Medical definition of posterior median sulcus: a shallow groove along the midline of the posterior part of the spinal cord that separates the twoâ¦ a shallow groove along the midline of the posterior part of the spinal cord that separates the two posterior funiculi and is the externalâ¦
Zooplankton Fact Sheet. Zooplankton are microscopic invertebrate animals that swim or drift in water. They are at the base of the food chain, feeding on microscopic plants and being fed upon by aquatic insects, fish and salamanders.ooplankton Fact Sheet. Zooplankton are microscopic invertebrate animals that swim or drift in water. They are at the base of the food chain, feeding on microscopic plants and being fed upon by aquatic insects, fish and salamanders.
Many zooplankters are herbivores on the phytoplankton (diatoms and dinoflagellates). Almost every marine animal phylum has a larval stage that can be found in the plankton (sponges, sea anemones, worms, snails, crabs, lobsters, sea stars).iatoms are important oxygen producers in marine ecosystems (usually the first step in the food chain). They are holoplanktonic. When conditions are bad they die, sink, the cell decomposes and the frustule breaks up and mixes with sand and mud.