# Pacific Acorn Barnacle (*balanus glandula*) The Pacific Acorn Barnacle is a tiny animal that sticks to rocks and shells in the ocean. They have a hard shell that looks like a little acorn, and they open up to eat tiny food from the water! - **Category:** [Invertebrate](https://www.snappit.app/explore/categories/invertebrate) - **Rarity:** Common - **Danger:** 0/5 · No known danger - **Snaps:** 2 - **Habitat:** Rocky shores and tidal pools along the Pacific coast. - **Also known as:** Common Barnacle, Rock Barnacle ![Pacific Acorn Barnacle](https://commons.wikimedia.org/w/index.php?title=Special:Redirect/file/Balanus_glandula01.jpg&width=800) Photo: DOI (Department of the Interior), Public domain · [Wikimedia Commons](https://commons.wikimedia.org/wiki/File:Balanus_glandula01.jpg) ## Appearance The Pacific Acorn Barnacle is a small, whitish-grey cone with a rough, often ridged surface. Its top has a diamond-shaped opening made of four movable plates. It looks like a tiny volcano glued to rocks, distinct from smooth, flat limpets. ## Taxonomy - **Kingdom:** Animalia - **Phylum:** Arthropoda - **Class:** Maxillopoda - **Order:** Sessilia - **Family:** Balanidae - **Genus:** Balanus ## Interesting facts - Barnacles are actually crustaceans, which means they are related to crabs and lobsters! - Some barnacles can live for many years, often ten times longer than a pet hamster! - They spend their whole adult life upside down, sticking their head to a rock! - Wow! Baby barnacles swim like tiny shrimp before finding a spot to glue down! ## Special abilities - **Super Glue Anchor:** Pacific Acorn Barnacle can make an incredibly strong natural cement because of specialized glands that helps them stick to rocks forever. - **Feathery Food Sweeper:** Pacific Acorn Barnacle has feathery 'cirri' legs that helps them sweep tiny food particles from the ocean water. - **Shell Fortress:** Pacific Acorn Barnacle can close its shell plates because of strong muscles that helps them stay safe and moist during low tide. - **Double Trouble:** Pacific Acorn Barnacle has both male and female parts that helps them reproduce even when neighbors are scarce. ## Measurements & details - **Length:** 1.5 cm - **Weight:** 0.5 g - **Lifespan:** 10 years - **Arm Count:** 12 - **Colony Size:** hundreds_to_thousands - **Shell Hardness:** 3 Mohs ## Diet & Feeding They sweep tiny ocean critters and plant bits from the water using their feathery legs. - **Primary Foods:** plankton, algae spores, detritus, larval invertebrates - **Foraging Method:** Filter feeding ## Ecological connections - **Eaten by:** [Ochre Sea Star](https://www.snappit.app/explore/ochre-sea-star) (*Pisaster ochraceus*) — Pries open shells to eat the soft body. - **Eaten by:** Emarginate Dogwinkle (*Nucella emarginata*) — Drills a tiny hole through the shell. - **Eaten by:** Tidepool Sculpin (*Oligocottus maculosus*) — Nips at the feathery feeding legs. ## Traits - [Social](https://www.snappit.app/explore/traits/social): Social animals live in organized groups, cooperating for survival benefits such as foraging, defense, and raising offspring. - [Filter Feeder](https://www.snappit.app/explore/traits/filter-feeder): Filter feeders obtain nutrients by straining suspended food particles and small organisms from water. - [Coastal](https://www.snappit.app/explore/traits/coastal): Coastal habitats are dynamic environments located along the interface between land and sea, influenced by tides, waves, and saltwater. - [Aquatic](https://www.snappit.app/explore/traits/aquatic): Aquatic habitats encompass environments where organisms live predominantly in water, including oceans, rivers, lakes, and wetlands. - [Marine](https://www.snappit.app/explore/traits/marine): Marine habitats encompass all saltwater environments of the Earth's oceans, supporting an immense diversity of aquatic life. ## Collections - [Invertebrates](https://www.snappit.app/explore/collections/invertebrates) ## Safety **Danger:** 0/5 · No known danger No special safety notes yet. ## Frequently Asked Questions ### How to identify Pacific Acorn Barnacle? Look for fins, arms, tentacles, shells and body symmetry. Underwater light shifts colors, so structure and markings usually matter more than shade. Sea Creature Identifier: upload a photo and compare the visible details. ### How long is Pacific Acorn Barnacle? 1.5 cm ### How much does Pacific Acorn Barnacle weigh? 0.5 g ### How long does Pacific Acorn Barnacle live? 10 years ### What does Pacific Acorn Barnacle eat? They sweep tiny ocean critters and plant bits from the water using their feathery legs. ### Where is Pacific Acorn Barnacle usually found? Rocky shores and tidal pools along the Pacific coast. ### How does Pacific Acorn Barnacle hunt? Filter feeding ### How many arms does Pacific Acorn Barnacle have? 12 ## Where to spot - [Alaska SeaLife Center](https://www.snappit.app/guides/places/alaska-sealife-center) — Alaska, US · Zoo - [Bodega Bay](https://www.snappit.app/guides/places/bodega-bay) — US · Natural Landmark - [Porteau Cove Provincial Park](https://www.snappit.app/guides/places/porteau-cove-provincial-park) — British Columbia, CA · State Park - [Magnolia Park](https://www.snappit.app/guides/places/magnolia-park) — Washington, US · Park [View all places to see Pacific Acorn Barnacle](https://www.snappit.app/guides/where-to-see/pacific-acorn-barnacle) ## More Invertebrate - [Coral](https://www.snappit.app/explore/coral) - [Crab Spider](https://www.snappit.app/explore/crab-spider) (*Mecaphesa asperata*) - [Garden Spider](https://www.snappit.app/explore/garden-spider) (*Araneus diadematus*) - [Brown Recluse Spider](https://www.snappit.app/explore/brown-recluse-spider) (*Loxosceles reclusa*) --- Source: [Pacific Acorn Barnacle: Facts & Places to See — Snappit](https://www.snappit.app/explore/pacific-acorn-barnacle)