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Homework Assignment I – Sponges and Jellies - Answers
1. What body type (asconoid, syconoid or leuconoid) does Spongilla have? What are the advantages of
this body type?
Spongilla has a leuconoid body type, which has the highest amount of internal folding, creating
flagellated chambers. The body type has the overall largest internal surface area and is competent to
carry out the most filtration.
2. Why are there spicules surrounding the gemmules of sponges? Be inclusive with the justification of
this answer.
Gemmules are overwintering bodies of fresh and shallow water sponges. As such, they contain
undifferentiated archaeocytes that, once the overwintering bodies burst open will give rise to new
sponges. Since overwintering bodies are formed prior to the cold times of the year, the spicules are a
means of protecting the internal archaeocytes from exposure to the elements. The mineralized nature of
the spicules also makes it difficult for predators to open the overwintering bodies and consume the
archaeocytes. In addition, the mineralized nature of the protective spicules prevents any bacterial
infection of the archaeocytes.
3. Why does Cassiopeia swim upside down? Bes specific and provide all information necessary to
discuss this phenomenon. Remember: Most jellyfish do not have a constant upside down swimming
motion.
The upside down or mangrove jellyfish Cassiopeia contains zooxanthellae in the oral arms.
Zooxanthellae (dinoflagellates) are photosynthetic organisms that require light in order to be able to
produce oxygen and simple sugars. Since Cassiopeia in part relies on nutrition and oxygenation
through the zooxanthellae they expose their oral arms to light by swimming with the arms pointing
towards the light so that the zooxanthellae have maximum exposure to light.
4. What is the lifecycle for members of the Octocorallia (Phylum Anthozoa) (draw, label and describe
in a few words) (2 pts)
Anthozoans lack a medusa stage entirle, therefor a polyp is either male or female. During reproductive
times the polyps will release their respective gametes (eggs or sperm). Fertilization is external and the
resulting larval stage is the planula. The mobile planula will eventually settle and grow into an adult
polyp that has eightfold symmetry.
5. Pleurobranchia display tentacles as part of their morphology. What is the function of these
tentacles?
The tentacles of Pleurobranchia are used to capture prey and stuff it into the mouth for digestion.
These tentacles are not generally means of locomotion, which is accomplished by the ctene rows and
their synchronized ciliary beats.
6. What are the morphological and developmental differences of members of the orders Cydippida,
Lobata and Beroida?
Morphological differences: Cydippida = oval to cylindrical with distinct tentacles used in capturing
prey, Lobata = large lobes growing out at or near the oral end, Beroida = oval to cylindrical but lacking
both tentacles and lobes to aid in feeding, instead beroid ctenophores open up their mouth giving the
organism a sac-like appearance in order to engulf their prey.
Developmental differences: Cydippida and Beroida do not show the presence of true cydippid larvae
and are therefore considered to be more primitive, Lobata display a typical cydippid larva.
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