Starfish Dissection Notes

Overview of Starfish Dissection

  • Objective of Video

    • After watching this video, students should be able to:
    1. Name the organs of the starfish.
    2. Identify features that serve as adaptations for starfish.
    3. Describe the correct procedure for dissecting a starfish.

  • Conservation Note

    • Starfish are facing numerous natural and man-made threats leading to a decline in their populations.

Introduction to Starfish

  • Classification

    • Starfish, also known as sea stars, are radially symmetric marine invertebrates belonging to the phylum Echinodermata.
    • They exhibit the deuterostome pattern of development.
    • Starfish are considered keystone species, indicating their ecological importance in marine environments.

  • Physical Characteristics

    • The starfish has a spiny surface known as the endoskeleton:
    • Composed of calcium-rich plates.
    • The surface features protruding white spines which project through a thin layer of epidermal skin covering the endoskeleton.

  • Body Structure

    • The body of the starfish has two sides:

    • Aboral side (top side)

    • Oral side (bottom side)

    • Central Disc and Madroporite:

    • Found on the surface of the aboral side.

    • Mouth:

    • Located in the center of the central disc on the oral side; it is surrounded by spines.

    • Ambulacral Grooves:

    • Extends from the mouth to the tip of each arm, lined with suction cup-like structures known as tube feet.

Starfish Dissection Procedure

  • Dissection Overview

    • Instead of individual dissection, students will view a dissection video and use this information to answer lab questions.

  • Dissection Steps

    • Cutting the Arms:

    • Begin dissection by cutting one arm at a time; tips of the arms are cut off.

    • Make cuts toward the central disc, keeping them as close to the skin as possible.

    • Lift the skin while cutting; use the point of scissors to assist in lifting and cutting.

    • Remove the flap of aboral surface tissue to unveil internal organs.

    • Repeat for the other two arms.

    • Central Disc Removal:

    • Carefully remove the central disc, avoiding damage to the madroporite.

    • Cuts are made just inside the madroporite.

  • Identifying Internal Organs

    • In one arm, observe the pyloric cecum:

    • Appears as brown material beneath the skin and functions as digestive glands, secreting enzymes and storing nutrients.

    • Upon removal of the pyloric cecum, gonads can be observed:

    • These are involved in sexual reproduction and are clustered, resembling grapes.

    • In another arm, after removing both the pyloric cecum and gonads, observe the ampullae of the tube feet:

    • Jelly-like bulb structures lining the ambulacral ridge, connecting to the podium of the tube feet.

  • Water Vascular System

    • The path of water through the system:
    1. Enters through the madroporite.
    2. Travels along the stone canal.
    3. Leads to the ring canal, which encircles the central disc.
    4. From the ring canal, extend the radial canals located under the ambulacral ridge.
    5. Radial canals connect to the ampullae and subsequently to the tube feet.
    • This system is known as the water vascular system:
    • It plays a crucial role in locomotion and feeding.
    • Water fills the ampullae which, when squeezed, pushes water into the tube feet causing them to expand or contract, acting like a hydrostatic skeleton.

Conclusion

  • Echinoderms possess several unique features:
    • The water vascular system comprises canals that transport water, aiding in movement and feeding.
    • Adult echinoderms exhibit radial symmetry, unlike other deuterostomes that display bilateral symmetry.
    • The endoskeleton is a shared structural feature linking echinoderms to deuterostomes like chordates.