Category Archives: invertebrates

More tales from the pilings—a patriotic nudibranch

Hai and I spent yesterday morning poking around the pilings at Kawaihae. Lots of interesting nudis.

How about this red(-dish)-white-and-blue nudi for Independence Day? This is one of many nudibranch species with no common name. The scientific name is Caloria species #3. This one, a little less than an inch long, has its mouth parts curled around the hydroid it’s crawling on and eating. (Hydroids are tiny, colonial relatives of jellyfish.) The erect appendages on the animal’s head are rhinophores—sensory organs possessed by most nudibranchs. Most nudis lack the longer, curved appendages you see here. Those are called “cephalic tentacles.”

This majestic (for a sea slug) Gloomy Nudibranch bucks a head current on an exposed piling. Gloomies are the most conspicuous nudibranchs at Kawaihae.

Here’s another nudi with no common name. Scientifically, it goes by Doto species #2. These tiny guys—only about 5 mm long—have only been observed at Kawaihae. They live on, and likely dine on, a different hydroid, probably Pennaria disticha. (I got all this from


An improbable shrimp—the blind watchmaker strikes again

Back in May, Hai and I saw a tiny, leggy creature hiding among the branches of a large cauliflower coral in Kawaihae harbor. It was clearly some sort of crustacean, but it was too small—a little over half an inch in total length—and too far down in the coral to tell exactly what type. I, with my presbyopic  eyes, thought it was a hermit crab. Hai, despite his better vision, wasn’t sure what it was, but he took a few photos and we moved on. Later that day Hai emailed me the amazing photo posted below. It was an Eyespot Shrimp, a reclusive species widely distributed through the indopacific. It appears to be rather rare throughout its range, or at least rarely observed.

We’ve revisited the spot several times since that first encounter, hoping to get better—or at least additional—photos. Turns out there are two of these shrimp living in our coral head, but we’ve not been able to get any more decent photos. The camera-shy little guys retreat deep into the coral when we come by. I’d been delaying posting this until we’d gotten a few more photos, but I’ve gotten tired of waiting, so here it is:

Hai’s Eyespot Shrimp. How (and for that matter, why) did nature come up with this design? The wild array of antennae, furry forelegs, and googly eyes; the crazy-striped walking legs; the polka-dotted body; and that vivid eyespot on the tail! Any one of these would make this shrimp an outstanding find; the unlikely combination is mind-blowing.

Here’s the best I could do since that first day. The shrimp taunts me from deep in the coral. Is that its tongue sticking out at me?

Eighteenth century theologian William Paley postulated the “watchmaker analogy” to support the idea that an intelligent creator was responsible for our unimaginably complex natural world. The argument goes that if one finds a watch lying in the sand at the beach it can be assumed that someone or something had intentionally created it, since it is too complex to have arisen by accident. Variations of this argument still live among the creationist crowd. The argument is robustly (at least to me) rebutted in Richard Dawkins’ 1986 The Blind Watchmaker. Dawkins shows with considerable mathematical rigor how the simple process of natural selection can produce results that appear to be impossibly unlikely. No watchmaker is needed. Or, if there is a watchmaker, she is blind. I won’t belabor the point further, but rather refer you to Dawkins. So do you think a watchmaker created this unlikely shrimp? Not me.

A nudibranch holds its breath

Nudibranchs are endlessly weird. Weird, psychedelic colors; weird diets, including lots of toxic organisms; weird anatomy… No wonder so many of us find them fascinating. The other day I discovered yet another strange thing about these oh-so-strange creatures: some of them can withdraw their gills entirely into their bodies. I kind of think of this as the physiological equivalent of holding their breaths.

Hai took this photo of two presumably mating Painted Nudibranchs. Both have their gills—the tufted plumes in the middle of their backs—fully extended, which is their normal state.

I photographed the same pair a minute later. The gills of the lower animal have started to retract.

A few seconds later the gills have completely disappeared into the nudi’s body. What a cool trick. So how does it breath with retracted gills? A little Googling revealed that these nudibranchs, like many small aquatic animals, can breathe through the surface of their bodies—at least when they’re in well-oxygenated water.

Examining photos I’d taken of a different Painted Nudi, I stumbled onto another strange fact: its anus is located in the middle of its gill plumes. I saw what looked like it might be fecal matter protruding from the gills of this animal, so I Googled nudibranch anatomy and found that the gill-anus association is characteristic of the nudibranch suborder Doridacea. All this is probably not so strange to students of invertebrate biology, but this vertebrate-oriented guy found it pretty weird.

A Painted Nudibranch relieving itself.

