Arecent study of the marine hawksbill turtle's stomach contents revealed that sponges constitute a major portion of their diet. sponge beds are generally protected from predators by the sponge's calcium and silica crystals, but these were found in quantity in the turtles' digestive systems. these structures that protect the sponges from most predators, but not turtles, are .

These structures that protect the sponges from most predators, but not turtles, are spicules.

Explanation:

Sponges skeleton is composed of calcium carbonate and siliceous micro-structures called spicules. Their morphology is so varied that it is used in taxonomy for identification and classification.

There are different kinds of spicules:

-         Monoaxonic spicule: needle-shaped, straights or curves

-         Tetraxonic spicules: they have four prolongations

-         Triaxonic or Hexaxonic spicules

-         Poliaxonic spicules 

Two terms can be applied to any of these spicules kinds:

-         Megaspicules: They are elongated and compose the main architecture of the sponge skeleton

-         Microspicules: Variable in shape and size, with ancillary functions

Sponges have few predators thank to the spicule structures and their high toxicity. Many of them are capable of perforating soft tissues and producing urticant substances.

answer: c.

explanation:

the man is bald so he has no hair to get wet