Haemoglobin is dissolved in the plasma of

Haemoglobin circulates dissolved in the plasma (hemolymph) of many annelids such as earthworms. Annelid blood often contains large extracellular hemoglobins (e.g., hexagonal bilayer hemoglobin) that are free in the coelomic fluid/hemolymph rather than sequestered inside red blood cells [2]. In contrast, vertebrates — including man, fish and frog — package haemoglobin inside erythrocytes (red blood cells), so it is not dissolved in plasma; human haemoglobin is specifically present within RBCs [1], and vertebrate circulatory systems transport oxygen via cellular haemoglobin in erythrocytes. Therefore the correct option is earthworm.

Sources

1. [2] https://pmc.ncbi.nlm.nih.gov/articles/PMC6400237/
2. [1] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Do You Know? > p. 90