Let us learn about the comparison between balanoglossus, ascidia and branchiostoma.
Comparison # Balanoglossus:
1. The pharynx is an elongated structure which is internally divided into 2 incomplete upper and lower halves by a longitudinal parabranchial ridge or Para pharyngeal ridge. The upper one is called the respiratory portion and the lower part is the digestive chamber.
2. The pharynx is contained in the branchiogenital region of the trunk.
3. The mouth leads into a short buccal tube which opens into the pharynx.
4. The pharynx leads directly into the straight intestine.
5.The pharynx is attached with the body by the dorsal mesenteries.
7. The upper respiratory half is perforated by numerous U-shaped pharyngeal slits which increase in number with age. Each pharyngeal slit leads into a branchial sac which, in turn, communicates to the exterior by a gill-pore. In Balanoglossus misakiensis the first four branchial sacs fuse to form a common branchial sac opening by a single branchial pore. The gill-bars contain innumerable long vibratile cilia.
8. The cavity is almost uniformly lined by cilia and mucous cells.
9. No such structure is present.
Comparison # Ascidia:
1. The pharynx is a saclike chamber of large dimension. The internal wall of the pharynx is complicated. In a related urochordate, Herd- mania, the internal cavity is longitudinally folded to increase the surface area.
2. Extended from the mouth nearly to the base of the body.
3. The mouth is situated at the centre of the velum and placed in the posterior end of the oral funnel. The mouth opens into the pharynx.
4. The pharynx is communicated with the stomach through a narrow oesophagus.
5. Only the ventral side of the pharynx is attached with the mantle along the middle line.
6. A special cavity called the atrium or peribranchial cavity encloses the pharynx on all the sides except the ventral one. The atrium opens to the exterior through the atriopore situated on one anterolateral side of the body.
7. The pharynx is pierced on all sides except the line of attachment with the mantle by innumerable vertical stigmata. The stigmata bear series of papillae containing muscles and cilia.
8. The cilia and glandular elements are restricted into definite tracts.
9. A highly developed endostyle is present in the ventral side of the pharynx. Endostyle acts as a fly-paper. The endostyle has two rows of mucous cells separated by rows of ciliated cells. A group of median cells with extremely elongated cilia is present at the middle.
10. On the mid-ventral line of the pharyngeal cavity, i.e., just opposite to the endostyle, there lies the dorsal lamina from which hangs a number of curved bodies, called the languets.
11. The dorsal lamina and the endostyle are joined by the peripharyngeal ciliary bands.
Comparison # Branchiostoma:
1. The pharynx is a large cylindrical and highly compressed chamber. Like that of Ascidia, the pharyngeal cavity is very much complicated.
2. Extends nearly to the anterior half of the body.
3. The mouth is situated at the end of the vestibule which is preceded by the oral hood and buccal cirri. A wheel organ is present in the vestibule. The mouth leads into the pharynx. Like that of Ascidia, the mouth is guarded by velum.
4. The pharynx opens into a straight midgut via a short oesophagus.
5. Only the dorsal side of the pharynx is united with the body wall.
6. The atrium envelopes the pharynx on ail the sides except the dorsal. The atriopore is located posteriorly.
7. The lateral wall of the pharynx is perforated by obliquely arranged vertical gill-slits. There are two types of gill-slits, the primary and secondary ones. There are about 200 gill-slits which increase in number with age. Each gill-slit opens directly into the atrium. The tongue- bars are provided with long cilia.
8. Like that of Ascidia, definite ciliated tracts are also present in Branchiostoma
9. Endostyle consisting of tracts of ciliated cells alternating with mucus- secreting cells is present
10. A median groove, called the epipharyngeal or hyper pharyngeal groove, is present opposite to the endostyle.
11. The epipharyngeal groove and the endostyle are connected anteriorly by peripharyngeal ciliated tracts.