aybe it is their duality: periodicity, recording them in equivalent a benign nature coupled numbers at high tides both day and night with a bizarre, almost throughout much of the prime spawning otherworldly appear- months of May and June. During what ance: a crusty Darth might be termed their mating arribadas, Vader helmet enclosing the females, some as much as a foot wide, an articulating chaos of are typically observed dragging along Slow M jointed, pincer-tipped legs one or more clinging males. that look dangerous, but Somewhat reminiscent of a nesting are not; hauling a spiny sword of a tail turtle, a female horseshoe crab (hsc) that looks like a dreadful weapon, but is intent on reproduction excavates a actually harmless. hand-deep depression in wet sand for What is it about the members of Slow Nation that so fascinates us? Nation Or maybe it is their mystery: When the her nest. The larger she is, the more planet seems filled with the fluid of light eggs she will deposit. A male fertilizes and salt, these markers of high tides and her eggs as she deposits them. Since it spring’s flowering seem to arrive magi- is an external fertilization, more than cally, sloshing sensually around in the one male may father her young. Biologist warming waters of our embayments as Alison Leschen [formerly with the Mas- if drunk on the newly-long days, bent on sachusetts Division of Marine Fisheries love when the full moon hangs, cham- (DMF) and now the Reserve Manager at pagne-colored, in the night sky. Waquoit Bay National Estuarine Research Or perhaps, if we have seen them on Reserve] and her colleagues have con- their backs on wave-washed beaches, ducted research on Limulus in Pleasant awkwardly struggling to right them- Bay, Cape Cod. She reports that females selves, we identify with an endearing “return to the breeding beach in waves,” klutzy aspect to their character and em- to deposit 1-15 golf-ball-sized clutches pathize with their travails. That they can of eggs per nest in a series of a dozen or right themselves at all is an evolutionary more individual nests. and gymnastic feat. During this reproductive marathon, The scientific name of these strange females may produce up to three mul- organisms, Limulus polyphemus, roughly tiple-clutch nests per tidal cycle over translates as “askew one-eyed giant” a period of two or three cycles. The or “sideways-looking Cyclops” and was final total amounts to a lot of eggs: “For probably derived from a mistaken belief example,” says Leschen, “a large female that the animals each had but a single could lay 8 clutches of 1200 eggs in each eye. (Polyphemus, son of Poseidon in of three different nests, return a second Greek mythology, was a giant Cyclops time on another tide and do the same, who enjoyed snacking on humans; he ate and lay a total of [from] 58,000 to 63,500 six of Odysseus’s men. His name is also eggs.” Other researchers have estimated given to one of our large moths with an annual egg production as high as 88,000 eyespot on each hindwing.) The members eggs per large female. of Slow Nation are, of course, horseshoe The eggs are soft and gelatinous when crabs, captivating creatures of manifold first deposited, but quickly harden to strangeness; aliens from a long lost, an- resemble BB-sized pepper corns. About cient Earth that still live among us. five days later, a proper tailless baby Resembling giants’ fingernails digging crab becomes discernable inside the egg. in the sand, horseshoe crabs congregate The tiny crabs hatch in 2-4 weeks and to mate at the high tides of late spring and emerge from the sand when liberated early summer in the ancestral swash wa- by a high tide. Equipped with spines ters and intertidal muck near the crest of to deter predators, they drift and slosh the water’s reach. While some authorities about as plankton in tidal waters for three have reported that peak breeding occurs weeks, then settle down on the intertidal by Lee Stephanie Roscoe during the new and full moon dates, es- substrate. pecially at night, others report no such Photo © Bill Byrne 24 25 No one knows for sure, but it is esti- sedimentary rocks in Manitoba, recogniz- Cryptic Median Eyes mated that only 10 or fewer of the eggs able horseshoe crabs have been around produced annually by a large female will for nearly half a billion years. They have safely hatch and survive their planktonic swum through epochs, navigated around and juvenile stages to reach adulthood. dividing continents, been pushed about Female horseshoes are ready to breed at by the rise and fall of mountain ranges, around nine or ten years of age, while the and have spawned on the shores of un- males (preferring older women) are