Odd Ocean Critters to Inspire Your Next Halloween Costume

By Rachel Plunkett

October 2023

It’s spooky season, and if you’re an ocean-lover looking for unique DIY Halloween costume ideas, we have some inspiration from across your National Marine Sanctuary System. Learn a few fun facts about strange and interesting animals found in the ocean, along with ideas on how to make a one-of-a-kind costume utilizing common craft supplies, such as paint, ribbons, and construction paper, and items found around the house, like cardboard, an old sheet, or a milk jug. These costumes can be made for anyone from babies to adults. Take the ideas below, get creative, and make it your own! While you’re out trick-or-treating in your homemade Halloween costume, don’t forget to share the fun ocean animal facts you learned in this guide.

Gulper Eel (Eurypharynx pelecanoides)

gulper eel
This gulper eel was sighted in Papahānaumokuākea Marine National Monument during the 2018 E/V Nautilus expedition. Photo: OET/NOAA

The gulper eel, also known as a pelican eel, is a deep-sea-dwelling eel found at depths of 1,600 to almost 10,000 feet in tropical and temperate regions. In 2018, the E/V Nautilus had a rare opportunity to film a gulper eel within Papahānaumokuākea Marine National Monument, showcasing their unique abilities. These odd eels have a pouch-like throat and stomach that they can quickly inflate in order to scoop up larger prey, such as a big squid, a school of fish, or a swarm of shrimp. This behavior reminds many people of a pelican expanding its throat pouch to scoop up fish, which is where the nickname comes from.

gif of a gulper eel
Gulper eels can quickly inflate their throat and stomach to engulf large prey. Video: OET/NOAA

While their mouths are an impressive adaptation, they’re actually not the best of hunters because they have very small eyes, making it tough for them to locate prey in the deep, dark, depths that they live in. They have a very thin whip-like tail and lack pelvic fins, which help fish with balance, and do not have a swim bladder, which help fish maintain buoyancy. For these reasons, they are not the best of swimmers.

DIY Gulper Eel Costume
  • Make a frame for the gulper eel’s jaw and head using recycled cardboard.
  • Paint the cardboard cutout dark purple or black.
  • Draw, cut out, and glue on felt pieces to represent the eyes and teeth. If you don’t have felt available, you can cut the pieces out on recycled construction paper, cardboard, or paper towel rolls and paint them the desired color. You could even do a beach clean up and use the plastic scraps you collect to create the eyes and teeth of this costume.
  • Attach a long trail of black fabric to the back of the cardboard piece, representing the eel-like body.
  • Wear a dark purple or black outfit and put on your homemade gulper eel headpiece!

Portuguese Man O’ War (Physalia physalis)

The Portuguese man o’ war in the water
The Portuguese man o’ war is recognized by its balloon-like float, which may be blue, purple, or pink and rises up to six inches above the water line. Photo: A. Scott/NOAA
The Portuguese man o’ war on the beach
A type of plankton that drifts with the wind and ocean currents, Portuguese man o’ war often wash up on beaches. Photo: Elizabeth Condon/National Science Foundation

Portuguese man o’ war may look like a type of jelly, but they are actually a type of siphonophore, which are closely related to corals and jellies. These colonial animals are made up of groups of specialized organisms, known as zooids, that work together as a unit. Each of the four specialized zooids of a man o’ war is responsible for a specific task, such as floating (the pneumatophore), capturing prey (the dactylozooids, or tentacles), feeding (gastrozooids), and reproduction (gonozooids).

These ocean drifters generally live in warm tropical and subtropical waters and get carried by wind and currents into the waters such as Florida Keys National Marine Sanctuary, Gray’s Reef National Marine Sanctuary, and Flower Garden Banks National Marine Sanctuary, and can appear in groups of more than 1,000. The top part of their body is a float, or a sail, referred to as a “pneumatophore,” that is partially filled with carbon monoxide. Like other animals in the Phylum cnidaria, Portuguese man o’ war have stinging organelles, called nematocysts, that line their long dactylozooids and are meant to stun and capture their prey. These long tentacle and polyp colonies that extend below the ocean’s surface from the float can reach lengths of up to 30 feet!

