Wildlife traditionally refers to non-domesticated vertebrates, but has come to broadly refer to all wild plants, animals and other organisms . Domesticating wild plant and animal species for human benefit has occurred many times all over the planet, and has a major impact on the environment, both positive and negative. Wildlife can be found in all ecosystems. Deserts, forests, rain forests, plains, grasslands, and other areas including the most developed urban sites, all have distinct forms of wildlife. While the term in popular culture usually refers to animals that are untouched by human factors, most scientists agree that wildlife around the world is impacted by human activities. Humans have historically tended to separate civilization from wildlife in a number of ways including the legal, social, and moral sense. Religions have often declared certain animals to be sacred, and in modern times concern for the natural environment has provoked activists to protest the exploitation of wildlife for human benefit or entertainment.
Sclerocytes secrete the mineralized spicules ("little spines") that form the skeletons of many sponges and in some species provide some defense against predators. In addition to or instead of sclerocytes, demosponges have spongocytes that secrete a form of collagen that polymerizes into spongin, a thick fibrous material that stiffens the mesohyl. Myocytes ("muscle cells") conduct signals and cause parts of the animal to contract. "Grey cells" act as sponges' equivalent of an immune system. Archaeocytes (or amoebocytes) are amoeba-like cells that are totipotent, in other words each is capable of transformation into any other type of cell. They also have important roles in feeding and in clearing debris that block the ostia. Porocytes are tubular cells which make up the pores of a sponge. Covering the sponge is a layer of cells, very similar to skin, but it's slightly different. To scientists, these cells are known as pinacocytes. In a sponge, pinacocytes are a thin, elastic layer which keeps water out. Between the pinacocytes, there are the porocytes. These let water into the sponge. Myocytes, little muscular cells, open up the porocytes and close them. Once through the pores, water travels down canals. Using the food and oxygen in the water the sponge cells stay alive and carry out other processes such as making new sponges and repairing cells. The opening porocytes surround is called an ostium.