Today you will learn everything about the Comb Jellies. Many people think is a lie, since they are a true beauty when they are in the sea, due to the colors that they usually reflect. More than one person gets stunned with these creatures, but few know exactly everything about them.
Table Of Content
The Comb Jellies’ Main Characteristics
The comb jellies belong to the phylum Ctenophora which is allied to the cnidarians, and they are similar to them in many ways.
They are characterized by having a primitive structure and being large predators. They are abundant at the Antarctic´s surface waters and are found from the surface up to 3,000 meters or more in depth. (We invite you to learn our article jellyfish to learn about cnidarians
They are radially symmetrical and their body is constituted mainly of water. Comb jellies capture their prey using their tentacles as cnidarians do, but there are also many differences between both species.
Comb jellies are approximately 1.5 cm long and egg-shaped, with one mouth on one end and anal pores on the other one ( aboral end). They have two long tentacles up to 15 cm long which can extend and retract towards the pods (wraps) near the aboral end.
Along their body run eight ciliated bands (rows of combs) which are their main mean of locomotion as well as the main reason for their names.
Instead of nematocysts, comb jellies have ctenophores (colloblasts), which are quite complex structures that produce glue which adheres to the animals that they capture as food.
This is a fishing method similar to that used by cnidarians, but obviously evolved independently. However, there are some types of ctenophores that use nematocysts instead of colloblasts, which proves the theory of the cnidarian origin of the ctenophores.
The digestive tract of these individuals is constituted by a complex network of meridional channels that cross the periphery towards the inner portion of their central digestive channel. Digested foods can be excreted through the mouth or anal pores.
Pleurobrachia and other comb jellies have a statocyst, an organ of balance visible at the aboral end. This organ contains a solid structure called statolith found in a well surrounded by four patches of balancing cilia.
When the animal is tilted, the statolith comes in contact with one of the patches, and a neuronal signal is sent to tilt it back to its «vertical» position by the differential beating of the rows of the comb. The comb jelly also has additional control of its position, for example, turning its mouth towards a tentacle with a captured prey.
Unlike the cnidarians, ctenophores are hermaphrodites, with both sexes in the same individual. The gonads are separated, a set of testicles and ovaries in each. Eggs and sperm are thrown out through the mouth. The larva that develops from fertilized eggs looks a lot like a small version of the adult in this species.
One of the special features of some comb jellies is the rainbow effect of their rows of combs when viewed in bright light. The movement of the cilia scatters light in such a way as to cause this effect; It is not bioluminescence.
Apart from a few crawling and parasitic species,ctenophores float freely suspended in the water. They are often swept into vast swarms, especially in bays, lagoons and other coastal waters. Except for a parasitic species, they are all carnivorous and eat thousands of small planktonic animals.
When abundant in a region, ctenophores consume most of the young fish, larval crabs, clams and oysters, as well as copepods and other planktonic animals that would otherwise serve as commercial fish feed such as sardines and herring. In turn, comb jellies are consumed by certain fish.
Their nervous system is of diffuse type, with the presence of a sensory organ of aboral position (statocyst). The sensory organ contains four elongated plumes of cilia that hold a small statolith, inside a bell-shaped cover. It governs the orientation regarding the gravity and the coordination of the movements of the pectinate sheets. Underneath each pectinate plate there is a nervous cord.
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Classification.
Ctenophoros and cnidarians were placed together on the Coelenterata phylum. However, modern authorities have separated cnidarians and ctenophores based on the following characteristics of ctenophores:
(1) The lack of stinging cells (nematocysts) that is characteristic of cnidarians
(2) The existence of a defined mesoderm in the ctenophores
(3) Fundamental differences in embryological development between the two groups
(4) The biradial symmetry of the ctenophores. However, it is generally thought that the ctenophores and cnidarians share a common evolutionary ancestor.
Main Types of Comb Jellies
Cydippida:
This is a group of tentacled ctenophores that are characterized by having spherical or oval bodies, and by the fact that their tentacles are branched and can retract in pouches on both sides of the pharynx.
Their shape is rounded, being able to be almost spherical, cylindrical or egg-shaped.
From the body’s opposite sides extend a pair of long, thin tentacles, which are typically bordered with little ramifications, although some genera have simple tentacles without these lateral branches.
Tentacles are densely covered with microscopic colloblast with which they capture the prey when sticking to them.
Lobates
They are defined by two flattened lobes that extend from the typical ctenophore body rounded down below the mouth. They also have short tentacles and tend to grow more than Cydippida:
Beroids
They are sac-shaped and have no tentacles at all, but have a very large mouth, which can be closed tightly.
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