Earthworm (Pheretima) Anatomy and Body Wall Structure

Vocabulary terms covering the histological layers of the earthworm body wall and the segmental distribution of internal structures.

Cuticle

A thin and elastic non-cellular double-layered protective membrane made up of collagen fibres and polysaccharide secreted by the underlying epidermis.

Epidermis

A cellular, single layer consisting of 4 different types of cells (supporting, gland, basal, and receptor) resting on a basement membrane.

Supporting cells

Cells that form the main bulk of the epidermis and provide nutrition to the embryo.

Mucus cells

A type of gland cell in the epidermis that secretes mucus.

Albumen cells

A type of gland cell that secretes albumin and is abundant in the clitellum.

Basal cells

Cells found at the inner sides of glands and supporting cells, also referred to as replacing cells.

Circular muscles

An outer thin layer of muscles containing pigment cells, connective tissue, nerve fibres, and blood capillaries; their contraction increases the length of the animal while decreasing thickness.

Longitudinal muscles

A thick layer of muscle fibres found beneath the circular layer in the form of bundles; their contraction shortens the earthworm's length but increases thickness.

Coelomic epithelium

The innermost layer of the body wall, also known as somatic peritoneum or parietal layer, consisting of a single-celled layer with small nuclei.

Prostomium

The structure attached with the 1st segment of the earthworm.

Peristomium

The 1st segment of the earthworm where the mouth is located.

Buccal cavity

The digestive structure located within the segments $1\text{st}-3\text{rd}$.

Pharynx

The digestive structure located within the segments $3\text{rd}-4\text{th}$.

Oesophagus

The digestive structure located within the segments $5\text{th}-7\text{th}$.

Gizzard

The digestive structure located within the segments $8\text{th}-9\text{th}$.