Question

Pharyngeal gill slits
(a) Are unique characteristics of chordates
(b) Are found in fishes, crab, snails, aquatic insects
(c) Are found in higher vertebrates and invertebrates
(d) Are not found in a protochordate, but present in vertebrates at least during the embryonic life

Answer 1

Hint: Pharyngeal slits are repeated openings that appear along the pharynx caudal (near the nasal cavity) to the mouth. It is assumed that pharyngeal slits first assisted in filter- feeding (feeding by filtering out plankton or nutrients suspended in the water), and later with the addition of gills along their walls, aided in respiration in the aquatic ecosystem.

Complete answer:
Pharyngeal gill slits are unique characteristics of chordates. These are also found in invertebrates (without a backbone) and hemichordates in the aquatic environment.
- Pharyngeal slits resembling gill slits are transiently (for a short time) present during the embryonic stages of tetrapod development.
- The presence of pharyngeal slits in the hemichordates led to an assumption that whether this structure was a similar structure to the slits found in chordates or a result of convergent evolution.
- Pharyngeal slits are openings in the pharynx that develop into gill arches in the bony fishes and into the jaws and inner ear in the terrestrial animals.
- The vertebrate pharyngeal apparatus, serving the dual functions of feeding and respiration in chordates, has its embryonic origin in a series of bulges found on the lateral surface of the head, the pharyngeal arches.
- In chordates, four common features appear at some point of development in its life cycle: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post- anal tail.

So, the correct answer is, ‘Are unique characteristics of chordates.’

Note: Pharyngeal slit is a third chordate feature. They have been modified to a large extent in the course of evolution. In primitive chordates, these slits are used to filter food particles from the water but now the slits bear gills and are used for gas exchange, in fishes and some amphibians.