BRANCHIOSTOMA-APERTURES

The trunk bears three openings mouth ,atriopore and anus.The oral hood formed by dorsal and lateral projections of the body. Mouth is formed by margin by oral hood. Atriopore is a small ventral aperture just in front  of the ventral fin. The large atrial cavity surrounding the pharynx opens to outside through atriopore.The anus lies asymmetrically to the left of mid-ventral line at the base of caudal fin. The small posterior body region the anus is the tail.

BALANOGLOSSUS-DIVISION OF BODY

The body of  balanoglossus is divisible into two region the trunk and tail. The anterior end of trunk projects in front as a pointed snout or rosrtum.

BRANCHIOSTOMA-SIZE, SHAPE, COLOUR

Branchiostoma is small elongated narrow fish-like animals 5to 8 cm in size.Body is whitish,like a ''lancelet''.The streamline body is used for burrowing as wellas swimming. The posterior end is tapering and pointed than the anterior end.

BRANCHIOSTOMA-HABITS AND HABITAT

Is marine animal found in shallow waters. It leads a double mode of life . Is a typically ciliary feeder. It feeds in planktonic micro-organisms. Male and female are separate.They release their gametes in water. Development is indirect involving a free-swimming larval stage which gradually assumes the shape of the adult.

BRANCHIOSTOMA-GEOGRAPHICAL DISTRIBUTION

About 9 species of branchiostoma are found.It is more common in Mediterranean sea.The species common in India are Branchiostoma indicum, B.pelagicum and B.ceribbaeum. of all B.lanceolatum is most common.

DERIVATION OF NAMES-BRANCHIOSTOMA

The branchiostoma is refers to Amphioxus for cephalochordates.The cephalochordata is aiso called as Acrania. The old generic name Amphioxus name ''lancet''OR ''LANCELET'' which are sharp, pointed and lance-like.

BRANCHIOSTOMA-AMPHIOXUS

INTRODUCTION- The subphylum Cephalochordata are small,marine,and look like fish.It also called as Lancelet.Pallas in 1778.COSTA in 1834 called as BRANCHIOSTOMA LANCEOLATUM.In 1936 Yarrel called as AMPHIOXUS LANCEOLATUS.

UROCHORDATA-ORDER-POLYSTYLOPHORA

House biradially symmetrical,having single aperature.
Pharynx without endostyle.
e.g Kowalevskia.

UROCHORDATA-ORDER-ENDOSTYLOPHORA

Bilaterally symmetrical.
Pharynx with endostyle.
e.g Oikopleura,Appendicularia.

UROCHORDATA-CLASS-LARVACEA

Small,solitary free-swimming,pelagic neotenic larva-like forms, notochord,nerve cord and brain.
Test forming a temporary.
Atrium and atrial apeerture absent.
Gill-slits 2, opening directly to outside.
Sexes united
No metmorphosis.
.

UROCHORDATA-ORDER-SALPIDA

Body barrel-shaped.
Muscle bands form 8 bands.
Gill-slits small.
Tailed larva absent.
Pharynx communicates with atrium.
e.g Salpa, Scyclosalpa.

UROCHORDATA-DOLIOLIDA

Body characteristically barrel-shaped.
Muscle bands incomplete.
Pharynx communicates freely with atrium
Tailed larva absent..
e.g Salpa ,Scyclosalpa .

UROCHORDATA-ORDER-PYROSOMIDA

Colony compact,tubular,phosphorescent in life
Zooids embedded in a common test..
Muscle bands confined to body ends
Gill-slits tall, numerous to 50.
Absent of larval stage.e.g pyrosoma..

UROCHORDATA-CLASS-THALIACEA

Free -living, pelagic in warm.
Solitary or colonial
Body shape are variable.
Tunic permanent, thin and transparent,having muscle bands.
Atriopore located posteriorly..
Pharynx with 2 large or many gill-slits.
Sexes united.
Larva formed or abesent.
Adult is without notochord.
Asexual budding.
Life history with an alteration of generation.

UROCHORDATA-PLEUROGONA

Body is undivided.
Neural gland dorsal or lateral to ganglion.
Gonads is present in mantle wall.
Larva is otolith.
Eye is seperate.
e.g Herdmania, Botryllus ,Molula, Styela.

UROCHORDATA-SUBORDER-APLOUSOBRANCHIA

Pharynx with longitudinal vessels.
Budding process. e.g Clavelina.

UROCHORDATA-SUBORDER-PHLEBOBRANCHIA

The pharynx present with longitudinal vessels.
Budding rarely present.e.g  Ascidia, ciona, phallusia.

UROCHORDATA-ORDER-ENTEROGONA

Body divided intothorax and abdomen.
Neural gland ventral to ganglion.
Gonads1 in intestinal loop.
Larva with 2 sense organs(ocelli and otolith).

UROCHORDATA-CLASS -ASCIDIACEA

Solitary,colonial or compound.
Bottom living.
Body form and size variable.
Test permanent,well developed and thick.
Atrium opens dorsally by atriopore.
Pharynx large with many persistent gill-slits.
Sexes united
Larva free-swimming and highly developed.
Stolon simple
Adult sessile after retrogressive metamorphosis
Tail are lost and brain reduced to a dorsal ganglion.

UROCHORDATA-CLASSIFICATION

Tunicata includes nearly,2000 fixed and 100 pelagic species.In 1891 Herdman classified, Lahille1895, perrier 1898,Hartmeyer 1909-1911and S.M Dass in 1957.The subphylum urochordata is divided into three classes.

UROCHORDATA-GENERAL CHARACTERS

Exclusively marine and cosmopolitan, present in seas depths.
Mostly sedentary,pelagic or swimming.
May be solitary,or colonial.
size 0.25 to 250mm, shape and size.
Having no tail.
Body covered with tunicine similar to celluse so called as tuniacta.
Coelom absent
Notochord present only in larval stage hence called as urochordata..
Alimentry canal complete.
Ciliary feeders.
Respiration through test and gill-slits.
Blood-vascular system open.
Excretion by neural gland, pyloric gland and nephrocytes.
Mostly hermaphrodite.
Fertilization external.
Metamorphosis retrogressive.
Asexual reproduction by budding.

HEMICHORDATA-GRAPTOLITA

The graptolita were more in ordovician and silurian periods.e.g Dendrograptus .Their tubular chitinous skeleton and colonial habits show an affinity with Rhabdopleura.

HEMICHORDATA-PLANCTOSPHAEROIDEA

It consist small, rounded transparent pelagic larvae,as tornaria larvae called as plactosphaera pelagic.
Alimentary canal is l-shaped.
The larvae body is covered by ciliary bands.

HEMICHORDATA-CEPHALODISCIDA

Solitary or several zooida living unconnected in a commoa gelatinous
Collar with several tentaculated arms.
Gill-slita single pair present.
Gonads single pair present.
e.g,Cephalodiscua,Atubaria.

HEMICHORDATA--- RHABDOLEURIDA(ORDER)

Colonial,zooids connected by a stolon.
collar with two tentaculated arms.
Gill-slits absent.
Gonads single.
e.g rhabdopleura.