As a career biologist with keen interest in invertebrate animals, I’d like to share with my ABLE colleagues some insights about the biology and natural proclivities of one fascinating invertebrate group -- the sponges. Curiously, these animals are generating considerable attention and debate in the press. So, to clarify, here are some biological features about sponges that you may wish to share with other teachers and student groups.
To date, there are about 8,000 known species of sponges on the earth. Most sponge species are marine, but a few hundred species live in freshwater. In fact, living sponges are commonly found in lakes, rivers, and wetlands of my home state of Iowa, as well as most other states.
Most sponge species are ‘hermaphrodites’ – that is, one individual sponge produces both male and female sex cells. Sexual reproduction by combination of these sex cells results in a free-swimming larva that eventually settles and transforms into a new sponge.
Sponges can also reproduce asexually by simple fragmentation, a method of natural cloning. Yet another type of asexual reproduction occurs in freshwater sponges. This involves formation of many tiny, coated spheres, called gemmules. Sponge cells inside these gemmules survive amazingly harsh conditions such as drought, deep freezing, or extreme heat. In spring, when conditions become more favorable, the gemmules hatch and the emerging cells develop and grow into a new sponge.
I invite teachers and students at all levels to learn more about the biology of sponges by viewing images of living sponges on my university website: http://www.eeob.iastate.edu/faculty/DrewesC/htdocs/invert-thumbs.htm
I hope this helps to set the biological record straight.