1. Phylum
    2. 1. Classification of Animals
    2. Protozoa
    3. Porifera
    4. Coelenterata
    5. Platyhelminthes
    6. Nemathelminthes
    7. Annelida
    8. Earthworm
    9. Arthropoda
    10. Cockroach
    11. Mosquito
    12. Honey bee and Silk moth
    13. Mollusca
    14. Echinodermata
    15. Hemichordata
    16. Chordata
    17. Pisces
    18. Amphibia
    19. Frog
    20. Reptile
    21. Aves
    22. Mammalia
    23. Rabbit bone
  2. Animal Behaviour and Adaptation
    3. 24. Animal behaviour
    25. Animal adaptation
    26. Migration
  3. Developmental Biology
    4. 27. Development of Animals
    28. Development of Frog
  4. Human Biology
    5. 29. Tissues
    30. Sense organs
    31. Digestive system
    32. Circulatory system
    33. Respiratory system
    34. Nervous system
    35. Endocrine system
    36. Reproductive system
    37. Excretory system
    38. Skeletal system
    39. Basic concept of Immunology
    40. Human diseases
  5. Evolutionary Biology
    6. 41. Origin of Life
    42. Organic Evolution
    43. Theories of Evolution
    44. Evolution of Human beings
    45. Horse Evolution
Phylum
15. Hemichordata
HEMICHORDATA
▢ Habitat: Exclusively marine
▢ Habit: Solitary or Colonial
▢ Body Structure:
❖ Type:
  1. Mostly tubiculous
  2. Soft and fragile
  3. Vermiform
▢ General Features:
❖ Symmetry: Bilaterally symmetrical
❖ Segmentation: Unsegmented
❖ GermLayers: Triploblastic
❖ Coelom:
◉ Type: Eucoelomate (Enterocoelous)
◉ Divisions:
◈ Protocoel: Proboscis
◈ Mesocoel: Collar
◈ Metacoel: Trunk
▢ Body Wall:
❖ Epidermis:
◉ Type: Single layered
◉ Glands: Mucous glands present
❖ Dermis: Absent
▢ Digestion:
❖ AlimentaryCanal:
  1. Complete
  2. Straight or U-shaped
❖ BuccalDiverticulum: Foregut gives out a hollow buccal diverticulum into proboscis, once considered a notochord
▢ Gill Slits:
❖ Location: Dorso-lateral pharyngeal region
❖ Pairs: 1 to several pairs
❖ Feeding: Ciliary filter feeders
❖ Note: Shared character with Chordata
▢ Circulatory System:
❖ Type: Simple and open
❖ Heart: Dorsal heart
❖ Vessels:
  1. One dorsal longitudinal vessel
  2. One ventral longitudinal vessel
▢ Excretion:
❖ Organ: Proboscis gland or Glomerulus
❖ Mechanism: Connected to blood vessels for excretion
▢ Nervous System:
❖ Type: Primitive
❖ Components:
  1. Subepineural nerve plexus
  2. Dorsal collar nerve cord (hollow)
▢ Reproduction:
❖ Mode: Mainly sexual
❖ Sexes: Usually separate
❖ Gonads: One to several pairs
❖ Fertilization: External
❖ Development:
◉ Type: Direct or indirect
◉ Larval forms:
  1. Tornaria larva
▢ Notochord:
❖ Presence: Only in anterior part of proboscis
❖ Type: Stomochord (not homologous to chordate notochord)
❖ Description: Flexible hollow tube from embryonic gut roof extending into the proboscis and connected to oral cavity
▢ Classification: Four Classes among which Balanoglossus belong to class Enteropneusta
BALANOGLOSSUS (ACORN WORM OR TONGUE WORM)
▢ Habitat:
❖ Type: Marine
❖ Distribution: World-wide
❖ Location: Bottom of shallow water; some in deeper water
▢ Habit and Body Shape:
❖ Nature: Tubiculous, burrowing
❖ Form: Worm-like with soft, elongated, cylindrical body
❖ SizeRange: 10 cm to 2.5 m
▢ General Features:
❖ Symmetry: Bilaterally symmetrical
▢ Body:
❖ Divisions:
  1. Proboscis (Protosome)
  2. Collar (Mesosome)
  3. Trunk (Metasome)
❖ Proboscis:
◉ Description: Anterior, conical part tapering anteriorly
◉ Proboscis Stalk:
◈ Position: Posterior extension, continuous with inner dorsal collar wall
◉ Preoral Ciliary Organ:
◈ Location: Below stalk base
◈ Structure: U-shaped ciliated depression
◈ Function: Chemoreceptor
◉ Coelom:
◈ Name: Protocoel
◈ Opening: Mid-dorsal proboscis pore near base
❖ Collar:
◉ Description: Middle, short, thick belt-like part behind proboscis
◉ SurfaceFeatures: Circular grooves or elevations
◉ Collarette:
◈ Structure: Funnel-like anterior collar part surrounding proboscis stalk
◉ Mouth:
◈ Position: Ventral, below proboscis stalk inside collarette
◉ Coelom:
◈ Name: Mesocoel / Collar coelom
◈ Structure: May be divided by dorsal and ventral mesenteries
◈ Openings: Opens into first pair of brachial sacs via collar pores
❖ Trunk:
◉ Description: Posterior and largest part of body
◉ Features:
  1. Flattened with superficial annulations
  2. Mid-dorsal and mid-ventral longitudinal ridges
◉ Regions:
◈ Branchiogenital Region:
■ GillPores:
● Description: Longitudinal rows on each side of mid-dorsal ridge
● Structure: Mounted on ridge-like elevations
■ GenitalWings:
● Description: Thin, leaf-like extensions on sides
● Contents: Gonads
● Openings: Gonopores (microscopic)
● Note: Usually folded over to conceal gill-pores
◈ Hepatic Region:
■ Description: Middle region with numerous paired transverse folds
■ Structures: Hepatic caeca
■ Color: Dark brownish or greenish
◈ Post-Hepatic Region:
■ Description: Posterior tapering region
■ Feature: Bears terminal anus
▢ Circulation:
❖ HeartLocation: Located in proboscis
❖ RespiratoryPigment: Vanadium
▢ Larval forms:
  1. Tornaria (larva of Balanoglossus)