Podcast
Questions and Answers
Which of the following genera of lung fishes is known as the 'Nile lungfish'?
Which of the following genera of lung fishes is known as the 'Nile lungfish'?
Dipnoi primarily respire through gills and can also use lungs for respiration.
Dipnoi primarily respire through gills and can also use lungs for respiration.
True
Which of the following structures are present on either side of lung-fishes?
Which of the following structures are present on either side of lung-fishes?
What is the primary function of the internal nares in Dipnoi?
What is the primary function of the internal nares in Dipnoi?
Signup and view all the answers
The lung-fishes primarily rely on gills for respiration.
The lung-fishes primarily rely on gills for respiration.
Signup and view all the answers
The Dipnoi have a specialized heart that is nearly _____-chambered.
The Dipnoi have a specialized heart that is nearly _____-chambered.
Signup and view all the answers
What feature allows lung-fishes to perform aerial respiration?
What feature allows lung-fishes to perform aerial respiration?
Signup and view all the answers
Match the following features with their corresponding descriptions:
Match the following features with their corresponding descriptions:
Signup and view all the answers
The __________ is a single massive gland that is slightly divided into two unequal lobes in lung-fishes.
The __________ is a single massive gland that is slightly divided into two unequal lobes in lung-fishes.
Signup and view all the answers
What type of tooth structure do the lung-fishes possess for crushing molluscan shells?
What type of tooth structure do the lung-fishes possess for crushing molluscan shells?
Signup and view all the answers
Which of the following is NOT a characteristic of Dipnoi?
Which of the following is NOT a characteristic of Dipnoi?
Signup and view all the answers
Neoceratodus is the only living genus of the Ceratodontidae family.
Neoceratodus is the only living genus of the Ceratodontidae family.
Signup and view all the answers
Match the following lung-fish features with their descriptions:
Match the following lung-fish features with their descriptions:
Signup and view all the answers
Name one of the rivers where Neoceratodus can be found.
Name one of the rivers where Neoceratodus can be found.
Signup and view all the answers
The lungs of lung-fishes contain no muscle fibers.
The lungs of lung-fishes contain no muscle fibers.
Signup and view all the answers
What is the unique characteristic of the intestinal structure of lung-fishes?
What is the unique characteristic of the intestinal structure of lung-fishes?
Signup and view all the answers
Which of the following is not a part of the heart of lung-fishes?
Which of the following is not a part of the heart of lung-fishes?
Signup and view all the answers
The kidney type in Dipnoi is mesonephric.
The kidney type in Dipnoi is mesonephric.
Signup and view all the answers
What structure is present on the roof of the diencephalon in lung-fishes?
What structure is present on the roof of the diencephalon in lung-fishes?
Signup and view all the answers
The ________ are paired and elongated in female lung-fishes.
The ________ are paired and elongated in female lung-fishes.
Signup and view all the answers
Match the parts of the nervous system to their characteristics:
Match the parts of the nervous system to their characteristics:
Signup and view all the answers
What percentage of nitrogenous waste do lung-fishes normally excrete through their gills?
What percentage of nitrogenous waste do lung-fishes normally excrete through their gills?
Signup and view all the answers
In the reproductive system of Dipnoi, sexual dimorphism is present in all species.
In the reproductive system of Dipnoi, sexual dimorphism is present in all species.
Signup and view all the answers
Which part of the heart in lung-fishes is complicated by the presence of valves?
Which part of the heart in lung-fishes is complicated by the presence of valves?
Signup and view all the answers
Where are the oviducts located in lung-fishes?
Where are the oviducts located in lung-fishes?
Signup and view all the answers
The testes of lung-fishes are generally triangular in cross-section.
The testes of lung-fishes are generally triangular in cross-section.
Signup and view all the answers
What type of scales cover the body of dipnoi?
What type of scales cover the body of dipnoi?
Signup and view all the answers
Dipnoi are considered as a specialized or degenerate descendants of more primitive ______ fishes.
Dipnoi are considered as a specialized or degenerate descendants of more primitive ______ fishes.
Signup and view all the answers
Which feature is NOT associated with the affinities of Dipnoi with Elasmobranchi?
Which feature is NOT associated with the affinities of Dipnoi with Elasmobranchi?
Signup and view all the answers
Dipnoi have persistent notochords.
Dipnoi have persistent notochords.
Signup and view all the answers
Name one characteristic that distinguishes Holocephali from Dipnoi.
Name one characteristic that distinguishes Holocephali from Dipnoi.
Signup and view all the answers
Which feature is NOT an affinity with Crossopterygii?
Which feature is NOT an affinity with Crossopterygii?
Signup and view all the answers
Dipnoans are considered the most advanced Pisces from which amphibians could evolve.
Dipnoans are considered the most advanced Pisces from which amphibians could evolve.
Signup and view all the answers
What type of fins do dipnoans possess that reflect their affinity with Crossopterygii?
What type of fins do dipnoans possess that reflect their affinity with Crossopterygii?
Signup and view all the answers
Dipnoans have __________ nostrils, which is also an affinity with Amphibia.
