Sponges

Sponges, animals in the phylum Porifera, are simple, multicellular organisms distinguished by porous bodies and a canal system that facilitates filter feeding. They lack true tissues and organs; instead, specialized cells such as choanocytes drive water flow and particle capture.

A typical sponge body consists of an outer pinacoderm, a gelatinous mesohyl, and an inner choanoderm. Skeletal support is provided by spicules (silica or calcium carbonate) and, in many sponges, a fibrous protein network called spongin. Body form ranges from simple asconoid to more complex syconoid and leuconoid types, with water entering through ostia and exiting via oscula.

Feeding occurs as water currents bring bacteria and detritus to choanocytes, which trap food particles and enable intracellular digestion. Respiration and excretion proceed by diffusion. Sponges lack nervous, digestive, and circulatory systems.

Reproduction is both sexual and asexual. Most species are hermaphroditic; sperm are released into the water and fertilize eggs within the mesohyl, producing free-swimming larvae. Asexual modes include budding, fragmentation, and, in freshwater species, gemmule formation to survive adverse conditions.

Ecology and distribution: sponges occur in oceans and some freshwater habitats worldwide, from shallow coastal waters to deep sea. They contribute to water filtration, nutrient cycling, and provide habitats for other organisms. Many harbor symbiotic microbes and produce bioactive compounds of interest to science and medicine.

Human use and conservation: natural sponges have historically been used for cleaning, while modern research explores their chemistry and potential pharmaceuticals. Sponges face threats from pollution, sedimentation, overharvesting, and climate change, underscoring the need for habitat protection and sustainable management.