Polisus

Captain Serge Stone's Log, Research Starjumper "Cognition-5"; Expedition to Planet Kepler-213d (Zaraphon); Entry No. 29501117:

"So... I would like to inform the crew about an incident that I hope will serve as a lesson to everyone eager to swim in the ocean without a suit, without waiting for the results of a biological examination. To begin with, let me remind you that the marine life pen was created for the purpose of cultivating certain marine organisms in close proximity to the camp. It is a section of the bay shore enclosed by a barrier. Water is pumped into the pen from the ocean and is also used to cool the reactor, as this does not harm the animals living in it. Svyatoslav is breeding some species of sponges and algae there, as well as small benthic saprotrophs—known as 'whistlers.' These crab-like creatures are excellent bait for oceanic research and are not picky eaters—they consume any kind of waste. In short, they are good experimental specimens from the local biota.

During the hurricane, the barrier was breached by waves, and the pen was connected to the ocean. Along with the cold water, some uninvited guests entered Svyatoslav's 'paradise': a few silver Swimmers and a medium-sized Waterwing—a fast marine predator. The guests caused some damage, but we managed to drive them back into the ocean and reseal the breach with a net. However, this is not the main issue.

A few weeks later, Svyatoslav noticed strange behavior among the whistlers—instead of hiding under rocks, they began to crawl onto the shore of the pond. Moreover, these individuals developed strange bright orange branches at the rear of their bodies, which had never been observed in these inconspicuous creatures before. An autopsy of the strange whistlers revealed the culprit behind the odd changes. Meet the Parasitic Hairworm (Pilosus parasiticus)—a multicellular parasite whose intermediate host is the whistler. I will describe its life cycle in a way that even the most impatient members of the crew will remember for a long time.

The hairworm's eggs settle on the seabed along with organic debris, and they can easily be ingested with seawater. That's exactly what the whistlers do. A larva hatches from the egg, attaches itself to the host's intestinal wall, and begins sucking blood. Over the course of a week, the larva rapidly grows until it turns into an adult about 2 inches long. It becomes difficult for it to get enough oxygen from the host's blood alone, so it extends its branched filaments outside to breathe on its own. And it extends them—yes, you guessed it—through the host's anus. These filaments, as mentioned earlier, are brightly colored. Additionally, the parasite starts injecting a toxin into the host's blood, causing partial blindness. As a result, infected whistlers begin seeking higher ground, such as rocks or reef tops, where they are more exposed to sunlight. There, in plain sight and with a bright orange 'flag' behind them, they usually become easy prey for predators like Waterwings. In their intestines, the adult hairworms, several of which gather there, mate and lay eggs, which are then scattered throughout the ocean along with the host's feces. This is likely how they ended up in our pen, subsequently infecting approximately 40% of the last batch of whistlers.

In conclusion, I would like to remind the members of the research team that we are not at a resort but on a little-explored planet populated by unknown creatures, including parasites. Any contact with the external environment outside the camp is only possible in a bio-protective suit. To be fair, the Hairworm cannot parasitize a human body—our blood biochemistry and stomach acidity are unsuitable for them. However, this does not mean that there isn't another parasitic creature in the ocean with more fitting appetites. As your captain, I bear full responsibility for your health, and I would not want to discover that one of my colleagues is starting to go blind, and, pardon me, has a red bush growing out of their behind! Thank you for your attention."