Lab9_Echinoderms

Lab9_Echinoderms - Laboratory 9 Echinodermata 170...

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Echinodermata Laboratory 9
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170 Laboratory 9: Echinoderms OBJECTIVES After completing this lab you will be able to: 1. Compare the starfish and the cockroach in seven traits body symmetry body cavity support circulation gas exchange reproduction development LAB PREPARATION In preparation for this laboratory you should do the following: 1. Read and study this laboratory. 2. Read Chapter 32, Chapter 33, and Chapter 47, in Campbell (7 th Ed.) 3. Bring your dissection instruments to lab. 4. Bring personal protective gear (lab coat, goggles, gloves) to lab. INTRODUCTION Starfish (or sea stars) are in the Phylum Echinodermata (Gk. echino, spiny; derma, skin), Class Asteroidea. The phylum has five other Classes: Echinoidea (sea urchins), Ophiuroidea (brittle stars), Holothuroidea (sea cucumbers), Crinoidea (sea lilies), and Concentricycloidea (sea daisies). Echinoderms are exclusively marine animals and the only major group of deuterostome invertebrates (see Development below). Unlike other radiate phyla (e.g., sponges, cnidarians, and ctenophores), the echinoderms possess a true coelom and an internal mesodermal skeleton (endoskeleton). A portion of the coelom is modified into a water vascular system, i.e., tube feet and associated structures, which is a unique adaptation of the phylum. They lack any excretory organs (which is a likely reason for their exclusivemarineexistence),heart,or segmentation. The most striking characteristic of the group is their pentaradiate symmetry; their body can usually be divided into five parts around a central axis. This unique symmetry, however, is secondarily derived from a bilaterally symmetric ancestral form (all echinoderm larvae are bilaterally symmetric). Because of this symmetry, the surfaces of echinoderms are not divided into dorsal and ventral, but oral (bearing the mouth) and aboral (opposite the mouth). A. Support & Movement Support in the starfish is by an endoskeleton, and movement is achieved mainly by action of the tube feet or podia, components of the water vascular system.
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Laboratory 9: Echinoderms 171 1. The Skeleton The starfish body is supported by a calcareous endoskeleton composed of adjacent, articulating skeletal plates. Although the skeleton may appear to be outside the body of the organism, it is actually covered with a thin epidermal layer and is derived from mesoderm. While the skeleton’s primary function is protection and support, it also assists in locomotion. In the arms of starfish, the body wall muscles are arranged in bands between the plates, providing various degrees of arm motion. In addition to short spines or tubercles, pincer-like pedicillariae (which are modified spines) cover the outer surface of the star fish Ffigure 9-1). A pedicillariae can be divided into a basal stalk and more distal jaws. Their primary functions are to keep the exposed portions of the star fish clean, protect the more delicate tube feet and gills, and capture small prey organisms. When first discovered, in 1778, they were thought to be parasitic organisms and were given the scientific name Pedicellaria. They vary in size and density and react
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This note was uploaded on 04/10/2008 for the course BIO 172L taught by Professor Gerald during the Spring '08 term at Hawaii.

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Lab9_Echinoderms - Laboratory 9 Echinodermata 170...

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