The opithosoma contains chiefly the musculature for the operation of the book gills and the telson, though the horseshoes 1 distinct muscle groups comprising over 750 individual muscles are not limited to this. Once its food is digested, waste products leave the horseshoe crabs body through its anus. First, as previously mentioned, the book gill of horseshoe crabs the. The horseshoe crab s heart is a long tube that runs down the middle of the cephalathorax and abdomen. Horseshoe crabs are generally nocturnal animals, coming out of the shadows in the darkness in order to. The scanning electron microscope sem was used to study the development of the opisthosomal appendages and book gills of the horseshoe crab, limulus polyphemus.
The telsons main function is to help the horseshoe crab turn over when they are flipped, and it is not poisonous as one would assume at first glance. A look at the underside of the horseshoe reveals six paired appendages. The horseshoe crab has five flaps that make up the book gills. On the underside of the abdomen are muscles, used for movement, and gills for breathing. Identify the horseshoe crabs external organs, including the book gills, telson tail, compound eyes, mouth, chelicerae and other legs. The appearance of the horseshoe crab is thought to have changed very little from when it first evolved around 500 million years ago.
Introduction in his treatise on the horseshoe crab limulus polyphemus, patten 1912 described a set of sensory structures on the endopodites of the branchial appendages i. Previously reported examples of book gills in fossil horseshoe crabs include the. Hooray for horseshoe crabs noaa office for coastal. This is where the breathing takes place under water. Pulverized food passes into this part of the horseshoe crab to be digested. Why are the appendages of abdominal segments of the horseshoe crab called book gills. Although horseshoe crabs can swim on their backs, propelled by the beating gill flaps, they usually plow through the mud, arching the body and then pushing with the telson and last pair of. Pdf book gill development in embryos and first and. It looks like a triangle with spines on the sides and a ridge in the center.
Near the beginning of the horseshoe crabs digestive tract, these parts gather the food together and grind it to a pulp. Book gill development in embryos and first and second. Students examine the form and function of different horseshoe crab anatomical features. Among the chelicerate possessing fanglike front appendages arthropods for example, scorpions, spiders, ticks, and mites, the horseshoe crab, limulus, has a series of book gills gills arranged in membranous folds on either side of. The horseshoe crabs six pairs of gills that they use to breathe are called book gills because they are broad and flat and lie like pages in a book. Book gills of yunnanolimulus luopingensis and extant horseshoe. These sets of flaps are called book gills and are the center of the respiratory system ruppert and barnes 1991. Gill receptor arrays in the horseshoe crab limulus.
Each horseshoe crab has six pairs of book gills, and the outermost flaps are a covering called an operculum some sources dont include the operculum as one of. They are more often found on the ocean floor searching for worms and molluscs, which are their. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Pdf ultrastructure of book gill development in embryos. Horseshoe crabs breathe using book gills, which are thin plates found on the abdomen of the horseshoe crab. Ultrastructure of book gill development in embryos and. The light microscope was used in some early studies comparing the development of. Fact cards, and the book harry horseshoe crab by suzanne tate, live horseshoe crab or shell if possible. The gills also function as paddles to propel juvenile horseshoe crabs. The outer shell of these animals consists of three parts. It is located on the underside of the body right at the base of all the walking legs. Their legs are attached to the underside of the prosoma while book gills are attached to the opisthosoma. The gills also function as paddles to propel juvenile horseshoe crabs through. Book gills are still found in the marine arthropod limulus horseshoe crabs which have five pairs of them, the flap in front of them being the genital operculum which lacks gills.
Oxygen is allowed to pass through but the book gills keeps the water out. The long, straight, rigid tail can be used to flip itself over if turned upside down, so a horseshoe crab with a broken tail is more susceptible to desiccation or predation. A book lung is a type of respiration organ used for atmospheric gas exchange that is present in. Respiratory system book gills gills eg crayfish book gills. Interestingly, the crab can absorb water through the book gills. Six pairs of gills located below the legs look like folded pages, and are known as book gills. The horseshoe crab limulus polyphemus a living fossil.
