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Gnathostomulida
Gnathostomulids, or jaw worms, are a small phylum of nearly microscopic marine animals. They inhabit sand and mud beneath shallow coastal waters and can survive in relatively anoxic environments. They were first recognised and described in 1956. Anatomy Most gnathostomulids measure in length. They are often slender to thread-like worms, with a generally transparent body. In many Bursovaginoidea, one of the major group of gnathostomulids, the neck region is slightly narrower than the rest of the body, giving them a distinct head. Like flatworms they have a ciliated epidermis, but in contrast to flatworms, they have one cilium per cell. The cilia allow the worms to glide along in the water between sand grains, although they also use muscles, allowing the body to twist or contract, for movement. They have no body cavity, and no circulatory or respiratory system. The nervous system is simple, and restricted to the outer layers of the body wall. The only sense organs are modifi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gnathostomulida
Gnathostomulids, or jaw worms, are a small phylum of nearly microscopic marine animals. They inhabit sand and mud beneath shallow coastal waters and can survive in relatively anoxic environments. They were first recognised and described in 1956. Anatomy Most gnathostomulids measure in length. They are often slender to thread-like worms, with a generally transparent body. In many Bursovaginoidea, one of the major group of gnathostomulids, the neck region is slightly narrower than the rest of the body, giving them a distinct head. Like flatworms they have a ciliated epidermis, but in contrast to flatworms, they have one cilium per cell. The cilia allow the worms to glide along in the water between sand grains, although they also use muscles, allowing the body to twist or contract, for movement. They have no body cavity, and no circulatory or respiratory system. The nervous system is simple, and restricted to the outer layers of the body wall. The only sense organs are modifi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gnathifera (phylum)
Gnathifera (from the Greek '' gnáthos'', “jaw”, and the Latin '' -fera'', “bearing”) is a clade of generally small spiralians characterized by complex jaws made of chitin. It comprises the phyla Gnathostomulida, Rotifera, Micrognathozoa, and Chaetognatha. It may also include the Cycliophora. Gnathiferans include some of the most abundant phyla. Rotifers are among the most diverse and abundant freshwater animals and chaetognaths are among the most abundant marine plankton. Description The most distinctive characteristic of gnathiferans is the presence of complex sclerotized mouthparts made of chitin. In most gnathiferans, the anus opens on the dorsal surface of the animal. In micrognathozoans and gnathostomulids, the anus is transient and only forms during defecation. Unlike other gnathiferans, in chaetognaths and '' Amiskwia'' the anus is located on the ventral surface in a subterminal position. Development All known gnathiferans are direct developers. Though g ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bursovaginoidea
Bursovaginoidea is one of the two orders in the phylum Gnathostomulida. Appearance and anatomy Bursovaginoids are rather small, ranging from a half of a millimeter to a full millimeter in length. Many species in the order Bursovaginoidea have a narrow neck, making their head stand out more than other bursovagionoids and all filospermoids. Bursovaginoids, unlike filospermoids, have paired sensory organs and a penis. Also, all species in Bursovaginoidea have a sperm-storage organ called a Bursa (Anatomy), bursa. In suborder Scleroperalia, the bursa is cuticular, while in Conophoralia it is not. Species in order Conophoralia tend to have larger sperm than those in Sceloperalia. Distribution Sightings of bursovaginoids have been reported in various parts of the world, including England and the north-western and south-eastern parts of the United States. Bursovaginoids mostly live in oceans near the coasts, in depths of under 500 meters (1650 feet), most commonly around 300. F ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Filospermoidea
Filospermoidea is an order within the phylum Gnathostomulida. Filospermoids are generally longer than gnathostomulids in the order Bursovaginoidea, and have an elongate rostrum. It lives in North America, off the coasts of the southern United States and the Caribbean, primarily in the Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United ..., as well as in southeastern Denmark. Classification The order Filospermoidea contains 29 species in 2 families and 3 genera. * Family Haplognathiidae [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coelom
The coelom (or celom) is the main body cavity in most animals and is positioned inside the body to surround and contain the digestive tract and other organs. In some animals, it is lined with mesothelium. In other animals, such as molluscs, it remains undifferentiated. In the past, and for practical purposes, coelom characteristics have been used to classify bilaterian animal phyla into informal groups. Etymology The term ''coelom'' derives from the Ancient Greek word (), meaning 'cavity'. Structure Development The coelom is the mesodermally lined cavity between the gut and the outer body wall. During the development of the embryo, coelom formation begins in the gastrulation stage. The developing digestive tube of an embryo forms as a blind pouch called the archenteron. In Protostomes, the coelom forms by a process known as schizocoely. The archenteron initially forms, and the mesoderm splits into two layers: the first attaches to the body wall or ectoderm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Micrognathozoa
