Animal Classification and Body Plans

Animal Body Plans

• Animal body plans are descriptions of how animals are built. They are considered the "blueprint" of cellular organization.
• Animal body plans are influenced by embryonic development patterns, germ cell layers (diploblasts vs. triploblasts), body symmetry, and body cavity type.

Classifying Animals

• The use of body plans to classify animals describes the way animals are built.
• Animal body plans are considered the "blueprint" of cellular organization.

Summary of Body Plans in Animals

• Animal body plans are categorized based on their developmental patterns.
• Acoelomate animals lack a body cavity.
• Protostomes exhibit spiral cleavage, with cell fates determined at an early stage.
• Deuterostomes exhibit radial cleavage, and cell fates are not determined until later.

Embryonic Development Patterns

• Embryonic development patterns are categorized as protostomes and deuterostomes.
• Protostomes and deuterostomes differ in the developmental fates of the first few cells, the formation of the mouth and anus, and the origin of mesoderm and coelom.
• Protostomes exhibit spiral cleavage. Their mouth develops from the blastopore, and their mesoderm differentiates near the blastopore. They have schizocoelom.
• Deuterostomes exhibit radial cleavage. Their anus develops from the blastopore, and their mesoderm originates from outpocketings of the archenteron. They have enterocoelom.
• Protostomes, such as flat worms, lack a body cavity, while deuterostomes, such as chordates, have a body cavity (coelom).

Germ Layers

• Diploblasts have two germ layers: ectoderm and endoderm. Examples include jellyfish, corals, and anemones.
• Triploblasts have three germ layers: ectoderm, mesoderm, and endoderm. Examples include flatworms, chordates, and most other animals.

Primary Cell Layers in Embryos

• Endoderm: the innermost layer that forms the lining of the gut.
• Mesoderm: the middle layer that forms the muscles of the body wall and other structures.
• Ectoderm: the outermost layer that forms the external covering and the nervous system.

From Germ Layers to Tissues and Organs

• Tissues are groups of similar differentiated cells specialized for particular functions.
• Tissues are usually isolated from other tissues by membrane layers

Polarity of the Digestive System

• Blastopore is the first opening formed.
• Later, a second opening forms at the opposite end.
• The second opening transforms the pouch like structure into a digestive tube.
• This determines the position of the mouth and anus in the developing embryo

Origin of the Mesoderm

• In Protostomes, mesoderm differentiates near the blastopore. Coelom forms as a split in the mesoderm (schizocoelom).
• In Deuterostomes, mesoderm originates from outpocketings of the archenteron (primitive gut). Coelom forms from spaces in these outpocketings (enterocoelom).

Body Symmetry

• Radial symmetry can be divided equally by any longitudinal plane passing through the central axis.
• Bilateral symmetry can be divided along a vertical plane at the midpoint to create two identical halves.

Animals with Radial Symmetry

• They are usually diploblastic.
• They lack a clear left or right side and have a top and a bottom.
• They often have circular or tubular shapes with a mouth at one end.

Animals with Bilateral Symmetry

• They are typically triploblastic.
• They have a definite head end (anterior) and tail end (posterior), as well as top (dorsal) and bottom (ventral) sides.
• Most bilateral animals exhibit cephalization
• They typically contain segmentation

Segmentation

• Repeated structures along the anterior-posterior axis
• Advantages: movement, specialization

Deuterostome Body Cavity (Coelom)

• A fluid-filled cavity between the intestines and the body wall.
• Found in most bilaterally symmetrical animals.
• Formed from the mesoderm of the embryo.

Protostome Body Cavities

• Acoelomates have no body cavity.
• Pseudocoelomates have a body cavity between the endoderm and the mesoderm.

Challenges for Animals

• Extract nutrients and energy from the environment.
• Eliminate metabolic wastes.
• Detect environmental changes and adapt.
• Maintain homeostasis.

Unifying Concepts

• Animals are diverse, but share common principles.
• Physiological processes obey the laws of physics and chemistry.
• Physiological processes are usually tightly regulated (homeostasis).

Example: Electrical Laws

• Electrical laws describe membrane function in all cells, including excitable cells like neurons and muscles.

Next Week

• Communication and integration in the animal body, relating to homeostasis and nervous systems.