The Earth-Bound Vermes

Earthworm Dissection Aaron Wong Per.6 Guzman

On the Vermes

Originally, the earthworm was a part of the class Vermes. Carolus Linnaeus originally made a class of non-arthropod invertebrate animals called Vermes, which contained intestina, mollusca, testacea, lithophyta, and zoophyta. Today, the animals in Vermes have been split into many phyla, including cnidaria, echinodermata, and annelids. This was mainly because of development into the theory of evolution, which showed that these many diverse animals were not strongly ancestrally linked.

Objectives

Students will be observing the internal and external structure of the earthworm. Students will take note of the organs, structures, and functions of the digestive system. Students will learn about the ecological role of the earthworm.

Lumbricus terrestris

Earthworms, Lumbricus terrestris, are commonly found in soil. Earthworms feed on live and dead organic matter in the soil. Earthworms are preyed upon by many kinds of bird, snake, mammal, and invertebrate. Earthworms perform a major role in any ecosystem by converting organic matter into humus, the biotic part of soil through digesting and excreting organic material such as manure. Earthworms are adapted to this environment by having setae to allow movement through the soil, being hermaphroditic to increase the chance of having offspring, and having a special cuticle that secretes mucus to facilitate movement through the dirt. Earthworms are in the phylum annelida, or the segmented worms. Annelids are closely related to arthropods. annelids are the beginning of segmentation in evolution and share features such as a ventral nerve cord, dorsal and ventral muscles, and a dorsal blood vessel with arthropods. An earthworm cannot grow segments throughout life, meaning that an earthworm is born with the number of segments that earthworm will have throughout the lifespan.

Look! The Innerworm!

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Diagrams of the major organs of an earthworm.

Digestive System

The digestive system of an earthworm involves the mouth, pharynx, esophagus, crop, gizzard, and intestine. Soil enters the earthworm through the mouth and is sucked by the pharynx. The crop stores food for a small time. The gizzard grinds the soil through muscular contractions. The soil then travels through the intestine to be digested.The digestive system absorbs nutrients for energy and homeostasis. The process of digestion in the earthworm helps all animals in that ecosystem as earthworms are able to place minerals in the soil in a way that significantly helps plant growth. Earthworms also help aerate the soil as they dig holes and push air through those holes and mix the soil together by ingesting some soil and placing the soil in a foreign place. This allows earthworms to be a kind of fertilizer and are often found in gardens and farms as they promote plant growth.
This web page has animations of the digestive system of the earthworm.
This webpage compares the body systems of various animals, including the earthworm.
Earthworm Dissection
This video goes over the entire dissection of an earthworm.
This website goes over the earthworm dissection.