Question

Name the Phylum in which pharyngeal gill slits are present.

Answer 1

Hint: Pharyngeal gill slits are filter- feeding organs that act as an opening between the pharynx and the outside.

Complete answer:
Pharyngeal gill slits are found in invertebrate chordates (lancelet and tunicate) and hemichordates living in the aquatic environment. Pharyngeal gill slits are present in all chordates in the embryonic stage which is later replaced by gill arches in fishes and inner ear and jaw bone in terrestrial animals.
 - Pharyngeal gill slits are the third chordate feature besides notochord and a hollow dorsal nerve cord.
- Balanoglossus is a ciliary feeder or filter feeder. The food particles enter the body and are then filtered by the cilia lining the gill- slits.
- Paired Pharyngeal gill slits take part in the circulation of water for respiration.
- In higher chordates, they occur only in the embryonic stage.
- In vertebrate Fishes, Pharyngeal gill slits develop into the gill arches which can be bony or cartilaginous.
- In Terrestrial Animals including aves and mammals, gill slits are only present in the embryonic stage. These later develop into the jaw and inner ear bone.
- In fishes and amphibians, some slits bear grylls and are used for the exchange of gases.
- There are five oblique openings known as gill slits, behind the head on each side of a Scoliodon.
- Gill slits are separate and without operculum (gill covering) in cartilaginous fishes. For example, shark, Scoliodon, etc. Except in Chimaera.
- Bony fishes have four pairs of gills, covered by an operculum on each side which helps to differentiate them from cartilaginous fishes.

Note: In amphibians, gills are present at least in the larval stage which help in respiration. Other respiratory organs are lung, buccopharyngeal cavity, and skin. Some hemichordates can have as many as 200 gill slits.