Two very important concepts in biology and environmental studies are the nouns, habitat and niche. An organism’s habitat is quite simply put, its address in the environment. Does it live on land or in the water? If it is in the water, is it swimming, floating or crawling along the bottom? If it lives at the bottom of a body of water, is it visible or living on top of the sediment (epifaunal) or does it burrow into the bottom like a clam (infaunal)? An animal’s habitat still gives us little or no clue as to its lifestyle. In the marine (oceanic) habitat, an animal may be harmless scavenger or a savage pursuit predator capable of running down and killing animals much larger than itself. Conversely, the word niche is far more comprehensive and definitive than the word habitat. An animal’s niche is in effect, its profession, e.g. filter feeder, scavenger, detritus feeder, etc. More important, the animal’s niche designates very precisely where that animal fits into a food chain or food pyramid. In other words, the animal’s niche tells us not only what it eats, but who it’s predators are. The quickest method of guessing at an animal’s lifestyle is by the design of its body. Animals with an attached, or sessile lifestyle usually display what is called, radial symmetry, or symmetry around a line. An example in the plant world is a flower. Mobile animals, such as vagrants (crawling) or nektonic (swimming) or flying usually display symmetry around a plane. In other words their body is “bilaterally symmetrical” with their left side being a mirror image of their right side. Pelagic or planktonic animals suspended within the water column may have symmetry about a point (spherical) so the body is shaped like a ball. We may also guess by the surface structure on the shell of an animal, its habitat in that animals with a smooth or near-smooth body (no long spines) may be infaunal. We find that mollusks living in high energy, surf conditions usually have a massive, thick, robust shell whereas those in low energy, deepwater conditions may have a paper-thin shell. In a global view, as a general rule, animals at very cold high (polar) latitudes where it is difficult to extract chemical elements from seawater to make minerals, have shells with architecturally complex struts and buttresses, whereas mollusks in shallow, warm tropical waters, where the chemical extraction of elements to make a shell is simple, tend to have thick massive shells.
• With this potpourri of guidelines in mind, what would be the possible lifestyle or symmetry of a: crinoid, coral, trilobite, brachiopod, sand dollar, fish, eel, pollen grain, crocodile, housefly, bird, whale and bat?*
• Describe a hypothetical imaginary animal that is a pursuit predator living in very cold, arctic waters.
• What would the body plan be for a filter feeding, infaunal animal?
• What kind of body structure would you expect to see in a free-floating, microscopic protozoan in tropical water?
• Describe a detritus feeder that lives in very cold, deep water on a soft mud bottom.
• What does it mean when an animal, like a jellyfish that is nektonic (swimming)? has an obvious radial symmetry, like a flower? (There are two answers to this last question).