Arthropods and Echinoderms
Science

An arthropod’s respiratory organ, with folded walls arranged like pages in a book
Book lung
An arthropods respiratory organ, with folded walls arranged like pages in a book. Book lung. A book lung is a breathing organ in some arachnids, like spiders, that looks like stacked pages and helps them exchange gases with the environment.

The shell of a turtle or tortoise, or the plate that covers the head of a crustacean
Carapace
The shell of a turtle or tortoise, or the plate that covers the head of a crustacean. Carapace. In science, a carapace is a hard protective outer covering found on certain animals, like turtles and crustaceans.

Metamorphosis with 4 stages, where the young and the adults look very different
Complete metamorphosis
Metamorphosis with 4 stages, where the young and the adults look very different. Complete metamorphosis. Complete metamorphosis is when an insect undergoes four distinct stages egg, larva, pupa, and adult, each looking different from the others.

Metamorphosis with 3 stages, where the young and the adults look alike
Incomplete metamorphosis
Metamorphosis with 3 stages, where the young and the adults look alike. Incomplete metamorphosis. Incomplete metamorphosis is when an insect changes form in three stages egg, nymph, and adult, and the young nymphs resemble the adults.

Sieve-like structure that filters particles from an echinoderm’s water vascular system
Madreporite
Sieve-like structure that filters particles from an echinoderms water vascular system. Madreporite. The madreporite is a small, porous plate on the surface of echinoderms that acts like a filter to manage water flow into their water vascular system.

A fused head and thorax found in some arthropods the mouthpart adapted for biting and chewing food, in most arthropods
Mandible
A fused head and thorax found in some arthropods the mouthpart adapted for biting and chewing food, in most arthropods. Mandible. A mandible is the jaw or jawbone, particularly in arthropods, used for biting and chewing food.

A flexible, rod-like structure that runs along the upper part of a chordate’s body
Notochord
A flexible, rod-like structure that runs along the upper part of a chordates body. Notochord. The notochord is a supportive structure found in embryos that helps in the development of the spinal column in vertebrates.

The second pair of appendages in arachnids, used for sensing and for holding prey
Pedipalp
The second pair of appendages in arachnids, used for sensing and for holding prey, is called a pedipalp. In simple terms, a pedipalp is a specialized limb in spiders and scorpions that helps them sense their environment and catch food.

A chemical released by an animal, that affects the behavior of other animals of the same species
Pheromone
A chemical released by an animal, that affects the behavior of other animals of the same species. Pheromone. Pheromones are natural chemicals that animals release to send signals to others, like attracting mates or marking territory.