So, all recovered from my exam, a week to go til the next one, and not so panicked about that, so back to regular posting!
Last time I said that the next post would be about an organism that has a lophophore but no shell, unlike the brachiopods. This will just be a short post, to illustrate the same structure in a different organism.
Today we are looking at the phylum Phoronida, also known as horseshoe worms. I think this phylum is particularly beautiful, and from an evolutionary viewpoint it is interesting to see how two organisms have developed slightly differently. As we saw with the Brachiopods, some of those are worm-like creatures which burrow vertically, but have developed a shell on part of their body for protection, and the shell also controls the flow of water over their lophophore, to help with gathering food. Phoronida have no shell, and so have developed a different way of protecting themselves from predators.
So, let me introduce you to some members of this beautiful phylum:
These beautiful pictures are only the top end of the animal, these are the tentacles of the lophophore that we saw curled up inside of the brachiopod last post
The full animal sits in a burrow, as these diagrams show:
Instead of secreting shells, Phoronida secrete tubes which they live inside. They can wiggle around freely within these tubes, which protect the edges of their burrows, and they stick their lophophore out of the burrow opening to collect food particles, which are passed down into the stomach, before passing along the intestine for excretion below the mouth (therefore reducing the risk of re-ingesting their excrement).
These also have hemoglobin (the stuff which carries oxygen around our blood, and this may be because some species live in environments with low oxygen content within the water, and hemoglobin is very efficient for transporting oxygen through blood. We will see this again in some extremophile worms we meet later
This post has been quite short, as there are very few species of Phoronida known, with around 12-15 known species, and there is a lot of research and work to still be done to fully understand these organisms and their place within the evolutionary tree. There are other organisms which have this same fringe like structure for feeding, but they are currently classified in other phyla, so I will cover them when we get to those phyla.
There were not a lot of videos I was able to find with Phoronida in, so I will leave you with one showing a stress response, which means how the animal responds when threatened, and how it returns to normal behaviour afterwards.