Serina: Starlight Mothfish

One of the most common varieties of snark during the hothouse era is a subgroup of deepwater escardines known as the mothfish, named for their broad and expansive front fins. Although small, never measuring over a foot in body length, and having only a few dozen species, they exist in utterly vast shoals that can number in the hundreds of billions or even into the trillions. However, their sheer numbers are often unapparent due to the fact they spend most of their time in the twilight zone, far away from starlight, only rising at night en masse in one of the largest migrations of animal life in the world to feed on the swell of planktonic life that drifts to the surface. Unlike on Earth, there are no truly massive filter-feeders in this era of Serina's history, and in their place are animals such as these; plankton-eaters which are individually tiny, but exist in such massive populations that they, by biomass, make up a significant fraction of animal life on Serina and are a crucial link in the marine food web, being a staple prey item for a huge number of seagoing predators and filtering countless megatons of marine snow as it falls from the shallows, cycling the nutrients. Despite this, you might not even know such animals exist if you lived your entire life on land or in the shallows, since they are only found in waters far from the coasts, and their nocturnal emergences make them highly elusive.

Mothfish are unusual for being one group of escardines which have re-evolved fore-fin propulsion, while the tail fin has been relegated to being a primarily immobile rudder. Because they feed mostly on plankton, marine snow, and occasionally, small free-swimming animals, their rounded fins are used only for keeping them stably afloat and adrift, and are not built for speed; they primarily rely on their uncountable numbers for defence. The pelvic fin equivalents in the mothfishes have been modified into stalk-like communicative organs with bioluminescent tips to help coordinate their shoals. Because they live their existence in perpetual dimness, their eyesight has greatly atrophied, and is now incapable of distinguishing objects more complex than vague shapes, although it remains sensitive to light differences, allowing their glow to remain effective visual identifiers. This feature is in part from what they derive their names, for they are drawn to these lights like a moth to lamplight.

The starlight mothfish is an unusual species of mothfish because it spends its entire life near the surface rather than engaging in nightly vertical migrations from the depths. This is because it dwells in the eternal twilight of the floating forest, a vast interconnected flotilla of sargassum-like macroalgaes stretching for over a hundred-thousand square kilometres in the midst of the Unbroken Ocean, where the constant shadow of such densely-packed floating flora simulates the dimmer conditions of the mothfishes' usual daytime dwellings close enough that one species became adapted to the oceanic oasis, where food was plentiful in the midst of a region that otherwise required their shoals to travel far and wide to sustain their numbers. In particular, they have adapted to feed on the organic film of bacterial and protistic microorganisms which settles upon the fronds of the seaweed, as well as the tiny planktonic animals which feed upon it, grazing upon them with their eversible proboscis like a gigantic herd of tiny underwater cattle, while leaving the macroalgae itself unharmed. This helps promote the health of the floating forest, clearing out competing commensals and parasites, and is in turn a reliable food supply due to the fast growth rate at which it reappears. They can also feed normally on plankton, free-floating algae, and organic particles in the water column, and are surprisingly effective scavengers. A normally passive school can suddenly turn into a ravenous horde upon the scent of decaying flesh in the water, scrapping away tissue with rows of chitinous hooks normally used for filter-feeding or biofilm grazing.

When kept in balance, the mothfish are ultimately very beneficial to the seaweed, but in greater than normal population booms, they can briefly swell to plague-like numbers where they can subsume most of the available edible matter in the water which fuels the growth of the seaweed, becoming detrimental to the ecosystem's health. Like many pelagic escardines, mothfish breed continuously, giving live birth to smaller, but otherwise near-exact replicas of their parents, capable of swimming and feeding themselves from birth. In a single year, a female starlight mothfish can birth over a hundred young, which in turn are able to themselves reproduce within five to six months, contributing to their great numbers. Although reaching only four to five inches in body length, their total population normally ranges from several hundred million into the low billions, depending on seasonal conditions, making them by far the most common endemic of the floating forest, and this single species make up roughly one-third of the ecosystem's total animal biomass (although, by mothfish species standards, it's actually rather rare). They are one of the fundamental building blocks of the environment's food chain, and are a regular menu choice for most of the floating forest's aquatic hunters, which usually keeps them from ever becoming overly numerous.

When threatened, the starlight mothfish clumps together into dense, synchronized shoals, their pigmented skin shimmering and moving in a swirling mass in an attempt to make it more difficult for predators to pick out an individual out of groups often countless thousands strong. In the darkness, the mass twinkling of such mesmerizingly coordinated escardines drifting just beneath the shadow of the buoyant seaweed masses resembles a constantly shifting landscape of stars in the night sky. While feeding close to the seaweed, their speckled, dark-green skin renders them hard to differentiate from the mottled green fronds of algae that surrounds them; it is not uncommon for a larger swimming animal to brush against a seeming innocuous clump of seaweed, only for hundreds of the small marine molluscs to suddenly emerge from it, frantically flapping away instinctively from a possible threat. An extremely high rate of predation by many shallow-water carnivores that normally do not encounter mothfish often is the price the starlight mothfish pays for their existence in this oasis.

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To reiterate, this was a sponsored commission for a species of mothfish which lived in the floating forest (since mothfish as a groups have not been introduced yet, the introduction is included here).

(This lives 290 MYH)