Chrysaora Colorata.jpg - Wikipedia, the free encyclopedia. Nerve net. Nettle Jelly Evolution[edit] Metazoan phylogenetic showing the phylum Cnidaria The emergence of nervous systems has been linked to the evolution of voltage-gated sodium (Nav) channels. The Nav channels allow for communication between cells over long distances through the propagation of action potentials, whereas voltage-gated (Cav) calcium channels allow for unmodulated intercellular signaling. It has been hypothesized that Nav channels differentiated from Cav channels either at the emergence of nervous systems or before the emergence of multicellular organisms, although the origin of Nav channels in history remains unknown. Nerve nets are found in species in the phyla Cnidaria (e.g. scyphozoa, box jellyfish, and sea anemones), Ctenophora, and Echinodermata. Developmental Neurogenesis[edit] Anatomy[edit] Physiology[edit] Each sensory neuron within a nerve net responds to each stimulus, like odors or tactile stimuli.
See also[edit] References[edit] Plankton. Plankton (singular plankter) are a diverse group of organisms that live in the water column and cannot swim against a current.[1] They provide a crucial source of food to many large aquatic organisms, such as fish and whales. Though many planktic (or planktonic—see the next section below) species are microscopic in size, plankton includes organisms covering a wide range of sizes, including large organisms such as jellyfish.[2] Terminology[edit] The name plankton is derived from the Greek adjective πλαγκτός - planktos, meaning errant, and by extension "wanderer" or drifter.[3] It was coined by Victor Hensen.[4] Plankton typically flow with ocean currents. While some forms are capable of independent movement and can swim hundreds of meters vertically in a single day (a behavior called diel vertical migration), their horizontal position is primarily determined by the surrounding currents. The study of plankton is termed planktology and a planktonic individual is referred to as a plankter.[5]
Cnidaria. Most cnidarians prey on organisms ranging in size from plankton to animals several times larger than themselves, but many obtain much of their nutrition from endosymbiotic algae, and a few are parasites. Many are preyed upon by other animals including starfish, sea slugs, fish and turtles. Coral reefs, whose polyps are rich in endosymbiotic algae, support some of the world's most productive ecosystems, and protect vegetation in tidal zones and on shorelines from strong currents and tides. While corals are almost entirely restricted to warm, shallow marine waters, other cnidarians live in the depths, in polar seas and in freshwater. Fossil cnidarians have been found in rocks formed about 580 million years ago, and other fossils show that corals may have been present shortly before 490 million years ago and diversified a few million years later.
Fossils of cnidarians that do not build mineralized structures are very rare. Distinguishing features[edit] Description[edit] Aboral end Oral end. Medusa (biology) Jellyfish are found in every ocean, from the surface to the deep sea. A few jellyfish inhabit freshwater. Large, often colorful, jellyfish are common in coastal zones worldwide. Jellyfish have roamed the seas for at least 500 million years,[1] and possibly 700 million years or more, making them the oldest multi-organ animal.[2] Terminology The English popular name jellyfish has been in use since 1796.[3] It has traditionally also been applied to other animals sharing a superficial resemblance, for example ctenophores (members from another phylum of common, gelatinous and generally transparent or translucent, free-swimming planktonic carnivores now known as comb jellies) were included as "jellyfishes".[4] Even some scientists include the phylum ctenophora when they are referring to jellyfish.[5] Other scientists prefer to use the more all-encompassing term gelatinous zooplankton, when referring to these, together with other soft-bodied animals in the water column.[6] Anatomy Nervous system.
Evolution of sensory structures in basal metazoa. + Author Affiliations 1E-mail: djacobs@ucla.edu Abstract Cnidaria have traditionally been viewed as the most basal animals with complex, organ-like multicellular structures dedicated to sensory perception. However, sponges also have a surprising range of the genes required for sensory and neural functions in Bilateria. Introduction The word “animal” implies muscle-driven motility coordinated by neural integration of sensory stimuli produced in specialized multicellular sensory structures.
Do sense organs share a common evolutionary origin with other structures or organs? Not all of the preceding questions can be definitively answered at this time. In this work, we touch on the features that distinguish sense organs. What do sense organs have in common? Cells generally have an ability to assay aspects of their surroundings. It is important to note that not all GPCRs are involved in sense organs or sensory perception. Common aspects of sense-organ developmental gene regulation Fig. 1.