make a donation to help with conservation. The horseshoe crab has been on Earth for 350 million years. From a top view, moveable spines are visible along the edge of the abdomen. The gills also function as paddles to propel juvenile horseshoe crabs through the water. The illustration shows the underside of the horseshoe with the appendages removed. The female genital pores are broad convex structures similar in appearance to small bumps. Each pair of gills has a large flap-like structure covering leaf-like membranes called lamellae. Several eyes are found on the exterior of the prosoma. Drawn by Dana Song and Garfield Kwan Written by Garfield Kwan Edited by Dr. Jennifer Taylor, Dr. Greg Rouse, Linsey Sala, and Kaitlyn Lowder Special thanks to the Scripps Marine Invertebrate Collection for their help in identifying and verifying various eye structures . These three sections comprise the horseshoe crab's hardened exoskeleton. The horseshoe crab has 6 pairs of appendages on the posterior side of the prosoma. The horseshoe crab has been described as an armored box that moves. The exoskeleton is shed periodically as the crab grows. (Check out a diagram of the horseshoe crab's 10 eyes). Each of these eyes detects ultraviolet (UV) light from the sun and reflected light from the moon. Each compound eye has about 1,000 receptors or ommatidia. There are also 2 small chelicera appendages that help guide food into the mouth. (You can mouse over the "Divisions of the Body" in the illustration for a closer look). To learn more, visit the links on the left. The new legs (adapted pedipalps) have a hooklike structure that resembles a boxing glove. The opithosoma contains chiefly the musculature for the operation of the book gills and the telson, though the horseshoe's 113 distinct muscle groups (comprising over 750 individual muscles) are not limited to this section of the body. The ommatidia are adapted to change the way they function by day or night. A long tubular heart runs down the middle of the prosoma and abdomen. An ancient and complex anatomy hides within its domed shell. (tail) - The tail is attached to the abdomen at the terminal base. Also, a pair of ventral eyes is located near the mouth, as well as a cluster of photoreceptors on the telson. From a top view, it is shaped like a horse's shoe. The bases of the appendages attach to the axial platform, beginning at the top with the chelicerae, which the crab uses … Towards the front of the prosoma is a small ridge with three dark spots. (You can mouse over the "Divisions of the Body" in the illustration for a closer look) The prosoma contains a sizeable intestinal tract with an esophagus and proventriculus (used to grind food), a nervous system … These are used for finding mates during the spawning season. Anatomy: The Horseshoe Crab has a hard outer shell (an exoskeleton), 5 pairs of jointed legs and a pair of pincers. There are three main regions on the underside of the horseshoe crab: the doublure , the vault, and the axial platform. Of the six "pages" of the book gills, the first has an operculum with genital openings and the other five have small sensory branches and gill leaflets. (cephalothorax) - The largest section of the horseshoe crab. Subscribe to 'In The Zone' Email Newsletter, (Check out a diagram of the horseshoe crab's 10 eyes). These are sometimes referred to as the cephalothorax, the abdomen, and the tail. The cones and rods of the lateral eyes have a similar structure to those found in human eyes, but are around 100 times larger in size. As the legs are moving, food is crushed and macerated. Blood flows into the book gills where it is oxygenated in the lamellae of each gill. Several eyes are found on the exterior of the prosoma. The last pair of legs has a leaflike structure at the terminal end that is used for pushing and clearing away sediments as the crab burrows into marine bottom. Females can grow up to 60 cm (24 in) in length, including tail, and 4.8 kg (1…
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