Which organs and tissues are absent in animal sponges?

Sponges, which belong to the phylum Porifera, are distinct from other animals because they lack true tissues and organs. Instead of organized tissue layers, they possess a cellular grade of construction where specialized cells perform specific functions within an amorphous, gelatinous substance known as the mesohyl.1234

Because they lack these complex biological structures, sponges also do not have specific systems found in more advanced animals, including:

• Respiratory organs: Oxygen is obtained through direct exchange between the cells and the surrounding water.5
• Nervous system: Adult sponges lack a defined nervous system.6
• Musculature: They do not possess muscles and do not exhibit conspicuous movements of body parts.6

While sponges are classified as animals due to their cellular structures and biological functions, their simple body plan—consisting of canals and chambers for water circulation—is fundamentally different from the organ-based systems of other multicellular organisms.123