Balanoglossus-BUCCAL CAVITY

The short buccal cavity occupies the collar region.Its epithelial wall contains glandular goblet cells.Anteriorly its dorsal wall forms a short, stiff and hollow buccal diverticulum that projects into the proboscis coelom.Posteriorly it exends up to the collar-trunk septum behind which it continues into the pharynx.

Balanoglossus-MOUTH

It is a wide and circular opening situated ventrally in a groove between the proboscis stalk and collarette. According to Knight-jones(1952),it can be closed or opened and does not remain permanently opens as previously supposed.It has two sets of muscle fibres,the radial fibres to open it and the concentric fibres to close it.The mouth leads into buccal cavity.

Balanoglossus-Digestive system

Alimentary canal-The alimentary canal is a complete and straight tube running between themourh and anus.It is supported throughout its length by the dorsal and ventral mesenteries.Its wall is made sp of ciliated epithelium covered externally by a basement membrane,but peculiarly,muscle layers are abesent.The alimentary canal comprises:The mouth
The buccacavity
Pharynx
Oesophagus
Intestine
Anus.

Balanoglossus-Endoskeleton

Ballanoglossus has no definite endoskeleton of bone or cartilage . The four stiff structures are present:
Buccal diverticulum-A short stiff, thick-walled,holllow projection extend forwards through the proboscis stalk into the proboscis coelom.Its wall is composed of a single layer of tall,slender,vacuolated endodermal cell.
Proboscis skeleton-The proboscis or nuchal skeleton is a y-shaped chitinous structures formed by the thickening of the basement membrane.It consists of a broad,flat,roughly rectangular median plate priduced ventrally into a keel and posteriorly into two diverging horns
Branchial skeleton-It is formed by the thickening of the basement membrane.It consists of numerous M-shaped chitinous skeletal rods that lie in the wall of the pharynx and support the U-shaped gills that perforate.
Pygochord-In the post-hepatic region of the trunk,mid-ventrally between the intestine and body wall,develops a rod-like thickening called pygochord.

Balanoglossus(coelom)

Balanoglossus has a spacious coelom lined by coelomic epithelium and enterocoelous in origin .The adult coelom is represented by five separate cavities which originate as independent pouches from the archenteron of the embryo.
Proboscis coelom-The proboscis coelom communicates with the outside through a proboscis canaland a proboscis pore situated mid-dorsally at the base of the proboscis stalk.The unpaired proboscis coelom or protocoel is greatly obliterated by connective tissue and muscle strands.
Collar coelom-The collar coelum or mesocoel is represented by two narrow lateral cavities.The collar coelum does not communicates with the proboscis coelum.
Trunk coelum-The trunk coelum or metacoel is represented by a pair of closed cavities between the body wall and gut wall.The trunk coelum is obliterated by the musculature.
Coelomic fluid-The coelomocytes originate from the coelomic epithelium.The trunk coelom is filled with a watery coelomic fluid containing amoeboid coelomocytes,each with a large vacuole.

Balanoglossus(Body wall)

The body wall is composed of epidermis, musculature and peritoneum.
Epidermis-The outermost layer or epidermis consists of a single layer of mostly tall,slender,columnar and ciliated cells.Gobletgland cells are flask-shaped with fine granules.  Reticulate gland cells have vacuolated cytoplasm.Mulberry or granular gland cells contain coarse granules and also secrates amylase.The gland cells are more abundant in tha collar region.Dermis are absent.Besides, neurosensory cells,which stain darker,are present in the epidermis of proboscis and anterior part of the collar.
Musculature-The muscules are smooth,weak and mostly longitudinal.In the trunk region, only longitudinal muscle fibres are present.
Peritoneum-THe coelom is lined by the parietal coelomic epithelium or peritoneum which covers the inner surface of the body wall musculature.