Dipnoans have __________ nostrils, which is also an affinity with Amphibia.
Signup and view all the answers
Match the following features with their corresponding category:
Match the following features with their corresponding category:
Signup and view all the answers
Study Notes
Dipnoi (Lungfishes)
- Dipnoi are a small order of freshwater bony fishes.
- They are characterized by short jaws, crushing plate-like teeth, internal nares, reduced exo- and endo-skeleton, and a diphycercal tail.
- The air bladder, or "lungs," are one or two and are functional with related changes in the circulatory and heart systems.
Distribution of Dipnoi
- Modern lungfishes show discontinuous distribution.
- The three surviving genera of lungfishes are:
- Neoceratodus: The only living genus of the family Ceratodontidae, found only in the Burnett and Mary rivers of Queensland, Australia. Commonly called the "Burnett Salmon" or "Australian lungfish."
- Protopterus: Found in large lakes and rivers of tropical Africa. Commonly called the "Nile lungfish" or "African lungfish".
- Lepidosiren: Found in the Amazon and Paraguay basin of South America. Commonly called the "Amazon lungfish" or "South American lungfish".
Primitive Characters
- Unconstricted notochord
- Presence of a cloaca
- Spiral valves in the intestine
- Valves in the conus
- Diphycercal tail
- Ventral inferior nostril
- Persistent notochord without constriction
- Cartilaginous autostylic skull
Specialized Characters of Dipnoi
- Internal nares, possibly helping with breathing through the nose.
- Respiration by lungs (modified air bladder) in addition to gill respiration.
- Auricle partially divided into two and nearly a three-chambered heart.
- One paired auricle receives oxygenated blood through a special pulmonary arch from the lungs.
- Conus arteriosus spirally twisted and contractile.
- Separation of pulmonary and systemic circulation.
- Large paired cerebral hemispheres.
- Well-developed Mullerian duct.
- Characteristic tooth plates, used for crushing shelled invertebrates.
- Bones absent in the jaw.
External Structures of Dipnoi
- Elongated piscean body covered with overlapping cycloid scales.
- Dorsal, anal, and tail fins are continuous.
- Pectoral and pelvic fins are usually designated as the "limbs," extremely elongated, filamentous structures, devoid of fin rays.
- Tail is diphycercal in the living genera.
- Operculum and a slit-like branchial opening present on either side.
- External nostrils enclosed within the upper lip, and two internal nostrils open into the mouth cavity.
- Lateral line sensory system is well developed.
- Cloacal aperture lies at the root of the tail.
- Two abdominal pores usually open into the cloaca.
Digestive System of Dipnoi
- Teeth form characteristic tooth plates for crushing mollusc shells.
- The tooth plates are formed by the fusion of many small denticles.
- The alimentary canal is a simple tube, pharynx leads into an oesophagus.
- Lungfishes lack a distinct stomach.
- Intestine is ciliated and contains a spiral valve running the length of the intestine, making about six and a half turns.
- Liver is a single massive gland, slightly divided into two unequal lobes.
- Gallbladder is large and situated on the left margin of the liver.
- Pancreas remains embedded within the walls of the gut, islets of Langerhans are not seen in the pancreas of dipnoans.
- Spleen is composed of vascular tissue, attached to the right dorsolateral wall of the stomach.
- The alimentary canal exhibits little histological difference, the whole of the gut is lined by columnar, ciliated, and goblet cells.
Respiratory System of Dipnoi
- Dipnoans possess both gills and lungs, but mostly use the lungs.
- Nostrils help in aerial respiration.
- Swim bladder is modified into the "lung," similar to other tetrapods in structure and function.
- The walls of the lungs contain muscle fibers, and the internal cavity produces numerous alveoli, leading into minute alveolar sacs. In Protopterus and Lepidosiren, the supply of blood to the lungs is elaborate.
- Aquatic respiration takes place through the gills.
- Neoceratodus, the most aquatic of the dipnoans, and Protopterus and Lepidosiren obtain 98% of their oxygen from the air.
Circulatory System of Dipnoi
- Circulatory system is well-developed.
- The heart is enclosed in a stiff pericardium.
- The heart consists of three parts: the auricle, ventricle, and conus arteriosus.
- The auricle becomes dilated on either side of a thin and perforated interauricular septum, dividing the cavity of the auricle.
- The ventricle appears to be divided into two parts by the presence of a septum, but the ventricular cavity is single and lies anterior to the interauricular septum.
- The conus arteriosus becomes spirally twisted, and the cavity becomes complicated by the presence of valves.
Nervous System of Dipnoi
- The telencephalon becomes evaginated into a pair of well-marked cerebral hemispheres.
- Olfactory lobes are sessile and lie dorsal to the anterior ends of the cerebral hemispheres.
- The diencephalon is relatively small, its roof is formed of a large mass of choroid tissue, the saccus dorsalis.
- A pineal body is present on the saccus dorsalis, its stem extends back towards the posterior commissure.
- Hypothalamus bears small inferior lobes.
- Optic lobes are slightly developed and become fused to form a single oval mass in front of the cerebellum.
