Question

Flame cells/solenocytes are main excretory structures of
A. Colentrates
B. Platyhelminthes
C. Annelids
D. Echinodermata

Answer 1

Hint: Solenocytes are extended, flagellated cells found in most lower invertebrates, such as platyhelminthes, that aid in the clearance of nitrogenous wastes. Flame cells are another name for Solenocytes.
Solenocytes are flagellated cells that help with excretion, ion control, and osmoregulation in many animals, including some chordates in the Cephalochordata subphylum. These are the cells that create protonephridium subtypes alongside the other kind, flame cells.

Complete answer:
Option A: Hydra, like other coelenterates, lacks distinct excretory organs. Diffusion removes nitrogenous waste products such as ammonia from the body's general surface. Some nitrogenous waste products, as well as indigestible materials, are expelled via the mouth.
So, option A is not correct.
Option B: This is the major excretory organ of platyhelminthes, and it is a cup-shaped cell with a clump of cilia. In Platyhelminthes, solenocytes are responsible for excretion and osmoregulation.
So, option B is correct.
Option C: Nephridia are tubules that are unblocked on both sides in most annelids and mollusks. The internal unblocking leads to the formation of coelom, whereas the exterior unblocking leads to the formation of nephridiopores.
So, option C is not correct.
Option D: There are no specialised excretory organs in echinoderms for excretion. Excretion occurs in them either through diffusion or osmosis, or through an active transport mechanism.
So, option D is not correct.

So, option B is the correct answer.

Note:
Solenocytes are long, extended cells with a constantly moving long flagellum that wafts excretory material through the tubule. They are derived from mesoderm. The tube's walls are made up of pillar-like rods and are quite thin. The excretory liquid is created when body fluids are ultra-purified through the wall.