Hemichordates

Hemichordates

 

  • Hemichordates are a phylum of marine invertebrates that exhibit some characteristics of both chordates and invertebrates.
  • They are often referred to as "acorn worms" due to their acorn-like shape.

 

Characteristics-

Body Organization:

    • Hemichordates exhibit bilateral symmetry.
    • Hemichordates possess a triploblastic organisation, meaning their body is composed of three primary germ layers: ectoderm, mesoderm, and endoderm.
    • Hemichordates have a well-developed organ-system level of organisation.
    • Hemichordates are coelomates
    • Hemichordates have a body plan consisting of three main regions: proboscis, collar, and trunk.
    • The proboscis is a muscular, tubular structure used for feeding and respiration.
    • The collar lies behind the proboscis and contains structures related to filter feeding.
    • The trunk is the elongated region behind the collar and contains the main organs.

 

 Balanoglossus

Locomotion:

    • Hemichordates primarily move by peristalsis, which is the rhythmic contraction and relaxation of muscles.
    • They have cilia or muscular bands that help in locomotion.
    • Some hemichordates also have structures called "stomochords" that assist in maintaining body shape and aid in movement.

Reproduction:

    • Hemichordates can reproduce both sexually and asexually.
    • Asexual reproduction occurs through budding, where a new individual develops as an outgrowth of the parent organism.
    • Sexual reproduction involves the production of eggs and sperm.
    • Hemichordates can be either hermaphroditic (possessing both male and female reproductive organs) or dioecious (having separate sexes).

Feeding Strategies:

    • Hemichordates employ different feeding strategies based on their lifestyle and habitat.
    • Many hemichordates are suspension feeders, filtering small particles from the water.
    • They use structures like cilia and mucous-lined grooves to capture food particles.
    • Some hemichordates are deposit feeders, consuming organic matter present in sediments.
    • A few species are also known to be predators, capturing and consuming smaller organisms.

Example:

    • An example of a hemichordate is the acorn worm (genus: Balanoglossus).
    • Balanoglossus is a common hemichordate found in marine environments worldwide.
    • Another example is Saccoglossus.

Saccoglossus and Ptychodera