This document discusses the reproduction and lifecycles of amphibians. It notes that while some salamanders lay eggs in water that hatch into swimming larvae, others reproduce on land with the eggs hatching into miniature adults. Some salamanders have become fully terrestrial with eggs developing fully into tiny adults inside the mother's body. Caecilians also show various reproductive strategies from laying eggs in water or land, to giving birth to larvae or miniature adults.
11. Tadpole
Long, finned tail
Both internal, external gills
No legs
Specialized mouthparts for herbivory
(salamander larvae are carnivorous)
Highly specialized internal anatomy
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25. Compared to the anurans, salamanders
are less able to remain on dry land,
although some can live in dry areas by
remaining inactive during the day.
Salamander lay their eggs in water and
like anurans they hatch into swimming
larva.
26. Other species can reproduce in damp land
environments.
Eggs laid on land hatch into miniature adult
salamanders
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30. The tailed amphibians show many
variations on this life history. The European
spotted salamander is viviparous (i.e., it gives
birth to active young).
Pairing takes place on land and the
egg s develop within the female. The tadpoles
are born when the female enters the water.
The black salamander has carried
the process a step further. The adults do not
return to the water at all.
31. The eggs develop, pass through the tadpole
stage, and change into tiny adults before leaving the
mother's body.
The free-living larval stage is thus
suppressed. A number of salamanders lay their eggs
in damp soil, under stones and similar objects.
The tadpole staged is passed within the eggs
and miniature adults emerge. The American worm
salamander is an example.
These last examples show how salamanders
have become completely terrestrial, but some species
have gone the other way and are exclusively aquatic.
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36. Earliest amphibians probably covered with
scales - still apparent in some cacaelians
Epidermal layers highly glandular
although glands actually located in dermis
Mucus secretions for reduction of water
loss.
venom glands - poisonous or toxic substances
Pheromonally stimulates female to clasp and
reproduce
Males usually lacking claws, some with cornified
extensions similar in appearance
37. All caecilians are believed to have internal
fertilization. This is achieved by means of the
phallodeum, a copulatory organ in males that is
modified from the cloacal wall.
Eggs of all members of the families Some are
deposited in burrows in mud that is close to water.
The females watch over these clutches, which may
hold up to 54 eggs.
Upon hatching, the larvae leave the burrows to
make their homes in ponds and streams.
Some caecilians deposit eggs on land, and in
different species these hatch as larvae or small adults.
38. Three families have viviparous species to
which usually no more than four young are born
at one time.
Some aquatic are viviparous and produce
larvae. The caecilian fetus emerges from the egg
membrane as soon as its meagre yolk supply is
exhausted.
It uses its deciduous teeth, adapted for
scraping, to obtain secretions and epithelial
tissues from the oviduct lining.
39.
40. Sexual reproduction starts with the
combination of a sperm and an egg in a
process called fertilization.
This can occur either inside (internal
fertilization) or outside ( external
fertilization) the body of the female.
Humans provide an example of the former
whereas seahorse reproduction is an
example of the latter.
41. External fertilization usually occurs in
aquatic environments where both eggs and
sperm are released into the water.
After the sperm reaches the egg,
fertilization takes place.
Most external fertilization happens during the
process of spawning where one or several
females release their eggs and the male(s)
release sperm in the same area, at the same
time.
42. The release of the reproductive material
may be triggered by water temperature or
the length of daylight.
Nearly all fish spawn, as do crustaceans
(such as crabs and shrimp), mollusks (such
as oysters), squid, and echinoderms (such
as sea urchins and sea cucumbers).
