BIOLOGY
FORM 4
INVERTEBRATES
•ARTHROPODS
ARTHROPODS
•Phylum TARDIGRADA
•Phylum PENTASTOMA
•Phylum ONYCHOPORA
What is Arthropods
• Protostome
• Very diverse BUT share TWO characteristics
anatomical features:
• Pair of legs along all OR part of the body
(served by ganglionic swellings on the
latitudinal nerve cords
• Pseudocoelomic body cavities (filled with
blood – haemocoels)
Cont.
• Arthropod body plan:
– Small anterior region (acron)
– Equivalent posterior portion (telson) without legs
– Number of intervening section (segments) with a pair
of legs each
• BUT non-leg-associated (respiratory, excretory) organs
are not serially repeated
Phylum TARDIGRADA
e.g: water bears
Water bears??
What is Phylum
TARDIGRADA?
400 living species in 1 class
• Characteristics [size: 0.05 – 1.2 mm]
1. Bilaterally symmetrical, minute, squat
2. Body more than 2 cell layer thick
3. Straight gut
4. Body monomeric –
– four pair of short unjointed claw-bearing legs
– Crawl by extrinsic muscle
– Legs served by nerve ganglia
5. Well develop pseudocoelomic cavity => hydrostatic skeleton
6. Body wall with cuticle-covered epidermis without muscle
1. Non-chitinous cutilce moulted, bear spines or thickened into plates
2. Network of smooth muscle criss-cross the body
Cross Section of water bears
Phylum PENTASTOMA
Cont.
100 species placed in 1 class
• Characteristics [size: 2 – 16 cm long]
1. Bilaterally symmetrical, flattened, vermiform
2. Body more than 2 cell layer thick
3. Straight gut
4. Body monomeric –
–
–
–
annular
2 pair claw-bearing legs at anterior
OR two pair of claw
5. Pseudocoelomic hydrostatic skeleton
6. Body wall with cuticle-covered epidermis
1. Layer of striated circular and longitudinal muscle
2. Cuticle chitinous, porous and moulted
Cross Section of Pentastoma
Phylum ONYCHOPORA
Cont.
Phylum ONYCHOPORA
70 species placed in 1 Class, 1 Order
• Characteristics [size: up to 15 cm long]
1. Bilaterally symmetrical, elongately and cylindrically vermiform
2. Body more than 2 cell layer thick
3. Straight gut bearing pair of mouthpart with 2 claw-like mandible
–
Fore- and hind-guts line with cuticle without digestive diverticula
4. Body 14-43 pairs of short unjointed fleshy legs along
–
–
Each leg: hollow evagination of body, padded terminally, with pairing claws and
intrinsic muscle
Legs associated with a pair of heart ostia and excretory organ
5. Well developed haemocoelomic body hydrostatic skeleton with tubular
heart but no other blood vessel
Cross Section of ONYCHOPORA