Identifi cation And Life History Of Common Aquatic Invertebrates By Kenneth Williams Identifi cation And Life History Of Common Aquatic Insects By Kenneth Williams Illustrations by the author For further information on aquaculture, pond management, koi or water gardens; please view our website at: www.luresext.edu/aquaculture/aquahome.htm. Or contact us at: Phone: 405.466.6106 email: [email protected] Address: P.O. Box 1730 Langston, OK 73050 Table of Contents Zooplankton..................................................... 3 Fresh-water sponges ...................................... 4 Hydra ................................................................ 5 Fresh-water jellyfi sh ....................................... 6 Flatworms ........................................................ 7 Bryazoa ............................................................ 8 Leeches ............................................................ 9 Crayfi sh ............................................................ 10 Water mites ...................................................... 14 Snails ............................................................... 15 Mussels ............................................................ 15 Common Aquatic Pond Invertebrates any pond owners develop a fascination little pond water. Hold the jar of water in the light. for the myriad small aquatic creatures Plankton large enough to be visible will be seen as Mfound inhabiting the pond. Some, like gray to white, pinhead or smaller organisms moving the crayfi sh are edible delicacies: others are useful about in the water. They eventually concentrate near to humans or play important parts in the aquatic the bottom of the container. Zooplankton can be community. Many are microscopic. Some of more closely observed by using a magnifying glass the more common, readily observed species are or low power microscope. Protozoa and other tiny discussed below. planktonic organisms require use of a microscope to be seen. Zooplankton Zooplankton Are very small to microscopic organisms that live in the water column. Large populations of these creatures can best be seen in clear, green ponds during the summer. Many species of zooplankton migrate daily, spending time in cooler less well lit areas of the pond during the day and rising to the surface at night. Zooplankton often lack pigmentation or other protection from the ultraviolet rays of the sun and would die if continually exposed to strong sunlight. Also, predators are less likely to fi nd zooplankton that remain in darker depths of the pond during the day. In daylight hours most zooplankton will be found in shaded areas of the pond. A plankton net made to catch these creatures can be purchased from a biological supply house or made Representative groups of zooplankton. A - copepods, from the leg of a pair of pantyhose or women’s B and D cladocerans, C - amphipod, E - ostrocods stockings. Attach one end of the stocking to a wire hoop about 12 inches in diameter. Cut the stocking to about a length of 2 feet and tie a knot in the bottom. Zooplankton are primary consumers. They feed on To use the net, sweep several times just below phytoplankton (microscopic plants), detritus other the water surface. Evert the stocking over a wide zooplankton and bacteria. They are also an important mouth jar and rinse the contents into the jar with a food item for larval fi sh and other aquatic organisms. Page 3 Common Aquatic Pond Invertebrates Zooplankton are comprised of a very diverse group Growth forms may be mat-like or the sponge may of animals including protozoa, rotifers, nematodes, have branches or lobes depending on substrate and crustaceans and other arthropods. Most of the environmental conditions. Sponges can be found zooplankton visible to the naked eye or with a small attached to any fi rm substrate, most commonly, magnifying glass are crustaceans including ostracods, branches, stones, logs and other aquatic debris. copepods, cladocerans and amphipods. Sponges are not often found in polluted or silt laden waters, or on muddy pond bottoms. Intolerance to Fresh-water sponges water pollution has brought about the extinction of There are about 30 species of fresh-water sponges several species. in the U.S. Usually no more than 2-3 species will be found in the same location. The most common On close examination with a magnifying glass or low power microscope, the sponge can be seen to have two general sizes of pores on the body surface. Small pores are called ostia and the large pores are called oscula. Flagellated cells in the interior of the sponge create a current that brings water into the sponge through the ostia. The water enters incurrent canals that go to spherical chambers lined with fl agellated cells. Food is collected and absorbed by cells lining the chamber called amoebacytes. Water leaves the chamber through Spongilla lacustris - Fresh-water sponge on a the excurrent canal branch. located opposite the incurrent canal. species is Spongilla The excurrent lacustris. The sponges canal leads to an are highly