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Polychaeta
Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. More than 10,000 species are described in this class. Common representatives include the lugworm (''Arenicola marina'') and the sandworm or clam worm ''Alitta''. Polychaetes as a class are robust and widespread, with species that live in the coldest ocean temperatures of the abyssal plain, to forms which tolerate the extremely high temperatures near hydrothermal vents. Polychaetes occur throughout the Earth's oceans at all depths, from forms that live as plankton near the surface, to a 2- to 3-cm specimen (still unclassified) observed by the robot ocean probe ''Nereus'' at the bottom of the Challenger Deep, the deepest known spot in the Earth's oceans. Only 168 species (less than 2% of all polychaetes) are known fro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alitta Succinea
''Alitta succinea'' (known as the pile worm or clam worm) is a species of marine annelid in the family Nereididae (commonly known as ragworms or sandworms). It has been recorded throughout the North West Atlantic, as well as in the Gulf of Maine and South Africa. Description The clam worm can reach up to in length, but most specimens are smaller than this. It is brown colored at the rear, and reddish-brown on the rest of its body. It has an identifiable head with four eyes, two sensory feelers or palps, and many tentacles. The head consists of two segments: the anterior and posterior prostomium. The last body segment is known as the pygidium. Life cycle It is a freeswimming polychaete, scavenging on the bottom of shallow marine waters. It feeds on other worms and algae. To feed, it uses a proboscis, which has two hooks at the end, to grasp prey and draw it into its mouth. Clam worms are an important food source for bottom-feeding fish and crustaceans, though they can protec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Abyssal Plain
An abyssal plain is an underwater plain on the deep ocean floor, usually found at depths between and . Lying generally between the foot of a continental rise and a mid-ocean ridge, abyssal plains cover more than 50% of the Earth's surface. They are among the flattest, smoothest, and least explored regions on Earth. Abyssal plains are key geologic elements of oceanic basins (the other elements being an elevated mid-ocean ridge and flanking abyssal hills). The creation of the abyssal plain is the result of the spreading of the seafloor (plate tectonics) and the melting of the lower oceanic crust. Magma rises from above the asthenosphere (a layer of the upper mantle), and as this basaltic material reaches the surface at mid-ocean ridges, it forms new oceanic crust, which is constantly pulled sideways by spreading of the seafloor. Abyssal plains result from the blanketing of an originally uneven surface of oceanic crust by fine-grained sediments, mainly clay and silt. Much of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chaeta
A chaeta or cheta (from Greek χαίτη “crest, mane, flowing hair"; plural: chaetae) is a chitinous bristle or seta found in annelid worms, (although the term is also frequently used to describe similar structures in other invertebrates such as arthropods). Polychaete annelids, ('polychaeta' literally meaning "many bristles") are named for their chaetae. In Polychaeta, chaetae are found as bundles on the parapodia, paired appendages on the side of the body. The chaetae are epidermal extracellular structures, and clearly visible in most polychaetes. They are probably the best studied structures in these animals. Use in taxonomy and identification The ultrastructure of chaetae is fundamentally similar for all taxa but there is vast diversity in chaetal morphology. Moreover, chaetae bear precise characters for determination of species and taxonomic assessment. The shape, absolute and relative size, number, position, ornamentation and type are important taxonomic characters ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alitta Virens
''Alitta virens'' (common names include sandworm and king ragworm; older scientific names including ''Nereis virens'' are still frequently used) is an annelid worm that burrows in wet sand and mud. It was first described by biologist Michael Sars in 1835. It is classified as a polychaete in the family Nereididae. Sandworms make up a large part of the live sea-bait industry. To fulfill the needs of this industry, some sandworms are commercially grown. " Sandworming", or the harvesting of sandworms from mudflats, employs over 1,000 people in Maine. , the population of sandworms had diminished greatly over the preceding few years due in large part to overharvesting before the worms are able to reproduce by spawning. Sandworms eat seaweed and microorganisms. They have many distinctive traits, including * often reaching great lengths, sometimes exceeding four feet * numerous, highly vascularized parapodia along both sides of their bodies * blue heads with two large pincer teeth wh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scolecida
Scolecida is an infraclass of polychaete worms. Scolecids are mostly unselective deposit feeders on marine detritus. Characteristics Scolecids have parapodia with rami that are all alike. The prostomium is distinct. The head has no appendages or palps and is usually conical, though in the Scalibregmatidae, it has a "T"-shaped tip, and in Paraonidae, there is a single, central antenna. In some families there are sometimes some tiny eyespots. The oesophagus is evertable forming a sac-like proboscis which may have several finger-like lobes. The anterior segments and their appendages are all similar. The notopodia and neuropodia consist of unbranched capillary chaetae, sometimes with hooks. There is a single central gill in Cossuridae on an anterior segment and simple segmental gills are present in some other families. Systematics The families Arenicolidae, Capitellidae and Maldanidae were formerly part of the order Capitellida. They are now included in infraclass Scolecida al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Palpata
