When discussing the topic of mucus, as one does on a daily basis, the species that by far produces the most amount of mucus has to be the Hagfish. The mucus produced by the Hagfish is more known as slime, produced in massive quantities when provoked.
These eel-like creatures can mass produce slime due to the fact that there are several mucus glands spaced evenly across their whole bodies (Downing et al 1981) and that the mucus is three times as diluted as typical mucus (Fudge et al 2005). Additionally, it is a two part compositional mucus of coiled slime threads (‘skeins’) and mucin vesicles that are thought to erupt in contact with seawater (Fudge et al 2005). Whether or not there is the potential harm of vesicles erupting in the Hagfish tissue before release is unknown.
There is also little knowledge of how these two components interacted with each other, where initially it was thought that the skeins were predominately the basis of the slime, in striated alignment held together by the mucin to produce a sheathing arrangement (Fudge et al 2005). However, in 2005 Fudge et al produced a study that concluded the slime is most likely is a “discontinuous fibre-reinforced composite”, illustrated to them by the fact that the skeins were tapered at both ends, and produces a very fine sieve like structure.
In addition to answering parts of the question of how these components work together, they unintentionally answered mine, of why this adaptation came to, hypothesized to be to constrain gill breathing for potential predators when threatened or attacked, as illustrated by this video.
How it evolved is a little trickier to answer. Compared to typical mucus it is, as mentioned before, highly evolved slime. To be able to answer this question there needs to be further research into the historic progression of how the Hagfish evolved this very specific adaptation, and increase knowledge regarding the components of the slime. At the moment most research is increasing understanding of the proteins within the mucus, which has been thought to be a source to produce fabric, while not so much on the evolutionary aspect of it.
Next week we will have a look on altruism as a form of defense mechanism.