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BALANOGLOSSUS:A HEMICHORDATE-By Pranjal Gupta(0047),Bsc(H) ZoologyRamjas College

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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

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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

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B.gigas is The largestSpecies, found in Brazil. Measures to2.5m.

Balanoglossus secretes iodoform like foul smellingcompound as a defense mechanism

Balanoglossus is used asfish-bait bylocal fishermen.

It is also calledTongue worm dueto the resemblanceof the proboscis &genital wings toOx tongue.

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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.

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EXTERNAL MORPHOLOGYprobosciscollarette

collar

Branchial regionGill pores

Genital wings

Mid dorsal ridge

hepatic caeca

Hepatic reg.

Anus

Post hepatic

reg.

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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

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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.

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INTERNAL MORPHOLOGY

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REPRODUCTION Fertilization is external and development

includes tornoria larva.

Reproduction in Balanoglossus

Tornoria Larva resembles

echinoderm larva

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EMBRYO DEVELOPMENT AND NEURULATION.

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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

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