Annelids and arthropods have long been considered each other's closest relatives, as evidenced by similarities in their segmented body plans. An alternative view, more recently advocated by investigators who have examined partial 18S ribosomal RNA data, proposes that annelids, molluscs, and certain other minor phyla with trochophore larva stages share a more recent common ancestor with one another than any do with arthropods.
World View. More From Reference. Are U. National Weather Service Forecasts Accurate? The five classes of arthropods are Crustacea shrimp, crayfish, and lobster , Arachnida spiders, ticks, mites, and scorpions , Chilopoda centipedes , Diplopoda millipedes and Insecta bees, butterflies, roaches and beetles.
A bee is shown in figure 2. Annelida: Annelida refers to an animal phylum that consists of coelomates with elongated, segmented body. Arthropoda: Arthropoda refers to an animal phylum that consists of haemocoelomates with a segmented body, joint appendages, and chitinous exoskeleton. Annelida: Annelids are commonly called segmented worms. Arthropoda: Arthropods are commonly called animals with jointed legs.
Arthropoda : The body of the Arthropoda is differentiated into a distinct head, thorax, and abdomen. Annelida: Annelida consists of a fully segmented body, which is called the metameric segmentation. Arthropoda: Arthropoda does not consist of a fully-segmented body. Annelida: Annelida lacks jointed appendages. Arthropoda: Arthropoda consists of joined appendages. Annelida: Annelida consists of coelomate animals. Arthropoda: Arthropoda consists of haemocoelomate animals.
Annelida: Annelida consists of a hydrostatic skeleton. Arthropoda: Arthropoda consists of both hydrostatic skeleton and exoskeleton. Annelida: Annelida consists of a closed circulatory system. Arthropoda: Arthropoda consists of an open circulatory system. Annelida: Annelida consists of several, simple hearts. Arthropoda: Arthropoda consists of one heart. Annelida: Annelida consists of antennae, palps, eyes, statocysts, lateral organs, and nuchal organs. Arthropoda: Arthropoda consists of antennae, statocysts, simple eyes, and compound eyes.
Two worms rub against each other to exchange sperm and to fertilize one another's eggs. 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. 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. Because the closed system is less efficient for oxygen transportation, many arthropods have supplemental systems for carrying oxygen to their organs.
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