13 (4 points) What is the characteristic body structure feature of the organism shown in Figure 10.15 of the BIOL 181 Lecture notes? Flattened body covered by eight calcareous plates held together by a girdle They have two valves (shells) attached dorsally by ligaments Segmented exoskeleton Large, coiled shell with multiple chambers filled with gas

BIOL 181: Life in the Oceans = Lecture iwurce Nautilus Shell Cut in Half, by Chris 73, is available under a Nautilus Palau, by Manuae, is available under a Creative Creative Commons Attribution-ShareAlike 3.0 Unported Commons Attribution-ShareAlike 3.0 Unported license. license. Figure 10.15a and b. Nautilus, live (a) and section of shell (b). Coleoid Cephalopods Coleoid cephalopods include squid, octopus, and cuttlefish. These cephalopods have the most complex nervous system of all invertebrates, and have highly developed eyes and well- developed tactile senses. They release a cloud of ink when disturbed to distract predators. Squid have a large cylindrical body with a pair of fins derived from the mantle. Squid have an internal shell remnant called a pen, which is made of flexible, hard protein. They have 10 appendages: eight short arms, and two long tentacles. Octopuses have eight arms and no tentacles. Their bodies are sac-like and lack fins, and since they have no shell at all, they are very flexible and can fit into very small openings