Arthropod - Evolution and paleontology | misjon.info
approach — Morphology. Introduction. The phylogenetic relationships among major spiralian metazoans, the annelids, molluscs, and arthropods, have been the. What is the difference between Annelida and Arthropoda? Annelida consists of coelomate animals; Arthropoda consists of haemocoelomate. The difference between Annelida and Arthropoda is Annelida have no distinct heads where in the later body is divided into head, thorax and.
On the other hand, arthropods have more complex segmented bodies covered in an exoskeleton that protects their organs and muscles. Most arthropods also have visible distinctions between their heads, bodies and legs; this is not the case for annelids.
What is the difference between Annelida and Arthropoda?
Reproduction Methods Reproduction among arthropods usually involves a male and a female of the species mating in order to fertilize eggs in the female, who then lays the eggs. Some arthropods fertilize their eggs externally. Most species are dioecious, meaning they have two distinct sexes.
The polychaete class of annelids is also dioecious, but most members of the other two classes are not. For example, a single earthworm will produce both eggs and sperm. Two worms rub against each other to exchange sperm and to fertilize one another's eggs.
How Are the Annelid & the Arthropod Different? | Animals - misjon.info
The polychaete class can also reproduce through epitoky. In some of these cases, part of the worm separates from the rest of the body and leaves the burrow to reproduce.
The remainder of the worm stays behind in the burrow. Circulatory Systems Another difference between annelids and arthropods is their circulatory system. Annelids and humans have closed circulatory systems in which the heart pumps blood into vessels. The blood is always contained in the vessels -- it does not enter the rest of the body. Arthropods, however, have open circulatory systems, so the blood actually pumps the blood into parts of the body cavity known as sinuses, where it surrounds tissues.
These are secreted by the one-cell deep epidermis outermost skin layer.
A few marine annelids that live in tubes lack cuticles, but their tubes have a similar structure, and mucus -secreting glands in the epidermis protect their skins. Below this are two layers of muscles, which develop from the lining of the coelom body cavity: The simplest are unjointed and form paired bundles near the top and bottom of each side of each segment.
The chetoblasts produce chetae by forming microvillifine hair-like extensions that increase the area available for secreting the cheta.
Annelid - Wikipedia
When the cheta is complete, the microvilli withdraw into the chetoblast, leaving parallel tunnels that run almost the full length of the cheta. Parapodia are unjointed paired extensions of the body wall, and their muscles are derived from the circular muscles of the body.
They are often supported internally by one or more large, thick chetae. The parapodia of burrowing and tube-dwelling polychaetes are often just ridges whose tips bear hooked chetae. In active crawlers and swimmers the parapodia are often divided into large upper and lower paddles on a very short trunk, and the paddles are generally fringed with chetae and sometimes with cirri fused bundles of cilia and gills.
From each segmental ganglion a branching system of local nerves runs into the body wall and then encircles the body. Vertebrates have a different system, in which one neuron controls a group of muscle fibers.
How Are the Annelid & the Arthropod Different?
Their large diameter decreases their resistance, which allows them to transmit signals exceptionally fast. This enables these worms to withdraw rapidly from danger by shortening their bodies. Experiments have shown that cutting the giant axons prevents this escape response but does not affect normal movement. Each septum forms a sandwich with connective tissue in the middle and mesothelium membrane that serves as a lining from the preceding and following segments on either side.
Each mesentery is similar except that the mesothelium is the lining of each of the pair of coelomata, and the blood vessels and, in polychaetes, the main nerve cords are embedded in it. Parts of the mesothelium, especially on the outside of the gut, may also form chloragogen cells that perform similar functions to the livers of vertebrates: In some species coelomocytes may also contain a respiratory pigment — red hemoglobin in some species, green chlorocruorin in others dissolved in the plasma  — and provide oxygen transport within their segments.
Respiratory pigment is also dissolved in the blood plasma. Species with well-developed septa generally also have blood vessels running all long their bodies above and below the gut, the upper one carrying blood forwards while the lower one carries it backwards. Networks of capillaries in the body wall and around the gut transfer blood between the main blood vessels and to parts of the segment that need oxygen and nutrients.
Both of the major vessels, especially the upper one, can pump blood by contracting. In some annelids the forward end of the upper blood vessel is enlarged with muscles to form a heart, while in the forward ends of many earthworms some of the vessels that connect the upper and lower main vessels function as hearts.