Echinoderms exhibit both direct and indirect development. Indirect development includes various larval stages that are bilaterally symmetrical and undergo metamorphosis into the radially symmetrical adult. The main larval forms are the Bipinnaria and Brachiolaria in starfish, Ophiopluteus in brittle stars, Echinopluteus in sea urchins, Auricularia in sea cucumbers, and Doliolaria and Pentacrinoid in feather stars. These larval forms are hypothesized to have evolved from a common ancestral larva such as the Dipleurula or Pentacula and share similarities with the tornaria larva of acorn worms, providing

1. Larval forms in Echinodermata
Presented by- Aanchal Manchanda
M Sc. Zoology

2. • Echinoderms are unisexual animals.
• Sexual dimorphism is absent.
• Fertilisation takes place in water.
• The development may be direct or indirect.
• If the development is indirect it includes larva
stages.
• In different classes of echinoderms, different
types of larvae complete the development.
• The larval form is bilaterally symmetrical. It
undergoes metamorphosis and radial
symmetrical adult is developed.

3. Class of Phylum
Echinodermata
Larval form
1. Asteriodea
2. Ophiuroidea
3. Echinoidea
4. Holothuroidea
5. Crinoidea
Bipinnaria & Brachiolaria
Ophiopluteus
Echinopluteus
Auricularia
Dololaria & Pentacrinoid

4. Dipleurula larva
• The dipleurula form is reached during development and is
characterized by its bilaterally symmetrical, egg-shaped body.
• The ventral concave side bears the mouth and is encircled by a
circumoral ciliated band.
• The anus is disposed ventrally.
• The digestive canal is differentiated into oesophagus, stomach and
intestine.
• The pre-oral lobe which is situated at the anterior to mouth, bears an
apical sensory plate and a tuft of cilia.
• The ciliation on the surface of the body becomes reduced to a ciliard
band.
• This Dipleurula form is regarded by many as the hypothetical ancestral
form of Echinoderm, as this form is universally present. The Dipleurula
concept was first propounded by Bather (1900). The major changes
involved in other Echinoderm larvae are due to differential disposition
of the ciliated bands.

5. Pentacula larva
• This larval stage is regarded as the next
evolutionary step of the Dipleurula larva. This
concept has been supported by Semon (1888),
Burry (1895), Hyman (1955) and many others.
• The Pentactula larva has five tentacles around
the mouth.
• The hydrocoel is separated from the rest of the
coelom to form the future water vascular
system.

7. Bipinnaria larva:
• It is the larva form seen in the life history of Star fish. The
fertilised egg is homolecithal. ft undergoes holoblastic cleavage
and develops into blastula and gastrula stages. The gastrula
elongates in length and it gives rise to Bipinnaria larva.
• It is a bilaterally symmetrical free swimming pelagic larva.
• The pre-oral region is elongated. Post-oral region is broad. The
anterior end forms pre-oral lobe.

8. • The ciliated band at the pre-oral lobe forms into 2 separate bands, Pre-
oral band of cilia, and post oral band of cilia. These 2 bands of cilia are
drawn into many arms. They are nothing to do with the arms of the star
fish. They are,
• Ventro-median arm.
• A pair of pre-oral arm.
• Median dorsal arm.
• A pair of antero-dorsai arm.
• A pair of posterio-dorsal arm.
• A pair of posterio-lateral arm.
• A pair of post oral arm.
• The digestive system is developed with mouth and anus. This larva
resembles Tomaria larva of Balanoglossus.
• This larva slowly grow s into the next larval form called Brachiolaria
larva.

9. Brachiolaria larva
• Bipinnaria larva swims for few weeks in the
sea water.lt finally transforms into next larval
stage called Brachiolaria larva.
• It is bilaterally symmetrical larva.
• It is pelagic larval form, it shows 3 brachiolar
arms with suckers. They are one median and
two lateral in position.
• At the tip of brachiolar arms adhesive
structures will make their appearance and
they are for attachment.

10. • The larva shows all the arms that are seen in the
Bipinnaria, but these arms are very long and
hanging. These ciliated arms will be helpful for
swimming in the water.
• The digestive system is completely developed
with definite stomach and intestine.
• This larva after swimming for few days settles on
a solid object and gets attached to it by its
adhesive arms. Posterior end of the larva
enlarges and lifts to the right-side. From this
rudiments of 5 arms will arise. Thus slowly the
larva metamorphosis into an adult.

