The document discusses the phylum Hemichordata and its two classes, Pterobranchia and Enteropneusta, which are small marine worms that share similarities with echinoderms and chordates. It describes characteristics of acorn worm larvae and adults, including a tripartite coelom and pharyngeal slits, that are also seen in echinoderms. Conflicting views are presented on deuterostome phylogeny, with some evidence supporting hemichordates as the sister group to echinoderms (Ambulacraria) rather than chordates, despite similarities in features like the dorsal nerve cord between hemichordates and chordates.
DENTITION IN MAMMALS
The study of arrangement structure and number of types of teeth collectively is called as dentition. Teeth are present in the foetal as well as in adults of mammals, based on the presence of teeth Mammals are two types.
Edentata : In some animals teeth are absent hence called as edentate. e.g., Echidna or spiny ant-eater (Tachyglossus) the teeth are absent in all stages of life.
Dentata : Teeth are present in all mammals though a secon¬dary toothless condition is found in some mammals. Modern turtles and birds lack teeth. The adult platypus (Ornithorhynchus) bears epidermal teeth but no true teeth are present. In platypus embryonic teeth are replaced by horny epidermal teeth in adult.
Classification According to the Shape and Size of the Teeth:
Homodont:
Homodont or Isodont type of teeth is a condition where the teeth are all alike in their shape and size in the toothed whales e.g., Pinnipedians. Fishes, amphibians, reptiles and in the extinct toothed birds.
Heterodont
Heterodont condition is the usual feature in mammals, i.e. the teeth are distinguished according to their shape, size and function. The function is also different at different parts of the tooth row.
According to the Mode of Attachment of Teeth:
Thecodont : The teeth are lodged in bony sockets or alveoli of the jaw bone and capillaries and nerves enter the pulp cavity through the open tips of the hollow roots e.g., mammals, crocodiles and in some fishes.
Acrodont: The teeth are fused to the surface of the underlying jawbone. They have no roots and are attached to the edge of the jawbone by fibrous membrane e.g., fishes, amphibians and some reptiles.
Pleurodont:
The teeth are attached to the inner-side of the jawbone. The tooth touches the bone only with the outer surface of its root. In acrodont and pleurodont types of dentition, there are no roots, and nerves and blood vessels do not enter the pulp cavity at the base, e.g., Necturus (Amphibia) and some reptiles.
According to the Succession or Replace¬ment of Teeth:
DENTITION IN MAMMALS
The study of arrangement structure and number of types of teeth collectively is called as dentition. Teeth are present in the foetal as well as in adults of mammals, based on the presence of teeth Mammals are two types.
Edentata : In some animals teeth are absent hence called as edentate. e.g., Echidna or spiny ant-eater (Tachyglossus) the teeth are absent in all stages of life.
Dentata : Teeth are present in all mammals though a secon¬dary toothless condition is found in some mammals. Modern turtles and birds lack teeth. The adult platypus (Ornithorhynchus) bears epidermal teeth but no true teeth are present. In platypus embryonic teeth are replaced by horny epidermal teeth in adult.
Classification According to the Shape and Size of the Teeth:
Homodont:
Homodont or Isodont type of teeth is a condition where the teeth are all alike in their shape and size in the toothed whales e.g., Pinnipedians. Fishes, amphibians, reptiles and in the extinct toothed birds.
Heterodont
Heterodont condition is the usual feature in mammals, i.e. the teeth are distinguished according to their shape, size and function. The function is also different at different parts of the tooth row.
According to the Mode of Attachment of Teeth:
Thecodont : The teeth are lodged in bony sockets or alveoli of the jaw bone and capillaries and nerves enter the pulp cavity through the open tips of the hollow roots e.g., mammals, crocodiles and in some fishes.
Acrodont: The teeth are fused to the surface of the underlying jawbone. They have no roots and are attached to the edge of the jawbone by fibrous membrane e.g., fishes, amphibians and some reptiles.
Pleurodont:
The teeth are attached to the inner-side of the jawbone. The tooth touches the bone only with the outer surface of its root. In acrodont and pleurodont types of dentition, there are no roots, and nerves and blood vessels do not enter the pulp cavity at the base, e.g., Necturus (Amphibia) and some reptiles.
According to the Succession or Replace¬ment of Teeth:
All birds are in the Animalia Kingdom, Phylum of Chordata (with a backbone), and Class Aves (birds). At the Order level, the birds begin to diverge. For instance, the pelicans are in the Pelecaniformes Order while the nuthatches are in the Passeriformes Order.
ORIGIN OF CHORDATES
Animal kingdom is basically divided into two sub kingdoms:
Non-chordata- including animals without notochord.
Chordata- This comprising animals having notochord or chorda dorsalis.
Chordates were evolved sometime 500 million years ago during Cambrian period (invertebrates were also began to evolve in this period) .
Chamberlain (1900) pointed out that all modern chordates possess glomerular kidneys that are designed to remove excess water from body.
It is believed that Chordates have originated from invertebrates.
It is difficult to determine from which invertebrate group the chordates were developed.
Chordate ancestors were soft bodied animals. Hence they were not preserved as Fossils.
However, early fossils of chordates have all been recovered from marine sediments and even modern protochordates are all marine forms.
Also glomerular kidneys are also found in some marine forms such as myxinoids and sharks. That makes the marine origin of chordates more believable.
Chordates evolved from some deuterostome ancestor (echinoderms, hemichordates, pogonophorans etc.) as they have similarities in embryonic development, type of coelom and larval stages.
Many theories infers origin of chordates, hemichordates and echinoderms from a common ancestor.
