Marine Invertebrates Ebook
In 1828, his father sent him to Christ's College, Cambridge, to take the common arts degree, with the idea that he should become a clergyman. Even in his youth Charles had expressed great interest in natural history, and at Edinburgh he learned of Lamarck's theory of evolution under the tutelage of Grant, who directed him in a study of marine invertebrates and who, as Darwin later recalled, burst forth in high admiration of Lamarck and his views on evolution. 14 At Cambridge Darwin associated with several university faculty, including John Stephens Henslow, professor of botany Adam Segwick, professor of geology and William Whewell, professor of mineralogy. Darwin took his degree in 1831, tenth in the list of those who did not seek honors. He did not pursue a religious vocation. Instead, his career took an unforeseen turn.
Remoteness in time could influence the assignment of two taxa to different taxonomic groups of equal rank. Raup (1983) found that the mean geologic age of first occurrences of the 27 readily preservable class-level taxa of marine invertebrates is 533 million years. Twenty of the 27 taxa first occur in the Cambrian at the time of this study. Because high taxonomic rank is based on genealogical relationship, overall similarity, and species richness, it is not clear whether this early origin is a function of true early morphological diversification or just an inherent property of higher taxa, whose early origins are bound to make them subtend many subordinate taxa that arise by branching of the stem taxon. But it is not unusual to draw an equivalence between high taxonomic rank and fundamental body plans or occupancy of major adaptive zones (Gould 1989 Simpson 1944, Valentine 1969, Van Valen 1984).
Fins perform many functions other than locomotion, among them, feeding, defense, camouflage, breeding, and social display. Many species, such as the lumpfish (Cyclopterus lumpus), have pelvic fins modified as suction disks to prevent detachment from the substrate. Fins also are used for feeding, or to deter predation, in a variety of ways. Sea robins (family Triglidae) use sensory cells on the pectoral fins to find marine invertebrates buried in sediment on the ocean floor. Anglerfishes (order Lophiiformes) are named for the structure of the first dorsal spine, which has been modified into a fishing pole and bait, called, respectively, the illicium and the esca, held over the anglerfish's mouth. With this complex
Tardigrades may be carnivorous, herbivorous, or bacteri-ovorous. Furthermore, a few marine tardigrade species are parasites on other marine invertebrates. Tetrakentron synaptae is found on the holothurian, Leptosynapta galliennei, where it punctures the epidermal cells of the holothurian and sucks out the cell contents. This species is the only tardigrade that has true adaptations for parasitism. It is dorso-ventrally flattened and all the sensory structures are reduced. As well, the claws are armed with three large hooks that are used to penetrate the epidermis of the holothurian. Females in particular are less mobile and are located in small depressions in the
The name Acoela comes from two Greek words that mean without a body cavity it refers to a distinguishing feature of this order (or phylum) of tiny wormlike multicellular marine invertebrates. Species in this group have no true body cavity or coelom. A true coelom is a fluid-filled body cavity formed from mesodermal tissue. It lies between the outer body wall of epidermal tissue and the gut or digestive tract.
Paramyxea Endoparasites in marine invertebrates and of economic importance in bivalves, paramyxids mostly occur as amoeboid cells but form multicellular spores. SSU rRNA sequences are very divergent, although one recent analysis indicates a position within Haplosporidia (Cavalier-Smith and Chao 2003a).
It is well established that natural products play an important role in the discovery and development of new drugs. More recently the importance of the potential of natural marine products as sources of new drugs covering a very wide range of pharmacological effects has increased. In fact the interest in marine compounds for the treatment of neurological disorders appears to be an emerging field 11 . The prominent role that marine invertebrates have played in the generation of novel GSK-3 inhibitors, including hymenialdisine, meridianines, indirubines, manzamines, furanosesquiterpenes, and isofla-
With their bipartite structure already present in primitive marine invertebrates 49 , the GPHr have evolved a specific way to become activated after binding of their hormones to the ectodomain. On the other hand, their membership in the rhodopsin-like family of GPCRs implies that basic molecular mechanisms implicated in the activation of their serpentine domain must be shared with this protein family. We believe that these peculiarities provide a unique opportunity to dissect the molecular steps of activation of type I GPCRs. The particularly wide spectrum of activating mutations in GPHr are expected to mimic (and allow us to explore) the sequential conformational changes that begin after binding of agonists and terminate with activation of the G protein.
His turn to natural history occurred when at age twenty-one, he signed on as assistant surgeon on the H.M.S. Rattlesnake, a Royal Navy frigate assigned to chart the seas around Australia and New Guinea. On that voyage, he collected and studied marine invertebrates, in particular cnidarians (hydra and jellyfish) and tunicates (i.e., sea squirts, or ascidians, sedentary filter feeders with cylindrical bodies, usually found attached to rocks) as well as cephalopod ( head-foot ) mollusks (octopus, squid, and nautilus). His studies of fossils and his contributions to comparative anatomy and embryology earned him acceptance into the highest ranks of the English community of naturalists. Professional positions as scientists, as the Cambridge don William Whewell had named them in 1840, were rare. Most naturalists were affluent amateurs, but Huxley managed to support himself on a stipend from the navy and by writing popular science articles. After leaving the navy in 1854, he secured a...
Adult animals fall into two broad categories in relation to gamete exchange spawners and copulators. Lower metazoans demonstrate a broad range of variations within both of these categories. The vast majority of spawners release their gametes directly into the surrounding water, an activity known as broadcast spawning. Broadcast spawning is the most common method of gamete exchange in free-living marine invertebrates, but is rare among most freshwater groups. In the very lowest phyla (e.g., Porifera, Placozoa, Cnidaria) spawning is the only method of gamete exchange. In some groups, only the males spawn while the females take up the sperm while retaining their oocytes for internal fertilization. In others, both sperm and oocytes are spawned, resulting in external fertilization. For broadcast spawning with external fertilization to be successful, the parent animal must use some strategy to increase the chances of the gametes coming together. The most common strategy involves...
Large, soft-bodied, gelatinous marine invertebrates that swim by contracting their umbrella-shaped swimming bell and catch small prey by means of stinging tentacles Large, soft-bodied, gelatinous marine invertebrates that swim by contracting their umbrella-shaped swimming bell and catch small prey by means of stinging tentacles
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