Mesohyl: cell layer between the choanocytes and external/internal body wall of sponge, this is where skeletal elements are produced and gametes are stored by many sponge cell types.Spongocytes: cells that secrete spongin.Sclerocytes: cells that secrete spicules.Pinacocytes: cells that create an outer covering of the sponge, like ‘skin’.Choanocytes: or ‘collar cells’ are flagellated cells in the body wall, which create currents to capture food particles.Archaeocytes: amoeboid cells that ingest/digest food particles and transport nutrients to other cells.Check out the video below to see different sponge cells in action! Sponges have several kinds of specialized cells that carry out specific life tasks. They essentially act as stem cells and switch to different forms when needed. Most cells in a sponge are totipotent, meaning they can move around and change function throughout their lifetime. Sponges also have several microscopic features that are more difficult to see with the naked eye. In this chapter we will explore the diversity and fossil record of phylum Porifera. They have a global distribution, occupy shallow to deep water conditions, and occur in virtually all marine and freshwater environments. Sponges encompass a vast diversity of asymmetrical shapes, sizes, and even hardnesses (ranging from soft and flexible to rock-hard). The beating flagella of the choanocytes create water currents that flow through the canals and pores in the sponge, bringing in oxygen and particles of food that are consumed. The cells lining the inside of the sponge are called choanocytes(‘collar cells’), which have a ‘tail-like’ flagellum. Spongin is the flexible material that makes up the body wall of the sponge, while spicules are hard, spiny secretions that help to provide a reinforced structure. Having no digestive tract, localized sensory region, or true tissues, they are little more than a cluster of cells supported by a structure of sponginand spicules.
Sponges make up the simplest animal group on the planet: phylum Porifera (from the Latin porus ‘pore’ and ferre ‘to bear’).
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