It discusses basic information regarding a hemichordate animal called Balanoglossus or Acorn worm, which is also a good connecting link between the non-chordates and chordates.
This presentation provide information about salient feature of cyclostomata with proper examples and explanation why they are classified in this class.
The chordates are named for the notochord: a flexible, rod-shaped structure that is found in the embryonic stage of all chordates and also in the adult stage of some chordate species.
It is located between the digestive tube and the nerve cord, providing skeletal support through the length of the body.
In some chordates, the notochord acts as the primary axial support of the body throughout the animal's lifetime.
Chordata is the last phylum of kingdom Animalia.
Which is further subdivided into subphylums, divisions and classes.
The Slides shows the classification of the phylum along with the basis on which it is classified.
(includes examples along with pictures for easy understanding and memorizing)
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All birds are in the Animalia Kingdom, Phylum of Chordata (with a backbone), and Class Aves (birds). At the Order level, the birds begin to diverge. For instance, the pelicans are in the Pelecaniformes Order while the nuthatches are in the Passeriformes Order.
ORIGIN OF CHORDATES
Animal kingdom is basically divided into two sub kingdoms:
Non-chordata- including animals without notochord.
Chordata- This comprising animals having notochord or chorda dorsalis.
Chordates were evolved sometime 500 million years ago during Cambrian period (invertebrates were also began to evolve in this period) .
Chamberlain (1900) pointed out that all modern chordates possess glomerular kidneys that are designed to remove excess water from body.
It is believed that Chordates have originated from invertebrates.
It is difficult to determine from which invertebrate group the chordates were developed.
Chordate ancestors were soft bodied animals. Hence they were not preserved as Fossils.
However, early fossils of chordates have all been recovered from marine sediments and even modern protochordates are all marine forms.
Also glomerular kidneys are also found in some marine forms such as myxinoids and sharks. That makes the marine origin of chordates more believable.
Chordates evolved from some deuterostome ancestor (echinoderms, hemichordates, pogonophorans etc.) as they have similarities in embryonic development, type of coelom and larval stages.
Many theories infers origin of chordates, hemichordates and echinoderms from a common ancestor.
It discusses basic information regarding a hemichordate animal called Balanoglossus or Acorn worm, which is also a good connecting link between the non-chordates and chordates.
This presentation provide information about salient feature of cyclostomata with proper examples and explanation why they are classified in this class.
The chordates are named for the notochord: a flexible, rod-shaped structure that is found in the embryonic stage of all chordates and also in the adult stage of some chordate species.
It is located between the digestive tube and the nerve cord, providing skeletal support through the length of the body.
In some chordates, the notochord acts as the primary axial support of the body throughout the animal's lifetime.
Chordata is the last phylum of kingdom Animalia.
Which is further subdivided into subphylums, divisions and classes.
The Slides shows the classification of the phylum along with the basis on which it is classified.
(includes examples along with pictures for easy understanding and memorizing)
Larval forms and their significance in arthropodaRekha Jalandra
This presentation is all about the larval forms being found in phylum arthropoda. It starts with the introduction of phylum arthropoda and then detailed information about the larval forms and their significance. i have included total 9 larval forms in this presentation.
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Hemichordates.pptx
1. Phylum Hemichordata (85 species)
Class Pterobranchia (Sea Angels)
Class Enteropneusta (acorn worms)
Small group of marine worms that show
similarities
to Echinoderms and Chordates
2. Tornaria of Acorn Worms Auricularia of
Sea Cucumbers
Has a deuterostome embryology and resembles in ciliation
feeding mechanism (opposed band) and general appearance an
auricularia larva of sea cucumbers
Also shares with echinoderms:
- Adult axial complex similarity (hemal –excretory system)
- Tripartite coelom
3. Adult Characteristics of Acorn Worms
3 partite coelom like echinoderms
Proboscis for digging (protocoel)
Collar with mouth (mesocoel)
Stomochord first considered a
notochord
Main body is the trunk (metacoel)
Up to 100 pair of pharyngeal slits
N.S. An epidermal net…. Like the
echinoderm nervous system but..
in some a dorsal hollow nerve cord
4. Ch Hemi Echino C H E
Conflicting views of Deuterostome phylogeny
Pharynx
DNC
larvae
Axial
complex
From Bromham and Degnan, 1999
Traditional Hemi + echino
Proto”D” Proto”D”
5. C E H
Conflicting views of Deuterostome phylogeny
From Bromham and Degnan, 1999
Proto”D”
Hemichordate
Echinoderms
Fossil
Stylophoran
(Calcichordate)
6. C H E C H E
Conflicting views of Deuterostome phylogeny
C E H
Pharynx
DNC
larvae
Axial
complex
Fossil
stylophoran
From Bromham and Degnan, 1999
Traditional Hemi + echino Calcichordate
-- Mitochondrial and 18s r-RNA sequence analysis strongly supports the
Hemichordate-echinoderm (lineage Ambulacraria) relationship to the
exclusion of the chordate clade.
Proto”D” Proto”D” Proto”D”
7. C H E
Conflicting views of Deuterostome phylogeny
larvae
Axial
complex
From Bromham and Degnan, 1999
Hemi + echino (Ambulacraria)
-- Hemichordates, Fossil
Stylophorans, and
Chordates all have
pharyngeal slits and a
dorasal nerve chord, but
Echinoderms do not, yet
Hemichordates are the
sister group of Echinoderms
and not of Chordates, and
Stylophorans are more
related to echinoderms
then they are to chordates.
Proto”D”
How is this possible??
