The “Animalia” Kingdom under Eukarya

The Animalia Kingdom consists of cellular and multicellular organisms. The cells in this kingdom lack cell walls and chloroplasts and contain specialized organelles.

Components of an animal cell- Source: ThoughtCo.

The multicellular organisms in this kingdom are (by increasing complexity) tissue, organs, insects, animals and humans. Animals can be classified as vertebrates and invertebrates (Click HERE for more info).

Within Animalia, cells are categorized as follows: insect cell lines, stem cells, tissue cells (from differentiation of mesenchymal stem cells or MSCs), blood cells (from differentiation of hematopoietic stem cells or HSCs), animal cell lines (animal tissue), and human cell lines (human tissue).

Stem cells are classified as follows: totipotent, pluripotent and multipotent (MSCs and HSCs).

Examples of tissue cells are: muscle cells, nerve cells, epithelial cells, endothelial cells, and neuronal cells.

For the blood cells: all blood cells trace their origin back to hematopoietic stem cells in the bone marrow. HSCs differentiate through two main lineages: myeloid and lymphoid. Myeloid and lymphoid cells are an important part of the immune system. Below is a structured breakdown:

1. Myeloid Lineage

• Erythrocytes (Red Blood Cells)

• Function: Oxygen transport via hemoglobin.

• Megakaryocytes → Platelets (Thrombocytes)

• Function: Blood clotting and wound repair.

• Granulocytes

• Neutrophils – First responders in infection, phagocytosis.

• Eosinophils – Defense against parasites, allergy modulation.

• Basophils – Release histamine, mediate allergic responses.

• Monocytes → Macrophages & Dendritic Cells

• Monocytes circulate in blood.

• Macrophages: Tissue-resident phagocytes.

• Dendritic cells: Antigen-presenting cells for adaptive immunity.

2. Lymphoid Lineage

• B Lymphocytes (B Cells)

• Produce antibodies; differentiate into plasma cells.

• T Lymphocytes (T Cells)

• Helper T cells (CD4+) – Coordinate immune response.

• Cytotoxic T cells (CD8+) – Kill infected or cancerous cells.

• Regulatory T cells – Suppress immune overactivation.

• Natural Killer (NK) Cells

• Destroy virus-infected and tumor cells without prior sensitization.

Summary Table- Blood cells derived from HSCs (Source: Allen Institute for Immunology)

Source: Allen Institute for Immunology