Merostoma. Artropodos. Invertebrados.
Caracteres generales
Los merostomas son artrópodos quelicerados marinos.La especie más típica Cacerola de las Molucas, o Límulo, oxifosuro es descendiente de los artrópodos fósiles de la Era Primaria: los Gigantostráceos de más de 2 m de longitud.
Especie típica
- Limulus polyphemus.
MEROSTOMATA
The horseshoe crabs are a relatively small group of fossil and living forms. Examine the preserved horseshoe crab,Limulus, on display. Limulus is common in shallow marine waters off the Atlantic coast from Nova Scotia to Yucatan. Notice that there are two main body regions, an anteriorcephalothorax covered by carapace (hard, shell-like outer covering) which is shaped like a horseshoe, giving the animal its common name, and a posterior abdomen. The carapace represents a fusion of the primitive head and thorax regions. At the posterior end of the abdomen is a tail spine. The tail spine is used to push the animal forward when it burrows and to right the animal if it is overturned.
Examine the underside of the specimen. Note that there are seven pairs of jointed appendages attached to the cephalothorax. The first is a pair of chelicerae, which are used mainly to capture and break up food. Just behind them is the mouth. The next four pairs are leg-like and used primarily in locomotion. Each ends in a small pincer. The next pair of appendages is also used primarily for locomotion, but they end in leaf-like structures used to clean mud and silt off the gills. The last pair of appendages is very small and highly modified. The abdomen is unsegmented, but bears six pairs of appendages. The first flap is related to the reproductive system, but the last five are plate-like and bear gill lamellae; these are called book gills.
The horseshoe crabs are a relatively small group of fossil and living forms. Examine the preserved horseshoe crab,Limulus, on display. Limulus is common in shallow marine waters off the Atlantic coast from Nova Scotia to Yucatan. Notice that there are two main body regions, an anteriorcephalothorax covered by carapace (hard, shell-like outer covering) which is shaped like a horseshoe, giving the animal its common name, and a posterior abdomen. The carapace represents a fusion of the primitive head and thorax regions. At the posterior end of the abdomen is a tail spine. The tail spine is used to push the animal forward when it burrows and to right the animal if it is overturned.
Examine the underside of the specimen. Note that there are seven pairs of jointed appendages attached to the cephalothorax. The first is a pair of chelicerae, which are used mainly to capture and break up food. Just behind them is the mouth. The next four pairs are leg-like and used primarily in locomotion. Each ends in a small pincer. The next pair of appendages is also used primarily for locomotion, but they end in leaf-like structures used to clean mud and silt off the gills. The last pair of appendages is very small and highly modified. The abdomen is unsegmented, but bears six pairs of appendages. The first flap is related to the reproductive system, but the last five are plate-like and bear gill lamellae; these are called book gills.
Hay cuatro especies vivas en esta clase. Los cangrejos de herradura que se ven hoy en día han cambiado poco desde los cangrejos de herradura que podría haber visto hace 250 millones de años.
Los cangrejos de herradura tienen tres segmentos del cuerpo, elprosoma , el opistosoma , y el Telson . El prosoma es la parte frontal en forma de herradura del cuerpo del cangrejo herradura.El cangrejo de herradura tiene diez ojos en la parte superior del prosoma y seis pares de apéndices en la parte inferior del prosoma.
Cinco pares de apéndices son para caminar y un par dequelíceros ayudan a la herradura a mover los alimentos cangrejo en su boca. El opistosoma o abdomen se conecta a la prosoma con una bisagra. El telson o la cola se encuentra junto a la opistosoma. Algunas personas piensan que el telson es un aguijón, pero no lo es. El cangrejo herradura utiliza el telson para dirigir a sí mismo y dar la vuelta en sí sobre si se excita la espalda!
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