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The upcoming discussion will update you about the difference between lampreys and hagfish.
Difference # Lamperys:
1. Habit and habitat:
Live usually in the sea and migrate to the rivers for spawning. The adult are semi-parasitic but the larva leads independent life.
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2. Shape of the body:
The body is cylindrical and stout.
3. Fins:
The dorsal fin is divided into two portions by a notch. The caudal fin is well-represented.
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4. Mouth:
The mouth is sub-terminal in position due to the overdevelopment of the upper lip region to form a funnel-like structure. Terminal in position and is surrounded by soft lips.
5. Sensory tentacles around mouth:
Absent
6. Buccal funnel:
Present
7. Sucking devices:
Moderately developed
8. Nostril:
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Paired external nasal apertures lie on the dorsal side of the head and occupy a median position.
9. ‘Thread cells’ in the skin:
Present
10. Myotomes:
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The myotomes are separated into the dorsal and ventral portions by myosepta.
11. Cartilaginous oral ring:
Present
12. Lingual cartilage:
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Feebly developed
13. Root of the skull:
Mainly membranous with a narrow bar across the posterior region.
14. Teeth:
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Horny teeth are present in the buccal funnel and ‘tongue’. The teeth present on the tongue are larger in size.
15. Tongue:
Feebly developed
16. Paired salivary glands:
Present as a pair of pigmented sacciform structures within the hypobranchial muscles. True nature of these glands is controversial.
17. Respiratory and digestive portion:
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The buccal cavity leads into two tubes, the dorsal one is the oesophagus and the ventral one is the respiratory tube.
18. Respiratory tube:
It is closed behind and the open anterior end is guarded by velum. The gill-pouches open directly into the respiratory tube.
19. Spiral valve in the intestine:
Present
20. Liver, gall bladder and bile ducts:
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The liver is a massive conical structure. It is bilobed, but the lobes are joined. The gall bladder and bile ducts are present in larval stage, but usually disappear in adult.
21. Branchial region:
Voluminous
22. Gill – pouches:
Seven pairs of gill-pouches are present which do not open into the gut, but into the respiratory tube.
23. External gill- slits:
Seven pairs in adult. An additional pair may be present in the larva.
24. Pericardial sac:
Thick-walled and supported by a cartilaginous skeleton.
25. Shape of RBC:
Circular in outline.
26. Blood forming tissue:
Present in kidney and below the spinal cord
27. Ductus Cuvieri:
Only the right one is present and the left one is absent in an adult, although both persist in the larva.
28. Aortic arches:
Each arch divides and sends branches to the posterior hemi-branch and anterior hemi- branch of the adjacent gill- pouches.
29. Nerve supply to heart:
The heart gets the nerve fibres from the vagus nerve and contains nerve cells.
30. Brain:
Brain is comparatively well- developed
31. Formation of central nervous system:
The central nervous system is formed as a solid ectodermal keel which becomes hollow to form the neural tube.
32. Olfactory lobe:
Smaller
33. Choroid plexus:
Present
34. Cranial nerves:
Ten pairs of cranial nerves are present.
35. Lateral line branch of vagus:
Present and well – developed.
36. Blood vessels in the spinal cord:
There is no blood vessel within the spinal cord.
37. Nerves to the eye – muscles:
The eye-muscle nerves are present.
38. Roots of the spinal nerves:
The dorsal and ventral roots of the spinal nerves remain separate.
39. Paired eyes:
Functional and well –developed.
40. Pineal eye:
Present.
41. Semicircular canals:
Two semicircular canals. Each with an ampulla is present.
42. Nasohypophysial duct:
Ends blindly
43. Anterior lobe of pituitary:
Differentiated.
44. Kidneys:
The pronephros does not persist in an adult. The mesonephros is the functional adult kidney. The mesonephric tubules are complicated and lack segmental disposition.
45. Urinogenital sinus:
Present
46. Reproductive system:
The sexes are separate in adults, but the ova may be present in the testis. In the young Ammocoetes larva, the gonad is hermaphroditic in nature and contains both spermatocytes and oocytes.
47. Eggs:
The eggs are small and are devoid of horny shell. The eggs are ovoid in shape and are essentially isolecithal although an accumulation of large yolk material is observed at the vegetal pole.
48. Segmentation:
Holoblastic.
49. Developments:
The development is accompanied by metamorphosis of the ammocoetes larva.
