The Slow and the Spineless

The Phoenix Islands "Greatest Hits" highlights continue...


The invertebrates of this trip deserve to be in the top 10; but on this blog thus far, they've barely received an honorable mention. Mea culpa! Because of the scientific interests of the expedition members, invertebrate diversity attention has been taxonomically-eclipsed by the coral invertebrates, the remarkable fishes, and the algae. But, invertebrate diversity is important and interesting, and I'm not the only blogger who thinks so! Check your backbone at the door and go visit Chris Mah's Echinoblog, as well as The Other 95% (written by Kevin Zelnio and Eric Heupel) if you like inverts. Full disclosure: I do not know all of the taxonomic identifications of the critters posted here, so I invite you to join me in this adventure (semi wiki-style)! If you post the ID in the comments section below, I will amend the blog to include the correct ID and give you credit for the match. :-)

Without further ado, allow me to introduce a few of the "the slow and spineless" Phoenix Islands critters. Most of these images will enlarge when you click on them.

The Christmas Tree worm is aptly named for it's shape (photo above by David Obura). They also come in all sizes and colors (see shots below).

Spirobranchus giganteus on Porites lobata corals (photo: R. Rotjan)

Time for a little echinoderm shout-out (for more, check out Chris Mah's blog here). You may not realize it, but echinoderms are a whole lot more than just sea stars! But, we'll start with a Linckia spp. on the left (not sure which one, any guesses? Also, anyone notice anything a little unusual about this Linckia? Count the arms...). But, sea cucumbers (holothurians) are also echinoderms (photo on the right). New England Aquarium Researcher Tim Werner works on these. I think this one is an Actinopyga spp., and Tim Werner has confirmed that it is A. mauritiana. Thanks, Tim!

Linckia spp. sea star and holothurian sea cucumber (photos: R. Rotjan)

Phoenix Island Sea Urchins (photo: R. Rotjan)

Above are two more echinoderms - a Diadema spp. and an Echinometra spp. sea urchins; I think! Let's go check out some more inverts. There are two focal invertebrates in the photo below. The one to the left is an echinoderm (a Culcita novaguinae seastar). But take a look at the invert on the right-- definitely NOT an echinoderm.

Culcita novaguinae cushion star(left) and Tridacna spp. clam (right) (Photo: R. Rotjan)

The photo below shows a bunch of molluscs (Tridacna spp. clams nestled amidst the coral). The photo above shows a clam also - on the right side, next to the cushion star. Chris says that all of these clams are Tridacna maxima. Thanks, Chris!

Tridacna spp. clams (Photo: R. Rotjan)

Molluscs are great; they include clams, mussels, snails, octopus, and squid. They also include nudibranchs, which are shell-less snails like the one below. I think this nudibranch is a Phyllidia spp.; any other ideas?

Nudibranch (Photo: R. Rotjan)Below is another confusing photo. There is no mollusc in the photograph (only a crustacean), but the crustacean is using a snail shell. Yup, it's a land hermit crab (Coenobita perlatus).

Coenobita perlatus hermit crab (photo: R. Rotjan)

Hermit crabs are very interesting creatures, and they are very picky about their shell choice. While we're on the topic of crustaceans (e.g. shrimp, lobsters, crabs), check out this terrestrial land crab (often called a sally lightfoot). Eric Heupel suggests that it might be Graspus tenuicrustatus.

Sally lightfoot crab (Photo: R. Rotjan)

Back to my favorite group--the cnidaria (e.g. corals, jellyfish, anemones). Below are some beautiful hydrozoans. These animals have the appearance of a feather, but the branches have polyps (just like corals).

Hydroids (Photos: R. Rotjan)

Of course, corals will always have my heart. Hard corals, scleractinians, have been featured on many posts here already, and are the main focus of our reef recovery attention. The reason why? Well, hard corals may be slow and technically spineless, but they are the backbone of coral reefs. They have calcium carbonate skeletons that create the complex reef structure. In an earlier post, we showed you lots of dead coral skeleton covered by crustose coralline algae. That skeleton is made by the coral animal via a symbiosis with a photosynthetic algae and provides shelter for most of the other organisms on the reef. To see more about the symbiosis, check out the Blue Impact Tour and click on "color changing corals".

Acropora table coral closeup and colony 

But the main point here is that coral animals and their calcium carbonate skeletons create the complex structure of reefs.

So spineless? Hardly. These inverts are themselves the backbone of coral reefs. No bones about it.




  1. Awe inspiring collection of invertebrates! The terrestrial crab looks like it may be Graspus tenuicrustatus, native to Central and Indo-Pacific, but I am no expert to be sure!

    I love the image with the Tridacna and the echinoderm! Always will have a soft spot for those most colorful clams!

    The Acropora looks marvelous! I'm jealous I haven't seen large healthy colonies in a very long time.

  2. Hi Eric, thanks! I've changed the ID above. Sadly, we didn't see as much Acropora as we would have liked - but in certain habitats (shallow lagoons, mostly), it was doing quite well. We suspect there are some successional dynamics to recovering reefs - let's hope that in time, the Acroporids will once again dominate.

  3. Great photo's

    FWIW all of the clams are Tridacna maxima

  4. Hello! This is Celeste Young & her biology class! What is the scale of the christmas tree worm picture? (From Susanna Y.)

  5. Very cool Maxima's

  6. Note to readers, Randi answers Celeste's question here.

  7. Great images and write up. I absolutely love the big green porites colony. Almost looks like velvet. They may be spineless...but they're beautiful. Sorry it took me so long to find it :)