About Animals Part 4

All creatures are composed of cells, girdled by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. (15 15) During development, the creature extracellular matrix forms a like flexible framing upon which cells can move about and be reorganised, making the layout of complex structures possible. This may be calcified, forming structures matching as shells, bones, and spicules. (16 16) In unlikeness, the cells of other multicellular organisms ( primarily algae, workshops, and fungi) are held in place by cell walls, and so develop by progressive growth. (17 17) Critter cells uniquely retain the cell junctions called tight junctions, gap junctions, and desmosomes. (18 18)

With some exceptions-in particular, the spongers and placozoans- critter bodies are separated into handkerchiefs. (19 19) These include muscles, which enable locomotion, and willies handkerchiefs, which transmit signals and coordinate the body. Normally, there's also an internal digestive chamber with either one opening (in in Ctenophora, Cnidaria, and flatworms) or two openings (in in uttermost bilaterians).