Porifera (Sponges)

Sponges are mainly marine. The best known sponge is the commercial bath sponge, which is a marine sponge. Many marine sponges are conspicuous, some being relatively large and erect and often exhibiting brilliant colors. But the few species of freshwater sponges generally have a low plant-like growth form and when living are usually a greenish color, due to symbiotic algae within the sponge (Plate 3.1). All freshwater sponges, about 150 species world-wide, are in the Class Demospongiae, Family Spongillidae. Freshwater sponges occur throughout Alberta in both running and standing water.

Freshwater sponges, similar to their marine relatives, are nothing but little pump stations. Almost all the life processes of sponges are based on their ability to pump water through the numerous canals within the body of the sponge. Sponges basically have two types of cells. One type is bell-shaped, known as a collar (or choanocyte) cell; the other basic cell type is called an amoebocyte. Each collar cell bears a flagellum. The beating of the flagella of the thousands of collar cells (which line the canals of the sponge) assists in drawing water into the sponge. Water enters via minute holes called ostia, circulates in the canals, and eventually exits via large openings, each called an osculum. In the water are small food particles, such as algal cells. The particles are engulfed by the collar cells, and the collar cells pass the food particles to the amoebocytes. Amoebocytes therefore function in digestion. But this cell type has many other roles. Specialized amoebocytes form the "skin" of the sponge. Other specialized amoebocytes are important in forming the ostia, which lead into the sponge's body. Still other specialized amoebocytes produce the skeleton of the sponge. These amoebocytes, called sclerocytes, produce minute, silicious rod-shaped structures called spicules Plate 3.2. Spicules are of paramount importance in identifying sponges.

Since freshwater sponges tend to grow close together in colony-like growths, it is difficult to say what constitutes an individual sponge. The old idea was that everything drained by a single osculum represents an individual sponge. Another suggestion is that an individual sponge is everything enclosed within a continuous "skin" layer, which sponge specialists call a pinacoderm.

Freshwater sponges reproduce both sexually and asexually. Sexual reproduction has been studied in detail for only a few freshwater sponges. A consensus scenario would have the sperm developing from the collar cells and the eggs from amoebocytes. Sperm of one sponge will leave via the osculum, enter a second sponge via the ostia, and as was found for food particles, be engulfed by the collar cell. The collar cell then sheds its collar and carries the sperm to the egg. The fertilized egg will eventually develop into a small ciliated larva that will leave the sponge, settle onto the substratum and grow into a mature sponge. This is the general picture, but there are many variations. For example, it is possible that some populations of freshwater sponges, especially in northern areas, do not reproduce sexually at all.

Freshwater sponges reproduce asexually by one of two methods. A bit of the mature sponge simply breaks off, or buds off, the parent sponge and eventually grows into a new sponge. The other method is gemmule formation. Gemmules are small "seed-like" structures usually about a half a millimeter in diameter (see PORIFERA pictorial key). They form when undifferentiated amoebocytes stream together and clump together. Specialized amoebocytes, called spongiocytes, will then stream over the clump and secrete the test, or case, of the gemmule. Within the case are embedded minute gemmule spicules, which, like the body spicules, are important in identifying sponges (Plates 3.1 and 3.2 ). The gemmules will eventually be freed from the sponge. If the gemmule receives the correct environmental stimuli, the undifferentiated amoebocytes will rupture out of the case and develop into a new sponge.

Freshwater sponges, although not uncommon in Alberta, are usually inconspicuous and not easily spotted from the banks of streams or from the shores of ponds and lakes. Sponges usually live in fairly shallow water, but occasionally are found in deep water. Sponges are rarely collected by sweeping a pond-net over the substratum. A better method is to hand-pick objects, such as submerged tree branches, from shallow areas of small lakes, ponds, and slow moving streams.

Pieces of sponge can be preserved in about 70% alcohol. For identification, the microscopic gemmule spicules and body spicules must be isolated. A simple method is to cut a gemmule in half with a razor blade. Add a couple drops of a household bleach; wait about five minutes and then pick off the gemmule layer with a pin and mount on a slide. Another method is to take a small piece of sponge tissue and pick out several gemmules-a small bore pipette works well in isolating these small gemmules. Place the gemmules and the sponge tissues on separate slides. Add a couple of drops of concentrated nitric acid (strong bleach also works) to each, and hold over a Bunsen burner, or other flame, until dry (preferably in a fume hood). Do not inhale or spill the nitric acid; it is very caustic and can result in a severe burn. Use enough nitric acid that little or no blackened carbon remains. This treatment will destroy the sponge tissue and the case of the gemmule but not the spicules. Add a little water to the residue and examine under a microscope. A better procedure is to add a drop of mounting medium, such as PVA (see METHODS), instead of water, and cover with a coverslip. Gemmule spicules are very small and should be viewed under high power of the microscope.

The sponge fauna of Alberta is poorly known. Four species are known to occur in the province, but probably there are other species in Alberta. In central Alberta, Ephydatia fluviatilis and Spongilla lacustris are much more common than the other two species. A major revision of the freshwater sponges worldwide is that of Penney and Racek (1968).

