What lies beneath (part 3) - Calanoid Copepods
The last enews featured the Cyclopoid Copepods. This time, it is the turn of the Calanoid Copepods. These, like the Cyclopoids, are tiny animals, approx 0.7mm (700µm) to 1.7mm in length. They differ from the Cyclopoida in that they look like a torpedo, with long antennae stretching the length of their body.
Photo courtesy Ulrich Hopp.
In Australian inland waters there are 2 Families: the Centropagidae with 41 species found across the country, and the Diaptomidae occurring in northern Australia with 2 species. The picture below is typical of the Centropagidae (e.g. the Genera Boeckella and Calamoecia).
These are found mainly in the open water environment of Australian inland slow-moving waterways (eg Murray River) and standing bodies of water, such as reservoirs, billabongs, wetlands, farm dams, ditches, ponds, and even bird baths.
Copepods have a hard exoskeleton, many legs (used for swimming and gathering food), a segmented body, and jointed appendages. Although lacking compound eyes, they have a single simple eye in the middle of the head which is used to differentiate between light and dark. This orientates the copepod to where the water surface is. There are two pairs of antennae; one pair is long (refer photo above) and one pair is short.
Typical body length is 0.7mm to 1.7mm with some reaching 4.5mm. The copepods move through the water in jerky motions by the use of their swimming legs.
Calanoids generally eat bacteria, algae, diatoms, and other tiny, single-celled organisms in the water. Some are predatory, opportunistically eating rotifers, other small micro-fauna, macroinvertebrate larvae and even fish larvae.
They are important in our waters as this group of animals provide a link between the bacterial cycle, the decomposition cycle and the food webs present in our waters. Plus, they are the main food source of many macroinvertebrates, small fish species (e.g. Galaxids, purple spotted gudgeon) and the juvenile stages of large fish species such as Murray Cod.