Table 9-6. Character states of coelomate animals Coelomate Animals Outgroup Nema
ID: 217308 • Letter: T
Question
Table 9-6. Character states of coelomate animals Coelomate Animals Outgroup Nematode Mollusc Character Annelid Arthropod Echinoderm Chordate Bilateral pentaradial Symmetry Bilateral Digestive tract Complete Tissue layers Triploblastic Enterocoelous Radial Indeterminate Anus Coelom Pseudocoel Schizocoelous Spiral, Mouth Yes Yes Cleavage RotationalDeterminate Fate of blastopore Mouth Radula Mantle Segmentation Exoskeleton No No No No Yes No No Chitin Water vascular systemNo No No No No No Jointed Variable Appendages Larval notochord Dorsal nerve chord Pharyngeal slits Yes Yes 217Explanation / Answer
From Nematodes to chordates:
1. Symmetry: All of them have bilateral symmetry. Exception: echinoderms, larva shows bilateral whereas adults show radial symmetry.
2. Digestive system is complete in all with two openings mouth and anus.
3. Tissue layer: All of them have three germ layers and thus triploblastic.
4. Coelom: Nematodes - pseudocoelomates; annelida, arthropoda and mollusca are schizocoelomates; echinoderms and chordates are enterocoelomates.
5. Cleavage: Nematodes - Holoblastic rotational; annelida and mollusca - Spiral; Arthropoda - Superficial cleavage; Echinoderms - Radial; Cleavage patterns within the Chordates. Ascidians, lancelets, and lamprey display holoblastic cleavage, suggesting that it is the ancestral cleavage pattern in chordates. Ascidians have bilateral cleavage, while lancelets display radial cleavage. Lamprey and amphibians have mesolecithal eggs, with larger, yolky cells confined to the vegetal half of the embryo. Present day teleost fish show meroblastic cleavage, which evolved independently in fish and amniotes. Mammals show a reversion to holoblastic cleavage, but exhibit rotational cleavage.
Cleavage is determinate in protostomes and indeterminate in deuterostomes.
6. Fate of blastopore: nematodes, annelids, arthropods and molluscs are protostomes; echinoderms and chordates are deterostomes.
7. Radula and mantle: Seen in phylum mollusca.
8. Segmentation: Both external and internal in Annelida; Only external in arthropoda; only internal in chordates
9. Exoskeleton: Chitinous in arthropods
10. Water vascular system: Seen in echinoderms
11. Appendages: Aquatic annelids posses lateral appendages, parapodia which help in swimming.
All the arthropods have jointed appendages.
12. Larval notochord: in chordates
13. Dorsal nerve cord - in chordates; invertebrates show ventral nerve cord
14. Pharyngeal slits: seen in chordates
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