Question

Fertilization in leucosolenia is
A) Cross and internal
B) self and external
C) self and internal
D) cross and external

Answer 1

Hint: Leucosolenia belongs to phylum Porifera (Sponges). Generally in most of the Porifera, sperm comes from another sponge through a water current and then fertilization occurs inside the body of the sponge.

Complete answer:Leucosolenia belongs to class Calcarea of the phylum Porifera (sponges) and hence they are also called calcareous sponges.
Although these sponges are hermaphrodite, self-fertilization usually does not occur in them as male and female gamete mature at different times.
They possess cross-fertilization, They have a characteristics cell called choanocytes (collar cell) lining their inner portion of the body. These cells have flagella which help them in generating water current, trapping food particles, and also in reproduction. They trap (flagella of collar cell) the sperms present in water current from other sponges and bring it to the egg and fertilisation occurs.
After fertilization, a zygote is formed which develops into larvae. there are two types of larva present in them called (1) Solid parenchymella and (2) hollow amphiblastula. these larvae swim freely in the water and as they grow adult , they attach to startatum and become sessile.
Since fertilization is occurring inside the body of the sponge so it is called internal fertilization and sperm comes from other sponges so it is called cross-fertilisation
So option (A) is correct.

Note:Hermaphrodite: This is the condition in which both male and female sex organ are present in the same organism. Examples: Mostly invertebrates are hermaphrodite like earthworm, Platyhelminthes member, poriferans, molluscans and annelidans .
Self-fertilization: it means the fusion of gametes that comes from the same indivisuals and the gametes also mature at the same time.