Animals, Invertebrates, Cnidarians, Mollusks
Science

A circulation system in which blood flows within a network of vessels
Closed circulatory system
A circulation system in which blood flows within a network of vessels. Closed circulatory system. A closed circulatory system is where blood is contained within vessels, allowing efficient nutrient and oxygen transport throughout the body.

The fluid-filled main body cavity, lined with mesoderm, it contains the internal organs
Coelom
The fluid-filled main body cavity, lined with mesoderm, it contains the internal organs. Coelom. The coelom is a hollow space within the body that houses and protects internal organs, allowing them to move independently from the body wall.

Inner germ layer in most animals, it develops from the inner surface of the gastrula
Endoderm
Inner germ layer in most animals, it develops from the inner surface of the gastrula. Endoderm. The endoderm is the innermost layer of cells in an embryo that develops into the lining of the digestive and respiratory systems.

Embryo development stage with two or three cell layers, it follows the blastula stage
Gastrula
Embryo development stage with two or three cell layers, it follows the blastula stage. Gastrula. The gastrula is an early stage in embryonic development where the embryo starts forming distinct layers that will become different tissues and organs.

The fluid-filled cavity that aids movement in animals like earthworms
Hydrostatic skeleton
The fluid-filled cavity that aids movement in animals like earthworms hydrostatic skeleton. A hydrostatic skeleton is a structure in some soft-bodied animals where a fluid-filled cavity is used to support the body and help with movement.

The cell layer between the ectoderm and endoderm, it develops into the circulatory, reproductive and excretory systems
Mesoderm
The cell layer between the ectoderm and endoderm, it develops into the circulatory, reproductive, and excretory systems. Mesoderm is the middle layer of an embryo that forms muscles, bones, and other internal organs.

A cnidarian’s nervous system, made of a network of nerve cells spread through its body
Nerve net
A cnidarians nervous system, made of a network of nerve cells spread through its body. Nerve net. A nerve net is a simple system with interconnected nerve cells that allow cnidarians to respond to their environment without a central brain.