General Character And Affinities Of Hemicordates
Answers
Explanation:
General Characters of Hemichordata:
1. Solitary and colonial, mostly tubicolous, exclusively marine.
2. Body soft, fragile, vermiform and divisible into proboscis, collar and trunk.
3. Body wall with a single-layered epidermis.
4. Coelom enterocoelous, divisible into protocoel, mesocoel and metacoel.
5. Buccal diverticulum, earlier considered as notochord, present in the proboscis.
6. Digestive tract complete; in the form of straight or U-shaped tube.
7. Gill-slits, when present, are paired and one to numerous.
8. Circulatory system simple and well developed; closed type; usually with a contractile heart vesicle and two longitudinal vessels, one dorsal and one ventral, interconnected by lateral vessels and sinuses.
9. Excretion by a single glomerulus situated in the proboscis.
10. Nervous system primitive comprising mainly of an intra-epidermal nerve plexus.
11. Reproduction mostly sexual. Sexes separate or united.Gonads one to several pairs.
12. Fertilisation external. Development mostly indirect through a free swimming tornaria larva. Direct development is also found in some forms.
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