Horseshoe Crab
Limulus polyphemus
Summary 4
The Atlantic horseshoe crab, Limulus polyphemus, is a marine chelicerate arthropod. Despite its name, it is more closely related to spiders, ticks, and scorpions than to crabs. Horseshoe crabs are most commonly found in the Gulf of Mexico and along the northern Atlantic coast of North America. A main area of annual migration is Delaware Bay, although stray individuals are occasionally found in Europe.
Description 5
The horseshoe crab, Limulus polyphemus, is more closely related to chelicerates such as spiders, scorpions, ticks and mites than it is to true crabs and other crustaceans. Horseshoe crabs are considered to be "living fossils" that have evolved little in the past 250 million years. Limulus is an ancient genus which has probably existed since the Silurian period (440 to 410 million years ago), and shows little morphological change from the now extinct genus Paleolimulus that lived about 200 million years ago. Limulus polyphemus is believed to be the closest living relative of trilobites (Shuster 1982).Like all chelicerates, members of the Order Xiphosurida have a two-part body consisting of a prosoma, or head region; and an opisthosoma, or abdominal region. The prosoma contains 6 pairs of legs, all of which bear claws except the last pair. The prosoma also contains 2 types of eyes: 2 compound eyes, or ommatidia, are located on either side of the head; and 2 simple eyes, or ocelli, are located in the center of the head. The opisthosoma contains an additional 6 pairs of appendages which aid in respiration, reproduction, and locomotion. The first pair of abdominal appendages form a genital operculum which houses the genital pores. The remaining 5 pairs of appendages are modified into a series of overlapping plates which function as gills. The underside of each plate is highly folded into leaf-like folds, or lamellae, which provide the actual surface for gas exchange. Due to their morphology, the abdominal plates have become known as book gills. In addition to their respiratory function, the opisthosomal appendages also function as paddles in locomotion. A long spine, called a telson, is located behind the opisthosoma and gives this order its name: Xiphos being Greek for "sword", and uros meaning "tail."
Geographic range 6
Along the Atlantic Coast, from Nova Scotia to the Yucatan.
Biogeographic Regions: nearctic (Native ); neotropical (Native ); atlantic ocean (Native )
Size 7
Horseshoe crabs are long-lived and slow to mature in comparison to most other invertebrate groups. Males reach sexual maturity between 9 - 11 years of age, and females between 10 - 12 years of age (Cohen and Brockmann 1983). The average life span is believed to be approximately 20 - 40 years; however, it is difficult to accurately assess age in horseshoe crabs (Botton and Ropes 1988). The adult size of Limulus polyphemus shows a distinct latitudinal gradient, with larger animals found toward the center of the range, and smaller animals found at the extremes of the range, north of Cape Cod, along the Florida coast, and in the Gulf of Mexico. Limulus polyphemus shows distinct sexual dimorphism, with males approximately 1/3 the size of the females (Shuster 1982). Adult females in the Indian River Lagoon have an average prosomal width of 189 mm, while the average adult male has a prosomal width of 136 mm.
Reproduction 8
The first pair of the six, flap-like appendages on the underside of the abdomen acts as a cover for the genital pore. The egg or sperm are released through this pore during spawning.
Link to Access Genomic Data 9
http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=6850&lvl=0
Sources and Credits
- (c) Tracy Barbaro, some rights reserved (CC BY-NC-SA), http://www.flickr.com/photos/48757934@N08/4459318303/
- (c) Biopix, some rights reserved (CC BY-NC), http://www.biopix.com/PhotosMedium/Limulus%20polyphemus%2000003.jpg
- (c) Paul Williams, some rights reserved (CC BY-NC), https://www.flickr.com/photos/ironammonite/5727971007/
- Adapted by matbio from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Limulus_polyphemus
- Adapted by matbio from a work by (c) Smithsonian Marine Station at Fort Pierce, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/11526347
- Adapted by matbio from a work by (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/18655050
- Adapted by matbio from a work by (c) Smithsonian Marine Station at Fort Pierce, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/11526352
- (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/18655052
- (c) Emily Rose Sharkey, all rights reserved
