No. 62–The Enigmatic Porifera

From time to time I like to plumb the realm of the esoteric and the phylum Porifera (sponges) seemed to offer just such an opportunity. I will tell you upfront that it was another head scratching laymen’s journey into the world of the arcane.

There are approximately 5,000 known species with all being aquatic and the vast majority being marine organisms. The name Porifera comes from the Latin “porus” = pore and “ferre” = to bear, giving us animals most recognizable by their porus surface.

The term enigmatic applies because of ongoing phylogenetic (evolutionary relationships between species) squabbles regarding classification. What is not in dispute is that the phylum Porifera represents, along with Cnidaria*, one of the first two multicellular metazoan (animal) phyla. There is disagreement, however, on the multicellular nature of the beast. Some argue sponges to be singular creatures while others contend they are colonial animals.

What compounds the enigma surrounding sponges is that they lack true organs found in other metazoans and have the uncanny ability to move specialized cells about their structure to perform specific tasks. It’s been found in laboratory experiments that some have the ability to go through a blender, so to speak, and then reorganize themselves. Weird, eh?

The fossil record of living porifera dates back to the early Cambrian some half billion years ago with now extinct precursors found in the late Precambrian. Only the Protozoa’s preceded them in the long march of life on earth.

Sponges are found mostly in the shallower waters of all the world’s oceans though a few species have adapted to greater depths. There are also around 150 fresh water species. They display an amazing variety of shapes colors and sizes but the one thing that unites virtually all is that they are filter feeders.

With an aquiferous (plumbing) system unique in the animal kingdom, sponges pump oxygen and food bearing water in through the external pores using flagella to direct the flow through numerous chambers and tunnels. Oxygen is absorbed, food (primarily bacteria) is filtered from the flow and wastes are carried out through what are called excurrent openings.

Some species found in waters with sustained or intermittent currents get an assist from the movement of water over their surfaces. The flow creates low pressure over the excurrent openings drawing water from the interior as an assist to the flagella.

Sponges are able to regulate the amount of water flowing through them by constricting and opening the intake pores. They are capable of passing water through at a rate of 20,000 their volume in a 24 hour period.

There’s a fascinating exception to the filter feeding paradyne. The genus Asbestopluma has 7 known deep sea species of carnivorous sponges. They totally lack the aquiferous system of typical sponges. They are passive carnivores that entangle very small crustaceans in hooked filaments. Once ensnared the prey animal is doomed as the killer sponge sends out cells to engulf the hapless creature.

These sponges have no digestive cavity but rather use specialized cells to slowly break down and absorb the nutrients over time, a process that can take 8 to 10 days for larger prey.

I had no idea at the beginning of this piece that it would take us where it has and leave so much to cover as I’m running up to word count limitations. I have much more to learn in order to pass it along to you. We’ll take up this fascinating subject again next month.

Make sure you check out our second installment of The Enigmatic Porifera