In this article we will discuss about the habitat and features of Phylum Kinorhyncha.
Habitat of Phylum Kinorhyncha:
They live in the marine mud or in the interstitial spaces of marine sand. They are found in the intertidal zone to the depths of several thousand metres.
The phylum kinorhyncha is divided into two classes:
Class 1. Cyclorhagida:
Body with 14-16 closing plates in the neck region; trunk oval to triangular in cross section with many spines; adhesive tubes present, common in marine muds and sands.
Class 2. Homalorhagida:
Body with 6-8 closing plates in the neck region; trunk spines few and triangular in cross section, common in marine muds.
Features of Phylum Kinorhyncha:
1. Phylum Kinorhyncha are microscopic, marine animals.
2. Body length of Phylum Kinorhyncha is less than 1 mm.
3. Short, grub-like, segmented with flattened ventral surface.
4. Body of Phylum Kinorhyncha is covered by an external chitinous divisible cuticle.
5. Body of Phylum Kinorhyncha is divided into 13 segments (zonites) of which 1st segment is the eversible head, 2nd segment is the neck and the trunk includes the rest of 11 segments. The head is retractable into the neck.
6. Cuticle spiny and without motile cilia and forms hard articular segmental plates.
7. A pair of adhesive tubes on the ventral surface of the fourth segment in the males of Pyncnophyes and Kinorhynchus.
8. Head with several rings of curved spines at the base called scalids, serve locomotory and sensory functions and piercing stylets at the tip (Fig. 15.22).
9. Head can be withdrawn into the neck or within the first segment of the trunk.
10. The neck consists of a series of plates called placids (Fig. 15.22).
11. Body cavity of Phylum Kinorhyncha is a fluid-filled reduced pseudocoel or may be absent in some species.
12. Respiratory and circulatory systems are absent in Phylum Kinorhyncha.
13. One pair solenocytic protonephridial excretory system (Fig. 15.22).
14. Circumpharyngeal nerve ring with longitudinal nerve cords.
15. Sexes gonochoristic (sexes separate).
16. Tubular gonads.
17. Fertilization is probably internal in Phylum Kinorhyncha.
18. Periodic moulting occurs.
19. No free-swimming larval stage.