Episode 284 – Common Rock Barnacle: Reachable Goals

“And today we are talking about sea critters with their own clear, plastic-looking straw. But more on that later.”

Humans are social creatures, but we aren’t the only ones. Gregarious animals hang out together, especially during mating seasons. But what if you are both sedentary and gregarious, which is another way to say a friendly home-body? The common rock barnacle is in such a predicament. How can they put down roots and make friends and more barnacles? Sometimes you just need to reach out to others in Life, Death, and Taxonomy. 

Description of the Common Rock Barnacle 

  • They have six greyish wall plates surrounding a diamond-shaped operculum
  • When the tide rises to cover the barnacles, the operculum opens, and feathery cirri are extended into the water to filter food from the seawater 

Measure Up

Welcome to the beloved Measure Up segment. The official listener’s favorite part of the show! The part of the show when we present the animal’s size and dimension in relatable terms through a quiz that’s fun for the whole family. It’s also the part of the show that’s introduced by you when you send in audio of yourself saying, singing, or chittering the words Measure Up into ldtaxonomy at gmail dot com. We don’t have a new Measure Up intro!


  • 2.5 cm to 7.5 cm
  • How many barnacles go into the height of Samus Aran?
  • Hint: The Metroid character, Samus Aran, is a human that was adopted and raised by the mysterious alien race the Chozo. Though she is human by birth, she was infused with Chozo DNA. She is described as a super athlete beyond the capabilities of an average human. Her height is something of a debate. Her height is first listed in an issue of Nintendo Power under a section on personal data, which sounds like it is inherent to her, without her iconic orange suit. But when she is outside her suit, she is rarely depicted at her canonical height.
  • 25 barnacles. Samus is 6’3”


  • 15 millimeters (0.6 in) 
  • How many barnacle diameters go into the groove diameter of a rifle capable of firing the largest caliber rifle cartridge?
  • Hint: The cartridge was developed by weapon designer J.D. Jones for SSK Industries in Ohio. The cartridge propels a 3,600-grain bullet. 
  • 1.6 barnacles. The cartridge is the .950 JDJ, which is a diameter of 0.95 inches (24.1 mm). 

Fast Facts about the Common Rock Barnacle

  • Range: Lives in the intertidal zones of northern oceans, all over Scandinavia, Canada, and the UK. It can reach as far south as North Carolina. It only matures and breeds in colder waters – less than 45F. Intertidal zones are underwater when the tide is high and exposed when the tide is low.
  • Diet: Like most barnacles, it’s a filter feeder that uses its cirri (little fan tentacles) to capture zooplankton. If the current is strong, it will just hold its cirri out to catch what comes by. But if the current is weak, it will flap them around rhythmically.
  • Behavior:
    • Predation – they are often eaten by marine snails, small fish called shannies, sea stars, and nudibranchs

Major Fact

Barnacles are sedentary, which means they stick around. They don’t go on journeys to the lonely mountain. They remain in tidal pools, stuck to rocks, piers, and poorly maintained watercraft. 

However, they don’t reproduce asexually like a starfish. For barnacles, it takes two to tango. While they do set up camp in groups, the nearest neighbors could be inches away.   

Other animals in this predicament would go the way of plants and simply release genetic material into the area to be collected by receptive partners. In plants, it’s called seed dispersal. 

But barnacles prefer the old-fashioned way, challenges aside. So what can they do? 

They develop the longest male reproductive organ (relative to size) of any animal. To call these appendages [a male reproductive organ] is to simplify its capabilities. 

Barnacle doodads do more than make more. 

It has multiple senses, including touch, taste, and smell, which is necessary because how else can you tell if you’re reaching another barnacle or a scandalized crab?

When they reach another barnacle with eggs ready for fertilization, their barnacle senses tingle, and they release sperm. 

Barnacles are hermaphroditic, which means they have both male and female reproductive powers. Any barnacle in an area can have a clutch of eggs and a tidal tickler simultaneously. 

Once their eggs are fertilized, they will hold on to them and protect them until they hatch into nauplii, which are tiny larvae that roam the waters eating and growing. Then they turn into cyprids, which need to find a home quickly because they cannot eat during this stage. 

Then they become barnacles and start the process all over again. 

Ending: So find a wall, stick to it, and by golly, flap those cirri like your life depends on it, like the common barnacle here in LDT.