Answer: C) external fertilisation and indirect development.

Explanation:

Development from fertilization to metamorphosis of the enteropneust hemichordate Balanoglossus misakiensis. This is the first report to describe the complete development of an indirect-developing hemichordate under laboratory conditions. Mature adults were induced to spawn by shifting the temperature of seawater from 23 to 28 degrees C. Eggs (200 microm diameter) were enclosed within a non-mucilaginous membrane, and dispersed readily in seawater. After artificial insemination, a fertilization envelope was elevated from the egg surface beneath the egg membrane; this was followed by the formation of the first and second polar bodies within the envelope. Zygotes cleaved at 20-min intervals to form blastulae, and gastrulation started 9 h after fertilization. Embryos hatched 1 day after fertilization to become typical feeding tornaria larvae. The larvae metamorphosed 7-10 days after fertilization without undergoing the first or forth stage of indirect-developing hemichordate development. Larvae that were not fed failed to metamorphose. Juveniles completed adult body formation within a week of settling in sand at the bottom of the culture tube.

Answer:

Option C is the correct answer.

The fertilisation is mainly external i.e. in sea water.

The development is indirect with a free swimming larvae.