Last week I gave you this Blaschka glass model of a marine invertebrate to have a go at identifying:
It was a bit of a mean one, since it’s from a very poorly known group of animals – and I mean that in more than one way. The taxonomic group is poorly known and the model represents a group of animals, not just a single individual.
So while this looks a bit like a jellyfish, it’s actually a siphonophore, which is a type of colonial organism that has discrete cloned zooids which fulfil specialised functions, similar to organs that cooperative to create a metaorganism.
Generally in siphonophores, these zooids are arranged on a stem in an organised pattern, with either two or three main zones of specialised zooids, depending on the taxonomic Suborder.
The zooid zone common to all siphonophores is the siphosome made up of feeding zooids with stinging cells, reproductive zooids and sometimes zooids with defensive functions. The two other zooid zones are the nectosome, which is comprised of zooids that act like tiny jet engines for swimming and the pneumatophore, which is a gas-filled zooid at the top of the stalk that acts as a float:
The presence or absence of particular zones is indicative of the particular Suborder of siphonophore, where the Physonectae have all three zones, the Cystonectae lack the swimming zooid zone and the Calycophorae lack the float.
I’m telling you all of this because it helps in narrowing down the mystery object. As you can see, there is no single zooid at the top acting as a float, so it must be one of the Calycophorae.
Within the Calycophorae most families only have one or two swimming bells and although the nectosome in the mystery object is not quite up to the Blaschka’s usual level of detail, it clearly contains more than two zooids, which is a feature of the Hippopodiidae.
The Hippopodiidae only contains two genera, Vogtia and Hippopodius and the two can be distinguished by the shape of the nectophores – in Vogtia they’re pentagonal whereas in Hippopodius they’re a more simple crescent shape – as we see here.
Back when the Blaschkas were making their models, there were a few species included in the genus Hippopodius, but they only made one that’s mentioned in their catalogues:
“209. Hippopodius gleba, Leuckart (Hippopoda lutea, Qu. & G.)”.
These days all the various species have been synonymised to just one – Hippopodius hippopus (Forsskål, 1776).
So well done to everyone who recognised that this was a siphonophore, even better if you spotted it was one of the Calycophorae and bravo if you got the genus (and therefore species).
Next week I plan to have a change from Blaschkas, much to everyone’s relief I’m sure 😉
You need a degree to understand these weird things. If a zooid segment isn’t happy can it detach and join up with a different hippopus?
The zooids develop independently and then all join up when they’re grown? You would think hippopus would all look different when they’d formed a colony.
Definitely a better argument for intelligent design than the eye, etc.
Quite an education! Thanks.