In this presentation, phylum Phylum Chaetognatha is described. Phylum Chaetognatha known as arrow worms. After watching this you will learn the characteristics and Examples Sagitta, Spadella. The brief description of Phylum Chaetognatha along with reproduction and fertilization also described. It is part of BS Zoology Course, Animal diversity.

1. Phylum Chaetognatha Dr. Muhammad Moosa Abro
@Zoology by Miler and Harley

2. Examples Sagitta, Spadella.
Approximately 12 species.
Chaetognathans (arrow worms)
comprise a phylum of dart-shaped marine worms that are a
major component of plankton worldwide.
are carnivorous, preying on other planktonic animals.
The body (2 to 120 mm) is covered with a cuticle
and divided into a distinct head, trunk, and tail.
Phylum Chaetognatha Dr. Muhammad Moosa Abro

3. There are hooked, prey-grasping spines, on each side
of the head.
 —thus the phylum name, which means “bristle jaws.”
 The mouth is armed with tiny teeth.
The trunk bears one or two pairs of lateral fins and the tail
bears a caudal fin.
They have complex eyes and a nervous system.
They lack respiratory and circulatory systems.
All species are hermaphroditic.
Phylum Chaetognatha Dr. Muhammad Moosa Abro

4. Phylogenetic Relationships
Several fossil chaetognath species date to the Cambrian period.
Chaetognaths have been variously classified as deuterostomes,
ecdysozoan protostomes, and a group basal to both lophotrochozoan
and ecdysozoan lineages.
Possible deuterostome affinities are based on what are probably
erroneous reports of spiral cleavage in chaetognath embryos.
Ecdysozan affinities are suggested by the presence of a cuticle and
other similarities to nematode muscular and nervous organization.
Molecular studies place Chaetognatha close to the base of the
protostome tree or within the Ecdysozoa.
Phylum Chaetognatha Dr. Muhammad Moosa Abro

5. References
5
1. Miller, A.S. and Harley, J.B. ; 1999 , 2002., 2007, 2009, 2012 & 2016 Zoology, 4th , 5th, 6th, 7th,
8th , 9th& 10th Edition (International), Singapore : McGraw Hill.
2. Hickman, C.P., Roberts, L.C/, AND Larson, A., 2018. INTEGRATED PRINCIPLES OF ZOOLOGY,
15th Edition (International), Singapore: McGRAW-Hill