                        

Balanoglossus(Trunk)

The trunk or metasome is the posterior and largest part of the body.The trunk bears a mid-dorsal and a mid-ventral ridge, each accomodating nerve and blood vessel.The trunk is further differentiated into three regions: an anterior branchiogenital,a middle hepatic and a poaterior post-hepatic, abdominal or caudal region.
Branchiogenital region-The anterior or branchiogenital region of trunk is marked by a pair of lateral, thin,flat and longitudinal flaps,the genital wings,containing the gonads.The numbers of gillpores increases with the age of the animal..
Hepatic region-The middle or hepatic region of trunk is smaller than the genital region.It is greenish in colour and its dorsal surface has numerous irregular intestinal sacculations or hepatic caeca.
Posthepatic region-It is the posterior-most and the longest part of the trunk also called the abdomen or caudal region.

Balanoglossus(COLLAR)

The collar or mesosome is the middle ,short  and  cylindrical part. Its flap-like or funnel-like anterior margin,termed collarette, completely surrounds and conceals the proboscis stalk and the posterior part of proboscis.Ventrally, below mouth present.The wall of collar is thick,highly muscular and encloses a cavity, the collar coelom. It opens to outside through a pair of collar pores into the first pair of gill pouches behind.

Balanoglossus(Division of body)

The body is unsegmented but divisible into three distinct regions or parts: proboscis, collar and trunk.
Proboscis-The proboscis or protosome is the anterior most part of the body.It is short, club-shaped or conical and circular in cross-section.It has thick muscular wall and is hollow within.The proboscis narrows into a slender neck or proboscis stalk which is attached to the collar.

Balanoglossus(External Morphology)

Shape, size and colouration-The body is soft,elongated,worm-like,cylindrical and bilaterally symmetrical.It measures 10 to50 cm in length,accourding to species B.gigas attain a length of 1.8(Sawaya.1951) or 2.5(Spengel,1893). The colour is bright or drab with reddish or orange tints.

Balanoglossus(Movements & Feeding)

The worm is sluggish and little affected by external stimuli.It moves in its burrow by cilia covering its body surface.The most active part is proboscis.It elongates and shortens by muscular activity and helps in burrowing.
It swallows sand or mud to obtain diatoms,protozoans,other micro-organism and organic detritus on which it feeds.

Balanoglossus(Protective device)

The inner wall of the fragile tube is smoothly lined by sand particles cemented together into a tough cast with sticky mucus secreated by the skin mucous glands of the animals.A nother protective device is the secrection of a foul smelling odour similar to iodoform. one species shows phosphorescence.

Balanoglossus(Habits and habitat)

Balanoglossus is a marine,tubicolous or burrowing hemichordates inhabiting shallow coastal waters of intertidal zone,but a few occur in deeper water.B.clavigerus lives inside a u-shaped tube or burrow with the two vertical limbs 50-75 cm deep and two opening 10-30 cm apart .The anterior opening of burrow is funnel shaped and posterior end is rounded and concealed below the spirally coiled faecal matter of the animal.

Balanoglossus-geographical distribution

Hemichorsates(balanoglossus), is a marine animals having a world -wide distribution. About 20 species occur the world especially in the tropical . e:g B.australiensis(Australia),B.carnosus(Indopacific),B.misakiensis(Japan),B.jamaicensis(West-indies),B.gigas(Brazil),B.capensis(SouthAfrica) and B.clavigerus(Mediterrannean and British isles).

BALANOGLOSSUS-DERIVATION

Balanoglossus clavigerous was named by Delle Chiaje in 1829. The term balsnos means an"acorn"(fruit of oak) also called as acorn worm.The local fisher-men call Baianoglossus by the name " ox tongue".having the shape of its proboscis, collar and genital wings bearing a close resemblance to an tongue, hence the common name "tongue worm".

