Seed-shrimp

Seed-shrimps (Ostracods) are a very common group of very small life forms on Earth. They are often smaller than three tenths of a centimeter across, and can live in any aquatic environment from the mud at the bottom of a small pond to the continental shelf.

Seed-shrimp live inside small, flattened shells made of chitin (Like a crayfish). The Seed-shrimp shell is actually a combination of two shells attached together by the body of the Ostracod. Inside the shell, there are two body portions: the head and the thorax. While seed-shrimp have seven pairs of legs, only two pair are used for locomotion, rendering them bottom-dwellers. Their other legs do serve unique purposes though. Seed-shrimp have one pair of walking legs, two pair of feeding legs, and three pair of legs are used to clean and maintain the inside of their shell. Seed-shrimp also have a pair of antennae which stick out of the shell when it is open. These are very important to the mating of some species of seed-shrimp.

Seed-shrimp have been known to exhibit a wide range of pigmentations spanning nearly the entire visible spectrum. Some are blue, some are green, and others are orangish-brown (fishermen often refer to these orange-brown seed-shrimp as baked beans because of their similiarities) .

Seed-shrimp are intense scavengers; they are the most common scavenger (based upon quantities collected) of the sea. Their high rank is due to the evolution of a very efficient saw-like tool that could slice through fish skin with cruel efficiency. It rips through the flesh of decaying matter and has enabled the seed-shrimp population to be here today in such great numbers, just as it was millions of years ago…

Seed-shrimp have been found in rocks dating as far back as the Cambrian in the Burgess Shale quarries. Its very possible that some groups of seed-shrimp could predate the Cambrian; however, they have not been conclusively identified in any Vendian rocks.

This most interesting aspect of seed-shrimp existence is mating. Seed-shrimp exhibit a form of sexual dimorphism. The antennae of males exhibit a special iridescent quality in the form of halophores that act as an efficient diffraction grating. (Females do not have this to the same degree; their halophores are very inefficient compared to the males.) During courting, the male seed-shrimp will flash his antennae reflecting various wavelengths of light. The more primitive halophores reflect all wavelengths of light while the better-evolved ones reflect mainly blue. (In deep-sea environments, the most prevalent wavelength of light to reach these depths is blue).

The importance of this technique is due to the fact that so many different species of seed-shrimp live in such a small area. Each species’ mating reflection is just slightly different, whether in intensity, color, or pattern. This facilitates the mating of many similar species in such a diverse environment.

Attempts have been made to organize seed-shrimp in clades based on the efficiency of their iridescence. They have proposed a theory such that the more primitive seed shrimp reflect all wavelengths of light equally, while the more evolved ones reflect just blue, and do so with much more intensity.