Palpata is a subclass of polychaete worm. Members of this subclass are mostly deposit feeders on marine detritus or filter feeders. Palpata has become superfluous with the elevation of Canalipalpata to subclass. Characteristics Palpata includes the majority of genera and species of polychaete worms and is subdivided into the orders Aciculata and Canalipalpata.Rouse, G. W., and K. Fauchald. 1997. Cladistics and polychaetes. Zool. Scr. 26:139-204. The prostomium is characterised by a pair of sensory palps which gives the subclass its name and which are lacking in the other main taxon of polychaetes, the Scolecida. Aciculata is a large group including about half of all existing polychaete species and is equivalent to the old taxonomic group "Errantia", worms that can move about freely by crawling or swimming. These worms are characterised by having internal supporting chaetae in their parapodia. Aciculata is divided into suborders Eunicida and Phyllodocida. Canalipalpata is e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Annelid
The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecologies – some in marine environments as distinct as tidal zones and hydrothermal vents, others in fresh water, and yet others in moist terrestrial environments. The Annelids are bilaterally symmetrical, triploblastic, coelomate, invertebrate organisms. They also have parapodia for locomotion. Most textbooks still use the traditional division into polychaetes (almost all marine), oligochaetes (which include earthworms) and leech-like species. Cladistic research since 1997 has radically changed this scheme, viewing leeches as a sub-group of oligochaetes and oligochaetes as a sub-group of polychaetes. In addition, the Pogonophora, Echiura and Sipuncula, previously regarded as separate phyla, are now regarded as sub-groups of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Commensal
Commensalism is a long-term biological interaction ( symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit from each other; amensalism, where one is harmed while the other is unaffected; parasitism, where one is harmed and the other benefits, and parasitoidism, which is similar to parasitism but the parasitoid has a free-living state and instead of just harming its host, it eventually ends up killing it. The commensal (the species that benefits from the association) may obtain nutrients, shelter, support, or locomotion from the host species, which is substantially unaffected. The commensal relation is often between a larger host and a smaller commensal; the host organism is unmodified, whereas the commensal species may show great structural adaptation consistent with its habits, as in the remoras that ride attached to sharks and other fish ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pelagic
The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the surface of the sea and the bottom. Conditions in the water column change with depth: pressure increases; temperature and light decrease; salinity, oxygen, micronutrients (such as iron, magnesium and calcium) all change. Marine life is affected by bathymetry (underwater topography) such as the seafloor, shoreline, or a submarine seamount, as well as by proximity to the boundary between the ocean and the atmosphere at the ocean surface, which brings light for photosynthesis, predation from above, and wind stirring up waves and setting currents in motion. The pelagic zone refers to the open, free waters away from the shore, where marine life can swim freely in any direction unhindered by topographical constraints. Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ecological Niche
In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of resources and competitors (for example, by growing when resources are abundant, and when predators, parasites and pathogens are scarce) and how it in turn alters those same factors (for example, limiting access to resources by other organisms, acting as a food source for predators and a consumer of prey). "The type and number of variables comprising the dimensions of an environmental niche vary from one species to another ndthe relative importance of particular environmental variables for a species may vary according to the geographic and biotic contexts". See also Chapter 2: Concepts of niches, pp. 7 ''ff'' A Grinnellian niche is determined by the habitat in which a species lives and its accompanying behavioral adaptations. An Eltonian niche emphasizes that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gas Exchange
Gas exchange is the physical process by which gases move passively by diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid, a gas-permeable membrane, or a biological membrane that forms the boundary between an organism and its extracellular environment. Gases are constantly consumed and produced by cellular and metabolic reactions in most living things, so an efficient system for gas exchange between, ultimately, the interior of the cell(s) and the external environment is required. Small, particularly unicellular organisms, such as bacteria and protozoa, have a high surface-area to volume ratio. In these creatures the gas exchange membrane is typically the cell membrane. Some small multicellular organisms, such as flatworms, are also able to perform sufficient gas exchange across the skin or cuticle that surrounds their bodies. However, in most larger organisms, which have a small surface ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Luminescent
Luminescence is spontaneous emission of light by a substance not resulting from heat; or "cold light". It is thus a form of cold-body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions or stress on a crystal. This distinguishes luminescence from incandescence, which is light emitted by a substance as a result of heating. Historically, radioactivity was thought of as a form of "radio-luminescence", although it is today considered to be separate since it involves more than electromagnetic radiation. The dials, hands, scales, and signs of aviation and navigational instruments and markings are often coated with luminescent materials in a process known as "luminising". Types The following are types of luminescence: *Chemiluminescence, the emission of light as a result of a chemical reaction **Bioluminescence, a result of biochemical reactions in a living organism ** Electrochemiluminescence, a result of an electrochemical reaction ** Lyolumine ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
