Today is Halloween, and that means scary decorations, outrageous and frightening outfits, and fun. Although most people probably aren’t thinking about invertebrates on Halloween, we thought you might like to see what this holiday looks like from the perspective of Invertebrate Zoology.
Everyone knows phantoms haunt houses and cemeteries, but what about beaches? Most of us only visit the beach during the day. At night, another world of creatures comes out--including ghosts. Well, ghost crabs, anyway. These nocturnal crabs in the family Ocypodidae tend to blend into their sandy environment, and their ability to crawl across the sand at up to 10 miles per hour adds to their specter-like qualities, giving them their name.
The beach isn’t the only part of the marine ecosystem that’s haunted by invertebrates. Ghost shrimps also haunt the shoreline waters. Actually, the common name "ghost shrimp" is actually applied to more than one group of shrimp, illustrating just how scary it can be to communicate using common names!
One group of ghost shrimp, also called grass or glass shrimps, are in the genus Palaemonetes. While these shrimp may not be able to disappear and then reappear in another location, they are transparent, making them extremely difficult to observe. Thankfully, if you want to see this kind of ghost shrimp, you don’t need fancy electromagnetic equipment--just wait until these crustaceans have had a meal, or are brooding eggs. Their food shows up inside their digestive system, and/or babies are visible beneath their abdomens, making them very easy to spot!
Another kind of ghost shrimp can be found lurking in burrows in many nearshore environments. Shrimps of the infraorder Axiidea, which are also known as mud shrimps, have two sets of pincers (chelae), and a thin, flexible outer skeleton that is often whitish in color.
What kind of Halloween-themed invertebrate has two huge gnathopods (claws!), bulging eyes, a long and whispy body, and the ability to disappear among blades of grass? The skeleton shrimp, of course! Skeleton shrimp are “humerus” little animals in the family Caprellidae. Although they are called “shrimp”, they are actually amphipods, in the order Amphipoda. These striking organisms are delicate-looking and lean, much like a skeleton. They often lurk on hydroid colonies raking their rapacious claws through the water looking for unsuspecting victims.
If you were planning to wear garlic tonight to keep all of the vampires away, don’t even bother-- it won’t work on this family of vampires! The vampire squid, Vampyroteuthis infernalis, belongs to the family Vampyroteuthidae, along with only one other known species that is now extinct. These cephalopods were given their rather evil-sounding name, which translates to “Vampire Squid from Hell”, in the early 1900s due to their appearance, which resembles that of Count Dracula. Vampire squids range from dark red to black in color and have eyes that can appear red or blue, spines sticking out from their arms, and webbing that connects their arms. In fact, when threatened, vampire squids pull up their webbed arms over their bodies for cover, much like Dracula holds up his cloak over his face. But unlike Dracula, there is no need to worry about being bitten on the neck by a vampire squid—a study by the Monterey Bay Aquarium Research Institute showed that these little guys eat “marine snow” . This “snow” is the little particles floating in the water around them and containing dead organisms, feces, and other debris.
Eye of newt, and toe of frog, wool of bat star, and tongue of dog… Asterina miniata, the Bat star, is a sea star in the family Asterinidae. They, unlike the typical black, Halloween decorative bats, come in a variety of colors. But bat stars do have webbing between their arms, giving them their name. While they aren’t aggressive to the point where they will drive each other batty, they do occasionally “fight” with conspecifics if they run into each other, slowly pushing against each other with their arms.
Arachnophobes beware! Spiders are not just restricted to land-- there exists a whole class of arthropods, Pycnogonida, with organisms called sea spiders. While they are not exactly “spiders”, they are similar in appearance, with small bodies relative to their long legs, and a proboscis (their mouthpart). They use these mouthparts to suck the juices out of their prey, and their guts have branches that extend down into their long thin legs. While most of them are small, measuring millimeters to centimeters across, some can reach over 2 feet in diameter!
Talking about big monsters of the sea, the Japanese spider crab wins the medal for largest arthropod. Reaching up to 13 ft and 44 pounds, these gargantuan crabs tip the scales! But they need not be feared, as they mostly scavenge for dead animal and plant material, eating live invertebrates, kelp, and algae less frequently.
 MBARI researchers discover what vampire squids eat. (2012). Monterey Bay Aquarium Research Institute.
11 Intriguing Transparent Animals. (2011). Mother Nature Network.
Bat Star. Monterey Bay Aquarium.
Ghost Crab (Sand Crab). Animal Spot.
Myers, P. Pycnogonida. Animal Diversity Web.
Riebel, W. Macrocheira kaempferi. Animal Diversity Web.
Shapiro, L. Vampyroteuthis infernalis- Vampire Squid. (2012). Encyclopedia of Life.
Skeleton Shrimp. Monterey Bay Aquarium.