Hemichordata-Balanoglossus(tongue worm)

The most familiar hemichordate genus is Balanoglossus which belongs to the class Enteropneusta.The are Saccoglossus(Dolichoglossus),Glossobalanus,Ptychodera,Spengelia,etc.
SYSTEMATIC POSITION
Phylum   Chordata
Subphylum  Hemichordata
Class  Enteropneusta
Family  Ptychoderidae
Type  Balanoglossus(toung worm)

chordates-subdivision

Subphyla and classes-Hemichordata(or Adelochordata) considered as lowest chordates.They are not a true notochord but a stomochord.
                 Urochorata(or Tunicata) include three larvacea  Ascidiacea and Thaliacea)
mmmm
Cephalochordata include a single class (leptocardii)mm
Vertebrata is divided into (Ostracodermi,Cyclostomata,Placodermi,Chonrichthyes,Osteichyes,Amphibia,ReptiliaAves and Mammalia)

chordates-origin and Ancestry

The chordates originated prior to cambrian period as the oldest fossil .The similarites between the echinoderm(bipinnaria) and hemichordate(tornaria) larvae is taken as good evidence for common ancestry.The protochordates provide the connecting link between early chordates and vertebrates.

chordates-features

Limbs-derivation-From several segments
Notochord-present at some stage or replaced by a backbone made of ringlike vertebrae
Gut position-ventral to nerve cord
Pharyngeal gill-slits-present at some stage of life
Bloodvascular systems-closed
Dorsal blood vessle- Blood flows posteriorly
Hepatic portal systems-present
Respiration-Through gills or lungs
Nervous systems-Hollow
Brain- Dorsal to pharynx in head
Nerve cord-Single ,Dorsal, without ganglia

chordates-features

Regeneration power-usually poor
Reproduction-sexual reproduction predominant
Heart-ventrally placed
Roots of segmental nerves-Dorsal and ventral separate
Haemoglobin-In red blood corpuscles
Anus-Differentiated and opens before the last segment

chordates-features

Biradial
True metamerism
Usually present posterial anal tail
Organ-systems
3,triploblastic germ layer.
Truly coelomate.
Limbs derivation from several segments.
Cold or warm-blooded
Regeration usually poors

chordates-advancement

Efficient-respiration-The gills in aquatic chordates and lungs in terrestrial forms  is efficient organs of respiration.
Efficient circulation-Having efficient circulation systems.
Centralized nervous systems-Having growing tendency of centralization of nervous systems.

chordates-characters

Axiation-The body is having anterior and posterior axis.
Bilateral symmetry-The right and left side of body are mirror image of each other.
Triploblastic condition-The chordates have three germ layers-ectodermand mesoderm.
Coelm-Inannelids,molluscus,arthropods-schizocoelous,in echinoderms,brachiopods and branchiostoma-enterocoelus.
Metamerism-Is a condition in which the body is composed of a linear series of similar body segments,called metameres or somites.

Organ-systems-All the chordates and all non-chordates show organ-systems.


Living endoskeleton-Only chordates possess a living endoskeleton.

 

chordata-characters

The morphological features of chordates include.The hollow nerve cord.Rod-like notochord. Series of pharyngeal gill slits.

chordate-ecology

The chordates are ecologically more advanced than any other kingdom.e.g birds and mammals are able to penetrate cold climate because they have a constant body temperature.saltwater amphibians are unknown.

chordata-size

Having the number of species,the chordates have different size from medium to have large in size e,g the blue whale (Balaenoptera musculus) 35m and 120 tons in weight.Sharks(Rhineodon typus) 15m.Philippine goby(Pandaka) smallest fish 10mm long. 

Diversity of chordates

Numerical strength-Means 49000 species of animal kingdom i,e 1/2 of molluscs and1/10 arthropoda.urochordata & cephalochordata-2500 speacies.vertebrata-46500speacies.fishes-25000 species.amphibians-2500.reptiles-6000.birds-9000.mamals-4500.

chordata word meaning

chordata-The name of this phylum is derived from two Greek words,the chorde meaning a string or cord and ata meaning bearing.Thus chordata are animals having a cord i,e notochord.

what is Chordata

The last major group of  the animal kingdom is known as phylum Chordata. There was 30 animal phyla currently recognised.The phyla Chordata was created by Balfour in 1880.