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Article: Social spider

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The article describes social behaviours among spider species in contrast to the more common solitary predator behaviour of the majority of spider species. The content is organized in neat subsections with a photograph demonstrating this social behaviour, and doesn't include any unnecessary or irrelevant information.

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The article demonstrates a neutral and unbiased tone, and appears to draw the information from the listed sources, not personal opinion or experiences.

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The article is a part of WikiProject Spiders, and currently has a rating of C-class on the quality scale. There is very little conversation on this page other than changing the title of the article from plural to singular, and requesting the page be considered mid-importance.

Phototaxis in zooplankton
Phototaxis in zooplankton is well studied in the marine annelid Platynereis dumerilii:

Platynereis dumerilii trochophore and metatrochophore larvae are positively phototactic. Phototaxis there is mediated by simple eyespots that consists of a pigment cell and a photoreceptor cell. The photoreceptor cell synapses directly onto ciliated cells, which are used for swimming. The eyespots do not give spatial resolution, therefore the larvae are rotating to scan their environment for the direction where the light is coming from.

Platynereis dumerilii nectochaete larvae can switch between positive and negative phototaxis. Phototaxis there is mediated by two pairs of more complex pigment cup eyes. These eyes contain more photoreceptor cells that are shaded by pigment cells forming a cup. The photoreceptor cells do not synapse directly onto ciliated cells or muscle cells but onto inter-neurons of a processing center. This way the information of all four eye cups can be compared and a low resolution image of four pixels can be created telling the larvae where the light is coming from. This way the larva does not need to scan its environment by rotating. This is an adaption for living on the bottom of the sea the life style of the nectochaete larva while scanning rotation is more suited for living in the open water column, the life style of the trochophore larva. Phototaxis in the Platynereis dumerilii nectochaete larva has a broad spectral range which is at least covered by three opsins that are expressed by the cup eyes: Two rhabdomeric opsins and a Go-opsin.

However, not every behavior that looks like phototaxis is phototaxis: Platynereis dumerilii nechtochate and metatrochophore larvae swim up first when they are stimulated with UV-light from above. But after a while, they change the direction and avoid the UV-light by swimming down. This looks like a change from positive to negative phototaxis (see video left), but the larvae also swim down if UV-light comes non-directionally from the side. And so they do not swim to or away from the light, but swim down, this means to the center of gravity. Thus this is a UV-induced positive gravitaxis. Positive phototaxis (swimming to the light from the surface) and positive gravitaxis (swimming to the center of gravity) are induced by different ranges of wavelengths and cancel out each other at a certain ratio of wavelengths. Since the wavelengths compositions change in water with depth: Short (UV, violet) and long (red) wavelengths are lost first, phototaxis and gravitaxis form a ratio-chromatic depth gauge, which allows the larvae to determine their depth by the color of the surrounding water. This has the advantage over a brightness based depth gauge that the color stays almost constant independent of the time of the day or whether it is cloudy.

(clean up required, irrelevant information in several locations such as gravitaxis and awkward wording)

Phototaxis in jellyfish
positive and negative phototactic behaviour can be found in several species of jellyfish such as species from the polyorchis genus. Jellyfish utilize ocelli to detect the presence and absence of light, which is then translated into anti-predatory behaviour in the case of a shadow being cast over the ocelli, or feeding behaviour in the case of the presence of light. Many tropical jellyfish contain photosynthetic zooxanthellae within their cells and have a symbiotic relationship. The jellyfish receives nourishment, provides protection, and locomotion toward light sources such as the sun to provide the greatest exposure to the light. In the presence of a shadow the jellyfish can either remain still, or preform a quick burst of movement to avoid predation and also readjust toward a new light source.

This motor response to light and absence of light of is facilitated by a chemical response from the ocelli, which results in a motor response causing the organism to swim toward a light source.

(still need to add sources and link relevant terms and species)

Phototaxis in insects
Positive phototactic behaviour in insects can be found primarily in insects capable of flight such as many species of flies, moths, and grasshoppers. Drosophila melanogaster has been studied extensively on its innate positive phototactic response to light sources using controlled experiments to help understand the connection between airborne locomotion toward a light source. This innate response is common among insects that fly primarily during the night utilizing transverse orientation with the light of the moon to fly. Artificial lights in cities and populated areas result in a more bright and positive response compared to the distant light of the moon, resulting in the organism repeatedly responding to this new supernormal stimulus and innately flying toward it.

Evidence for the innate response of positive phototactic behaviour in Drosophila melanogaster was carried out by altering the wings of several individuals both physically via removal, or genetically via mutation. In all cases the organisms with wings removed and wings mutated there was a noticeable lack of positive phototactic behaviour demonstrating flying toward light is an innate response to the organisms photoreceptors receiving a positive response.

(Sources not attached yet, input more relevant terms and species)

Relation to magnetic fields
Under experimental conditions organisms that utilize positive phototactic behaviour have also shown correlation with light and magnetic fields. Under homogenous light conditions with a shifting magnetic field drosophila melanogaster larva reorient themselves toward predicted directions of greater or lesser light intensities as expected by a rotating magnetic field. In complete darkness the same organism orients randomly without any notable preference. This suggests a visible pattern can be observed by the organism in combination with light.