chordates
Chordates are a group of animals that possess a dorsal nerve cord, a notochord, pharyngeal slits, and a post- tail at some stage in their development. This group includes most animals that we commonly think of as vertebrates, such as fish, reptiles, birds, and mammals. However, there are also some non-vertebrate chordates, such as lancelets and tunicates. Chordates are known for their well-developed nervous system, which enables them to respond to and interact with their environment in complex ways.
Chordates are a phylum of animals characterized by the presence of a notochord, a stiff, elongated structure that supports the body. They also have a hollow, dorsal nerve cord, gill slits, and a post- tail. Chordates include a wide range of animals, from fish and birds to mammals and humans.
Here are the main steps to understand chordates:
Step 1: Chordate Characteristics
Chordates possess several key characteristics. These include the presence of a notochord, which is a flexible rod-like structure that runs along the length of the body. The notochord provides support and helps with locomotion. Chordates also have a hollow, dorsal nerve cord, which eventually develops into the spinal cord in vertebrates. Additionally, they possess gill slits, which are openings in the throat region that allow for respiration, and a post- tail.
Step 2: Classification of Chordates
Chordates are divided into three major subphyla: Urochordata (tunicates), Cephalochordata (lancelets), and Vertebrata (vertebrates). Urochordates and cephalochordates are often referred to as invertebrate chordates, while vertebrates are the more familiar group that includes fish, amphibians, reptiles, birds, and mammals.
Step 3: Urochordates (Tunicates)
Urochordates, commonly known as tunicates or sea squirts, are marine animals that live attached to rocks or other substrates. They possess a sac-like body covered by a tough, non-living outer covering called the tunic. Urochordates filter-feed by pumping water through their bodies using a specialized structure called the pharyngeal basket.
Step 4: Cephalochordates (Lancelets)
Cephalochordates, commonly known as lancelets or amphioxus, are small, slender marine animals that resemble fish in shape. They bury themselves in sandy or muddy substrates, leaving only their mouth and gill slits exposed. Cephalochordates filter-feed by pumping water through their pharynx.
Step 5: Vertebrates
Vertebrates include fish, amphibians, reptiles, birds, and mammals. They possess a backbone or vertebral column, which replaces the notochord in development. Vertebrates have a more complex body plan compared to invertebrate chordates and exhibit a variety of adaptations for different lifestyles.
Step 6: Evolutionary Significance
Chordates are considered a significant group in the animal kingdom due to their close relationship with humans. Humans are classified as mammals within the vertebrate subphylum. The presence of a notochord and a dorsal nerve cord in early chordates is believed to have provided the foundation for the development of the central nervous system in more complex animals like humans.