A Mermaid’s Purse: A Surprise Discovery Within

Recently, as I was volunteering at a local marine life center, a pair of fishermen brought in a large mermaid’s purse as they called it – offering it to the center for educational purposes. Of course, the staff and volunteers jumped at the chance to showcase this animal in our aquaria.

I’m delighted that this recent discovery aligns with the current Nature Book Club theme – learn more about this monthly link-up below.

image of a mermaid's purse or egg case from a big skate

A mermaid’s purse is an egg case or capsule of oviparous (egg laying) sharks, skates, and chimaeras. The egg cases are purse-shaped with long tendrils at the corners that serve to anchor them to structures on the sea floor.

The size of egg cases vary, depending on species. Most contain a single embryo but egg cases of larger species, like the big skate, can contain seven. As it happens, the mermaid’s purse that was brought to us was that of the big skate, Raja binoculata.

Though I had previously observed skates and rays at larger aquaria (most notable Monterey Bay Aquarium and the Aquarium of the Pacific – both in California), I had yet to observe them in the wild. The director was eager to provide the students, volunteers, and many visitors the opportunity to observe the development of the embryos up close.

Skates & Rays

This recent experience has inspired me to learn more about the skates and rays. I immediately went to our local library and checked out a couple books to get me started – even as an adult, I often go to the children’s section to find non-fiction books on topics of interest. I love the way authors bring it down to their level and the two highlighted here do just that.

Raja binoculata photo by Scott Stevenson – visit his site for more amazing photographs

There are over 500 species of skates and rays in the world and are easily distinguished from other fish by their disc-shaped, dorso-ventrally (i.e. from top to bottom) flattened bodies and expanded pectoral fins which attach to the sides of the head.

Their basic body shape allows them to live on or very close to the bottom of the ocean, where they bury themselves in mud or sand to ambush prey and avoid predators. Along with their basic body shape, they are characterized by ventral gill openings, eyes and spiracles located on the top of the head, pavement-like teeth, and lack of an anal fin.

Skates and Rays is a great book for children to introduce them to the subject. Any beachcomber who finds a “mermaid’s purse,” an egg case from a skate, must wonder what sort of creature can emerge from such a curiously shaped item. This book, part of the “Living Ocean” series, explores the world of rays and skates, of which there are more than 150 species.

Closely related to sharks, these animals make up a subclass of cartilaginous fish. Instead of having skeletons made of bone, elasmobranchs have skeletons made of soft, pliable cartilage. Like rays, skates are usually flat, with a long tail.

This book examines the behavior, habitats, and anatomy of these intriguing swimmers, describing how they catch prey, why they are important to oceans, and why many are in danger.

Another good choice is The Nature Company Guide to Sharks & Rays. This book has real photographs of sharks on every page, and rays are featured more prevalently than in most other books on the same topic. The species is clearly identified and portrayed in the field guide chapters, and following that are details about choice diving locales around the world.

It will be especially useful to the teen reader or marine naturalist/hobbyist. The information is well organized, detailed, and scientifically accurate. For someone less familiar with scientific terms, it could be a bit heavier, as it tends to use many terms, such as pelagic and elasmobranch, with only a brief definition provided.

A Mermaid’s Purse

Egg cases are made of collagen protein strands and most would describe the exterior texture as rough and leathery. Some egg cases have a fibrous material covering the outside of the egg case, thought to aid in attachment to substrate.

Egg cases without a fibrous outer layer can be striated, bumpy, or smooth and glossy. Egg cases are typically rectangular in shape with projections, called horns, at each corner. Depending on the species, egg cases may have one or more tendrils.

The mermaid’s purse that was brought into the learning center was prepared by one of the graduate student volunteers from the university. He carefully cut a hole into the flat side of the egg case and adhered a clear plastic covering. This provided a window by which we can watch the development of the embryos within as you can see from the video above.

Raja binoculata

The big skate is the largest species of skate (family Rajidae) in the waters off North America. They are found all along the Pacific coast from Alaska to Baja California, typically from the intertidal zone to a depth of 120 m (390 ft).

These impressive animals feed on benthic invertebrates and small fishes. As I stated previously, they are unusual among skates in that their egg cases may contain up to seven eggs each. This species is one of the most commercially important skates off California and is sold for food, though compared to other commercial fisheries, it is of only minor importance.

Typically caught as a by-catch of trawlers, fisheries have begun to market it more as a result of higher market value. Unfortunately, the big skates’ slow reproductive rate gives cause for some concern but population data is limited.

simple graphic image of tree with text The Nature Book Club

Welcome to the The Nature Book Club Monthly Link Up. Devoted to connecting children to nature, the monthly link up will begin on the 20th day of each month.

We welcome your nature book and activity related links. Read on for more details and for a giveaway!

See all the great posts from The Nature Book Club’s co-hosts in April:

The Nature Book Club is brought to you by these nature loving bloggers which are your co-hosts. Are you following them? If you don’t want to miss anything, be sure to follow each one.

Bird Nest/Eggs nature study pages from Barb at Handbook of Nature Study

Eggs: Nature’s Perfect Package from Erin Dean at the Usual Mayhem

Getting Started with Citizen Science – Nest Watch from Eva Varga

From Egg to Sea Turtle Unit Study & Lapbook from Tina’s Dynamic Homeschool Plus

Eggs Nature Study Free Printable Word Search from Faith and Good Works

Egg Scavenger Hunt with Egg Carton from Katrina at Rule This Roost

Felt Bag Handicraft from Melanie at Wind in a Letterbox

Clay Eggs Project from Emily at Table Life Blog

Online Book Club from Dachelle at Hide the Chocolate

Egg Identification Nature Bingo {Free Printable} from Cassidy at Freshly Planted

image of a stack of books in the grass with text overlay listing monthly themeParty Rules

  • Choose an engaging nature book, do a craft or activity, and add your post to our monthly link up.
  • The link up party goes live at 9:00 a.m. EST on the 20th of each month and stays open until 11:59 p.m. EST on the last day of the month. Hurry to add your links!
  • You can link up to 3 posts. Please do not link up advertising posts, advertise other link up parties, your store, or non-related blog posts. They will be removed.
  • By linking up with us, you agree for us to share your images and give you credit of course if we feature your posts.That’s it!
  • Let’s party.


About Eva Varga

Eva is passionate about education. She has extensive experience in both formal and informal settings. She presently homeschools her two young children, teaches professional development courses through the Heritage Institute, and writes a middle level secular science curriculum called Science Logic. In addition to her work in education, she is an athlete, competing in Masters swimming events and marathons. In her spare time she enjoys reading, traveling, learning new languages, and above all spending time with her family. ♥

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