🌟 Important Words & Concepts Explained
📚 Key Terms and Concepts – Phylum Chordata
1️⃣ Chordates
Animals that belong to a group with four special features: notochord, pharyngeal slits, tubular nerve cord, and post-anal tail at some stage of life.
2️⃣ Notochord
A flexible rod-like structure [نرم چھڑی نما ساخت] that gives support to the body.
- Present during embryo stage (or entire life in some)
- In vertebrates, it becomes the spinal column [ریڑھ کی ہڈی].
3️⃣ Pharyngeal Slits
Openings on the sides of the throat [گلے کی دیواروں میں سوراخ] during embryonic life.
- Turn into gills in fishes
- Modify or disappear in humans and other animals
4️⃣ Tubular Nerve Cord
A hollow nerve cord [نلکی نما نسوں کا سلسلہ] that runs along the back side of the animal.
- It develops into the brain and spinal cord [دماغ اور ریڑھ کی ہڈی].
5️⃣ Post-Anal Tail
A tail that extends behind the anus [مقعد کے پیچھے دم].
- May remain (e.g., in reptiles) or disappear (e.g., in humans)
6️⃣ Coelomate
Animals with a true body cavity [جسم میں اصل گُہا] that holds organs.
7️⃣ Triploblastic
Animals whose bodies are formed from three layers of cells in the embryo: ectoderm, mesoderm, endoderm. [تین ابتدائی خلیاتی تہوں سے بنا جسم]
8️⃣ Deuterostome
A type of animal development in which the anus forms before the mouth in the embryo. [ایسے جانور جن میں پہلے مقعد بنتی ہے، بعد میں منہ]
9️⃣ Invertebrate Chordates
Chordates without backbone
- Urochordata – Notochord only in larvae (e.g., sea squirts)
- Cephalochordata – Notochord throughout life (e.g., Amphioxus)
🔟 Vertebrates
Chordates with a vertebral column [ریڑھ کی ہڈی] and a skull [کھوپڑی].
🐟 Group Pisces (Fish)
11️⃣ Class Cyclostomata
- Jawless fishes
- Cartilaginous skeleton [کرکری ہڈی کا ڈھانچہ]
- External fertilization
- Example: Lampreys, Hagfish
12️⃣ Class Chondrichthyes
- Cartilaginous fishes (e.g., Sharks)
- Body covered in placoid scales (tooth-like) [دانت جیسے چھوٹے چھلکے]
- Spiracles (breathing holes) behind eyes [سانس لینے کے سوراخ]
- Internal fertilization
- No swim bladder
13️⃣ Class Osteichthyes
- Bony fishes (e.g., Rohu, Trout)
- Have bony skeleton [ہڈیوں کا ڈھانچہ]
- Swim bladder present – helps them float [تیرنے میں مدد دینے والی ہوائی تھیلی]
- Gills covered with operculum [ہڈی جیسا ڈھکن]
- External fertilization
14️⃣ Swim Bladder
A gas-filled sac [گیس سے بھری تھیلی] inside the fish’s body that helps in floating at different depths.
15️⃣ Operculum
A protective flap over the gills [گلپھڑوں کو ڈھاپنے والی ہڈی].
16️⃣ Cranial Nerves
Nerves that come directly from the brain, especially important for sensory functions.
- Fish have 10 pairs.
17️⃣ Unisexual
Separate male and female individuals [نر اور مادہ الگ الگ]