- A peculiarly lobed saccus endolymphaticus or endo-lymphatic sacs lies above the medulla oblongata. The cerebellum is small and forms a narrow transverse ridge.
- A sympathetic nervous system is associated with the vagus nerve.
Excretory System of Dipnoi
- The excretory system comprises a pair of elongated kidneys, separate anteriorly but usually fused at posterior ends.
- Kidneys are of mesonephric type and remain in intimate contact with the gonads.
- The kidneys extend throughout the greater part of the visceral cavity.
- Two thick-walled ducts, one from each kidney, may unite in Neoceratodus or remain separate in Protopterus and Lepidosiren, before opening into the cloaca.
- Lungfishes normally excrete 30-70% of nitrogenous waste products through the gills in the form of ammonia.
Reproductive System of Dipnoi
- Sexes are separate, sexual dimorphism is absent except for Lepidosiren, where males develop vascular papillae on the pelvic fins during breeding season.
-
Female Reproductive Organ
- Ovaries are paired and elongated.
- They are typically like other fishes and are kept in position in Protopterus by a mesovarium, but in Neoceratodus, they are attached to the dorsal body wall.
- The oviducts are located on the lateral side of the ovaries. Each oviduct (Mullerian duct) opens anteriorly into the body cavity by a fringed slit-like opening.
- Eggs are shed free into the body cavity and carried out by the oviducts.
-
Male Reproductive Organs
- Two elongated testes in lungfishes.
- In Lepidosiren and Protopterus, testes are narrow bodies and appear round in cross-section. But in Neoceratodus, testes are thick and triangular in cross-section.
- Testes are enclosed by fatty tissues and lie on the ventrolateral sides of the kidneys.
Affinities of Dipnoi
- Presence of lungs led to the view that Dipnoi are the ancestors of amphibians. This view is no longer supported.
- The current view is that they are a specialized or degenerate descendant of the more primitive lobe-finned fishes to which they resemble.
Affinities with fishes in general:
- Spindle-shaped, eel-like body.
- Body covered with scales (cycloid).
- Presence of paired fins.
- Diphycercal caudal fins.
- Persistent notochord.
- Skull with little ossification.
- Paired gill slits.
- Branchial respiration.
- Lateral line sense organs.
Affinities with Elasmobranchi:
- Endoskeleton mostly cartilaginous.
- Intestine with spiral valves.
- Conus arteriosus with valves.
- Each gill with two efferent arteries.
- Absence of nephrostome in uriniferous tubules.
- Small diencephalon with vascular roots.
- Similar female reproductive organs.
Affinities with Holocephali:
- Excurrent nostrils opening into the mouth cavity.
- Autostylic jaw suspensorium.
- Gills covered with operculum.
- No distinct stomach.
- Intestine with a spiral valve.
- Teeth fused to form dental plates.
- Identical kidneys, gonads, and gonoducts.
- Two efferent arteries in each gill.
Affinities with Actinopterygii:
- Blunt snout with a ventral nostril.
- Presence of cycloid scales.
- Strong palate and splenial teeth.
- Presence of operculum covering gills.
- Presence of a swim bladder.
Affinities with Crossopterygii:
- Diphycercal caudal fin.
- Powerful leg-like lobate fins.
- Identical skull bones.
- Vertebral column up to the tip of the caudal fin.
- Air bladder for pulmonary respiration.
- Internal nostrils.
- Presence of a contractile conus arteriosus.
Affinities with Amphibia:
- Semiaquatic habitat.
- Internal nostrils.
- Vomerine teeth.
- Autostylic jaw suspensorium.
- Multicellular cutaneous glands.
- Pulmonary respiration.
- Dermal scales as in Apoda (caecilians).
- Ventral aorta short or absent.
- Presence of anterior abdominal vein, posterior vena cava, pulmonary artery and veins.
- Thin-walled pericardium.
- Long and narrow cerebral hemispheres.
- Similar structure of eggs and development.
Dissimilarities with Amphibia:
- Paired lobate fins.
- Maxillae and premaxillae absent.
- Peculiar crushing tooth plates.
- Few anterior vertebrae fused with skull.
- Cartilaginous skull.
- Lungs lie dorsal to the gut.
- Urinary bladder from the dorsal wall of the cloaca.
Dipnoi Conclusion
- Dipnoi are not the most advanced Pisces from which amphibians could evolve. They are degenerate descendants of Crossopterygii.
- According to Jarvik (1968), Dipnoi are more specialized than crossopterygian.
- According to the latest view, both Dipnoi and amphibians originated from a similar crossopterygian-like ancestor.
- Therefore, Dipnoi are not the "fathers of the amphibia," but "uncles of the amphibian".
- Jarvik (1980) considers that the Dipnoi may be related to elasmobranchs than any other animal.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Explore the fascinating world of Dipnoi, or lungfishes, a unique order of freshwater bony fishes. Learn about their distinctive characteristics, distribution across continents, and various genera such as Neoceratodus, Protopterus, and Lepidosiren. This quiz provides insight into their primitive features and adaptations.
