They have no left or right, no front or back. They lack digestive systems and circulatory systems.
All of them share the same basic body plan: a measly two layers of cells, enveloping a jelly-like filling. Sponges exist in a rainbow of hues and can, in the case of the Caribbean giant barrel sponge, grow up to eight feet in diameter. There are around eighty-five hundred known species, and they live in both oceans and freshwater.
Sponges sit immobile, anchored to rock or rooted in sediment, filtering particles from water. The second dish turned out to contain a sponge (phylum: Porifera), an animal that looks like the antithesis of an animal. The unspoken corollary: we should perhaps focus instead on the slime. Midway through the allotted time, the invigilator observed aloud that many of us seemed to be trying to classify the rock. The other contained a rock in a thin layer of water, with a green, slimy film on one of its faces. The first contained a dead cockroach (phylum: Arthropoda). Now, more than a decade later, I can conjure up only two of the test dishes.
Our task was to classify the creatures to the phylum level. In the final exams for our undergraduate zoology degrees, my fellow-majors and I were given an assortment of petri dishes, each of them containing an animal.
0 kommentar(er)
