HERDMANIA TYPE STUDY

Affinities of Urochordates .

The typical tunicate looks like a non-chordate animal. If the life history of such animal is studied, the larval form reveals the chordate chara’4ters of that animal.
In 1816, Lamarck and Cuvier placed these animals in one class ‘Tunicata’. Allis described a compound Ascidian “Botryllus’ in 1756.KowalevskSi. Worked on the development ofthe Ascidian and placd them’in tunicates after observing the chordate features
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Urochordates-Resemblance. With Chordate. :- .

1. Presence of dorsal tubular nerve cord,
2. Presence of Notochord,
3. Well developed pharynx with gill-slits.
4. Presence of endostyle on the ventral side of the pharynx
.5. Presence of atrium around pharynx.
.6. Presence of post - anal tail, with tail fin.
, Because of these chordate features tunicates are included in chordates group.

Urochordates-Resemblance with Amphioxus:
1. Presence of notochord.
2. Presence of dorsal tubular nerve cord.
3. Presence of large pharynx with gill slits.
4. Presence of atrium and atriopore.
5. Presence of muscle band.
Thus, the Urochordates show close relation with Cephalochordates. But the



Urochordates differ with other Chordates because of the following peculiar characters.
1 .Presence of retrogressive metamorphosis.
2. Absence of segmentation.
Because of these characters zoologists included these animals in a
Separate sub-phylum Urochordates.
During recent years many zoologists regarded the tunicates as primitive and ancestral forms to chordates as a whole.
previous topic urochordata classification
Urochordata Classification
Classification of Urochordata

Subphylum Urochordata is divided into three classes.
CLASS 1. ASCIDIACEA CLASS 2. THALIACEA CLASS : 3 . LARVACEA (APPENDICULARIA)

CLASS 1. ASCIDIACEA:
1. These are sedentary tunicates.
2. The body is covered by a test.
3. Pharynx is large and contains gill-slits.
4. Notochord, nerve-cord and tail are absent
5. These are Bisexual animals.
6. Life-history includes a typicalTadpole larva. The class Ascidiacea is divided into two orders.
Order 1. Enterogona
These ascidians bear one gonad in the intestinal loop. Neural gland is ventral to the ganglion. Tadpole larva is seen:
Ex: Ascidia and Ciona.
Order: 1. Pleurogona:
In these ascidians,gonads are paired and are present in the atrial wall. Neural gland is dorsal to the ganglion:
Ex : Herdmania, Botryllus.

CLASS 2. THALIACEA :-
1. These Urochordates are free-swimming and pelagic forms.
2. They are covered by transparent test.
3. The brachial and atrial apertures are placed at anterior and posterior ends.
4. Pharynx is small.
5. Gill-slits number is less.
6. Notochord, nerve-cord and tail are absent in the adult.
7. Asexual reproduction is by budding.
‘8. These are bisexual animals.
9. Tailed larva may be present or absent.
10. Alternation of generations can be seen in the life history.
The class thaliacea is divided into three orders.
1. Doliolida, 2. Pyrosomida and 3. Salpida.
Order 1. Doliolida (Cyclomyarla)
1. Barrel shaped body is completely covered by Muscle bands,
2. Pharynx is small
3. Number of gill slits will be small.
4. Tailed larva is seen
5. Sexual Blasto-zooid and asexual oozooid stages will alternate in the life cycle.
Ex :Doliolum.
Order 2. Pyrosomlda :
1. This order includes colonial forms.
2. Muscle bands are small and present at the ends.
3. Gill-slits are many.
4. Tailed larval stage is absent.
Ex : Pyrosoma (Luminescent colonial form).
Order 3. Salplda (Hemimyaria) :-
1. This order includes organisms whose body is prism like.
2. Muscle bands are complete dorsally and incomplete ventrally.
3. Only one pair of lateral gill slits are present.
4. Tailed larval stage is absent.
5. Life history includes alternation of generations.
Ex: Salpa.

CLASS : 3 . LARVACEA (APPENDICULARIA)
1. These are free - swimming, pelagic tunicates.
2. True’ test covering is lacking
3. They show loose gelatinous house.
4. This house is useful for filter feeding.
5. Two gill slits re present.
6. Atrium is absent. ..
7. Notochord and nerve cord are Persistent
8. They show tail throughout their life.
9. Neotenic forms are included.
Ex: Oikopleura. ‘