DIY Portuguese Man O’ War Costume
  • Use a wide-brimmed hat for the base of your costume to represent the gas-filled pneumatophore and paint or tye-dye it blue and purple.
  • Take several pink and purple puffballs or painted cotton balls and glue them to the brim of the hat to represent the gonozooids.
  • Use short, purple, paper streamers to represent the gastrozooids. For a more sustainable option, you can use old shoe strings or paracord.
  • Recycle your old gift wrapping supplies! Attach some different blue, purple, and pink long ribbons to the brim of the hat to represent the long and often curly dactylozooids. If you don’t have ribbons to use, another option is to cut an old sheet into thin strips and dye the fabric blue and purple.
  • Wear a blue or purple outfit and put on your Portuguese man o’ war hat!

Black Seadevil Anglerfish (Melanocetus spp.)

female deep-sea anglerfish
The female deep-sea anglerfish is much larger than the male, and they have a lure with a light at the end to attract prey.
Photo: MBARI

The deep sea is a dark place, and food can be hard to find without a good strategy. An anglerfish is a type of bony fish that lives in the deep sea, that uses fishing rod-like projection with a light at the end to lure in its prey. The light is produced by millions of bacteria inside of a specialized organ (the “esca”) through a chemical process called bioluminescence. There are over 200 species of anglerfish, but the most widely known and recognizable is the black seadevil anglerfish, which has long, spiky teeth protruding from its jaws.

animation of female deep-sea anglerfish swimming downward
Deep-sea anglerfish have a wide, round body and do not swim very fast.
Animation clipped from video provided by: MBARI

The black seadevil anglerfish, like the one in this video from Monterey Bay National Marine Sanctuary, uses its bioluminescent lure to attract prey. When the timing is right and an unsuspecting prey swims too close, the anglerfish snatches it up. This sneak attack style of feeding is known as “ambush predation.”

DIY Anglerfish Costume
  • Spray paint a bike or skateboard helmet black.
  • Use cardboard cutout pieces to make the body, mouth, and fins of the anglerfish that will attach to the helmet and fit around your head, then spray paint the pieces black and glue them onto the helmet. You may need to layer the pieces to get the correct shape.
  • Cut a small slit in the top of the anglerfish's head through the cardboard and slide a battery-powered book light through the slit.
  • You can make the eyes of the anglerfish costume out of a variety of things. You can cut two circles out of a recycled plastic container, such as a milk jug, or you could use duct tape, cardboard, paper, or felt.
  • The teeth of the anglerfish can be cut from white craft foam, felt, or cardboard.
  • Wear a black outfit, put on your anglerfish helmet, and start luring in your prey!

Decorator Crab (Superfamily Majoidea)

decorator crab
This decorator crab in Gray’s Reef National Marine Sanctuary is hard to see because it has covered its body in pink tunicates, purple sponges, algae, and hydroids. Photo: Greg McFall/NOAA

Decorator crabs are one of nature’s masters of disguise. There are several different species of decorator crab, all belonging to the superfamily Majoidea. These creative crabs use materials from their environment to hide from, or ward off, predators. They do this by covering their hard outer shell (exoskeleton) and legs with algae and animals such as sponges, anemones, tunicates, and bryozoans in order to blend in with the seafloor environment.

gif of decorator crab
This decorator crab in Cordell Bank National Marine Sanctuary has sponges and anemones on its exoskeleton for camouflage. Video: NOAA/BAUE
Their bodies are covered in fine bristly hairs that act like a type of Velcro, latching onto the chosen decorations. Some decorator crabs are highly selective about the decorations they choose, such as the furcate spider crab (Stenocionops furcatus), which often chooses to wear the hitchhiker anemone (Calliactis tricolor) on parts of its body to deter predators. In this symbiotic relationship, the crab gets protection, and the anemone gets a place to live and discarded scraps of the crab's food. This particular relationship has been observed throughout the tropical Atlantic and Gulf of Mexico, and was first documented in Flower Garden Banks National Marine Sanctuary in 2007 during a Stetson Bank Long Term Monitoring Cruise.

Crabs are crustaceans that have 10 legs. Most decorator crabs are a type of spider crab, which tend to have long, thin limbs and a triangular carapace (shell). They have a front pair of legs with pincers, and the remaining four pairs of legs are pointy at the end. Like many other crustaceans, rather than the shell growing along with the body of the decorator crab, the crab has to shed its shell in a process known as “molting.” Each time the decorator crab molts, it carefully removes its anemones, sponges, and other decorations so it can use them on its newly grown exoskeleton.

Can you find the decorator crab hiding on the reef in this 360 video of Cordell Bank National Marine Sanctuary?

