Lab 7 - Echinoderms and Hemichordates

Lab 7 - Echinoderms and Hemichordates - PALEO LABORATORY #...

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PALEO LABORATORY # 7, PAGE 1 LAB # VII - ECHINODERMS, HEMICHORDATES AND CONODONTS A. Phylum Echinodermata The "spiny-skinned" animals, or echinoderms, are highly organized, exclusively-marine invertebrates. They are usually benthonic, living in an attached position or free-moving, but are never colonial. Their body plan and structural organization is very different from that of any other invertebrate group, and all members of the phylum are characterized by a strongly- developed radial symmetry following a five-fold (pentamerous) plan of organization. All echinoderms are further characterized by the possession of skeletal elements formed of calcite. This dermal skeleton usually consists of pentamerously arranged calcareous plates or of small, isolated, calcareous pieces embedded in the skin (and sometimes in the walls of the internal organs!). It is important to observe that the echinoderm skeleton is a product of internal secretion, like the bony skeleton of vertebrates, and that the hard parts may increase in size during the life of the organism. Although a radial plan of body organization is interpreted as a primitive character associated with animals which do not move about but live in fixed locations (e.g. corals), the body structure of echinoderms is much advanced over that of the Porifera and Cnidaria. From the mouth, centrally-located on the upper surface (in "cystoids", blastoids, and crinoids), or lower surface (in echinoids), a long coiled gut extends to the anus, at the opposite pole. An expansion of the digestive tract in some echinoderms corresponds to the stomach. Surrounding the digestive tube is a distinct body cavity. Within the body cavity and extending to the appendages are parts of the nervous system, reproductive parts, and a highly-organized water vascular system. No heart is present. The following classification is typical for the Echinodermata: Phylum Echinodermata Subphylum Blastozoa Class Blastoidea ______ Class Diploporita | formerly termed the Class Cystoidea Class Rhombifera _____| Class Eocrinoidea Class Parablastoidea Subphylum Crinozoa Class Crinoidea Class Paracrinoidea Subphylum Asterozoa Class Asteroidea Class Ophiuroidea Subphulum Echinozoa Class Edrioasteroidea Class Holothuroidea Class Echinoidea
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PALEO LABORATORY # 7, PAGE 2 The dominant Paleozoic echinoderms were attached to the sea floor by means of a jointed, flexible stalk. We may place these within the Subphyla Blastozoa and Crinozoa. The Asterozoa [including Asteroidea (sea stars or starfish) and Ophiuroidea (brittle stars)] have a relatively poor fossil record because their small plates are isolated in soft tissue and usually fall apart when the animal dies. Fossils of the Subphylum Echinoidea include the sea urchins and sand dollars, the sea cucumbers, and several lesser-known classes. The echinoid echinozoans are especially abundant in rocks of Mesozoic and Cenozoic age. 1. Subphylum Blastozoa
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Lab 7 - Echinoderms and Hemichordates - PALEO LABORATORY #...

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