An Overview of the Phyla of Animalia

Hey guys, this is part 2 of the Introduction to Animal Diversity posted by Neil earlier today. This post will cover the major phyla of Kingdom Animalia and give major features. It is assumed that you read and understand part 1 of this guide.

Lets jump in.

The phyla of Animals are extremely diverse as the definition of “Animal” is broad. Animals stretch from ants and sponges to humans and sea stars. Such diversity has to be separated into definite groups so that biologists can identify species faster and have more research done. Animals are separated by traits such as germ layers, symmetry or lack of it, and protostome vs deuterostome.

The animal phyla are as listed:

Porifera, Cnidaria, Ctenophora, Platyhelminthes, Nemertea, Rotifer, Nematoda, Mollusca, Annelida, Arthropoda, Lophophorates, Echinodermata, and Chordata.

This guide will only go over the bolded phyla as those are the ones that taxonomists are most sure about regarding their placements/ existence.


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Porifera, which are mainly sponges, have no true tissue and get nutrients through filtering ocean water. They do this will specialized cells called Spicules which are made of calcium carbonate and hold the sponge together. Water is drawn in through the Spongocoel and flows out of a opening nearby called an Osculum. The flow is made by cells called Choanocytes. More complex sponges may have more tissue that allows for greater filtering. Amoebocytes transport collected nutrients through filter feeding to other areas of the sponge such as the Mesohyl or the middle layer of the sponge border.



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Cnidaria are radial, true tissued, and diploblastic organisms which include jellyfish, hydra, and sea coral. They have 2 separate body plans with one thing in common – a digestive gastrovascular cavity called the coelenteron. Polyp is the plan that attaches to a surface and waits for prey to float by. The Medusa on the other hand will move through the water by drifting with currents as well as it own contractions. The tentacles of a Cnidarian are lined with Cnidocyte buds which function in defense and hunting. These Cnidocytes have Cnidae which explode outward if prey is in contact. This is where the name Cnidaria comes from.



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Platyhelminthes are bilateral, protostomal, acoelomate, flatworms. They all live in aquatic environments. They undergo triploblastic development. Because of their flat body structure and acoelomate nature, their gas exchange occurs through diffusion by the skin with the surrounding water. Their excretory mechanism is made through openings called protonephridia which open to the outside. Flame cells help control the concentrations of chemicals.


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Nematodes are bilateral, protostome, pseudocoelomate, roundworms. Their bodies are round and narrow, specialized for their parasitic lifestyle. These worms have muscles that line their inner cavity and have a rudimentary nervous system. One interesting feature of this group is that if conditions get too tough, they can suspend their life in a process called cryptobiosis.


We will continue our discussion in the next post.

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