Annelids may be either monoecious with permanent gonads as in earthworms and leeches or dioecious with temporary or seasonal gonads that develop as in polychaetes. However, cross-fertilization is preferred in hermaphroditic animals. These animals may also show simultaneous hermaphroditism and participate in simultaneous sperm exchange when they are aligned for copulation.
Phylum Annelida contains the class Polychaeta the polychaetes and the class Oligochaeta the earthworms, leeches and their relatives. The many chetae of polychaetes are also arranged within fleshy, flat, paired appendages that protrude from each segment called parapodia , which may be specialized for different functions in the polychates.
The subclass Hirudinea includes leeches such as Hirudo medicinalis and Hemiclepsis marginata. The class Oligochaeta includes the subclass Hirudinia and the subclass Brachiobdella. A significant difference between leeches and other annelids is the development of suckers at the anterior and posterior ends and a lack of chaetae. Additionally, the segmentation of the body wall may not correspond to the internal segmentation of the coelomic cavity.
This adaptation possibly helps the leeches to elongate when they ingest copious quantities of blood from host vertebrates. The subclass Brachiobdella includes species like Branchiobdella balcanica sketi and Branchiobdella astaci , worms that show similarity with leeches as well as oligochaetes.
Figure 3. The a earthworm, b leech, and c featherduster are all annelids. Phylum Annelida includes vermiform, segmented animals. Segmentation is seen in internal anatomy as well, which is called metamerism.
Annelids are protostomes. These animals have well-developed neuronal and digestive systems. Some species bear a specialized band of segments known as a clitellum. Annelids show the presence numerous chitinous projections termed chaetae, and polychaetes possess parapodia. Select personalised content. Create a personalised content profile. Measure ad performance. Select basic ads. Create a personalised ads profile. Select personalised ads. Apply market research to generate audience insights.
Measure content performance. Develop and improve products. List of Partners vendors. Share Flipboard Email. Laura Klappenbach. Ecology Expert. Laura Klappenbach, M. Updated January 20, Featured Video. Cite this Article Format. Klappenbach, Laura. Types of Circulatory Systems: Open vs. The gizzard uses stones that the earthworm eats to grind the food completely.
The food moves into the intestines as gland cells in the intestine release fluids to aid in the digestive process. The intestinal wall contains blood vessels where the digested food is absorbed and transported to the rest of the body. Circulatory System Another important organ system is the circulatory system. The earthworm has a closed circulatory system. An earthworm circulates blood exclusively through vessels.
There are three main vessels that supply the blood to organs within the earthworm. These vessels are the aortic arches, dorsal blood vessels, and ventral blood vessels. The aortic arches function like a human heart. There are five pairs of aortic arches, which have the responsibility of pumping blood into the dorsal and ventral blood vessels.
Respiratory System Earthworms do not have lungs. They breathe through their skin. Body fluid and mucous is released to keep its skin moist.
Earthworms therefore, need to be in damp or moist soil. These tissues enable an earthworm to detect light and not surface during the daytime where they could be affected by the sun.
Earthworm Reproduction Earthworms are hermaphrodites where each earthworm contains both male and female sex organs.
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