<P> Scallops have a large number (10--100) of small (about 1mm) eyes arranged along the edge of their mantle . These eyes represent a particular innovation among molluscs, relying on a concave, parabolic mirror of guanine crystals to focus and retro - reflect light instead of a lens as found in many other eye types . Additionally, their eyes possess a double - layered retina, the outer retina responding most strongly to light and the inner to abrupt darkness . While these eyes are unable to resolve shapes with high fidelity, the combined sensitivity of both retinas to light entering the eye and light retro - reflected from the mirror grants scallops exceptional contrast definition as well as the ability to detect changing patterns of light and motion . Scallops primarily rely on their eyes as an' early - warning' threat detection system, scanning around them for movement and shadows which could potentially indicate predators . Additionally, some scallops alter their swimming or feeding behavior based on the turbidity or clarity of the water, by detecting the movement of particulate matter in the water column . </P> <P> Scallops are filter feeders, and eat plankton . Unlike many other bivalves, they lack siphons . Water moves over a filtering structure, where food particles become trapped in mucus . Next, the cilia on the structure move the food toward the mouth . Then, the food is digested in the digestive gland, an organ sometimes misleadingly referred to as the "liver", but which envelops part of the oesophagus, intestine, and the entire stomach . Waste is passed on through the intestine (the terminus of which, like that of many mollusks, enters and leaves the animal's heart) and exits via the anus . </P> <P> Like all bivalves, scallops lack actual brains . Instead, their nervous system is controlled by three paired ganglia located at various points throughout their anatomy, the cerebral or cerebropleural ganglia, the pedal ganglia, and the visceral or parietovisceral ganglia . All are yellowish . The visceral ganglia are by far the largest and most extensive of the three, and occur as an almost - fused mass near the center of the animal--proportionally, these are the largest and most intricate set of ganglia of any modern bivalve . From these radiate all of the nerves which connect the visceral ganglia to the circumpallial nerve ring which loops around the mantle and connects to all of the scallop's tentacles and eyes . This nerve ring is so well developed that in some species it may be legitimately considered an additional ganglion . The visceral ganglia are also the origin of the branchial nerves which control the scallop's gills . The cerebral ganglia are the next largest set of ganglia, and lie distinct from each other a significant distance dorsal to the visceral ganglia . They are attached to the visceral ganglia by long cerebral - visceral connectives, and to each other via a cerebral commissure that extends in an arch dorsally around the esophagus . The cerebral ganglia control the scallop's mouth via the palp nerves, and also connect to statocysts which help the animal sense its position in the surrounding environment . They are connected to the pedal ganglia by short cerebral - pedal connectives . The pedal ganglia, though not fused, are situated very close to each other near the midline . From the pedal ganglia the scallop puts out pedal nerves which control movement of and sensation in its small muscular foot . </P> <P> The scallop family is unusual in that some members of the family are dioecious (males and females are separate), while other are simultaneous hermaphrodites (both sexes in the same individual), and a few are protoandrous hermaphrodites (males when young then switching to female). Red roe is that of a female, and white, that of a male . Spermatozoa and ova are released freely into the water during mating season, and fertilized ova sink to the bottom . After several weeks, the immature scallops hatch and the larvae, miniature transparent versions of the adults called spat, drift in the plankton until settling to the bottom again (an event called spatfall) to grow, usually attaching by means of byssal threads . Some scallops, such as the Atlantic bay scallop Argopecten irradians, are short - lived, while others can live 20 years or more . Age can often be inferred from annuli, the concentric rings of their shells . </P>

What is the yellow bit on a scallop
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