Today we are talking about Ctenophora, commonly known as comb jellies, marine animals that for many years were considered jellyfishes due to its apparent similarity. Here, we will give what features can we use to distinguish them from cnidarians and, in addition, we will present examples of the Mediterranean. 

INTRODUCTION

Ctenophora is a group of about 100 species of marine bioluminescent invertebrates that lives in all oceans, mainly in warm waters. The word ctenophora comes from Greek and means literally “comb carriers” and the reason is that they have eight comb rows, which are used for locomotion. Ctenophora are commonly known as comb jellies. It has been confused with cnidarians (anemones, jellyfishes, corals…) for years due to both groups present bilateral symmetry and for other features.

This ctenophore (Mnemiopsis leidyi) is an invasive species in the Mediterranean (William Browne, University of Miami).

There are some features to distinguish Ctenophora from cnidarians:

1. They don’t have nematocysts, poisonous cells that are shot when something touch them. The species Haeckelia rubra is an exception because it takes these cells from cnidarians that feeds on.
2. They have adhesive cells (colloblasts), which are used to catch preys.
3. Generally they have pharynx.
4. They never make up colonies; it means that every individual live independently.
5. They have anal openings.
6. They have 8 comb rows.

ANATOMY

Ctenophora are hermaphroditic animals with a gelatinous consistency that can measure from 5 cm to 2 meters length. The feature that best defines them is the presence of eight equidistant comb rows in their surface, which are distributed from the aboral pole (the place of the anal openings) to the oral pole (the place where the mouth is). Each row is constituted by transversal sheets of joined ciliums. Their beat is produced simultaneously and allow their movement, taking place from the aboral to oral pole, what causes a movement with the mouth ahead. They can achieve a speed of 5 cm for second, it is about 2 km/h.

In the case of having tentacles (Tentaculata class), these are long, massive and very extensive (till 15 cm). These can be kept inside a tentacular sheaths. In the surface, they have colloblasts or adhesive cells, which produce a sticky substance that let them capture and retain small animals. In the case of not having tentacles, they present lobules, an expansions each side that help them to capture their preys.

Ctenophore Dryodora glandiformis (Alexander Semenov): (1) comb rows y (2) tentacles.

HABITAT AND ECOLOGY

Ctenophora are swimming animals, except some sessile species. They usually live in surface waters, but some species cn live at 3000 meters depth. They constitute gelatinous plankton. They are predators and carnivore. It means that they feed on larvae fishes, small fishes, crustaceans, cnidarians and other ctenophora.

EXAMPLES FROM THE MEDITERRANEAN

In the Mediterranean sea, we can find different species of ctenophora.

Ctenophora Beroe ovata (Foto: Lyubomir Klissurov). This animal has a mitt-like shape with a milky colour, pink or reddish.

Ctenophora Mnemiopsis leidyi (Foto: Lyubomir Klissurov). This animal has a oval transparent body. Its rows produce blue-green colour when is disturbed (bioluminescence). In addition, it has iridisence (the property of certain surfaces that appear to change colour as the angle of view or the angle of illumination changes). It have several feeding lobes. It lives in the sea surface, in opened seas. It's an invasive species in the Mediterranean.

Ctenophora Pleurobranchia pileus (Foto: Lyubomir Klissurov). It has a pear-like shape, with long tentacles and its body is generally transparent, with some milky parts.

Ctenophora Callianira bialata (Foto: Jordi Regàs). Animal with clear pink lobes. In the lower part, adults have two horns, with a similar length of the body. They have two tentacles. This animal lives in the Mediterranean and North Atlantic.

Ctenophora Cestum veneris (Foto: Rokus Groeneveld). This cenophore has a belt-like shape of 1,5 meters lenght and 4 cm width. It's transparent. They live from sea surface to 200 meters depth.

REFERENCES

• Hickman, Roberts, Larson, Anson, Eisenhour (2006). Integrated principles of Zoology. Ed. McGraw Hill (15th edition).
• Notes of the subject Invertebrates of the Degree in Biology.
• Biology Diving Club: http://www.cibsub.cat/biofamilia-ctenofors-31948
• Marine Species Identification Portal: http://species-identification.org/species.php?species_group=zsao&id=2464

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