Question

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2.1 what role does the madreporite play in the water vascular system of sea stars?
2.2 does the sea star possess a heart or circulatory system? how do you suppose nutrients and oxygen are distributed to the tissues?
2.3 does the sea star possess an excretory system? how do you suppose metabolic wastes are eliminated from the body?
2.4 why are ossicles classified as an endoskeleton?
exercise 15 - 5
sea cucumbers (class holothuroidea)
materials needed
preserved sea cucumber
dissecting tools
dissecting pan
latex gloves
sea cucumbers belong to the class holothuroidea. this class contains approximately 1,700 species of cylindrical, soft - bodied, sluggish, filter - feeding echinoderms (fig. 15.1). sea cucumbers sometimes are categorized as deposit feeders, because they are also able to extract organic matter from the fine muddy deposits of the deep seafloor.
procedure
1 obtain a preserved sea cucumber and place it in your dissecting pan.
2 examine the external features of your sea cucumber and refer to table 15 - 4 as you review the anatomy. notice the warty, leathery texture of its skin. tube feet occur sparsely along the body wall and are arranged in five longitudinal rows, corresponding to the pentaradial symmetry characteristic of all echinoderms. near the mouth, the tube feet are modified into feathery tentacles that sea cucumbers use to capture suspended food particles from the surrounding water (fig. 15.12). sea cucumbers sometimes are categorized as deposit feeders, because they are also able to extract organic matter from the fine muddy deposits of the deep seafloor.
3 to view the internal anatomy of your specimen use dissecting scissors to make a longitudinal incision along the body wall from the tentacles toward the anus.
15.11 sea cucumbers are members of the class holothuroidea
306 exploring zoology: a laboratory guide

Explanation:

2.1 The madreporite is a sieve - like structure that allows water to enter the water vascular system of sea stars, regulating water flow.
2.2 Sea stars do not have a heart in the traditional sense. Nutrients and oxygen are distributed through the coelomic fluid in their body cavity and the water vascular system.
2.3 Sea stars have a simple excretory system. Metabolic wastes are likely eliminated through diffusion across their body surface and through the coelomic fluid.
2.4 Ossicles are classified as an endoskeleton because they are internal skeletal structures that provide support and protection within the body of echinoderms.

Answer:

2.1 The madreporite regulates water entry into the water vascular system.
2.2 No heart; nutrients and oxygen distributed via coelomic fluid and water vascular system.
2.3 Wastes eliminated by diffusion across body surface and coelomic fluid.
2.4 Because they are internal skeletal structures providing support and protection.