An obscure world record—we think

Last week Hai and I did a little snorkeling at Kawaihae Harbor. As usual, we started out at the big concrete platforms at the south end of the main harbor where the military ties up its landing craft. There was nothing much to see at the first platform so we moved on. It only took a minute or two at the second platform for Hai to zero in on the biggest Gloomy Nudibranch either of us had ever seen. It was just a few feet below the surface on one of the platform’s support pilings, and we guessed it was about five inches long. We marveled at it for a while, took some photos, and continued on to inspect the rest of the pilings. Soon Hai spotted another similar sized Gloomy, again just a few feet deep on a piling. (I don’t know how he does it—he seems to have a sixth sense  for finding invertebrates. He’s an architect, but he’d have made a great field biologist.) Both Gloomies were actively crawling around, apparently feeding on bryozoans. We took some more pictures, and this time Hai placed his dive scissors next to the nudi in order to establish a size scale.

After we got back to our respective homes we exchanged texts and photos and speculated about the size of these nudibranchs. We also did some research. Hoover, in Hawaii’s Sea Creatures, says that Gloomy Nudibranchs reach about three inches in length. The authoritative and amazingly comprehensive web site, said 76 millimeters (come on, you figure it out). And Keoki Stender’s says four inches. It was obvious to us that the specimens we saw that day were larger than four inches, so Hai took a picture of his dive scissors next to a tape measure so we could use it and his earlier photo to compare tape to scissors to nudibranch. He sent both photos to Dr. Cory Pittman, head honcho of Cory looked at the photos and proclaimed that our specimen was 121 mm long, a number now reflected on his web site. So we’re calling it a world record.

Here’s the first Gloomy Nudibranch we found that day. Notice the blue-green color of the highlights on the inside of the branchial plume (the gill tuft on the middle of the back).

This is the second Gloomy. Its inner branchial highlights are distinctly more blueish than those of the first individual. notes that this species is quite variable in coloration, and that the relative abundance of blue versus blue-green specimens has varied quite a lot over the last couple of decades.

Here’s Hai’s photo of the same individual as shown above, with dive scissors for comparison. (The body color here looks a bit different from my photo because I shot without flash—my camera batteries were dying—while Hai used flash.)

Hai got this fantastic closeup of the Gloomy’s “face.” It’s dining on a blue bryozoan, which says constitutes its sole, or at least primary, food source.

Kawaihae’s hung over gobies

Marla, Hai, and I spent a relaxed Sunday morning snorkeling around the landing craft platforms in Kawaihae Harbor. We were hoping to see the black frogfish that Hai had been seeing on one of the pilings, or maybe the lionfish that he’d seen there a time or two, but we pretty much just saw the usual suspects: a handful of nudibranch species, Gorgonian Gobies, featherduster worms, Hawaiian Dascyllus, etc.

A thick wire hanging into the water from the second landing craft platform is home to several Gorgonian Gobies. It’s amusing to watch as they periodically dart out from their stations on the wire to to snatch  passing particles of plankton, but these fish are so small—just over an inch long— that it’s hard for my and Marla’s old eyes to make out much detail. (Hai sees everything with his seeming supervision.) Examining photos after we got home we noticed that the gobies have bloodshot-looking eyes—a lot like mine would look after a long night of drinking back in the day. Like this:

One of several Gorgonian Gobies under the second platform. Look at that bloodshot eye! Gorgonian Gobies, also known as Sea Whip Gobies, are easily confused with the similar Wire Coral Goby. The latter are a bit smaller, have a less pointed snout, and are less reddish in color. Wire Coral Gobies are found pretty much exclusively on wire coral, while Gorgonian Gobies will live on anything shaped more or less like a wire or thin stick.

More of the usual suspects—a handsome family of Hawaiian Dascyllus.

Hawaiian Whitespotted Tobies among the Halameda on the rubble at the base of the breakwater. These cute little endemic puffers are very common throughout the Islands. So is Halameda, a pantropical genus of green macroalgae.

A nice sized Painted Nudibranch on the march on one of the pilings. These, Trembling, and Gloomy Nudibranchs can almost always be found at this site lately.

“Big” nudibranchs and search images

I mean bigger than one inch.

Most of the nudis in recent posts have been less than an inch in length—some less than half an inch. This one from last week at Kawaihae Harbor is all of an inch and a half. It’s Dendrodoris krusensternii, a relatively rare species in Hawaii with no common name. Hai, that preternaturally skilled critter finder, found it crawling on a piling a couple of weeks ago and brought Marla, Sandra, Jeff, and me out to see it last week. We swam out to the pilings where Hai’d spotted the nudi, but at first none of us could find it. Luckily, I’d studied a photo of this thing that Hai had previously posted and I’d developed a pretty good search image*. A good search image—a visual idea of just what one is looking for—is really useful for spotting nudibranchs. Pretty soon I located this one on a partially dead Cauliflower Coral growing on a piling a few feet below the surface.

