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