Porifera

Porifera is a phylum of simple, sessile aquatic animals known as sponges. They are multicellular but lack true tissues and organs. Most species are marine, with some freshwater members. Sponges feed by filtering water through their porous bodies, and they rely on choanocytes, flagellated cells, to capture tiny food particles.

The body comprises an aquiferous system of canals and chambers built from cells rather than tissues. Water enters via ostia, flows through canals, and exits through oscula. Choanocytes trap food, while amoeboid cells distribute nutrients. Sponges have no nervous, digestive, or excretory systems; gas exchange and waste removal occur by diffusion.

Skeletons may consist of calcareous or siliceous spicules, and/or flexible protein fibers called spongin. This supports diverse body plans: asconoid, syconoid, or leuconoid. Reproduction is sexual or asexual; most species are sequential or simultaneous hermaphrodites. Sperm released into water are captured by other sponges, resulting in free-swimming larvae. Some freshwater sponges produce gemmules, resistant embryo-like structures.

Ecology: Sponges are important filter feeders in benthic communities, often shaping water flow and providing habitat for other organisms. They host microbial symbionts and can contribute to nutrient cycles. The fossil record includes spicule-bearing remains dating to the Precambrian, making sponges among the earliest known animals.

Taxonomy: Porifera contains several classes, including Calcarea, Demospongiae, Hexactinellida, and Homoscleromorpha. Molecular data have led to revisions, and the exact relationships among groups remain debated. Sponges are a model system for studying multicellularity and early animal evolution.