what is difference between ostractodermi and plectodermi......?
Answers
Answer:Distinguish between ostracoderms and placoderms. ... Ostracoderms are extinct, primitive jawless fishes that were covered in an armor of bony plates while placoderms are extinct, primitive jawed fishes. Placoderms are among the earliest jawed vertebrates to appear on earth.
Explanation:
Answer:
Difference # Ostracoderms:
1. Originated in the Cambrian period about 500 million years ago.
2. Ostracoderms were jawless vertebrates included in superclass Agnathostomes.
3. First vertebrates.
4. Shell-skinned vertebrates.
5. Freshwater forms.
6. Mouth was terminal.
7. Teeth absent.
8. Gill slits 8-10 pairs.
9. Eyes were dorsal.
10. Eyes were not surrounded by bony plates.
11. Pineal opening was present behind the naris.
12. Paired fins were absent except Cephalaspis.
13. Vertebral column was absent.
14. Notochord was present.
15. They gave origin to placoderms.
16. Examples: Jamoytius, Pleraspis, Cephalaspis, Birkenia, Anglaspis, Drepanaspis, Lanarkia, Thelodus etc.
Difference # Placoderms:
1. Originated in Devonian period about 400 million years ago.
2. Placoderms were jawed vertebrates included in superclass Gnathostomata.
3. Originated possibly from ostracoderms (plausibly).
4. Plate-skinned vertebrates.
5. Later invaded sea.
6. Mouth was ventral.
7. Teeth present.
8. 5 pairs of gill slits.
9. Eyes were ventrolateral.
10. Eyes were surrounded by bony plates.
11. Pineal opening was situated between the eyes.
12. Paired fins were present.
13. A primitive vertebral column was present.
14. Notochord was surrounded by vertebral column.
15. They gave origin to bony fishes and cartilaginous fishes.
16. Examples: Coccosteus, Bolhrolepis, Macropetalicthyes, Phyllolepis, Rhamphodopsis etc.