Remarkable Fish. Special Reports. (Encyclopedia, texts, dictionary.)
RECOGNITION GROUP CHARACTERS
The commoner members of the several branches may be recognized by the following characters:—
1. The Protozoans are the only one-celled animals.
2. The Sponges are the only animals having pores all over the body for the inflow of water.
3. The Polyps are the only many-celled animals having a single opening into the body, serving for both mouth and vent. They are radiate in structure, and usually possess tentacles.
4. The Echinoderms are marine animals of more or less radiate appearance, having a food tube in the body separate from the body wall.
The following groups are plainly bilateral: that is, dorsal and ventral surfaces, front and hind ends are different.
5. The Vermes have usually a segmented body but lack jointed legs.
6. The Arthropods[[3]] have an external skeleton and jointed legs.