11. What specialized cells line the inner cavity and move fluids through filter feeding sponges?

Ctenophora, Cnidaria, and Bilateria ingest food through their mouths into an internal digestive system whose lining contain cells that secrete digestive enzymes to breakdown food and absorptive cells that take up the products of digestion. Other animals evolved mechanisms for extracellular digestion, which opened the way to feeding upon larger prey (reviewed by Fankboner and Columbia 2002 Monk and Paulin 2014 Nielsen 2012 Peterson et al. The cilia are motile and their beating generates water currents that carry bacteria into the canals where they are endocytosed and digested intracellularly by choanocytes and other cells that line the canals (Leys and Eerkes-Medrano 2006).Ĭhoanoflagellates and most Porifera only can eat organisms that are much smaller than a eukaryotic cell. Choanocytes, a type of cell in the lining of their canals, resemble choanoflagellates in that they possess an apical cilium surrounded by a collar of microvilli with interconnecting vanes (reviewed by Brunet and King 2017 Mah et al. Their bodies are perforated by a system of aquiferous canals with openings to the external surface through which water can flow in or out. Porifera, long thought to be the most ancient animals (although see Dunn et al. Beating of the cilium draws bacteria into the collar, where they are endocytosed and digested intracellularly (Dayel and King 2014). Choanoflagellates possess a motile cilium surrounded by a collar of microvilli linked together by distinctive vanes. The cell/s probably resembled choanoflagellates, eukaryotic cells that are the closest sister to Metazoa (Brunet and King 2017 Cavalier-Smith 2016 King 2004 King et al. 12: 201.Īll animals on earth today are descendants of a cell or colony of cells that lived over 600 million years ago.

The origin of the gut may represent the most important innovation in metazoan history, leading to co-evolutionary arms races that some workers have hypothesized are the ultimate cause of the Cambrian radiation.

11. What specialized cells line the inner cavity and move fluids through filter feeding sponges?