Starfish Preparation for Dissection
Background of Starfish • Phylum Echinodermata, class Asteroidea • Brittle Stars are in the class Ophiuroidea • Sharp spines, radial symmetry, and tube feet • Have no front or back, they can move in any direction without turning • Rather than using muscles, they move their hundreds of tube feet with a complex hydraulic system to move around, cling to rocks, or open shellfish
Objectives of Dissection • To observe the external and internal characteristics of a starfish • Name the organs that make up systems of the starfish • Describe the appearance and function of various organs found in a starfish
The dorsal side, on the opposite side of the mouth, is called the aboral surface • The ventral side, where the mouth is, is called the oral surface Aboral Surface Oral Surface
External Parts- Aboral Side • The central disc is the activity center of the starfish. • The arms of the starfish are rays. (5~40 rays) Central Disc Rays
Surface of the Aboral Side • The red structures are spines for protection • The blue structures are skin gills for exchange of gases and waste • The green structure is the pincer-like pedicellaria for keeping the surface free of other organisms like barnacles
Eyespot (Nervous System) • Starfish have microscopic eyespots on the tips of each arm to distinguish light and dark
External Parts- Oral Side Mouth Ambulacral Groove (Each groove has 2~4 rows of tube feet)
External Parts- Oral Side • Ambulacral Spines surround tube feet and are used for protection
Water Vascular System • The sieve-like intake valve for the water vascular system is generally on the top of the starfish, just off center, called the madreporite. Close up of madreporite Leather star
The ring canal is the ring in the center that is connected to all rays • Water is circulated from the madreporite, through the stone canal, to the ring canal, and into the radial canals. Calcium skeletal plates cover and protect canals. The radial canals carry water to ampullae, which squeeze water into tube feet.
The bubble or bulb-like structures above tube feet are the ampullae, and they work like an eyedropper to move water up and down tube feet, causing a suction to eat or move
The blue arrow is pointing to the ambulacral ridge • The part of the water vascular system found inside this ridge is the radial canal • The part of the nervous system that is found inside is the radial nerve, that coordinates tube feet movement Radial Nerve (Nervous System)
Circulatory System • The space around the organs is the coelem • The fluid hemolymphin the coelem surrounds organs and distributes oxygen and nutrients • No heart or blood vessels
Respiratory/Excretory System • No respiratory or excretory organs • Gases and nitrogen waste (ammonia) are exchanged between the hemolymph fluid and skin gills and tube feet
Digestive System • F= mouth, food enters • B= anus, wastes leave • A= stomach • The stomach connected to the mouth is the cardiac stomach. It is extruded from the mouth when feeding. • The stomach above is the pyloric stomach, connected to digestive glands=G.
Pyloric Stomach Cardiac Stomach
Digestive glands (pyloric caeca) digest food Gonads are the testes or ovaries of the reproductive system Ossicles are the calcium skeletal plates Gonads (Reproductive System) Ossicles (Skeletal System)
The long, greenish-brown digestive glands make bile, and absorb nutrients from the pyloric stomach. • The gonads below the digestive glands make sperm or eggs depending on the starfish’s sex. They may be small if it’s not breeding season or starfish are not sexually mature. Digestive Glands (Digestive System) Gonads (Reproductive System)
Sexual Reproduction • Gonads produce sperm OR eggs, which join in water outside the body (external fertilization). • The fertilized egg becomes bilaterally symmetrical bipinnara(free swimming, winged) larva, which undergoes metamorphosis into a radially symmetrical adult.
Asexual Reproduction • They have autonomy of arms, being able to self-amputate arms to escape predators, then regenerate them. • Some starfish can regenerate whole bodies from arms (comet form), while some can do so from fragments just 1cm long. • When larvae sense plentiful food, they will reproduce through budding.