They are external and there are five pairs of them. The largely terrestrial arachnids may have book lungs that occupy a similar position in the circulatory. Once its food is digested, waste products leave the horseshoe crab s body through its anus. Structurally, they are more like fishes gills than mammalian lungs a book lung is a series of vascularized membranes that absorbs oxygen from the surrounding. Pdf book gill development in embryos and first and second instars. When you have finished labeling the horseshoe crab diagrams, answer the following questions. Ultrastructure of book gill development in embryos and first instars of. Each gill contains approximately 150 lamellae that appear as pages in a book. The horseshoe uses them both for propulsion when swimming and for breathing. These act like the disc on a ski pole, pushing the horseshoe crab along to prevent its getting stuck in sand. If you would like to learn even more about the anatomy and adaptations of the horseshoe crab visit. The gills are ventilated by their rhythmic beating. Each horseshoe crab has six pairs of book gills, and the outermost flaps are a covering called an operculum some sources dont include the operculum as one of the book gills, so you may hear that. Blood flows into the book gills where it is oxygenated in the lamellae of each gill.
The blood is blue because it contains a copperbased respiratory pigment called hemocyanin. The horseshoe crab has 6 pairs of appendages on the posterior side of the prosoma. A book lung is a type of respiration organ used for atmospheric gas exchange and is found in arachnids, such as scorpions and spiders. Book gill definition of book gill by merriamwebster. Van beneden, 1872a, van beneden, 1872b and lankester 1881 are credited as the first to recognize that development in horseshoe crabs is more like development in arachnids than in crustaceans, and the book gills of the horseshoe crab may be homologous with arachnid book lungs kingsley, 1885. Other interesting facts about horseshoe crabs a horseshoe crabs blood has a blue to bluegreen color when exposed to air. An adult female horseshoe crab can lay over 80,000 of these each year. The book gills are versatile organs used not only to breathe but also for. There are three divisions to the body of the horseshoe crab.
Book gills are flaplike appendages that effect gas exchange within water and seem to have their origin as modified legs. Area of book gills on horseshoe crabs skills practiced knowledge application use your knowledge to answer questions about the location of book gills on horseshoe crabs and the way they breathe. Numerous earlier workers used light microscopy to compare book gill and book lung development 421. They use the gills to get oxygen from the water, but if taken out of the water they can get oxygen from air if their gills are kept moist. When swimming upside down in water, a while up on a dry beach the horseshoe crab is careful to keep its gills wet for breathing. The spines are movable and help protect the horseshoe crab. Behind their legs, they have book gills, which exchange respiratory gases and are also occasionally used for swimming. They are flaplike appendages and their function is to absorb oxygen from the water. Horseshoe crabs possess five pairs of book gills located just behind their appendages that allow them to breathe underwater, and can also allow them to breathe on land for short periods of time, provided the lungs remain moist. Procedures read harry horseshoe crab aloud, discussing content and pictures andor using information from the background section of this plan or your own research. When a horseshoe crab goes swimming, the book gills actually propel it through the water.
A tale of two species horseshoe crab anatomy nature. The gills also function as paddles to propel juvenile horseshoe crabs through the water. Horseshoe crabs use book gills to get oxygen from the water. Limulus, has a series of book gills gills arranged in membranous folds on either side of the body into which blood from the ventral sinus passes for oxygenation prior to return to the heart. The horseshoe crab is an omnivore and will eat anything varying from mollusks to algae. Book gill definition is a gill found in the horseshoe crabs that consists of membranous folds arranged like the leaves of a book. Functional morphology and expression of leg gap genes suggest that. Although horseshoe crabs can swim on their backs, propelled by the beating gill flaps, they usually plow through the mud, arching the body and then pushing with the telson and last pair of legs. Behind the legs is a transverse flap, or operculum, which covers the book gills. What are book lungs in arachnids and horseshoe crabs. Behind its legs, the horseshoe crab has book gills, which exchange respiratory gases, and are also occasionally used for swimming. Book gills are still present in the marine arthropod limulus horseshoe crabs which have five pairs of them, the flap in.