DIY Decorator Crab Costume
  • Trace a rounded triangle onto a piece of cardboard and cut out the shape.
  • Use felt or an old sheet and retrace the shape onto that, with about two inches of overhanging fabric.
  • Cut a few 1-inch slits into the edges of the fabric to make it easier to bend and fold.
  • Place the fabric over the cardboard cutout and begin folding the notched edges under and gluing the fabric to the cardboard on the underside. Leave a 5-inch opening for the next step.
  • Add stuffing into your crab’s exoskeleton through the gap. You can re-use the stuffing from an old, unwanted pillow or old stuffed animals.
  • Add straps to your exoskeleton so you can wear it on your back (just like a backpack).
  • To make the front pair of pincers you can use a pair of oven mitts.
  • For the remaining eight legs, draw them onto a piece of cardboard, paint them your desired color, cut them out, and glue them to the carapace.
  • To create the stalked eyes of the crab, glue googly eyes to styrofoam balls and attach them to a headband using hanger wire.
  • To make your crab stand out as a decorator crab, be sure to glue or Velcro some items to its exoskeleton! You can keep your costume realistic and create your own sponges, tunicates, anemones, and algae to glue to your shell, or you can be a more comical version — a “trashy” decorator crab — and attach random household objects to your shell, such as a hair brush, a pearl necklace, and socks.
  • To complete the costume, wear a brown, orange, or red outfit under your decorator crab backpack.

Dumbo Octopus (Grimpoteuthis spp.)

dumbo octopus
This dumbo octopus was observed in a 2014 NOAA Okeanos Explorer expedition to the Gulf of Mexico. Photo: NOAA

It’s not a flying elephant that lives in the sea; the dumbo octopus is a type of umbrella octopus that is found deeper in the ocean than any other type of octopus (over 13,000 feet). Umbrella octopuses swim by flapping a pair of very large fins that protrude from the mantle above the eyes. There are 14 known species of umbrella octopus, all belonging to the Grimpoteuthis genus. These eight-armed inhabitants of the deep-sea feed on snails, worms, bivalves, isopods, and other small prey.

Unlike many of the other octopuses found at shallower depths, dumbo octopuses lack chromatophores and are unable to color-change to camouflage with their surroundings. Their bodies are usually pale or unpigmented, with some dark purple pigmentation on the oral surface of the arms (the side that has the suckers on it).

animation of dumbo octopus
Rather than using jet propulsion from the siphon like other octopuses, the dumbo octopus propels itself through the water by flapping two strong fins. Video: OET/NOAA

Dumbo octopuses are a rare sighting and a special treat for researchers exploring the ocean, Recently, Ocean Exploration Trust’s E/V Nautilus spotted a dumbo octopus in Papahānaumokuākea Marine National Monument at over 5,250 feet (1,600 meters) deep while exploring Woollard Seamount, roughly 40 nautical miles north of Hōlanikū (Kure Atoll).

Fun fact: Octopuses do not have tentacles! They have eight appendages, each of which has rows of suckers running its length. But these are not “tentacles” like you would see on a squid. In strict anatomical terms, they are referred to as “arms.”

DIY Dumbo Octopus Costume
  • To create the eight arms of the dumbo octopus, you will need two different-colored fabrics: a pale pink (dorsal side) and purple (oral side). Make the oral piece slightly narrower than the dorsal piece.
  • Cut out eight 20–24 inch-long arms. The arms should be wider at the base (5–6 inches) than they are at the tip (about 1 inch), and the tip of each arm should be rounded.
  • If you want your octopus arms to curl slightly, you can sew a piece of elastic into the middle of the tentacle on the dorsal side (the lighter pink fabric).
  • Sew your pieces of fabric together on three sides, leaving the base end open for stuffing.
  • Stuff your eight octopus arms with recycled pillow stuffing or cotton balls, then close up the final edge.
  • Cut out a two-inch strip of fabric to create a waistband and sew it into a ring that will fit the costume-wearer.
  • Attach the eight arms onto the waistband.
  • To create the characteristic large, flapping fins of the dumbo octopus, you will cut a large oval (about 24 inches) out of the pink fabric and then cut the oval in half.
  • Use hot glue to attach one half of the oval to one side of a headband and the other half of the oval to the other side so when you wear the headband, you have a flappy fin on either side of your head.
  • Wear a pale pink outfit under the eight-armed “skirt” and start flapping your way around the deep sea.

Other Possibilities

There are lots of other bizarre-looking, funky, and spooky animals found throughout your national marine sanctuaries and beyond. If the examples above didn’t get you into the Halloween spirit, see if any of the other options below can inspire your next ocean-themed costume idea!


Rachel Plunkett is the writer/editor for NOAA’s Office of National Marine Sanctuaries