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Ossicles are small calcareous elements embedded in the dermis of the body wall of echinoderms. They form part of the endoskeleton and provide rigidity and protection. They are found in different forms and arrangements in sea urchins , starfish , brittle stars , sea cucumbers , and crinoids .
The ossicles from which the stem is composed are known as columnals. They are discs with a circular, pentagonal, star-shaped or elliptical cross section. The stem is flexible and the columnals are connected to each other with ligaments. At each node where the columnals articulate with each other there may be a whorl of five cirri. These ...
The ossicles may bear external projections in the form of spines, granules or warts and they are supported by a tough epidermis. Skeletal elements are sometimes deployed in specialized ways, such as the chewing organ called "Aristotle's lantern" in sea urchins, the supportive stalks of crinoids, and the structural "lime ring" of sea cucumbers. [13]
These ossicles fossilise well and there are beds of limestone dating from the Lower Carboniferous around Clitheroe, England, formed almost exclusively from a diverse fauna of crinoid fossils. [15] Stalked crinoid drawn by Ernst Haeckel. The stem of sea lilies is composed of a column of highly porous ossicles which are connected by ligamentary ...
Plants may bear either all bisexual flowers (hermaphroditic), both male and female flowers (monoecious), or only one sex (dioecious), in which case separate plants are either male or female flower-bearing. Where both bisexual and unisexual flowers exist on the same plant, it is called polygamous.
The ossicles (also called auditory ossicles) are three irregular bones in the middle ear of humans and other mammals, and are among the smallest bones in the human body. . Although the term "ossicle" literally means "tiny bone" (from Latin ossiculum) and may refer to any small bone throughout the body, it typically refers specifically to the malleus, incus and stapes ("hammer, anvil, and ...
In plants of the Asteraceae, what appears to be a single "daisy"-type flower is actually a composite of several much smaller flowers, known as the capitulum or head. By visually presenting as a single flower, the capitulum functions in attracting pollinators , in the same manner that other "showy" flowering plants in numerous other, older ...
A plant which completes its life cycle (i.e. germinates, reproduces, and dies) within two years or growing seasons. Biennial plants usually form a basal rosette of leaves in the first year and then flower and fruit in the second year. bifid Forked; cut in two for about half its length. Compare trifid. bifoliate