Anatomy of Starfish

The diagram of starfish shows that they do not possess a backbone rather have a skeleton beneath their skin. This endoskeleton is composed of a intricate arrangement of hard bony plates formed from calcium carbonate, held together by flexible tissues.

Aboral Surface of Starfish

• Eye: The common starfish has five eyespots on the end of each of its five arms. These eyespots can detect shadow and light.
• Tube Feet: The starfish diagram shows specialised structures known asa tube feet, resembling tentacles with small suckers at their ends, for movement. It also enables them to grip onto surfaces such as rock walls.
• Trivium: The three rays that are furthest away from the madreporite of the sea star.
• Bivium: The two rays nearest to the madreporite of the sea star.
• Anus: At the end of the digestive tract of a sea star lies the area where waste is expelled. However, in sea stars, most undigested food is regurgitated rather than passed through the anus.
• Madreporite or sieve plate: This is the reddish-orange, sometimes white spot located at the center-top of the starfish body allowing water to enter its water vascular system.
• Rays: Common sea stars typically have five rays, although they may loose one or develop an additional one. Most sea stars possess between 5 to 14 rays. If a sea star loses a ray due to predation or injury, it has the remarkable ability to regenerate it. This process of growing ray is termed regeneration.

Oral surface of the Starfish

• Spines: The surface of the sea star is covered in numerous white spines, which provide it with a rough texture and serves as a means of protection.
• Stomach: Sea stars possess two stomachs: the pyloric and the cardiac stomach. When feeding, they extend the cardiac stomach out of their body through the stomach located at the center of their underside to envelop their prey. Subsequently, they release digestive enzymes to break down the prey. Once digestion is complete, the partially digested food is transferred to the pyloric stomach as the cardiac stomach retracts.
• Mouth: The mouth of the sea star is situated at the center of its body, positioned underneath. A portion of the sea star stomach is linked to its mouth and when food is present, the stomach extends out from the mouth to consume it.
• Ambulacral groove: This region contains the tube feet of the sea star which is situated beneath each of its ray.

Water Vascular System of the Starfish

• Madreporite or sieve plate: A small, smooth plate serves as the entry point for the sea stars water vascular system, allowing it to draw in seawater. It is positioned slightly off-center on the aboral side of the sea star, this plate is responsible for regulating water intake.
• Stone canal: A tube links the sea star madreporite to its ring canal, constituting the second segment of its vascular system.
• Ring canal: The circular tube within the sea star’s water vascular system that links the stone canal to the ampullae located in its rays.
• Ampullae: A pouch-like part which enlarges and contracts to facilitate the movement up and down each tube foot. When the sea stars desired to generate suction at the end of its tube foot, its ampullae extracts water from the podia.
• Podia (tube foot): They are equipped with suction cups for gripping rocks and prey. Found along the underside of its rays, they aid in movement, gas exchange, and waste removal.

The diagram of starfish illustrates its anatomy and structure. The starfish are also known as sea stars that belong to Phylum Echinodermata. The diagram of starfish class 11 shows five arms extending from a central disc, with tiny tube feet lining the underside. The starfish diagram may also depict other features such as the mouth in the center of the underside.

A diagram of starfish and labels is given below: