08 December 2011

Tiny Ctenophores!

I stumbled upon information about these odd long 'strings' that I've been seeing on our leathery soft corals. It turns out they are tentacles produced by almost invisible ctenophores (pronounced 'ten-nah-fours' sound clip). This lump that closely resembles the soft coral which I accidentally photographed is possibly the ctenaphore.
Ctenophore on Leathery soft coral (Family Alcyoniidae)
Thanks to Hannah Shult and Nicholas Yap, I learnt that they are NOT cnidarians. Nick put together some awesome information about these beasts and kindly allowed me to reproduce it here. Thank you Nick!

I am now seriously struggling with reading up to write the new guidebook. That is how I came across a photo of similar 'strings' in the awesome book by Katharina Fabricius and Philip Alderslade,. Soft Corals and Sea Fans. It was a photo of a colony of Sacrophyton sp. leathery coral 'inhabited by translucent-yellowish sedentary ctenaphore (Coeloplana sp.) which use their extended tentacles for filter feeding'. A rudimentary search resulted in Bill Rudman's awesome page on ctenophores which has more info, photos and links to other shared sightings of them, some with similar 'strings'.

So it was really helpful to get lots more fascinating insights from Nicholas Yap, whom I look to for info on jellies, blobs and other curious critters. Here's what he shared...
On Phylum Ctenophora (sound clip of pronunciation -- different from Ctenophore!)

Commonly referred to as ‘comb jellies’. The name ‘Ctenophore’ means ‘comb-bearers’ (from the Greek root words of ‘ctene’ = comb and ‘phora’ = bearers). Usually these ‘combs’ are quite prominent on typical members of this phylum. These ‘combs’ are 8 distinct vertical rows of cilia that aid the Ctenophore to swim/move via beating (refer to that video of mine on the comb jellies: http://www.youtube.com/watch?v=RxfZd8eBPg4 , you can see the beating or rather, flapping in action).



While superficially resembling cnidarian jellyfish, Ctenophores are not Cnidarians. To digress a little… (apologies!)

Cnidarians are able to produce characteristic miniature capsules within specialized cells. These capsules are known as ‘cnidae’. The specialized cells that produce them are known as ‘cnidocytes’ or some books might call it ‘cnidoblast’.

The most well known group of cnidae (there are several groups of cnidae), are the nematocysts. The exact function of many nematocysts (there are also many types of nematocysts) isn’t clear – but it is inferred to aid in the role of defense and prey-capture. Nematocysts are what give Cnidarians its stinging ability. Unfortunately, nematocysts are often erroneously confused as ‘stinging cells’. Nematocysts are not ‘stinging cells’ and to re-iterate, they are capsules produced by the cells.

Saying all that, the difference between Ctenophore and Cnidarians, despite the former’s superficial resemblance, is that comb jellies cannot produce cnidae on its own (at this point in time… but who knows one day a hardcore zoologist might discover otherwise!) It can harbour cnidae to aid in its defense – and the way it obtains the cnidae is to eat a jellyfish prey.

Another difference between Ctenophores and Cnidarians is that most comb jellies have a characteristic bunch of cells that stud its tentacles. These cells have a sticky surface and are known as ‘collocytes’ or ‘colloblasts’. Think of those extendable stick pad toys that toyshops sold in the past. These adhesive cells aid in prey capture by sticking to its doomed victim.

On Coeloplana sp:

The genus Coeloplana was first described by a Russian naturalist in the 1880s based on a specimen collected from the Red Sea. The name Coeloplana is derived from two words: ‘Coelenterate’ (the old phylum category for Cnidarians… including sponges and Ctenophores) and ‘Planarian’ (of Phylum Platyhelminthes aka the flatworms!) due to its superficial resemblances to both animals!

Invertebrate zoologists classify Coeloplana in an order of comb jellies known as Platyctenida. Members of this group are characteristically dorsal ventrally flattened (unlike typical members of Ctenophora which are usually spherical looking), and with TWO fringe tentacles. Apart from the genus Coeloplana, the following genus also belong to Order Platyctenida: Vallicula, Ctenoplana, Tjalfiella, Gastrodes and Lyrocteis.

The funny bit about Coeloplana sp. is that it does NOT have the ‘combs’ that is the distinctive feature of Ctenophora, despite being classified as one! (The combs did give the phylum its name, as mentioned earlier). However, Coeloplana do have those sticky collocytes that most Ctenophores are also known for… so it is classified as such.

Coeloplana are ectosymbionts– they have been reported to thrive on a variety of marine flora and fauna surfaces, from seaweed, soft corals to echinoderms. In Singapore, Eeckhaut et al. 1997 reported that Coeloplana bannworthi is a symbiont of the long spined black sea-urchin (Diadema setosum). Coeloplana are bethnic beasties, seldom does one find it floating in the water column. It has also been reported with the ability to imitate the colors of its surrounding habitat. While Coeloplana do resemble flatworms, its two fringing tentacles is a dead-giveaway that it isn’t.

References:

Devanesen DW, Varadarajan SS (1939) On Coeloplana sp. discovered by Prof. W. M. Tattersall at Krisadai Island, Marine Biological Station, Gulf of Manaar. Indian Academy of Sciences 4: 157-159

Eeckhaut I, Flammang P, Lo Bue C, Jangoux M (1997) Functional morphology of the tentacles and tentilla of Coeloplana bannworthi (Ctenophora, Platyctenida),
an ectosymbiont of Diadema setosum (Echinodermata, Echinoida). Zoomorphology 117:165-174

Pearse C, Pearse J, Buchsbaum M, Buchsbaum R (1987) Living Invertebrates. The Boxwood Press, California

Thank you Nick for this invaluable information! I'm now highly motivated to look for these elusive creatures on our marine life and take better photos of them!

No comments:

Post a Comment

LinkWithin

Related Posts with Thumbnails