ready named seas that came and went long, long at eight years or so. Both sexes can live ago. They have survived asteroid strikes until about 20. It is not the crabs them- and numerous worldwide extinctions, selves, but the elements of the “mobile seemingly pulling their ocean world ever ecosystem” that they carry around on onward to the present. The oldest known Prosoma their backs – including barnacles, lim- prototype is named Lunataspis aurora: Lateral Compound Eye The first pair of walking legs provides pets, sponges, slipper shells, and algae “crescent moon shield of the dawn.” Two an easy way to identify the sex of a -- that help scientists determine their age. fossils, both of 1.5-inch specimens, have After mating, the adult crabs return from been discovered so far, but it is not yet horseshoe crab. That of the male, left, the intertidal gathering areas to the sub- known if these are tiny, full gown adults, is modified to grasp a female during tidal zones where they will spend most or simply juveniles that would have grown spawning, while that of a female, of their lives on the bottom, bulldozing to larger size. right, ends in a conventional pincer through the benthic landscape in search The hsc body is divided into three ma- claw. Collapsible, spatulate tips on of food items such as marine worms, last pair of walking legs, below, aid jor sections: the prosoma, or carapace, Opisthosoma algae, and shellfish. which houses six pairs of walking/feed- the animals in moving over soft sand ing appendages and most of the internal and mud bottoms. Evolution & Anatomy organs; the opisthosoma, which is hinged There are only four species of horseshoe to the prosoma and houses the book Movable Spines gills; and the telson, or tail spine, which crabs worldwide, all of which diverged Telson from a common ancestor, Mesolimulus is situated in a hinged pocket at the base walchi, about 150 million years ago. Our of the opisthosoma and equipped with species, the American Horseshoe Crab, light-sensing organs. The chelicerae, out- Dorsal View is the only one that inhabits the Atlantic. fitted with pincers and used primarily to It ranges from Maine (where it is scarce) locate and grasp food, are the first and First Walking Leg (male) down to Florida, and from there all the way smallest pair of appendages near the around the Gulf of Mexico, to finally fade front of the shell (and are a feature shared with spiders and scorpions). They are out on the northern tip of the Yucatan. Chelicera followed by five pairs of walking legs. On Horseshoe crabs are in the family the male, the first pair of these terminate Photos © Bill Byrne Limulidae and the phylum Arthropoda, in mitt-like appendages with a single claw, for rhythmic propulsion while swimming but are placed in their own class, Meri- somewhat comparable in look to an old (especially by the juveniles). The first stomata. They are not crustaceans and fashioned can-opener. They are used to pair of gills is called the operculum. It have no relation to the true crabs (which, clasp the female while mating. serves as a protective cover for the other among other things, lack compound eyes five pairs, and also houses the opening of and bear their eyes on stalks). They are On the female, this first pair of legs is the same as the next three pairs on both the genital pores through which eggs or thought to be related to the long-extinct sperm are released from the body. trilobites, or perhaps the equally long- sexes, ending in pincers similar to those on the ancillary legs of a lobster, and The telson – which people often fear extinct sea scorpions (and may even be is a stinger – is a harmless rudder and progenitors, rather than descendants, of exhibiting the same lack of force when it comes to gripping humans. (Place a junior “righting organ.” A hinge in the body, that group), but among surviving organ- along with the telson, allows the animal isms they are most closely related to the crab on your hand and there is an almost trusting delicacy to the feel of its legs on to torque itself into different positions in spiders and scorpions. The class name Mouth your skin.) The fifth pair of legs, larger water and on land, rather like a dancer means something like “thigh-mouth” in Operculum and longer than the rest, are equipped doing a contraction exercise. When an Greek, which is an appropriate sobriquet Book hsc finds itself upside-down (a com- since the horseshoe’s mouth is located at with collapsible, multiple-leaved “spatula feet” that, like a pair of snowshoes, help Spatulate Leg Gill mon and life-threatening predicament the center of the legs where the “thighs” all during the breeding season when many originate.