Protochordates Or Acraniata
Transcript of Protochordates Or Acraniata
Protochordates
Or Acraniata
Subphylum: Urochordata
Week 3
Assist. lec. Sawsan S. Hameed
Biology Department
Tishk international University
2021-2022
Domain Eukarya
Kingdom Animalia
Phylum Chordata
Sub phylum
UrochordataSub phylum
Cephalochordate
Sub phylum
Vertebrate
Protochordates
Or Acraniata
Higher chordates
Or Craniata
• The Urochordates are exclusively marine animals living on the substratum (bed rock).
• The most familiar member of the group is Hardmania; it possesses two siphons for the entry and exit of water.
• Characteristically they have a larval stage which undergoes retrogressive metamorphosis giving rise to the adult animal.
• Urochordates show all the basic characters of chordata at one or the other stage of life, they are supposed to be lower than Cephalochordata but higher than hemichorates from evolutionary point of view.
Subphylum I: Urochordata (tail-chordates)
Also called Tunicata
(Gr., oura= tail , L. chorda= chord
General characters
Small size 0.25-250mm, free swimming
Body is covered by protective tunic (covering membrane).
Notochord only in tail region and its depend on the presence or
lost of the tail
Dorsal nerve cord is degenerate into nerve ganglia in adult
Pharyngeal gill slits persistent, as the animal respire through it
Most species with two holes (openings), incurrent (mouth) and
excurrent (openings)
Mostly hermaphrodite & Fertilization is external
Subphylum I: Urochordata (tail-chordates)
Figure 1. Urochordate metamorphosis
Larval
More than 2000 species belong to 4 classes
Sub phylum
Urochordata
Class AscidaceaClass SorberaceaClass ThaliaceaClass Larvacea
These animals also called sea squirts
General character
Larval stage are free swimming with notochord, nerve
cord and gill slits in addition to long tail.
Adult are inactive or sessile - after retrogressive
metamorphosis, losing tail so notochord is also lost
nerve cord change to ganglion.
Gill slits persist in the pharyngeal region.
sexes are united (hermaphrodite)
Class Ascidiacea
Figure shows:
a) typical solitary adult tunicate.
b) Larval or tadpole life cycle phase
showing the notochord and the
dorsal nerve chord.
c) A typical mature colonial tunicate
showing a shared tunic and multiple
incurrent siphons (blue arrows) which
are always greater in number than the
excurrent siphons (pink arrows).
The class 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: 2. 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 Ascidiacea
Internal Structure of Ascidia
Test of Herdmania
Different types of tunicates
Herdmania External characters
is a marine and sedentary animal.
It is fixed to rocky sea by a flat
base.
When it is disturbed, it contracts its
body, and releases inner contents
through its apertures.
Hence it is called Sea squirt.
Phylum: Chordata
Sub-phylum:Urochordata
Class: Ascidiacea
Bluebell tunicate
General character
Adult larval-like, retain many larval
features including tail, notochord,
nerve cord
No metamorphosis, hence called
larvacea.
Gill slits in pharyngeal region also
persist throughout the life
Sex are united
Class II: Larvacea
Tail
Class Thaliacea
General character
Free-swimming and pelagic forms.
They are covered by transparent test.
The brachial and atrial apertures are placed at anterior and
posterior ends and pharynx is small.
Tunic with circular muscles
Adult lack notochord, nerve cord and tail region
Incurrent and excurrent opening opposite to each other, each at
one end of the body
Sex are united, reproduce by asexual reproduction by
budding.
Larval formed or absent
Tunic with circular muscle
Incurrent Excurrent
Thaliacea
The class Thaliacea is divided into three orders.
Order1. Doliolida (Cyclomyarla)
Barrel shaped body is completely covered by muscle bands
Pharynx is small.
Number of gill slits is less
Tailed larva is seen
ex Doliolum
Order2. Pyrosomlda
This order includes colonial forms.
Muscle bands are small and present at the ends.
Gill-slits are many.
Tailed larval stage is absent.
Ex: Luminescent colonial form.
Order 3. Salpida (Hemimyaria):
This order includes organisms whose body prism is like.
A pair of lateral gill slits are present
Doliolum
• Presence of retrogressive metamorphosis.
• Absence of segmentation.
• Because of these characters zoologists included these animals in a separate sub-phylum Urochordata.
• During recent years many zoologists regarded the tunicates as primitive and ancestral forms of chordates as a whole.
• The typical tunicate looks like a non-chordate animal.
If the life history of such animal is studied, the larval form reveals the chordate characters of that animal.
Urochordates differ from other chordates owing to the following characters:
Urochordate’s-resemblance with Chordate.
• Urochordates resemble the chorates owing to the following features-
• Presence of dorsal tubular nerve cord.
• Presence of notochord.
• Well developed pharynx with gill-slits.
• Presence of endostyle on the ventral side of the pharynx.
