Balanoglossus- A Hemichordate
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Balanoglossus, commonly known as the acorn worm, is a marine hemichordate classified under the phylum Chordata. It features a three-part body structure (proboscis, collar, and trunk), lives in shallow marine environments, and practices filter feeding. The species has external fertilization, develops through a tornoria larva stage, and exhibits similarities with annelids and echinoderms.
Balanoglossus- A Hemichordate
- 1. BALANOGLOSSUS: A HEMICHORDATE -By Pranjal Gupta(0047),Bsc(H) Zoology Ramjas College 1
- 2. CLASSIFICATION Phylum: Chordata (Deuterostome,presence of notochord, nerve cord & pharyngeal gill slits) Subphylum: Hemichordata (Small soft bodied,marine,notochord confined to head region, sexes separate) Class: Enteropneusta (Solitary form; straight alimentary canal, mouth and anus at opposite ends, two rows of caecae,numerous gill slits) Genus: Balanoglossus Common name: Acorn worm 2
- 3. HABITAT AND HABIT Geographical distribution: Worldwide or cosmopolitan. Habitat: Marine, live in shallow waters generally but few go deeper upto 15000 feet, lives inside U-tubes(tubicolous). Habit: Adapted for burrowing life in sandy bottoms. It burrow slowly by soft proboscis. Worm casting 3
- 4. 4 B.gigas is The largest Species, found in Brazil. Measures to 2.5m. Balanoglossus secretes iodoform like foul smelling compound as a defense mechanism Balanoglossus is used as fish-bait by local fishermen. It is also called Tongue worm due to the resemblance of the proboscis & genital wings to Ox tongue.
- 5. FEEDING HABIT AND RESPIRATION. Since Balanoglossus is a tubicolous animal, it feeds by filter-feeding mechanism. As the water enters the tube from the anterior opening. It opens its mouth situated in the collar and takes up the food particles, and filters out the unwanted. The same water gushes through the gill pores to provide necessary oxygen for respiration. 5
- 6. EXTERNAL MORPHOLOGY proboscis collarette collar Branchial region Gill pores Genital wings Mid dorsal ridge hepatic caeca Hepatic reg. Anus Post hepatic reg. 6
- 7. BALANOGLOSSUS:DISTINCT FEATURES It measures 10cm to 2.5metres, depending on species. Worm-like body divisible into three regions. >Anterior proboscis which is conical. >Middle collar which is funnel like >Posterior trunk which is cylindrical and further divided into: Branchiogenital region, hepatic region & abdominal region. Notochord represented by small buccal diverticulum. Development includes tornoria larva 7
- 8. LOCALIZATION OF INTERNAL ORGANS Proboscis • It contains heart vesicle, central sinus and buccal diverticulum. • coelom opens to exterior by proboscis pore Collar • It contains the mouth and collar coelom, which open to dorsal surface through collar pore. Trunk • It contains-pharynx, gonads or hepatic region. • Branchio-genital region contains: genital wings with gonad, branchial region with paired gills, hepatic caecae. 8
- 10. REPRODUCTION Fertilization is external and development includes tornoria larva. Reproduction in Balanoglossus Tornoria Larva resembles echinoderm larva 10
- 11. EMBRYO DEVELOPMENT AND NEURULATION. 11
- 12. AFFINITIES OF HEMICHORDATES • Worm-like and segmented body.With Annelids • Blastopore, enterocoelus coelom and ciliated bands in the respective larvae. With Echinoderms • Presence of pharyngeal gill slits, nerve cord and so-called notochord. With Chordates 12
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