---------Organism evolve in the Paleozoic era - Research Paper Example

Organism of Paleozoic Era Spider Introduction Paleozoic or the age of ancient life; extended from 544 to 245 million years ago, i.e. for approximately 300 million years (fig 1). The era is marked by significant events in evolutionary history of life on earth. Most invertebrate groups including the arthropods along with vertebrates such as Pisceans, amphibians originated and flourished during this period. The era witnessed the origin of terrestrial organisms marking “life’s conquest of land”.

Among the flora, the era saw the evolution of vascular plants. Geographical and geological events such as formation of supercontinent Pangaea and two ice ages occurred during this period. With the end of Paleozoic era came about the mass extinction of marine species, The Permian/Triassic extinction (Paleozoic era paleobiology).One of the organisms that evolved in Paleozoic era and managed to survive the vast and diverse geological and geographical changes spanning more than 300 years is Spider.

Their global presence even today cannot be denied. In the current paper is discussed the unique characteristics of this organism that contributed to its evolutionary success and present a brief description of its journey over the years.SpidersClassification (Penney & Selden, 11)Kingdom: AnimaliaPhylum: ArthropodaClass: ArachnidaOrder: AraneaeSuborders:1. Mesothelae: primitive with segmented abdomen, wide occurrence supported by fossil evidence but found exclusively in south-east Asia now.2. Opisthothelae:Mygalomorphae Tarantula like, bird eatingAraneomorphae: True spiders, the most abundant forms todayDescriptionSpiders belong to the order Araneae.

They are among the most abundant species superseded only by the class Insecta, and comprises of approximately 42000 existing species belonging to 109 families (Platnick). The oldest fossils of true spiders have been reported to be from the carboniferous era (312 million years old), but their evolution can be traced to the Devonian. They are in fact among the first organisms to have inhabited land (Penney & Selden, 8).The major identifying characteristics of spider are (The visual dictionary) (fig 2):Body unsegmented and divided in to two parts: cephalothorax and abdomen, joined by a pedicelFour pairs of a legs including a pair of pedipalp that is the tactile foot of spider Absence of wings and antennaePresence of silk spinning organs or spinneretsChelicara or the venomous hooks present in pair on spider’s headThe unique morphological and behavioral characteristics of spiders continue to amaze researchers and are responsible for the survival and almost ubiquitous presence of spiders.

Some of these characteristics are:Silk is the biggest tool and weapon of spider. It is used for shelter, movement, communication, and dispersal of spiderlings. Web making spiders are capable of staying motionless and concealed for long span of time and are mobilized by such stimulus as prey, mate or predator. Further they have adaptations such as median tarsal claws to enable them to walk on silk (Herberstein & Wignall, 8).During movement it leaves a dragline silk formed by the anterior spinnerets which acts as a safety line of communication for mate.

Depending on the environment they inhabit, they have developed organs for locomotion such as claw tufts for land and hydrophobic exoskeletons for water.The sense organs of spider viz. eyes, lyriform organs, trichobothria, and chemosensory organs are highly adapted to specific ecological niche they inhabitate. For e.g. cursorial spiders have better developed eyes than web spiders that have better vibratory senses (Herberstein & Wignall, 6).EcologySpiders though ubiquitous, live in very specific habitats to avoid competition from other species of spiders as well as other organisms.

Different species of spider live in varied temperature, wind, moisture and light intensity. Their habitat selection also depends on competition, predators and vegetation types. The small size and small spaces required by spiders means that many ecological niche may occur within a habitat that may be as close as within few centimeters (Ramel).Spiders mainly feed on insects and have developed intricate venom system that enables it to prey on the insects. They have even diversified their abilities to enable them to capture their prey in different ecological niche (Penney & Selden, 8).

The chelicerae besides venom hooks are also used for manipulation during preying. The chelicerae act according to the method of prey capture, for e.g. spitting spiders have larger venom glands and smaller chelicerae compared to those that poison by biting. Once poisoned, chelicerae crush the prey to enable consumption (Herberstein & Wignall, 12).There are many predators of spider depending on the niche occupied by them for e.g. frogs and toads in water and lizards on land. Certain species of spiders also feed on other spider species.

The major defense mechanisms of spiders include flight, venom, camouflage and mimicry. For e.g. Green lynx spiders (Peucetia viridans) found mostly in tropical areas have green colour that matches and enables them to conceal themselves against the green background of plants on which they live. Similarly Crab spiders (Thomisus onustus), have the color of flowers they feed on to escape the preying birds (Thery & Casas, 133). Ant mimicry has been reported frequently in thirteen species of spiders belonging to Clubionidae and Salticidae (Reiskind, 1).

The massive diversity and ecological adaptations of spiders have not only ensured its survival till date but are enabled them to occupy habitats globally.Figuresfig 1:: Geological Eras fig 2: Morphology of Typical Modern Day SpiderReferences1. Herberstein, M. E., & Wignall, A. (2011). Introduction Spider Biology. In M. E. Herberstein, Spider behaviour: flexibility and versatility (pp. 1-30). New York: Cambridge University Press.2. Morphology of a spider. (2014, March). Retrieved from The Visual Dictionary: http://www.

infovisual.info/02/051_en.html3. Paleozoic Era Paleobiology. (2012). Retrieved March 2014, from Virtual Fossil Museum: http://www.fossilmuseum.net/Paleobiology/Paleozoic_paleobiology.htm4. Penney, D., & Selden, P. (2011). Fossil Spiders: The Evolutionary History of a Mega-diverse Order. Manchester: Siri scientific press.5. Platnick, N. I. (2014). The World Spider Catalog, Version 14.5. Retrieved from American Museum of Natural History: http://research.amnh.org/entomology/spiders/catalog/index6. Ramel, G. (2014).

Spider ecology. Retrieved from Earthlife Web: http://www.earthlife.net/chelicerata/s-ecology.html7. Reiskind, J. (1977). Ant-mimicry in Panamanian Clubinoid and Salticid Spiders (Araneae: Clubionidae, Salticidae). Biotropica, 1-8.8. Thery, M., & Casas, J. (2012). Predator and prey views of spider camouflage. Nature, 133.