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A subclass of bivalve mollusks (class Bivalvia) that are unique in their possession of a muscular septum instead of a filamentous gill. The Septibranchia equate in great part to the superfamily Poromyacea, which includes the septibranch families Cuspidariidae and Poromyidae, and the Verticordiidae. The Verticordiidae have gills that are greatly reduced in size. Although there are a few cuspidariid species in shallow seas, the great majority of septibranchs are found at lower slope and abyssal depths which are deficient in food for filter-feeding bivalves. They live close to the surface in soft sediments. Most species are less than 20 mm maximum length.
Industry:Science
A subclass of bivalve mollusks characterized by a foot with a sole that is divided sagittally and longitudinally and has papillate margins. The foot is without a true byssus gland, although a nonhomologous byssal gland is frequently present in the heel. The byssal gland does not produce threads and has a structure totally different from the byssus gland of the subclass Lamellibranchia. The gill filaments, which are not reflected, are usually platelike with abfrontal cilia. Thus the gills (etenidia) resemble those of aspidobranch gastropods rather than those of the lamellibranch bivalves. Digestion is entirely extracellular.
Industry:Science
A subclass of bloodsucking crustacean arthropods, parasitic in the respiratory organs of vertebrates, that frequently are referred to as the Linguatulida or tongue worms. The adults are vermiform, with a short cephalothorax and an elongate, annulate abdomen that may be cylindrical or flattened. On the ventral surface the cephalothorax bears two pairs of hooklike, retractile claws. Respiratory, circulatory, and excretory organs are absent. The digestive tract is a straight tube with cuticle-lined anterior and posterior ends. The nervous system consists of subesophageal ganglia and a circumesophageal ring. Paired nerves extend from the ganglia to cephalic structures, and a midventral pair extends posteriad the length of the body. The sexes are separate; the females are two to five times the size of the males. The male genital pore is medial and ventral, at the anterior border of the abdomen. The female genital pore is anterior in the Cephalobaenida but located at or near the posterior end of the body in the Porocephalida.
Industry:Science
A subclass of Crustacea with eight orders. There are over 6000 species, most of which are free-living in aqueous environments, though many are parasitic or symbiotic with other aquatic animals. The free-living forms are the most abundant of all animals in the sea and directly constitute the main food for vast numbers of fishes, many invertebrates, and also at times for baleen whales.
Industry:Science
A subclass of Echinoidea (sea urchins, sand dollars, and heart urchins) in which the test plates are consistently arranged in double rows or columns. Five double rows bear the tube feet (the ambulacral rows), and these alternate with five which do not (the interambulacral rows). Eighteen orders are included within the Euechinoidea.
Industry:Science
A subclass of Echinoidea lacking stability in the number of columns of plates that make up the ambulacra and interambulacra. The ambulacral columns vary from 2 to 20, the interambulacral from 1 to 14. There are two orders, Bothriocidaroida and Echinocystitoida.
Industry:Science
A subclass of Liliopsida (Monocotyledons) of the division Magnoliophyta (Angiospermae), the flowering plants, containing two orders (Bromeliales and Zingiberales), with nine families and about 3800 species. The subclass has been associated with the Commelinidae and the Liliidae, sharing some features with each but aberrant in either, and it differs from both in usually having four or more supporting cells around each stomate. The flowers are usually epigynous, usually bisexual, and often irregular, and they are usually showy and adapted to pollination by insects or other animals. The pistil consists of three united carpels, often with septal nectaries opening at the top of the ovary. The seeds usually have well-developed, mealy or starchy endosperm.
Industry:Science
A subclass of living and extinct diapsid reptiles. Lepidosauria and their immediate ancestors constitute the Lepidosauromorpha, one of the two major clades of the Diapsida. By definition, Lepidosauria includes the last common ancestor of the living squamates (lizards, snakes, and the limb-reduced burrowing amphisbaenians) and the New Zealand tuatara (<i>Sphenodon</i>) and all of its descendants.
This is a narrower definition than that used in older literature, where Lepidosauria was used as a catchall group for all non-archosaurian diapsids. Lepidosaurs differ from archosaurs in that the lower temporal arcade (the inferior border of the lower temporal fenestra) is typically incomplete, there is never an antorbital fenestra in front of the orbit or a mandibular fenestra in the lower jaw, and the teeth are generally fused in position (acrodont or pleurodont) rather than implanted in sockets (thecodont). Other lepidosaurian characters include a specialized skin-shedding mechanism, paired male hemipenes (copulatory organs that characterize lizards and snakes), fracture planes in the caudal vertebrae that allow the tail to be shed if grabbed by a predator, and specialized knee, foot, and ankle joints that improve locomotion. As in mammals, the ends of lepidosaurian long bones develop separate centers of ossification (epiphyses) that fuse to the shaft at the end of skeletal growth.
Industry:Science
A subclass of Rhizopodea characterized by lobopodia predominantly, although certain of these protozoan species also may form slender pseudopodia, or even develop several different kinds. Lobosia are divided into two orders which differ in presence or absence of a test. The Amoebida include the amebas, which do not produce a test. The Arcellinida possess a one-chambered test ranging from a predominantly chitinous to a mainly siliceous covering. Pseudopodia emerge through the aperture of the test.
Industry:Science
A subclass of tapeworms including most of the members of the class Cestoda, which is a taxon of the platyhelminthes. All species are endoparasites of vertebrates, living in the intestine or related ducts.
Industry:Science
