Class 3. Demospongiae (Gr., dermos= frame+ spongos= sponge)

• Contains the largest number of sponge species.
• Small to large-sized.
•  Conical or solitary. 
• The body shape is a vase, cup, or cushion.
• Skeleton of siliceous spicules or spongin fibers, or both, or absent.
• Spicules are never 6-rayed, they are monaxon or tetraxon and are differentiated into large megascleres and small microscleres.
• The body canal system is leucon type.
• Choanocytes restricted to small rounded chambers.
• Generally marine, few freshwater forms.

Subclass I. Tetractinellida

• Sponges are mostly solid and simple rounded cushion-like flattened in shape usually without branches. Dull to brightly colored.
• Skeleton comprised mainly of tetraxon siliceous spicules but absent in order Myxospongida.
• The Canal system is a leuconoid type.
• Mostly in shallow water.

Order 1. Myxospongida

• Simple structure.
• Spicules absent.
• Examples: Oscarella, Halisarca.

Order 2. Carnosa

• Structure simple.
• Spicules are not differentiated into megascleres and microscleres.
• Asters may be present.
• Examples: Plakina, Chondrilla.

Order 3. Choristida

• Both large and small spicules present.
• Examples: Geodia, Thenea.

Subclass II. Monaxonida

• Occurs in a variety of shapes from rounded mass to branching types or elongated or stalked with funnel or fan-shaped.
• Spicules monaxon. Spongin present or absent.
• Spicules are distinguished into megascleres and microscleres.
• Found abundant throughout the world.
• Mostly in shallow waters, some in the deep sea, some in freshwater.

Order 1. Hadromerina

• Monaxon megascleres in the form of tylostyles.
• Microscleres when present in the form of asters.
• Spongia absent.
• Examples: Cliona, Tethya.

Order 2. Halichondrina

• Monaxon megascleres are often of 2 types i.e. monactines and diactines.
• Microscleres are absent.
• Spongia present and scanty.
• Example: Halichondria (crumb-of-bread sponge).

Order 3. Poecilosclerina

• Monaxon megascleres are of 2 types, one type in the ectoderm and another type in the choanocyte layer.
• Microscleres are typically chelas, sigmas, and toxas.
• Example: Cladorhiza.

Order 4. Haplosclerida

• Monaxon megascleres are of only one type i.e. diactinal.
• No microscleres.
• Spongia fibers are generally present.
• Examples: Chalina, Pachychalina, Spongilla.

Subclass III. Keratosa

• The body is rounded and massive with a number of conspicuous oscula.
• Horny sponges with the skeleton of spongin fibers.
• No spicules.
• Found in shallow and warm waters of tropical and subtropical regions.
• Examples: Euspongia, Hippospongia.