variable in expanded chamber color, often brown, that terminates in gray, yellow or greenish the osculum, the when in sunlight. The opening through green color is due to which water exits ingested algae that the sponge. continue to live for awhile and may even The sponge multiply before being maintains its form digested in the body of Enlargement showing spicules, oscula and gemmules. by means of silicate the sponge. structures called spicules. Spicules are often rod shaped and pointed at Sponges vary in size from a few cm2 to over 40m2 both ends, however other shapes may also be found , depending on age and environmental conditions. in the organism. Spicules are found bundled into Living tissue of the sponge is only about 1-4 mm columns and also randomly distributed throughout thick but it can look much thicker due to successive the sponge body. layers of new growth accumulating over dead tissue in the same location over a period of several years. Sponges feed on microscopic detritus, algae, bacteria Page 4 Common Aquatic Pond Invertebrates and tiny protozoans that enter the sponge body with the water current. Sponges are preyed upon by crayfi sh, particularly of the species Orconectes, Spongilla fl y larvae and other aquatic insect larvae. Reproductive structures called gemmules form in the body of the sponge, most often in the autumn but they can form anytime during the year. Gemmules are round, fl attened disks, about the size of a pin head, containing the necessary materials to regenerate a new sponge. In cold weather the sponge begins to disintegrate, leaving the gemmules to fall to the bottom or remain in place. In spring the gemmules open through a small pore and the sponge material fl ows out, covering the gemmule and Hydra attached to snail shell. forming a new sponge. Hydra have 4-12 tentacles that are used to capture prey. Zooplankton or microscopic aquatic animals Sexual reproduction also occurs through the warm are the main food source of the hydra although they months. Individuals may be of both sexes or a can capture insect larvae, larval fi sh and tadpoles. single sex. Sperm and eggs are formed in the sponge body and released through the osculum into the The hydra looks like a fl exible hollow tube with environment where they enter other sponges through tentacles attached at one end. The mouth is located the ostia. Fertilized eggs develop and migrate to in the center of the ring of tentacles. the oscula where they are released and form new sponges. The tentacles are covered with wart-like bumps that contain nematocysts or stinging cells. When prey Hydra come into contact with the tentacles the nematocysts Hydra are interesting and often unnoticed aquatic resembling long threads are released. These threads organisms are sometimes barbed and can pierce the prey. that can be found in most Chemicals contained in the nematocysts paralyze ponds. When the prey which is then guided to the mouth by the viewed with tentacles. Food is digested in the gastrovascular the unaided eye cavity. Indigestible food is ejected through the they appear as mouth. white, brown or light green Tentacles are also used for locomotion. Hydra can colored threads move by tumbling from its up right position onto its about ½ inch or tentacles and back to the upright position coming less in length. to rest on to its basal disc which usually anchors Most hydra the organism. are less than a 1/4 inch long A group of Hydra. when fully When the hydra is disturbed or inactive the extended. When viewed with a magnifying glass tentacles and body shorten. Tentacles and body or microscope, the tentacles and sometimes, extend during feeding periods or when the hydra reproductive buds become visible. is moving. Page 5 Common Aquatic Pond Invertebrates Reproduction Fresh-water jellyfi sh Sexual reproduction usually occurs during the fall Craspedacusta sowerbyi, the fresh-water jellyfi sh is although it can happen at other times of the year. related to the hydra. It was not realized that it’s Hydras are dioecious. Spermaries and ovaries hydroid form and medusa form, what is commonly develop as bumps on the outer body wall. A single thought of as a jellyfi sh , was the same animal until egg develops in each ovary and is exposed to the 1924. water. Sperm are released from the spermaries into the water where they contact the egg and fertilize it. The hydroid form usually consists of 2-4 individual The egg forms a protective shell and drops off the but connected animals although some hydroid parent. The embryo remains in the shell through the winter until it hatches in the spring. Hydras reproduce asexually during the summer by budding. A bud begins as a bump on the outer body wall of the hydra. A new body, mouth and tentacles form from the bud. It eventually develops into a mature individual that breaks off of the parent and lives as a separate organism. Collecting hydra Hydra can be found attached to the underside of the fl oating leaves of aquatic plants such as pond weed, Craspedacusta sowerbyi -fresh-water jellyfi sh water lilies and duckweed.