Labels:text | invertebrate | animal | trilobite | arthropod OCR: 550 MYA TRILOBITE HEAD SHIELD THERE WERE more than 10,000 species of trilobites. Trilobites were marine invertebrates (animals without a backbone) and most measured only 3-10 cm (1-4 in) in length. To protect themselves from predators, trilobites could curl up like wood lice. LONG THORAX FOSSILIZED TRILOBITE Trilobites ("three lobed") get their name from the body's three lengthwise sections. TAIL SHIELD