CLASSIFICATION OF SIPUNCULUS (PEANUT WORM)
Phylum :- Sipunculoida (Metamerically segmented, coelomate and bilaterally symmetrical.)
Genus :- Sipunculus (Peanut worm)
It is found in Europe and U.S.A. (Beufort, North Carolina, Key West).
HABIT AND HABITAT
Sipunculus is a burrowing sipunculid, found in sand at moderate depths. in the sand or mud, either free or in tubes or in snail shells.
GENERAL CHARACTERSTICS OF SIPUNCULUS (PEANUT WORM)
- Commonly called as peanut worm.
- Body is pale brown and cylindrical, about 40 cm long and covered by a thick, chitinous transparent and iridescent cuticle containing minute papillae. Appendages absent.
- Body is very contractile, unsegmented and without metameric appendages, spines or bristles and it is differentiated into anterior narrow retractile proboscis and a posterior broad trunk.
- Proboscis contains minute papillae, while rest of the body does not possess papillae.
- Proboscis contains mouth surrounded by tentacular fold without isolated tentacles. Mouth is borne at the end of retractile proboscis below which is a smooth zone. Below smooth zone is posterior papillary region of introvert
- Body wall is highly muscular. The posterior part of the body is marked by a series of squarish areas due to crossing of transverse and longitudinal muscles. Papillae are absent is this area.
- Body cavity is traversed by muscle fibres and connective tissue fibres.
- There are no definite gonads but gametes are produced seasonally from germinative cells on connective tissue. The nephridia function as gonoduct.
- Sexes are separate, but no sexual dimorphism. Fertilization is external and larva is a modified trochophore.
- Fertilization in external and larva is modified trochophore.
It contains retractile proboscis and all above features, hence it is Sipunculus.
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.