Giant Siphonophore (Prayja species)

Here’s another fabulously unique jelly-like drifter for you. It’s a “Giant Siphonophore” which can be up to 50 metres long. That’s right – 50 metres – albeit the sightings near the surface are usually much smaller like these two I saw north of Port Hardy (around 2 to 3 meters).

They are not usually common off the coast of British Columbia but, like the recent sightings of many pyrosomes, their presence indicates that there must be warmer waters. They are regulars off the coast of central California.

Paired swimming bells and long stem of a Giant Siphonophore (aka Bell-Headed Tailed Jelly) ©2017 Jackie Hildering.

Siphonophore jellies are so remarkable. While they appear to be a single animal, they are a colony of individuals (“zooids”) with very specialized jobs. The paired bells aid the propulsion of the colony (pneumatophores).  The units of the long stem are known as “cormidia”. Can you discern the individual units in the image below? Each of these segments has parts for reproduction (gonozooids), cacthing prey and digestion (gastrozooids), and defence (dactylozooids)by having stinging cells (nematocysts). While this species does deliver a bit of a sting, it packs no where near the punch of the most well-known siphonophore – the Portuguese Man o’ War.

Tail segment of a Giant Siphonophore with dive buddy and his video light in the background. This one did not have the swimming bells. The bright yellow colour of the “zooids” in the stem is distinct in this species of siphonophore. ©2017 Jackie Hildering.

What had me quite confused when I first saw the species, is that Giant Siphonophores often do not have the swimming bells – just the stem of individuals. These apparently have a role in reproduction (and are known as eudoxids) but cannot regenerate the whole colony. (Added bonus to this blog – more words for the next time you play Scrabble!)

Another perspective on the paired swimming bells (pneumatophores). ©2017 Jackie Hildering.

In what little information I could find on this species, there was this fabulously, dramatic descriptor: “The giant gelatinous predator moves silently through cold, dark waters, propelled by a pair of expanding and contracting swimming bells. Its rope-like body is actually a colony of almost a thousand individual subsections, each performing a specific task. Some provide propulsion, others, reproductive functions; but most specialize in capturing and devouring prey. When hunting, these sections deploy thousands of slender, stinging tentacles to capture drifting krill, copepods, small fish, and other jellies. Almost anything blundering into this deadly net of tentacles soon finds itself stuffed into the nearest waiting mouth.” (Source: The Ecology Center).

And just in case this all is not fascinating enough, the species is also bioluminescent. It produces a bright blue light when disturbed, briefly illuminating our dark, mysterious, life-sustaining sea.

Sources:

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