SEA STAR DISSECTION

SEA STAR LATIN meaning ANIMALIA ASTEROIDEA “star-like” KINGDOM _____________ PHYLUM _____________________________ CLASS _______________________________ ANIMALIA ECHINODERMATA “spiny skin” ASTEROIDEA “star-like”

Echinodermata Asteroidea (sea stars) Crinoidea (sea lilies & feather stars) Ophiuroidea (brittle stars) Echinoidea (sea urchins & sand dollars) Holothuroidea (sea cucumbers)

Sea Stars (starfish) Come in a variety of colors

But all echinoderms: Are marine Have spiny skin Have a water vascular system with tube feet Have radial symmetry as adults Have bilateral symmetry as juveniles

SYMMETRY ADULTS- Radial LARVA- Bilateral

PENTARADIAL (5 armed sea star)

SPINY SKIN SPINES for protection connect to ENDOSKELETON inside underneath skin

Respiration The spines on the aboral surface are extensions of the skeletal plates. Surrounding each spine are skin gills, which function in respiration. In addition, there are tiny structures called pedicellariae. These are composed of two jaws (moved by muscles) that open and shut, primarily to keep the body surface (and skin gills) clean of debris.

Madreporite Opening to water vascular system

TUBE FEET surfaces Part of water vascular system and can exchange gases and excrete nitrogen waste

AMBULACRAL GROOVE TUBE FEET sit in GROOVE

TUBE FEET Used for feeding & locomotion http://www.scsc.k12.ar.us/2001Outwest/PacificNaturalHistory/Projects/ReynoldsJ/starfish.jpg

The first incision on your sea star will be to cut through the top of the central disc and down one ray (arm).

Digestive System The central disc contains the complete digestive tract, extending from a mouth on the oral surface (ventral) to the anus on the aboral surface (dorsal side). There is an upper (cardiac) stomach and a lower (pyloric) stomach. Sea stars can evert their lower stomach out their mouth which allows them to eat large prey. Enzymes are produced in the digestive glands, which occupy most of the space in each of the arms. They drain their secretions into the stomach to help digest food. Waste passes out the anus on the top of the sea star.

Pyloric and Cardiac stomachs

DIGESTIVE SYSTEM ANUS DIGESTIVE DIGESTIVE GLANDS GLANDS MOUTH Image by Riedell

CARDIAC stomach connects to mouth (extruded during feeding) PYLORIC stomach connects to digestive glands and ANUS

ENDOSKELETON made of OSSICLES The sea star endoskeleton consists of a set of small calcium carbonate plates that lie buried below the skin of the sea star. The skeleton functions to both support and protect. With one exception, all skeletal plates in echinoderms are covered with tissue. Locomotion is not achieved by muscles attached to the skeleton. No echinoderm has an old age or senescence. In effect, unless they starve to death, get diseased, get eaten or suffer from some environmental disaster, they have the potential of immortality

OSSICLES Calcium carbonate plates form endoskeleton inside

Locomotion Sea Stars move around using a unique water vascular system. The internal canals of this system include a circular ring canal and its extensions into each arm, called radial canals. The stone canal links the ring canal to the outside through a hole on the aboral surface, called the madreporite. Branching from the radial canals are the tube feet, each with a bulb called an ampulla and a tube foot with a small sucker. The hydraulic action of the water vascular system provides the mechanism for locomotion. When the ampulla contracts, the fluid is forced into the tube foot to elongate it. When the stretching foot makes contact with the surface below the animal, the center of the sucker retracts to produce a vacuum. After the foot sticks to the surface, muscle fibers shorten the foot again. Each tube foot is very small and moves the starfish only a small distance, but they have many of them.

http://www.k-state.edu/organismic/echinoderms_and_protochordates.htm

GONADS

AMBULACRAL RIDGE covered by OSSICLES contains RADIAL NERVE (nervous) http://wwwbio200.nsm.buffalo.edu/labs/tutor/Starfish/ AMBULACRAL RIDGE covered by OSSICLES contains RADIAL NERVE (nervous) RADIAL CANAL (water vascular system)

AMBULACRAL RIDGE AMPULLAE (tops of tube feet)

Nervous System The presence of radial symmetry implies no front end, and indeed, no head is found anywhere in this phylum. They are truly brainless, and the remainder of the nervous system is poorly known as the nerves are exceptionally small and diffuse. However, they are sensitive to touch, light, temperature, orientation and the status of the water around them. The tube feet, especially those at the tips of the rays, are also sensitive to chemicals, enabling the starfish to detect odour sources such as food. There are eyespots at the ends of the arms. The starfish does not have the capacity to plan its actions. If one arm detects an attractive odour, it becomes dominant and temporarily over-rides the other arms to initiate movement towards the prey.

Sea Star Reproduction Digestive gland Gonad Ossicles Some sea stars are simultaneous hermaphrodites, but most are dioecious (have separates sexes) Ossicles During the breeding season, the arms also contain gonads that produce eggs or sperm, which are discharged from the body through gonopores in each arm. Fertilization is then external, and the larvae are planktonic and grow independently of the parents throughout their developmental stages. Why is this an adaptation for these organisms?