• Ephydatia fluviatilis (Linnaeus)
• Eunapius fragilis (Leidy)
• Ephydatia mulleri (Lieberkuhn)
• Spongilla lacustris (Linnaeus)

Species of Trochospongilla occur widely in North America. Trochospongilla specimens have birotulate spicules, but the expanded ends are entire, instead of having teeth as in Ephydatia. Trochospongilla pennsylvanica (Potts) is the one most likely to be found in Alberta; it has the two ends of the gemmule spicule very much unequal in size.

Apparently there have been no specific studies on Alberta's sponges. The following references have some information on Alberta's sponge fauna: Clifford (1972b), Proctor (1988, 1989).

As indicated in the Introduction, many of the references in the "Survey of References to Alberta's Freshwater Invertebrates" pertain to a large number of taxa or are more ecological than taxonomical. The BOTTOM FAUNA references are: Anderson (1968a), Anderson et al. (1983), Baird et al. (1986), Barton (1980a), Barton and Lock (1979), Barton and Wallace (1979a), Barton and Wallace (1979b), Bidgood (1972), Bond (1972), Casey (1986, 1987), Casey and Clifford (1989), Chapman et al. (1989), Ciborowski (1983a), Ciborowski and Clifford (1984), Clifford (1969, 1 972a, 1 972b, 1972c, 1982a), Clifford et al. (1989), Colbo (1965), Corkum (1984, 1989b), Craig et al. (in press), Crowther (1980), Culp (1988), Culp and Boyd (1988), Culp and Davies (1980, 1982), Culp et al. (in press), Daborn (1969, 1971, 1974a, 1975b, 1976b), Davies and Baird (1988), Dietz (1971), Donald and Anderson (1982), Donald and Kooyman (1977), Fillion (1963, 1967), Flannagan et al. (1979), Fredeen (1983), Gallimore (1964), Gallup et al. (1971), Gallup et al. (1975), Garden and Davies (1988, 1989), Gates et al. (1987), Gotceitas (1985), Hanson et al. (1 989a), Hanson et al. (1989b), Hartland-Rowe et al. (1979), Hodkinson (1975), Johansen (1921), Kerekes (1965, 1966), Kerekes and Nursall (1966), Kussat (1966), Lamoureux (1973), Mayhood (1978), Mitchell and Prepas (1990), Moore et al. (1980), Murtaugh (1985), Musbach (1977), Mutch (1977), Mutch and Davies (1984), Neave (1929b), Neave and Bajkov (1929), Nelson (1962), Nursall (1949, 1952, 1969a, 1969b), Osborne (1981, 1985), Osborne and Davies (1987), Paterson (1966), Paterson and Nursall (1975), Paterson et. al. (1967), Pinsent (1967), Pritchard and Arora (1986), Pritchard and Scholefied (1980b), Radford (1970), Radford and Hartland-Rowe (1971 a), Rasmussen (1979), Rasmussen (1988), Rasmussen and Kalff (1987), Rawson (1953a), Retallack et al. (1981), Reynoldson (1984), Robertson (1967), Robinson (1976), Robinson (1972), Rosenberg (1975a, 1975b), Scott (1985), Smith (1989), Thompson and Davies (1976), Timms et al. (1986) , Tsui et al. (1978), Walde (1985), Walton (1979), Wayland (1989), Whiting (1978), Whiting and Clifford (1983), Wrona et al. (1982), Zelt (1970), Zelt and Clifford (1972).

The zOOPLANKTON references are: Anderson (1967, 1968a, 1968b, 1970b, 1971, 1972, 1974, 1975, 1980), Anderson and De Henau (1980), Anderson and Green (1975, 1976), Bajkov (1929), Bidgood (1972), Clifford (1972a ,1972c), Culp (1978), Daborn (1975b), Donald (1971), Donald and Kooyman (1977), Gallup and Hickman (1975), Gallup et al. (1971), Gates et al. (1987), Hauptman (1958), Johansen (1921), Kerekes (1965), Kerekes and Nursall (1966), Lei and Clifford (1974c), Mayhood (1978), Miller (1952), Mitchell and Prepas (1990), Nursall and Gallup (1971), O'Connell (1978), Paterson et al. (1967), Pinsent (1967), Rasmussen (1979), Rawson (1942, 1953a, 1953b), Reed (1959), Roberts (1975), Rosenberg (1975a).

• Pictorial Key for Porifera
  

• Plate 3.2
  Upper, left to right: body spicules of Ephydatia mulleri [0.25 mm]; gemmule spicules of Spongilla lacustris [0.1 mm].
  Lower , left to right: gemmule spicules of Ephydatia mulleri [0.1 mm]; close up of E. Mulleri gemmule spicule [0.08 mm].
  
• Plate 3.1
  Upper, left to right: gemmule spicules of Ephydatia fluviatilis [0.08 mm]; gemmule spicules of Spongilla [0.1 mm].
  Lower: Spongilla lacustris [200 mm] and the clam Anodonta [100 mm].