Comprehensive Animal Phyla Overview: Placozoa to Mollusca

Phylum Placozoa

Simplest known animals with a flat, tiny, plate-like body made of only a few thousand cells and no true tissues or organs.

Placozoa Tissues & Symmetry

No true tissues; asymmetrical.

Placozoa Coelom

Absent.

Placozoa Digestive System

Uses external digestion by secreting enzymes; absorbs nutrients.

Placozoa Excretory System

Diffusion.

Placozoa Reproductive System

Asexual (budding, fission) and sexual (rare); no larva known.

Placozoa Nervous System

None (responds with simple cells).

Placozoa Respiratory System

Diffusion.

Placozoa Locomotion

Creeps using cilia; free-living.

Placozoa Habitat

Marine (warm coastal waters).

Phylum Porifera

Porous body with canal system; no true tissues or organs.

Porifera Tissues & Symmetry

No true tissues; asymmetrical or radial.

Porifera Coelom

Absent.

Porifera Digestive System

Intracellular (filter feeders using choanocytes).

Porifera Excretory System

Diffusion.

Porifera Reproductive System

Mostly hermaphroditic; internal fertilization; indirect development (larva = parenchymula).

Porifera Nervous System

None.

Porifera Respiratory System

Diffusion.

Porifera Locomotion

Sessile (non-moving).

Porifera Habitat

Aquatic, mostly marine.

Porifera Classes

Calcarea: Calcium carbonate spicules; Demospongiae: Silica spicules/spongin (most sponges); Hexactinellida: Glass sponges (silica).

Phylum Cnidaria

Have cnidocytes (stinging cells) and are diploblastic with radial symmetry.

Cnidaria Tissues & Symmetry

Diploblastic; radial symmetry.

Cnidaria Coelom

Absent (gastrovascular cavity).

Cnidaria Digestive System

Incomplete; gastrovascular cavity; carnivorous using tentacles.

Cnidaria Excretory System

Diffusion.

Cnidaria Reproductive System

Mostly dioecious; external fertilization; indirect (larva = planula).

Cnidaria Nervous System

Nerve net; no brain.

Cnidaria Respiratory System

Diffusion.

Cnidaria Locomotion

Polyps = sessile; Medusae = swim by jetting water.

Cnidaria Habitat

Mostly marine.

Cnidaria Classes

Hydrozoa: Mostly colonial, both polyp and medusa stages; Scyphozoa: Large medusa stage dominant; Anthozoa: Only polyp stage; sessile.

Phylum Ctenophora

Have 8 rows of cilia for movement and sticky cells called colloblasts.

Ctenophora Tissues & Symmetry

Diploblastic; biradial symmetry.

Ctenophora Coelom

Absent.

Ctenophora Digestive System

Complete; mouth and anus.

Ctenophora Excretory System

Diffusion.

Ctenophora Reproductive System

Hermaphroditic; external fertilization; indirect (larva = cydippid).

Ctenophora Nervous System

Nerve net.

Ctenophora Respiratory System

Diffusion.

Ctenophora Locomotion

Cilia rows (combs).

Ctenophora Habitat

Marine (open ocean).

Ctenophora Classes

Tentaculata: With tentacles; Nuda: No tentacles.

Phylum Platyhelminthes

Flattened body; first with bilateral symmetry.

Platyhelminthes Tissues & Symmetry

Triploblastic; bilateral symmetry.

Triploblastic

Organism with three germ layers: ectoderm, mesoderm, and endoderm.

Bilateral symmetry

Body plan that can be divided into two mirror-image halves.

Acoelomate

Organism that lacks a coelom, or body cavity.

Pseudocoelom

Body cavity that is not completely lined by mesoderm.

Incomplete digestive system

Digestive system that has only one opening for both ingestion and excretion.

Flame cells

Excretory structures that help in the removal of waste.

Hermaphroditic

Organism that has both male and female reproductive organs.

Cephalization

Concentration of nervous tissue and sensory organs at the anterior end.

Diffusion

Process by which substances move across membranes from areas of high concentration to low concentration.

Cilia

Hair-like structures that aid in movement and feeding.

Carnivorous

Organism that primarily feeds on other animals.

Parasitic

Organism that lives on or in a host and derives nutrients at the host's expense.

Turbellaria

Class of free-living flatworms, such as Planaria, known for their regenerative abilities.

Trematoda

Class of parasitic flatworms, known as flukes, that have complex life cycles with multiple hosts.

Cestoda

Class of parasitic flatworms known as tapeworms, which absorb nutrients directly from the host's intestines.

Rotifera

Phylum of microscopic organisms characterized by a ciliated corona for feeding and movement.

Nemertea

Phylum of ribbon worms known for their long, unsegmented bodies and eversible proboscis.

Nematoda

Phylum of roundworms characterized by a cylindrical, tapered body and a molting cuticle.

Mollusca

Phylum of soft-bodied animals with a mantle, muscular foot, and often a shell.

Radula

A feeding structure in mollusks, often described as a tongue with tiny teeth.

Dioecious

Organism that has distinct male and female individuals.

Trochophore

A larval stage in the development of some marine invertebrates.

Gastropoda

Class of mollusks that includes snails and slugs, often characterized by a single coiled shell.

Bivalvia

Class of mollusks that includes clams and mussels, characterized by two shells and filter-feeding habits.

Cephalopoda

Class of mollusks that includes squids and octopuses, known for their intelligence and jet propulsion.