Sample Problem

Which of the following characteristics would most likely be attributed to a hydra? Check all that apply.

(A) brain tissue

(B) diploblastic

(C) bilateral symmetry

(D) gastrovascular cavity


(B) and (D) are both correct. Hydra do not have a complex nervous system; they are diploblastic – have two germ layers instead of three; are radially symmetrical – symmetrical on multiple planes; and have, indeed, one cavity – called a gastrovascular cavity – through which substances flow in and out.