Phylum Echinodermata

Phylum Echinodermata is the correct answer. This phylum includes starfish, sea urchins, and sea cucumbers. Echinoderms are marine animals that are characterized by their spiny skin and radial symmetry.

Characteristics of Echinoderms:
1. Radial Symmetry: Echinoderms have a radial symmetry, which means their body parts are arranged symmetrically around a central axis. This is different from animals with bilateral symmetry, where the body is divided into left and right halves.

2. Spiny Skin: Echinoderms have a unique feature of having spiny skin. The spines help protect the animal and provide support. These spines can vary in size and shape depending on the species.

3. Water Vascular System: Echinoderms have a unique water vascular system, which is a network of fluid-filled canals that helps with movement, feeding, and respiration. This system is also responsible for the tube feet that echinoderms use for locomotion.

4. Tube Feet: Tube feet are small, flexible, and hollow structures that echinoderms use for various functions such as locomotion, feeding, and attachment to surfaces. These tube feet are operated by the water vascular system and can be extended or retracted as needed.

Examples of Echinoderms:
1. Starfish (Class Asteroidea): Starfish, also known as sea stars, are one of the most well-known echinoderms. They have a central disc-shaped body with multiple arms extending outwards. Each arm typically has rows of tube feet that help with movement and capturing prey.

2. Sea Urchins (Class Echinoidea): Sea urchins have a round or oval-shaped body covered in spines. They lack arms like starfish but have a mouth located on the underside of their body. Sea urchins use their spines and tube feet for locomotion and feeding.

3. Sea Cucumbers (Class Holothuroidea): Sea cucumbers have a long cylindrical body with a soft and leathery skin. They lack spines and have a mouth and anus at opposite ends of their body. Sea cucumbers can move using their tube feet or by contracting and expanding their body muscles.

In conclusion, the phylum Echinodermata includes starfish, sea urchins, and sea cucumbers. These marine animals are characterized by their spiny skin, radial symmetry, water vascular system, and tube feet.