Horseshoe crab (Limulus polyphemus): The horseshoe crab's compound eye and the (easily accessible) optic nerve that connects the eye to the brain are both relatively large, making this organism a great model for the study of vision.
MBL scientists have also made significant research breakthroughs related to the horseshoe crab's blood. The crab's amebocyte cells clot in response to bacteria, enabling the development of tools used to test humans, drugs, and sterile environments for toxins.
Skate (Raja erinacea): Human retinas have two kinds of light-sensing cells: rods and cones. Skate retinas have only rods--yet they can still sense light. MBL scientists have studied skate retinas to learn how eyes adapt to light changes, and to understand diseases that can cause blindness.
Green sea urchin (Strongylocentrotus droebachiensis): The female sea urchin can produce as many as a half million eggs during spawning season, and fertilization and embryonic development are external and rapid. Such factors make this research organism ideal for the study of reproduction and development. Sea urchin research, much of which was carried out at the MBL, has led to advanced reproductive technologies including test-tube fertilization.
Oyster toadfish (Opsanus tau): The broad, flat head of the toadfish contains a unique set of nerve wiring. The nerves leading to and from the toadfish brain are less tangled than those in humans and other creatures that must cram
Source:Marine Biological Laboratory