Invertebrate Histology. Группа авторов. Читать онлайн. Newlib. NEWLIB.NET

Автор: Группа авторов
Издательство: John Wiley & Sons Limited
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Жанр произведения: Биология
Год издания: 0
isbn: 9781119507604
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to trauma or predation. The diet varies widely by class, with Asterozoa being carnivorous, Echinozoa and Crinozoa being vegetarian browsers and filter feeders, and Holothuroidea being detritivores. Significant conservation concerns and anthropogenic stressors include commercial fisheries, which impact diet availability, particularly clams, mussels, and oysters, and the pet trade through individual animal collection and the collection of coral and live rock causing habitat loss. Environmental concerns include habitat destruction and direct animal impacts due to ocean acidification. Population declines due to disease such as the Caribbean Diadema antillarum mortality event in 1983–1984 (Carpenter 1990; Lessios 2016) and “wasting disease” events across multiple species of asteroid (Hewson et al. 2014; Menge et al. 2016) have more recently received significant focus. Certain Asteroidea are keystone species in their ecosystems, critical for controlling prey populations and diversity. Echinoidea and Holothuroidea are of paramount importance to marine ecosystems because of respective roles in counteracting macroalgal competition with corals, and recycling nutrients from decaying organic matter.

      Uniting features of all echinoderms include radial symmetry (pentamerous symmetry), a tricoelomate body cavity, and a body wall composed of calcite endoskeletal plates (dermal ossicles) connected by “mutable collagenous tissue.” Most internal features, including the alimentary system, reproductive system, nervous system, respiratory system, and a unique water vascular system, share similar basic plans between the subphyla. The basic echinoderm body plan has 10 divisions: five radii (rays or arms) which alternate with five interradii (interrays). Typically, there is an oral surface with a central mouth and an aboral surface that contains the anus. Despite these commonalities, morphology does vary widely and thus representative examples of each subphylum are discussed separately.

Photos depict the aboral (a) and oral (b) surface of a chocolate chip sea star demonstrating pentamerous symmetry. Labels include (A) radius, (B) interradius, (C) mouth, (D) ambulacral groove, (E) anus, and (F) madreporite. Photos depict the aboral (a) and oral (b) surface of a purple urchin demonstrating pentamerous symmetry. Labels include (A) ambulacral plates, (B) interambulacral plates, (C) mouth, (D) anus, and (E) madreporite. Photo depicts a white sea urchin demonstrating the distinction between ambulacral (A) and interambulacral (I) plates.

      Spines are arranged symmetrically in meridional rows along both ambulacral and interambulacral areas with the longest spines near the equator and shortest near the poles. Most urchins have long primary spines and shorter secondary spines equally distributed over the surface. Some species only have primary spines. Spines are cylindrical, taper to a point, and attach to the plates by a tubercle, resembling a ball and socket joint. Sand dollars and sea biscuits have a dorsoventrally compressed body plan compared to urchins, but similar anatomic features. The ventral ambulacral areas are called phyllodes and have tube feet modified for feeding and adhesion. The dorsal ambulacral areas are called petaloids (or petals) and tube feet are broad, flat, and specialized for respiration (gills).

Photos depict the ventral (a) and lateral (b) aspects of a California giant sea cucumber. Labels include (A) dorsal ambulacra, (B) ventral ambulacra, (C) buccal podia, and (D) anus.