, 6]. However, these sea urchin studies were examining orientational capabilities towards black circles on a light background; a stimulus that can be detected without using spatial resolution vision by following the gradient in light intensity. Other authors found that only certain regions of the sea urchin dermis were responsive to visual stimulation [2, 7] which could be explained by the relatively high opsin and pax 6 concentrations found in the tube feet of sea urchins [8, 9]. In addition, depressions in the skeleton of the sea urchin could provide the shading needed for directional sensitivity [10], providing an alternative hypotheses to the shading by the spines presented above.
The starfish eye represents the most advanced light receptive structure in the echinoderm phylum and was first described more than 200 years ago by Vahl in 1780, cited by Smith [17]. The starfish eye has been described as the optic cushion, or terminal eye spot and arises from the first developing, primary podium [18, 19]. This results in one eye at the base of the terminal tube foot, at the tip of each and every arm. In starfish, tube feet have a diversity of functions and are responsible for adhesion [20], locomotion [21], respiration and secretion [22] and they are prominent sense organs that contain many sensory cells [23]. Starfish have been found to respond to mechanical [24] and olfactory stimulation [25, 26], both of which are senses that can augment vision during orientation tasks.
Some authors argue that calcite structures in the epidermis could provide starfish with a second eye-based visual system, similar to the one found in brittle stars. Present day starfish [27], as well as fossilised starfish [28], were described to have putative calcite lenses. However, in contrast to brittle stars, no neurons have been described to be associated with these putative lenses which making it problematic to assign function.
Starfish have also been reported to have extra-ocular light sensitivity using a dermal light sense. The starfish Asterias amurensis [29, 30] and Asterias forbesi [31] have been shown to exhibit phototactic movements in response to visual stimulation in both intact and blinded animals, demonstrating that eyes are not a requirement for photaxis and extra-ocular photoreception suffices. Dermal light sensitivity in starfish is less sensitive than vision using the eyes [30], which would make it ineffective at visual tasks requiring spatial resolution [32] and is therefore only likely to be involved in simple visual tasks like phototaxis.
Compound eyes have been found in many of the examined starfish species, however only recently the function of the compound eyes of starfish was revealed in the blue Star, Linckia laevigata, which was shown to orient towards coral reefs using their compound eyes [33]. Blinded starfish, with their extra-ocular photoreception and olfaction intact, were unable to navigate towards the reefs. Similar results have been obtained in the crown-of-thorns starfish, Acanthaster planci [34, 35]. With these findings in mind, it is clear that the system supporting more advanced visually guided behaviours in starfish is the compound eye.
In this paper we set out to investigate which visual cues are used by the crown-of-thorns starfish for visual orientation. We present behavioural data from aquarium experiments, where the visual scene was controlled in detail. We tested whether the starfish use simple phototaxis or rely on true spatial vision for visual orientation tasks.
Behavioural arena. a Schematic representation of the behavioural arena. Visual stimuli were attached to a Plexiglas sheet (indicated by hatching) using Velcro, with the bottom of the stimulus on the floor of the arena. The sheet was lowered into the arena and fastened by clamps. The wall of the arena was white. For the experiments with black-and-white patterns, a mid-intensity grey cloth was attached to the inside wall of the arena. b Five different stimuli were presented to the animals: three black-and-white stimuli, a black circular stimulus and a grey circular stimulus. For each black-and-white stimulus the area of black was equal to the area of white. For all similar sized circular, or rectangular, stimuli the area of black was the equal. c The arena during an experiment. Recordings were made with a camera floating on the surface of the water. Abbreviations: c, camera; cl, clamps for attaching the Plexiglas sheet; m, middle of the arena; s, stimulus; sf, starfish. Example tracks for: d black circles (angular height 37) on a white background and e the control experiment with only the Plexiglas sheet on a white background. The stimulus is located at 0
The response to black rectangles centred in a white square, presented on a grey background (Fig. 3, Table 1), resembled the response to the previous experiment, although, a high proportion of the animals moved away from the stimulus, resulting in an axially directed response. Animals responded to the smallest stimulus of 5 and the largest two of 32 and 43. Axial responses occur more frequently in echinoderms and have also been observed in sea urchins [6], brittle stars [12] and other starfish [29]. The response to the 5 target cannot be readily explained. If the minimal object size that evokes a response really is 5, it is to be expected that there would have been responses to all larger stimuli in the same experiment and other similar sized stimuli, but this was not observed. Regardless of whether the animals are repelled or attracted, the stimulus has to be visually detected, and hence this experiment also confirms that the crown-of-thorns starfish uses true spatial vision.
Starfish were also presented with black-and-white circles against a grey background. Under these conditions the starfish did not show any directional response to the stimuli (Fig. 4), even though the area of black and white was equal to the previous two experiments. A possible explanation for the lack of response to the black-and-white circles on a grey background could be found in the white rim of the stimulus. The crown-of-thorns starfish has a narrow visual streak directed approximately 30 above the horizon [41]. As the animal moves from the centre of the arena, at a distance of 80 cm from the wall, to a position 20 cm in front of the stimulus, the relative area of white in the field of view of the eye directed towards the circle would increase in size four times (Fig. 5) compared to initial condition. Combining this with our observation that crown-of-thorns starfish prefers black over white it could imply that our circular stimulus gets increasingly unattractive as the animal moves closer.
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