Question

Which of the following is seen as evidence of choanoflagellates being sister to the rest of animals?

Primitive single-celled animals have the same mode of reproduction as choanoflagellates.

Several early-diverging animal lineages have collar cells but they are not found in any other non-animal lineage.

Both early animals and choanoflagellates move using flagella.

Choanoflagellates show signs of having primitive neurons, something only found in animals.

Some genes of choanoflagellates contain domains that are clearly homologous to those of animals.

The cells of choanoflagellates look almost indistinguishable from the collar cells of sponges.

Answer 1

Option 6. The cells of choanoflagellates look almost indistinguishable from the collar cells of sponges.

The choanocytes (also known as "collared cells") of sponges (considered among the most basal metazoa) have the same basic structure as choanoflagellates. They contain a central flagellum surrounded by a collar of microvilli which are connected by a thin membrane.

Choanoflagellates have a distinctive cell morphology characterized by an ovoid or spherical cell body 3–10 µm in diameter with a single apical flagellum surrounded by a collar of 30–40 microvilli