• Presence of atrium around the pharynx.
• Presence of post - anal tail with tail fin.
• Because of these chordate features tunicates are included in chordate’s group
Subphylum II: Cephalochordata Classification
• Domain: Eukarya (eukaryotes)
• Kingdom: Animalia
• Phylum: Chordata (chordates)
• Subphylum: Cephalochordata
Subphylum of the phylum Chordata.
Cephalochordate or lancelets, traditionally known as amphioxus
It has the five basic characteristics of chordates in simple form.
About 2.5 to 7 cm in length.
Amphioxus (Gr. Amphi, both ends, + oxys, sharp)
Subphylum II: Cephalochordata
Cephalochordata example; Amphioxus
General Characterstics of Cephalochordata
a) Two pairs of cerebral and several pairs of spinal nerves are present.
a) Presence of dorsal tubural nerve cord.
General Characterstics of Cephalochordata
q) Sexes are separate. Gonads are metamerically arranged and are without gonoducts.
r) Asexual reproduction never occurs.
s) Fertilization is external.
Classification And Systematic Position Of
Cephalochordata
Presence of a long notochord from anterior end to posterior end on the dorsal side, and
since it extends to the cephalic region, the group is called Cphalochordata.
The sub-phylum Cephalochordata includes a single class- Leptocardii, which has single
family Branchiostomidae.
The family contains only two genera Branchiostoma and Asymmetron.
Pallas described these animals first and named the Cephalochordatas Umax lancealatus.
In 1834, Costa described its chordate features. In 1836, Yarrel named it as Amphioxus.
The characteristics and body structure of cephalochordates can be described under
the following heads;
a) CHORDATE FEATURES OF CEPHALOCHORDATA
(AMPHIOXUS):
i. Presence of dorsal tubural nerve cord.
ii. Presence of a long notochord from anterior end to posterior end on the
dorsal side. Because, it extends to the cephalic region, the group is called
Cphalochordata.
iii. Gill silts are present in the Pharynx.
iv. Presence of post anal tail.
v. Presence of liver diverticulum.
vi. Development of hepatic portal system.
vii. Presence of myotomes which are useful for locomotion.
viii. Presence of dorsal, caudal and ventral fins.
b) PRIMITIVE CHARACTERS OF CEPHALOCHORDATA:
i. The excretory system contains protonephridia.
ii. In Chordata, the presence of solenocytes is not reported. But, in Amphioxus
solenocytes are associated with nephridium.
iii. Absence of heart and kidney.
iv. Absence of paired limbs or paired fins.
v. Absence of distinct head.
vi. Absence of distinct paired sense organs.
vii. Gonads are without gonoducts.
Special Characters Of Cephalochordata
i. Because of its ciliary mode of feeding, the pharynx is elaborated with many gill slits.
ii. Oral hood is well developed for ciliary mode of feeding.
iii. Because of its ciliary mode of feeding the atrium is very well developed. Thus,
Amphioxus shows some special characters which are developed because of its ciliary
mode feeding.
Figure 5. A slide of Amphioxus showing the mouth
Epipharyngeal groove
Endostyle
Gill slits
• Get a view of all of the structures.
• Identify the five chordates characteristics:
• Pharyngeal slits ‐ Look for the pharynx at the anterior end of the animal. The
slits run from anterodorsal to posteroventral. During filter feeding, water enters
through the mouth, passes through the pharyngeal slits, and exits through the
atriopore.
• Dorsal hollow nerve cord – This is a dark pink stripe that runs anterior to
posterior along the dorsal side of the animal.
• Notochord – This is a dark stripe that often stains a more orange color than the
nerve cord. It also runs along the dorsal side of the animal, located immediately
ventral to the nerve cord. It begins anterior to the nerve cord.
• Endostyle – The endostyle is a structure that is difficult to see in the whole
mount. It runs longitudinally along the ventral edge of the pharynx. In the whole
mount, it may appear as a darker pink stripe.
• Postanal tail – Locate the anus, which is ventral and posterior to the atriopore.
The part of the animal posterior to this is the post‐anal tail.
Draw the amphioxus slides. Label all the structures that you identify.
Draw all the provided picture to identify the tunicates species
Lab study: A slide of Amphioxus
References
For further reading please see:
Charles K. Weichert (2017). Elements of chordate anatomy. 3rd edition.
The McGraw−Hill Companies, New york.
Comparative anatomy | Definition, Examples, & Facts |
Britannicahttps://www.britannica.com › science › comparative-anatomy
Kardong, Kenneth V. (2019). Vertebrates: comparative anatomy, function,
evolution (8th edition). New York.
De Iuliis, G., & Pulerà, D. (2019). The dissection of vertebrates. 3rd
edition. Academic press. Elsevier, London.
Kenneth, S. S. (2017). The unity of form and function. 8th edition. The
McGraw−Hill Companies,. New york.
Comparative Anatomy. wwww.health.zone/