Urochordata Characters
Urochordata General Characters
The tunicates were first regarded as sponges. Lamark in 1816 placed Tunicata in between the Radiata and Vermes in his system of classification. Later, they were included in Mollusca. In 1866 Kowalevsky kept them in chordates.
Their chordate features are clearly seen in the larval stages. All Urochordates are marine and occur in all the seas. Majority of them are sedentary and some are pelagic.
1. Body shows variation in size and form.
2,. The body is un segmented and has no tail
3. The body is covered by a test. It is formed by tunicine which is
rallied to cellulose. Hence the name Tunicata.
4. Body wall shows one-layered epidermis, dermis is made by connective tissue and muscles, and atrial epithehum.
5.Celome is absent.
6. Atrial cavity surrounds the pharynx, into this cavity the gill slits,anus and genital ducts will open. It opens through atrial aperture.
7. Larva has notochord in the tail. It disappears during metamorphosis.
8. Respiratory system contains gills in the pharyngeal wall.
9. Ciliary mode of feeding is common.
10. Open type of Circulatory system is seen.
11. The heart is ventral and it periodically reverses its function.
12. Nervous system is represented by a single dorsal ganglion in the adult.
13. Excretion is carried on by nephrocytes.
14. Asexual reproduction is by budding.
15. Bisexual animal and cross fertilisation is favored.
16. Fertilization is external.
17. Development includes a minute, free swimming tadpole larva with a tail, a dorsal nerve cord, and a notochord in the tail. In some urochordates retrogressive metamorphosis is seen in the life history.
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Herdmania Excretory Organ:
Excretory Organ Of Herdmania:
A neural gland is present above the brain in herdmaina. it Is brown in colour. It is present In the mantle. 1t is 4mm in diameter. It show branching tibuIes. At one end it leads into a short duct which opens by ciliated funnel above the dorsal tubercle. In the blood nephrocytes cell are present. They coiled waste matter. They come to the neural gland from there, they are sent out The neural gland secretes a hormone. It help in metamorphosis. Neural gland is considered homologous to pituitary glands of vertebrates.

Herdmania- Spicules
Herdmania- Spicules in the test:
In the test of Herdmania two types of calcareous spicules are Present. They are:
1) Microscieres : These are 40 to 80 microns in length. They are minute.
2) Megascleres : These are long spicules. They show different shapes. They are 1.5 to 3.5 mm in length. They are two types.
a) Spindle shaped Megascleres. They are 1.5 to 2.5 mm in length.
b) Pipette shaped Megascleres. They are 3.5 mm. in length.
The rnicroscleres are present only in the test. But the megascleres occur in the test, body wall, and viscera.
Herdmania-Spicules Function:
1) They give support to the test
2) They protect the animal from predators.
3) They fix mantle with test.
Herdmania- Nervous System
NERVOUS SYSTEM OF HERDMANIA:
Herdmania shows brain or nerve ganglion. It is 4 mm long. It is present in the mantle in between the two siphons. A neural gland is present above the brain. From the brain three nerves arise, one goes to the bronchial siphon, and two will go to the atrial siphon. The brain represents the degenerated nervous system of the larva.

Receptors:
1. Red pigmented spots on the test are photoreceptors. They are sensitive to light.
2. Sensory cells of the margins of siphons and tentacles are tango receptors. They are sensitive to touch.
3. The cells on the margins of siphons are rheo receptors. They are sensitive to water currents.
4. Cells lining the siphons are thermo receptors. They are sensitive to changes of temperature.
Herdmania Gonads
Gonads of Herdmanla :
Ans: Herdmania is a bisexual animal. It is a protogynous animal. Ovary matures’ first. Hence cross fertilization takes place.
Herdmania contains a pair of gonads. The left gonad lies in the intestinal loop above the heart. Each gonad shows 10 to 25 lobes arranged in two rows. The median lobe is single and large. Other lobes are oval in shape.
Each lobe shows outer large testicular part and inner small ovarian part. The testicular part is brick red in colour and produces sperms. The ovarian part is pink in colour and produce ova. From each testicular part sperm ductule will arise. They open into spermduct. From each ovarian part ovarian ductule will come. They open into the oviduct. Each gonad has an oviduct and spermduct. They run parallelly and open separately into cloaca behind anus.
Herdmania -Retrogressive Metamorphosis
Retrogressive Metmorphosis in herdmania
During metamorphosis the larva will loose all the chordate characters and attains an invertebrate like form. This type of metamorphosis, where highly advanced larval form ends in a lowly organised adult is called retrogressive metamorphosis.
Fixation of the larva: The larva swims for some time without feeding. It is fixed to a sub- stratum with the help of the adhesive papillae. It stands erect with the tail upwards. Then it undergoes retrogressive metamorphosis.
Changes during metamorphosis:
1.Notochord, nerve cord muscles and tail will be reduced. All the above structures will help the larva to swim freely in the water. But they are not useful to the sedentary adult
2.. The alimentary canal becomes complicated. The pharynx en larges ln size. The number of gill slits will increase by divisions. The stomach and intestine will grow.
3. The nervous system is reduced and the anterior part of nervous system is developed into a small neuralganglion attached to it neural gland is present. ;:
4. The atrial cavity enlarges into a sac like structure.
5. The eyespot and statocyst will completely disappear.
6. Gonads develop from mesencyme.

