Question

Which one of the following statements about all the four of spongilla, leech, dolphin and penguin is correct?
A. All are bilaterally symmetrical.
B. Penguin is homeothermic while the remaining three are poikilothermic.
C. Leech is a freshwater form while all others are marine.
D. Spongilla has special collared cells called choanocytes, not found in the remaining three.

Answer 1

Hint: The spongilla belongs to the Porifera phylum, in which the choanocytes are the characteristic cells, these are not found in leeches, dolphins and also in the penguin. These distinctive cells lined the interior body walls of the sponges.

Complete answer: The spongilla is the genus of freshwater sponges present in the family Spongillidae found in the lakes and in the slow streams. The body of the sponge is cylindrical, asymmetrical, or has radial symmetry whereas leech, dolphin, and penguin have bilateral symmetrical. The sponges are aquatic animals and can be marine or freshwater. The sponges possess choanocytes or flagellated cells and help in the ingestion of food particles.
-Leeches are the segmented parasitic or predatory worms that belong to the phylum Annelida.
-The aquatic mammals commonly known as dolphins are within the infraorder Cetacea. The term dolphin usually refers to the extant families like the Delphinidae, Platanistidae, Iniidae, and the Pontoporiidae, and also the extinct Lipotidae. The dolphin is homeothermic. The dolphin belongs to the flightless birds and they contain the ability to maintain body temperature.
-The penguins are a group of aquatic flightless birds. They live mostly in the Southern Hemisphere, with only one species, that is the Galápagos penguin, found mostly in the north of the equator.
Therefore, the correct answer is option D.

Note: By cooperatively moving their flagella, the choanocytes filter particles out of the water and into the spongocoel, and out through the osculum. Choanocytes can turn into spermatocytes when needed for sexual reproduction, due to the lack of reproductive organs in sponges. They make up the choanoderm, which is a type of cell layer found in the sponges.