CLASSIFICATION OF PRIAPULUS
Phylum :- Priapulida(Introvert proboscis.)
Genus :- Priapulus
It is found in Arctic sea.
HABIT AND HABITAT
Priapulus is a marine, cylindrical, burrowing and unsegmented animal. It burrows in sand or mud at moderate depths in the colder seas.
GENERAL CHARACTERSTICS OF PRIAPULUS
- Body divisible into proboscis, trunk and caudal appendages.
- Proboscis has longitudinal ribs of papillae and spines. A constriction separates proboscis and trunk.
- No pre-oral segment. Mouth terminal and surrounded by spiny circumoral areas.
- Body wall contains an outer cuticular and an inner longitudinal muscle layer.
- There is a perivisceral coelom which extends into the posterior papillae.
- There are no blood vascular system and excretory system. Excretion is efffected by the genital ducts and their branches.
- Products of gonads are passed to the exterior by ducts of doubtful origin opening close to the anus.
- Body is unsegmented but is marked with many superficial annulations.
- Mid ventral nerve cord is like white line, non-ganglionated and without sense organs.
- Sexes separate. Caudal appendage has spines.
It has proboscis having ribs of papillae and all above features, hence it is Priapulus.
Characterstics of Minor Phyla
On the basis of presence or absence of a true coelom minor phyla are divided into two groups.
(A) Minor Acoelomate Groups 1. Mesozoa, 2. Ctenophora, 3. Endoprocta, 4. Nemertinea (Rynchocoela), 5. Acanthocephala, 6. Nematomorpha, 7. Rotifera, 8. Gastrotricha, 9. Kinorhyncha, 10. Nematoda
(B) Minor Coelomate Groups 1. Ectoprocta, 2. Brachiopoda, 3. Phoronida, 4. Chaelognatha, 5. Priapulida, 6. Sipunculida, 7. Echiuroidea, 8. Brachiata. Some of the representatives of the above phyla are discussed below.