12. Auricularia larva
• In Holothuroidea this larval form is seen.
• It is a free swimming pelagic larva.
• Arms are absent. Alimentary canal is developed.
It opens with mouth and ends with anus.
• Intestine is curved.
• In Japan and Bermuda very big auricularia larval
forms are developed. They are 15 mm in length.
Usually this larva is 1 mm in length.
• Ciliated bands are well-developed. Ciliated band
continues through oral loop and anal loop.

13. Pluteus larva
• This larval form (Fig. 21.39H, I) can be regarded as a modification of the auricularia larva of
Holothuroid.
• Like the auricularia larva it has a single ciliated band, but it possesses long arms with ciliated
bands at the margin.
• It has comparatively smaller pre-oral lobe.
• The post-anal part of the body is quite well-developed.
• The arms are also supported by calcareous rods.
• The pluteus larvae are of two kinds:
• (1) Ophiopluteus—in Ophiuroidea.
• (2) Echinopluteus—in Echinoidea.
• Both the larval forms possess the post-oral arms, antero-lateral arms, postero-lateral arms and
postero-dorsal arms.
• The typical ophiopluteus may be absent in certain forms.
• The larva may be elongated and without ciliated bands.
• The skeletal rods are usually absent; if present, only one in number.
• The presence of pluteus larva in both classes is an example of parallel evolution and the similarity
between the two larval forms e.g. ophiopluteus and echinopluteus, was once considered a closely
related group but phylogenetic analyses do not indicate this (Anderson, 1998).

14. Ophiopluteus larva
• This larva is seen in the life history of ophiuroidea(Brittle
star).
• It shows many long arms.
• It is bilaterally symmetrical.
• It is transparent.
• It is Pelagic.
• The arms are supported by calcareous rods.
• The arms are directed upwards.
• Pre-oral loop is reduced .
• Ciliated band is undivided.
• The postero-lateral arms are very long and they are
directed forwards.
• The digestive system is developed. It opens with mouth
and ends with anus. This larva swims for some time
before undergoing metamorphosis.

16. Echinopluteus larva
• It is seen in the life history of Echinoidea.
• It is a microscopic larva.
• It swims in water.
• This larva shows ciliated bands which are developed into arms.
• Fully developed echinopluteus larva 4 or 5 pairs of arms are
present. Usually 6 pairs of arms should be resulted.
• The arms are supported by (CaCO3) Calcareous rods.
• The digestive system is developed which shows mouth and anus.
• It develops hydrocoel and vestibule. These parts grow on the oral
side of the animal. From the hydrocoel five radial canals will
develop.
• This larva undergoes rapid metamorphosis and develops into an
adult.

17. Doliolaria larva
• In crinoidea group of animals the larval form is Doliolaria
larva.
• It is a free swimming larval form.
• It contains an apical tuft of cilia which will be sensory.
• On the mid ventral line near apical plate adhesive pit will be
present.
• The body shows 4 or 5 ciliated bands
• In between 3rd and 2nd ciliated bands vestibule is present.
• After swimming for some time it will develop a stalk. It is
called Pantacrinoid larva. It will attach to the substartum.
The internal organs will rotate at 90°. It develops into an
adult.

19. Antedon or yolk larva
• This particular larva is also called doliolaria larva or Vitellaria larva.
• This larval stage is present in Antedon and it has many structural
pecularities.
• It has a barrel-shaped body with slightly flattened ventral side.
• It is free-swimming and exhibits bilateral symmetry.
• The ciliated bands are in the form of four or five separate transversely
placed bands encircling the body.
• A tuft of cilia with stiff sensory hair springs from a thickened
ectodermal patch, called apical neural plate, which is comparable to
that of Tonaria larva of Balanoglossus.
• The anterior ciliated ring is ventrally incomplete.
• There is a ciliated depression or larval mouth which is ventrally placed
between the second and third ciliated rings.
• A small adhesive pit develops between the first and second ciliated
rings by which the larva adheres to the substratum.
• The internal structures become rotated at an angle of 90° from the
ventral to the posterior side.

20. Significance of these larval forms
• The larval forms of all classes in Echinodermata will
show general resemblance.
• The crinoidea larva differs from this pattern. In
general all the larvae show that they might have
come from same ancestor. Hence the common
ancestor is coelomate, bilaterally symmetrical and
free swimming.
• These larvae also show resemblance with Toronaria
of Balanoglossus.
• Thus the study of Echinoderm larva has a
phylogenetic significance.