When these changes are taking place, the region between the adhesive papillae and mouth grows very rapidly. At the same time the growth of the dorsal region is stopped. Because of this, the body rotates through 1800 angle and mouth is brought to the top
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HERDMANIA TADPOLE LARVA
ORGANISATION OF HERDMANIA TADPOLE LARVA:
Herdmania is a hermaphrodite animal. The fertilised eggs undergo holoblastic unequal clevage and it develops into blastula. it shows upper micromeres and lower macromeres. By invagination of the macromeres gastrulation takes place and gastrula is formed. This gastrula develops into a tailed larva called Ascidian Tadpole larva. (Herdmanis life history, is not clearly known. Clavilina’s life history is known. It is followed here.

The larva is 3 mm in length. It has short oval body and a long tail.
This larva shows all the chordate features.
1) The body is covered by thin test.
2) The tail is long and shows a tail fin or caudal fin.
3) The tail is supported by notochord. Hence it comes under urochordata.
4) On the dorsal side above the notochord hollow nerve cord is present. This nerve cord is enlarged at the anterior end as a cerebral vesicle. In the cerebral vesicle pigmented eye spot is present. Statocyst is also present. They work as sense organs.
5) On either side of the notochord in the tail region muscles are Present which are helpful in the locomotion.
6) On the trunk region digestive system is present. It shows large pharynx with few gills slits. They open into atrium. On the mid ventral floor of the pharynx an endostyle is present.
7) Atrium opens out through atriopore.
8) Below the pharynx on the ventral side a muscular heart is present.
9) On the anterior end of the trunk three adhesive papillae are present These are very much useful to attach the larva to the substratum
This Herdmania tadpole larva shows all chordate characters. This larvae ‘undergoes retrogressive’ metamorphosis and develops into adult Herdmania.
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Herdmanla -External characters
External characters of Herdmania
Herdmania is a simple ascidian, In Indian ocean this genus Is represented by 4 species. ,
1. Herdmania pallida, 2. H.ennurensis, 3. H.mauritiana 4. H. ceylonica.
Herdmania belongs to,
Phylum: Chordata,
Sub-phylum: Urochordata,
Class: Ascidiacea,
Order: Pleurogona.
Herdmania is a marine and sedentary animal. It is fixed to rocky substratum by a flat base. When it is disturbed, it suddenly contracts its body, and emits inner contents with force through its apertures. Hence it is called Sea squirt.
External Features :-
It is potato like in shape. It is pink in colour. On the free side, body shows two projections, the brançhial and atrial siphons. The branchial siphon is short. The branchial siphon shows a branchial aperture or the mouth. The atrial siphon is longer. It bears the atrial aperture. Both the openings are bounded by four lips.
Herdmania - external characters.

Test of Herdmania:The body of this animal is covered and protected by test. It Ls a thick, leathery covering of the body.It is secreted by the epidermis of the body wall. It has matrix, corpuscles, fibrils, blood vessels and spicules.
The matrix is composed of tunicin, which is cellulose. The cells in the test are of six types, large eosinophilous cells, amoeboid cells, small eosinophilous cells, vacuolated cells, receptor cells and nerve cells.
Fine fibrils present in the matrix. In the test blood vessels are present. In the test the spicules are calcareous spicules. They are microscleres, and megascleres.
The test protects the body. Anchors the animals to substratum. Its spicules form a supporting frame work.

Herdmania Body wall :
The body-wall of Herdmania is called Mantle. It is thick, and muscular in the antero-dorsal region of the body. It is thin, non-muscular and transparent in the postero ventral region. It shows epidermis, mesenchyme, and inner epidermis.
1.Epidermis : It Is single layer of cells. It covers the bronchial and atrial apertures and siphons. The epidermis is interrupted at places where spicules and blood-vessels pass from the mantle into the test.
. 2. Mesènchyme: It develops from the mesoderm. It has connective tissue containing blood-sinuses, muscle-fibers, nerve fibers and cells. The muscle fibers are long and flat. They contain large nuclei.
3. Inner Epidermis: It is single layer of flat cells. It forms the lining of the atrial cavity. .
‘1.The body-wall protects visceral organs.
2. The outer epidermis secretes the test.
3. The musculature brings contraction of the body and the siphons.
Herdmania Atrium:
In Herdmania coelome is not developed. Atrium is a spacious ectoderm lined cavity. it is covered by the mantle A part of the atrium surrounds the pharynx. The stigmata of the pharynx open into this cavity. Part of the atrium is dorsal to the pharynx. It is very wide and is called cloaca. The rectum and gonoducts open into this. The cloaca opens to the exterior through atrial siphon and trial aperture. The atrial siphon shows a ring of processes called atrial tentacles at its base.