Difference # Hagfishes:
1. Habit and habitat:
Exclusively marine and remain buried in sand and devour polychaetes and other worms. They usually attack the dying and just dead fishes and enter inside the body (possibly through the mouth) and suck the whole contents leaving the skin and bones. They also eat decomposed fishes:
2. Shape of the body:
The body is slender (‘eel-like’)
3. Fins:
The dorsal fin is ill-developed, narrow and undivided. The caudal fin is slightly developed.
4. Mouth:
Terminal in position and is surrounded by soft lips.
5. Sensory tentacles around mouth:
Three or four pairs of tentacles are present around the edge of the mouth.
6. Buccal Funnel:
Absent.
7. Sucking device:
Highly developed
8. Nostril:
Paired external nasal apertures are situated very close to the mouth and open terminally.
9. ‘Thread cells’ in the skin:
Present.
10. Myotomes:
The myotomes are not separated, i.e., myotomes of one side alternate with those of the other.
11. Cartilaginous oral ring:
Absent
12. Lingual cartilage:
Well- developed.
13. Root of the skull:
Exclusively membranous.
14. Teeth:
Small teeth are present on the ‘tongue’ along two rows.
15. ‘Tongue’:
Strongly developed
16. Paired salivary glands:
Absent.
17. Respiratory and digestive portions:
There is no separation of the digestive and respiratory parts.
18. Respiratory tube:
Absent. The branchial region is restricted to the roundish enlargements called gill- pouches which open into the pharynx.
19. Spiral valve in the intestine:
Absent
20. Liver, gall bladder and bile ducts:
The liver is divided into a dorsal and ventral portion. Gall bladder is present. Two bile ducts, one from each portion of the liver, open separately into the gall bladder. The two portions of the liver are not joined.
21. Branchial region:
Small and restricted.
22. Gill-pouches:
The number of gill-pouches vary from two to fifteen pairs. Myxine possesses five pairs of gill-pouches, while Eptatretus bears thirteen to fifteen pairs. The gill-pouches open directly into the gut.
23. External gill-slits:
One pair in Myxine, but thirteen to fifteen pairs in Eptatretus. In Myxine, the exit ducts from the gill-pouches unite to form two common tubes.
24. Pericardial sac:
Thin-walled and not supported by any skeleton.
25. Shape of RBC:
Elliptical in outline.
26. Blood forming tissue:
Scattered in the sub-mucosa of the gut and pronephros.
27. Ductus Cuvieri:
Both are present
28. Aortic arches:
Each supplies the hemi-branches of a single gill-pouch
29. Nerve supply to heart:
The nerves and nerve cells are absent in the heart.
30. Brain:
Brain is simpler and degenerated.
31. Formation of central nervous system:
In hagfishes (as studied in Eptatretus), it is formed from an open neural groove. The lips of the neural groove fuse and a hollow neural tube is cut off.
32. Olfactory lobe:
Larger
33. Choroid plexus:
Absent
34. Cranial nerves:
The oculomotor, trochlear and abducens nerves are absent
35. Lateral line branch of vagus:
Absent
36. Blood vessels in the spinal cord:
Blood vessels are present within the spinal cord
37. Nerves to the eye-muscles:
The eye-muscle nerve is absent.
38. Roots of the spinal nerves:
The dorsal and ventral roots are united.
39. Paired eyes:
Rudimentary and sunk beneath the skin. The eyes are devoid of lenses and eye-muscles. The optic nerves are reduced.
40. Pineal eye:
Absent
41. Semicircular canals:
Only one semicircular canal with ampullae, one at each end, is present.
42. Nasohypophysial duct:
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Opens posteriorly into the pharynx.
43. Anterior lobe of pituitary:
Undifferentiated
44. Kidneys:
The pronephros is retained in an adult. The functional kidney is of mesonephric type and simpler. The mesonephric tubules have segmental arrangement.
45. Urinogenital sinus:
Absent
46. Reproductive system:
The sexes are united. The anterior portion of the gonad acts as the ovary and the posterior part is testis-like.
47. Eggs:
The eggs are large and enveloped by cylindrical horny shell. The shell bears terminal hook-like processes. The eggs are elongated and typically telolecithal.
48. Segmentation:
Meroblastic (in Eptatretus).
49. Development:
The development is direct, i.e., the metamorphosis is unknown.
