It’s hard to see how a small, sessile organism with no apparent means of catching prey can lead a carnivorous lifestyle. Chondrocladia (Meliiderma) turbiformisis just 2cm long & lives at depths of around 1000 metres on the Chatham Rise, off the eastern NZ coast. One of them lives in NZ waters and this year was chosen as one of the international Top 10 New Species of 2010. But some deep-sea sponges turn out to be carnivores. Choanocytes (‘collar’ cells) line the cavity & their beating flagella draw water in through the pores they also trap small food particles drawn into the sponge on the water currents. Amoebocytes are able to move through the sponge’s body & transfer digested food from the choanocytes to porocytes & the epidermal cells that cover the outside of the sponge. Each pore is lined with a type of cell known as a porocyte (where ‘-cyte’ means ‘cell’) & leads in to the sponge’s inner cavity (the ‘spongocoel’. The simplest sponge body is rather like a hollow tube with perforated walls: the perforations, or pores, are what gives the phylum its Latin name, Porifera (literally, ‘pore-bearer’). You would not want to use a spicule-sponge in the bath, unless you were intending some serious exfoliating. Instead, what you get is an organism formed from just a few types of loosely-organised cells, all sitting (& moving) on & within a ‘skeleton’ made either of a protein (aptly enough, called ‘spongin’) or of spicules, which are something like fibreglass. I rather like them: no real tissue development, no organs, immobile, & a growth habit that looks distinctly plant-like. Sponges are strange organisms – classified as animals, they definitely look the odd one out.
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