Final answer:
Sponges, belonging to the phylum Porifera, lack definite shapes and true tissues. Despite this, they contain specialized cells that carry out functions similar to tissues and maintain structure with a mesohyl acting as an endoskeleton. Sponges filter feed through a central cavity, the spongocoel, and water exits through an osculum.
Step-by-step explanation:
Most sponges do not have a definite shape and do not possess tissues. Sponges are simple aquatic invertebrates from the phylum Porifera, commonly known as pore-bearers, because of the tiny pores present in their bodies. Unlike more complex organisms, sponges lack organized tissues. However, they have specialized cells that perform various functions within their body. For example, cells called pinacocytes form the protective outer layer, while other cell types like amoebocytes and sclerocytes are found within the jelly-like mesohyl that fills the space between different cell layers and functions as an endoskeleton to maintain their structure.
Sponges are filter feeders, with a unique feeding system that involves water flow through their pores into a large central cavity called the spongocoel. Food particles are filtered out by specialized collar cells, also known as choanocytes, which also have flagella to maintain water flow. After the nutrients are absorbed, the water exits through an opening called the osculum. In this process, gases and wastes are exchanged by diffusion, as sponges do not have a circulatory system.
Despite their lack of true tissues, sponges exhibit a functional complexity within their simple body plans, which allows them to thrive in various aquatic environments. With over 5,000 species, sponges have a wide range of morphologies, from simple tube-like bodies to more complex forms with varying sizes of the central cavity, or spongocoel, and different arrangements of the pores, or ostia.