Scoliodon is a cartilaginous fish under the class Chondrichthyes. In this article about Scoliodon, we will learn about the respiratory system of Scoliodon.
What Is the Respiratory System?
The respiratory system is a physiological process in every organism by which they produce energy typically with the intake of oxygen and release of carbon-di-oxide.
Respiratory System of Scoliodon
Fig: Respiratory System of Scoliodon
- The respiration of Scoliodon is aquatic.
- They breathe with the help of gills.
- The respiratory organs of Scoliodon consist of 5 pairs of gill pouches containing gills.
- All the five pairs of gill pouches are present in a series, in the lateral wall of the pharynx, behind the hyoid arch.
- Each gill pouch opens into the pharynx by a large internal branchial aperture and to the outside by a narrow vertical external branchial aperture or gill-slit.
- A gill septum or interbranchial septum separates the two adjacent gill pouches.
- The gill septum is covered by an epithelium and contains blood vessels, nerves, etc.
- The mucous membrane lining the gill pouches gives a series of horizontal branchial lamellae or gill lamellae.
- The gill lamellae are highly vascularised.
- The first gill pouch lies between the hyoid and the first branchial arches and the last one is present between the fourth and fifth branchial arches.
- The fifth branchial arch of Scoliodon is gill-less. Other branchial arches support gills.
- There are two types of gills are present in the Scoliodon. They are 1. Holobranch or complete gill, and 2. Demibranch or hemibranch or half gill.
Holobranch or Complete Gill
fig: Holobranch of Scoliodon
- The branchial arch bears two sets of gill lamellae.
- The first four branchial arches support holobranchs.
Demibranch or Hemibranch or Half Gill
- The branchial arch bears a single set of gill lamellae.
- The hyoid arch supports only a demibranch.
Mechanism of Respiration
fig: Mechanism of respiration of Scoliodon
- A series of hypobranchial muscles contract and the gill arches expand, thus pulling down the floor of the buccopharyngeal cavity and enlarging its cavity.
- As the external gill slits are tightly closed and the bucco-pharyngeal cavity is expanded, the water from the surroundings enters the bucco-pharyngeal cavity.
- Adductor muscles close the mouth.
- At the same time the constrictor and inter-branchial muscles contract.
- The floor of the pharynx raised and reduced its volume by the contraction of the constrictor and inter-branchial muscles.
- As a result, water is forced into gill pouches, over the gill lamellae, and out through the open external gill slits.
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