Question

Solenocytes and nephridia are respectively found in
A. Platyhelminthes and annelids
B. Annelids and Nematoda
C. Cnidaria and Mollusca
D. Mollusca and Echinodermata

Answer 1

Hint:- Solenocytes and nephridia are the excretory system found in some group of animals that helps in the elimination of metabolic waste from the body to the outside. These also help in maintaining osmoregulation in the body.

Complete Answer:- The phylum Platyhelminthes includes flatworms that are a triploblastic group of animals. Majority of forms are parasitic and free living. The parasitic forms have hooks and suckers. These are acoelomate organisms that have an organ system grade of organization. They have an incomplete alimentary canal. Their excretory system consists of peculiar flame cells or protonephridia or solenocytes that can help in osmoregulation and excretion. These animals are ammonotelic in nature.
Annelids are the aquatic or terrestrial, free living or parasitic animals. They have organ-system organization and bilateral symmetry. These are triploblastic animals and first true coelomate animals. They show metameric segmentation. Their alimentary canal is straight and complete so these have a tube-within-a tube body plan. Their digestion is entirely extracellular. The excretion and osmoregulation occur by segmentally arranged and metamerically disposed ectodermal coiled organs, nephridia.
The phylum Aschelminthes or nematodes includes roundworms. These include mostly free-living and may occur in water or within the soil. They have a bilateral symmetry and organ system level of organization. They have a tube within the tube body plan. Their excretory system consists of a pair of gland cells or intracellular canals or both.
The phylum Cnidaria has about 900 species that are exclusively marine forms. They have a tissue grade organization and are diploblastic animals. They have both intracellular and extracellular types of digestion. Excretion and respiration in these animals occur directly as all the cells are in direct contact with water.
The phylum Echinodermata includes the spiny skinned animals that are exclusively marine. They are triploblastic animals with organ system grade of organization. They do not have any excretory organ and the waste products are removed by diffusion through branchiae or amebocytes.

So the correct answer is 1. Platyhelminthes and annelids

Note:- The excretion occurs in different ways in different organisms. The animals with organization level below the tissue level usually lack excretory organs. Based on excretory products animals are classified as ammonotelic, ammonotelic and ureotelic.