''Limnognathia maerski'' is a microscopic freshwater animal, discovered living in warm springs on Disko Island, Greenland, in 1994. Since then, it was also found in Crozet Islands of Antarctica.). With an average length of 100 micrometers (μm), it is one of the smallest animals known. Description Feeding ''L. maerski'' mainly feeds on bacteria, blue-green algae, and diatoms. It has very complicated jaws, with fifteen separate elements. The parts of the jaw structure are connected by ligaments and muscles. The jaw parts are very small, ranging from 4 μm to 14 μm. The animal can extend part of its jaw structure outside its mouth while eating. It also extends much of its jaw structure outside its mouth when it is regurgitating indigestible items. Anatomy ''L. maerski'' has a large ganglion, or 'brain', in its head, and paired nerve cords extending ventrally (along the lower side of the body) towards the tail. Stiff sensory bristles made up of one to thr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Animal Phyla
Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in which their body consists of a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. Animals range in length from to . They have complex interactions with each other and their environments, forming intricate food webs. The scientific study of animals is known as zoology. Most living animal species are in Bilateria, a clade whose members have a bilaterally symmetric body plan. The Bilateria include the protostomes, containing animals such as nematodes, arthropods, flatworms, annelids and molluscs, and the deuterostomes, containing the echinoderms an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Animal
Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motility, able to move, can Sexual reproduction, reproduce sexually, and go through an ontogenetic stage in which their body consists of a hollow sphere of Cell (biology), cells, the blastula, during Embryogenesis, embryonic development. Over 1.5 million Extant taxon, living animal species have been Species description, described—of which around 1 million are Insecta, insects—but it has been estimated there are over 7 million animal species in total. Animals range in length from to . They have Ecology, complex interactions with each other and their environments, forming intricate food webs. The scientific study of animals is known as zoology. Most living animal species are in Bilateria, a clade whose members have a Symmetry in biology#Bilate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phylum
In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature for algae, fungi, and plants accepts the terms as equivalent. Depending on definitions, the animal kingdom Animalia contains about 31 phyla, the plant kingdom Plantae contains about 14 phyla, and the fungus kingdom Fungi contains about 8 phyla. Current research in phylogenetics is uncovering the relationships between phyla, which are contained in larger clades, like Ecdysozoa and Embryophyta. General description The term phylum was coined in 1866 by Ernst Haeckel from the Greek (, "race, stock"), related to (, "tribe, clan"). Haeckel noted that species constantly evolved into new species that seemed to retain few consistent features among themselves and therefore few features that distinguished them as a group ("a self-contained un ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cilia
The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike projection that extends from the surface of the much larger cell body. Eukaryotic flagella found on sperm cells and many protozoans have a similar structure to motile cilia that enables swimming through liquids; they are longer than cilia and have a different undulating motion. There are two major classes of cilia: ''motile'' and ''non-motile'' cilia, each with a subtype, giving four types in all. A cell will typically have one primary cilium or many motile cilia. The structure of the cilium core called the axoneme determines the cilium class. Most motile cilia have a central pair of single microtubules surrounded by nine pairs of double microtubules called a 9+2 axoneme. Most non-motile cilia have a 9+0 axoneme that lacks the central pai ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Epidermis (zoology)
In zoology, the epidermis is an epithelium (sheet of cells) that covers the body of a eumetazoan (animal more complex than a sponge). Eumetazoa have a cavity lined with a similar epithelium, the gastrodermis, which forms a boundary with the epidermis at the mouth. Sponges have no epithelium, and therefore no epidermis or gastrodermis. The epidermis of a more complex invertebrate is just one layer deep, and may be protected by a non-cellular cuticle. The epidermis of a higher vertebrate has many layers, and the outer layers are reinforced with keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up Scale (anatomy), scales, hair, Nail ... and then die. References Animal anatomy Epithelium {{animal-anatomy-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hypoxia (environmental)
Hypoxia refers to low oxygen conditions. Normally, 20.9% of the gas in the atmosphere is oxygen. The partial pressure of oxygen in the atmosphere is 20.9% of the total barometric pressure. In water, oxygen levels are much lower, approximately 7 ppm or 0.0007% in good quality water, and fluctuate locally depending on the presence of photosynthetic organisms and relative distance to the surface (if there is more oxygen in the air, it will diffuse across the partial pressure gradient). Atmospheric hypoxia Atmospheric hypoxia occurs naturally at high altitudes. Total atmospheric pressure decreases as altitude increases, causing a lower partial pressure of oxygen, which is defined as hypobaric hypoxia. Oxygen remains at 20.9% of the total gas mixture, differing from hypoxic hypoxia, where the percentage of oxygen in the air (or blood) is decreased. This is common in the sealed burrows of some subterranean animals, such as blesmols. Atmospheric hypoxia is also the basis of altitude ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
