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  🧬 Larval Forms in Protochordates Protochordate larvae, found in Cephalochordata (lancelets) and Urochordata (tunicates) , hold critical clues about chordate ancestry. These larval forms exhibit hallmark chordate traits that help illuminate evolutionary relationships. 🧒 Shared Larval Characteristics Notochord : Dorsally located, flexible rod supporting the body; precursor to the vertebral column. Dorsal Hollow Nerve Cord : Transmits signals; evolves into brain and spinal cord. Pharyngeal Slits : Aid in respiration or filter-feeding. Post-anal Tail : Enhances swimming and balance. 🌊 Major Larval Types 1️⃣ Tornaria Larva (Hemichordata: Balanoglossus ) Structure : Transparent, 3 mm body with anterior prototroch and posterior telotroch ciliary bands. Behavior : Rotates in water—swimming and feeding via ciliary movement. Discovery : Initially misclassified as echinoderm larva; corrected by Metchnikoff. Life Role : Free-swimming, planktonic stage before worm-lik...

  🐟 General Characteristics of Cephalochordata (Lancelets / Amphioxus) Small, fish-like marine organisms found in shallow tropical and temperate oceans. Adapted for both burrowing and swimming . Lack true head and paired appendages; possess dorsal, ventral, and caudal fins . Body wall includes: One-cell-thick epidermis Underlying dermis , connective tissue, and segmental muscles No exoskeleton 🧠 Key Body Features Notochord : Extends the entire body length from anterior to posterior Enterocoelic coelom , reduced in the pharyngeal region Long alimentary canal with ciliary feeding Gills for respiration Closed circulatory system, lacking heart and respiratory pigments Well-developed hepatic portal system Excretion via paired protonephridia with solenocytes Poorly developed brain, no distinct sensory organs No gonoducts; external fertilization with separate sexes 🔬 Chordate Features in Cephalochordates Dorsal tubular nerve cord Notochord persists t...

🐚 Urochordata Overview Urochordates, commonly called "sea squirts," undergo a dramatic transformation in their life cycle. Their chordate traits are more prominent during the larval stage, while adults resemble invertebrates more than chordates. 🐣 Larval Characters The elongated larva is called an ascidian tadpole . Notochord is confined to the tail region—hence the name Urochordata . A dorsal hollow nerve cord extends the length of the body. Pharyngeal gill slits are present. Larvae are highly active with efficient swimming tails. 🧍 Adult Characters Body is enclosed in a tunic made of tunicin (protein) and a cellulose-like polysaccharide. Adults are sessile , attached to marine substrates. Incurrent (branchial) siphon and excurrent (atrial) siphon direct water flow. Pharynx forms a branchial basket. Sensory tentacles around the incurrent siphon filter incoming water. Hermaphroditic; reproduce both sexually and asexually. 🧬 Classification...

  GENERAL CHARACTERISTICS AND CLASSIFICATION OF CYCLOSTOMES UPTO CLASSES .  Cyclostomata is a group of chordates that comprises the living jawless fishes: the lampreys and hagfishes. Both groups have round mouths that lack jaws but have retractable horny teeth. The name Cyclostomata means "round mouths". Their mouths cannot close due to the lack of a jaw, so they have to constantly cycle water through the mouth.     GENERAL CHARACTERS OF CYCLOSTOMATA: - Cyclostomes are jawless primitive vertebrates. They may be marine or fresh water. They include hag fishes and lampreys. Ø The body is long, eel like. It has a trunk and a compressed tail. Ø Paired fins are absent. Median fin is supported by cartilaginous fin-rays. Ø The skin i.e soft and smooth. It is slimy. It is scale less.   Ø Z-shaped myomeres are present in the trunk and tail. Protractor and retractor muscles move the tongue.   Ø In this group a true coelom is seen.   Ø These vertebrates do ...

                        Definition and Introduction Hemichordates is an independent phylum of marine invertebrates closely related to Echinodermata. They were previously classified as a subphylum of Chordata. Members exhibit the following key features:   - Enterocoelous coelom : Coelom develops through enterocoely in three compartments (protocoel, mesocoel, metacoel).   - Pharyngeal gill slits : Used for filter feeding.   - Stomochord: A buccal diverticulum, initially mistaken for a notochord.   - Body division: Vermiform structure with three regions – proboscis, collar, trunk.     Examples include Balanoglossus, Saccoglossus, and Glossobalanus, classified under Class Enteropneusta . Affinities with Chordata Similarities to chordates include:   - Pharyngeal gill slits - Dorsal hollow nerve cord in some species     Objections to Inclusion in Chordata: ...