ECOLOGY

Environment temperate coasts
Organization solitary, pair
Treasure none

A terrifying mix of prehistoric arthropod and heavily armored mantis, the tetrolimulus is the stuff of nightmares for shipwrecked and abandoned mariners. Plated with a spiny crustacean exoskeleton, the upper body of the tetrolimulus is reminiscent of a very robust kind of mantis.

Its raptorial forelimbs, folded as if in prayer, flash forward with frightening speed and precision to brutally slice opponents before they have had a chance to act. Captains and mutineers alike are quick to remind their enemies of these deadly claws and the creature's other name, the “beach guillotine,” for the brutal justice it exacts on those put ashore for choosing the wrong side in a mutiny.

With somewhat less panache, the tetrolimulus is often described as the “sea-mantis” because it resembles a crab's strong legs and shell merged with a mantis' powerful arms.

Trailing behind is a scorpion's deadly stinger. The creature's durable, spiked shell covers five pairs of blade-like legs that work together to produce remarkable speeds even through challenging terrain. Truly a master of the beaches, the tetrolimulus has caught many mariners off guard with a blazing charge over varied terrain, perforating a noiseless trail through wet sand, then clattering over rocks with the sound of dice thrown across a table.

Its final and most dangerous terror, held upright and waved like a regal scepter in combat, is the tetrolimulus's tail stinger. The stinger is razor sharp along its outer edge, but its neat incisions are nowhere near as dangerous as the poison that coats its blade. Those who succumb to a dose of poison—called tetrodotoxin—are soon to be a meal for the sea-mantis. Muscle spasms and cramps accompany a gradual slowing of movement, hinting at oncoming paralysis and the agony of a neat butchering while still alive for easy consumption.

Ecology

Out of the water, the tetrolimulus adopts an unusual swaying movement of the upper body. Although its purpose is not entirely clear, it is thought that, much like the land-dwelling mantis, the movement enhances the creature's primitive vision and makes picking out prey by its own relative movement easier. It has been suggested that remaining completely still when confronted by a tetrolimulus may prevent detection, but none have been able to confirm the success of this tactic, and there are none who are confident enough of the theory to test it in the field.

Female tetrolimuluses, the hunters of the species, are by far the more aggressive. Rarely seen, males live in deeper waters as bottom feeders, emerging only in the mating season in early spring. At this time for a few days each year, both sexes make great journeys, sometimes of hundreds of miles, to return to ancient coastal breeding grounds. Here dominant and aggressive females meet and mate with the strongest of the smaller and more delicate males. Only a small number of these males get a chance to breed, and an even smaller number survive to return to the oceans. The energy and effort of their travels exhaust the females, and once they've been impregnated, the easiest and closest source of food is the weaker males surrounding them. A fertilized female may even continue to exhibit signs of availability to encourage more males to approach her— not for reproduction, but to satisfy her more immediate hunger.

Young are born at sea, and perhaps as payment for their strength and power later in life, they spend their first few months at the bottom of the food chain. Without the thick shells of maturity, they are easy prey, which contributes a great deal to population control of their species. As their shells thicken and harden, they start to enjoy a less harried existence, and by 6 months old they start to fight back. They reach maturity in 12 to 18 months and can live for up to 50 years.

Tetrolimuluses' behavior is largely instinct-driven, but during the breeding season the normally nomadic creatures will fight viciously to protect the shores of their ancestral breeding grounds. Even male sea-mantises rise to combat, though at sea they more commonly flee than risk confrontation.

Much of tetrolimuluses' bulk is armor, and despite their size they can survive on relatively small quantities of food.

In perhaps the only mark of intelligence in their species, they try to avoid overfishing, instead roaming over several miles of coastline to balance their ecology. The majority of their diet is fish and cephalopods, but they are competent trackers and follow hints of habitation on their beaches to devour any coast-dwelling mammals foolish enough to find themselves on the beaches, including humanoids.

Tetrodotoxin

While none are stupid enough to actively farm sea-mantises, occasionally the corpse of one is washed up into the more accessible bays on the coasts. Some of the more enterprising residents have developed a method of harvesting the cruel tetrodotoxin poison, from which the tetrolimulus gets its name. A single dose of tetrodotoxin sells for 1,300 gp. Its rarity and potency make it a valuable product.

One dose of poison can be harvested from the corpse of a tetrolimulus, provided the lower half of the creature is intact. This requires a DC 25 Survival check, and even those who usually find themselves competent at skinning or gutting creatures struggle with the intricacies of the sharp tail stinger. In harvesting the tetrodotoxin poison, those without the poison use ability are subject to the standard 5% chance of self-poisoning.