Subcategories
Clams
Clams really are simple animals, anatomically speaking. In case you don't know, clams have two shells. The shells are connected at the bottom by a joint of 4 teeth that interlock. Clams also have a byssal opening which can be viewed on the bottom of the clam. The byssal gland consist of 4 muscles which produce threads to secure the clam to the substrate. The adductor muscle connects both shells and is responsible for opening and closing the two shells. The cardiovascular system is a small heart with two main arteries and two main veins. Clams use gills for gas exchange and filtering small food particles. They also have kidneys which remove toxic metabolic byproducts from the blood. The nervous system only consists of nerve bundles which control the organs and organ systems. Clams also have eye spots on the mantle called iridiphores which they can collect sensory data from. Clams can detects shadows passing over them.
Corals
Stony corals are often considered to come in two flavors - LPS and SPS which are acronyms for Large Polyped Stony, or as some would rather say, Large-Polyped Scleractinian and Small-Polyped Scleractinian. Sceleteria refers to stony or hard corals. The terms LPS and SPS are not a scientific terms. "LPS" refers to all hermaphytic sceleterian corals that have *large* fleshy polyps. "SPS" refers to all hermaphytic sceleterian corals that have *small* polyps and corallite structures. The term small is extremely subjective. Different hobbyists have different opinions on what small is. In general SPS means any sceleterian genus that contains polyps smaller then 5mm.
Fish
It is estimated that there are 20,000 to 30,000 different species of fish. Most of these are broken down into two main groups:
Chodrichthyes, with cartilaginous skeletons such as sharks, dogfish and rays. However, these are not the typical kind of fish kept in reef tanks. To our interest are the bony fish of the group Osteichthes.
Featues of Osteichthes (sometimes called Teleosts in older publications) include being a cold blooded critter with a bony skeleton, skull, fins with spines and rays, a swimbladder used to control buoyancy, outwardly orientated gills, and have a unique sense organ called a lateral line.
A few well-chosen fish will add color, movement and an increased sense of realism to a reef tank.
Odd Critters
The odd critters are marine invertebrates... they are only odd to us as over 98% of species on Earth are invertebrates that rely on other strategies than a backbone for support such as hydrostatic pressure, exoskeletonsexternal link, shells, and in some, even glass spicules.