Wednesday 29 February 2012

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.

Tuesday 28 February 2012

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.

Monday 27 February 2012

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.

Sunday 26 February 2012

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.

Saturday 25 February 2012

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.

Friday 24 February 2012

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.

Thursday 23 February 2012

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.

Wednesday 22 February 2012

UROCHORDATA-ORDER-POLYSTYLOPHORA

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

Tuesday 21 February 2012

UROCHORDATA-ORDER-ENDOSTYLOPHORA

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

Monday 20 February 2012

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.
.

Sunday 19 February 2012

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.

Saturday 18 February 2012

UROCHORDATA-DOLIOLIDA

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

Friday 17 February 2012

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..

Thursday 16 February 2012

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.

Wednesday 15 February 2012

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.

Tuesday 14 February 2012

UROCHORDATA-SUBORDER-APLOUSOBRANCHIA

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

Monday 13 February 2012

UROCHORDATA-SUBORDER-PHLEBOBRANCHIA

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

Sunday 12 February 2012

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).

Saturday 11 February 2012

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.


Thursday 9 February 2012

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.

Wednesday 8 February 2012

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.

Monday 6 February 2012

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.

Sunday 5 February 2012

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.


Wednesday 1 February 2012

HEMICHORDATA--- RHABDOLEURIDA(ORDER)

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