Echinoderms are a fascinating group of marine animals that include starfish, sea urchins, sea cucumbers, and sand dollars. These creatures are classified as deuterostomes, which distinguishes them from protostomes, despite their appearance sometimes suggesting otherwise. Notably, echinoderms are the only deuterostome animals that are not chordates. They exhibit bilateral symmetry, which can be visualized by drawing a line through a starfish, highlighting their symmetrical structure.
The term "echinoderm" is derived from their spiny skin, which is supported by an internal skeleton known as an endoskeleton. This endoskeleton is composed of plates that may either fuse together or be connected by soft tissues, resembling the layered armor of a knight. The skin grows over these plates, allowing the underlying structure to be somewhat visible, as seen in starfish.
Echinoderms have unique reproductive strategies, capable of both sexual and asexual reproduction. In sexual reproduction, individuals typically have separate sexes. A standout feature of echinoderms is their water vascular system, a network of fluid-filled tubes that serves multiple functions, including internal transport, respiration, and locomotion. This system allows them to move by circulating water, which is essential for their mobility.
Additionally, echinoderms possess tube feet, which are extensions of the water vascular system. These tube feet play a crucial role in both locomotion and feeding, enabling echinoderms to move and capture prey effectively. The intricate design of their water vascular system and tube feet exemplifies the unique adaptations that allow echinoderms to thrive in their marine environments.