A Blue Dragon nudibranch from a dive earlier this month at a North Kohala site called Ulua. It’s about three inches long. We saw much larger specimens at Backside Molokini last year. These relatively active nudibranchs are supposedly quite common in Hawaii.

*Funny, if you Google “search Image” in 2019 you get a bunch of links telling you how to search for images on line. In this old guy’s world, the term means as described in this fascinating link:


We’ve been seeing a lot of interesting crabs lately. Or maybe we’ve just been paying more attention.  Reef-dwelling crabs form a diverse assemblage, filling a wide variety of ecological niches. Many, like shrimp, live symbiotically with other reef creatures. Most are quite attractive. Here are two that have posed for us over the last few weeks:

This crab is often called the Spotted Reef Crab, but here in Hawaii it’s more commonly referred to as the Seven-Eleven Crab. The latter name comes from the seven spots on top of the shell and four more on the bottom. These large crabs are mostly nocturnal, but on several occasions we’ve seen them while snorkeling at Mahukona during the day. All of our sightings have been in the late spring to early summer.  Perhaps this seasonality is related to mating activity. Seven-Elevens are found in many parts of the tropical Pacific. They’re eaten in many places, including Hawaii.

We found this Yellow-spotted Guard Crab hiding among the branches of an Antler Coral while snorkeling at Kihei in Maui. A handful of species of guard crab live mutualistically in branching corals.  As the name suggests, they protect the corals from intruders, including the predatory Crown of Thorns Starfish. In exchange for their protective duties the crabs get to dine on the corals—presumably in moderation so as to not destroy their hosts. Hoover writes that if you put your hand over a coral that harbors these crabs you will get your hand pinched. We didn’t try it.

Kawaihae south

At the south end of Kawaihae Harbor is a small boat marina where a couple dozen private sailboats are moored.  The marina is protected by a rip-rap breakwater that opens out into shallow, rather murky Pelekane Bay. The bay is known for its resident Black Tip Reef Sharks. Hai has seen and filmed these beautiful, harmless sharks on numerous occasions (see but as of last week Marla and I had yet to see them. In an effort to correct that situation, Hai and Lottie escorted us out through the marina into Pelekane Bay last week. We were successful in spotting these elegant, wary animals, but weren’t able to get any photos. We did, however, see and photograph some interesting creatures, both on the swim out through the marina and in the bay itself.

As soon as we entered the water at the marina Hai spotted this Wavy Bubble Shell actively crawling on one of the dock pilings. These unusual little mollusks are sort of halfway between snails and nudibranchs—they have shells, but cannot fit their whole bodies into the shells. Like many nudibranchs, they dine on toxic organisms (bristleworms in this case) and incorporate their prey’s toxins for their own protection. That’s what allows this delicate little animal to move around in plain sight. The pan-tropical species reaches a length of about 3/4 inch, which is about the size of this individual.

Just a minute or two later Lottie found this pair of Banded Coral Shrimp living on the underside of the dock. These shrimp, quite common in Hawaii and throughout the tropics, are usually found in pairs like this. They’re a type of cleaner shrimp, but are infrequently seen in the act of cleaning fish.  Hoover speculates that this is because they do most of their cleaning at night.

Out in the bay I ran into this Old Woman Wrasse. Hoover says this endemic fish is only common in the unoccupied Northwestern Chain of the Hawaiian Islands. We see them rarely at Mahukona; I posted a photo of a juvenile here:  An alternate common name for this fish is Blacktail Wrasse, but the black tail is only found on terminal males. The Hawaiian name for this large wrasse, Hinalea Luahine, means old woman. This fish’s face has—to me at least—an oddly humanoid look, but not necessarily old woman-ish.

Small stuff at Kawaihae

Last weekend Marla and I snorkeled at Kawaihae Harbor, inside the breakwater, south of the platforms where the Army landing craft tie up. This is a warm, calm, relaxing place to snorkel—shallow, no waves, little wind. It’s also kind of barren relative to the sites we usually snorkel, with lots of dead coral, but several different coral species. And, like most sites, it yielded some interesting stuff.

We always make sure to visit the huge Plate and Knob Coral (Porites monticulosa) head southwest of the platforms. Oddly, this coral and others of its type don’t seem to be very attractive to fish. This lonely juvenile Convict Tang and a small group of juvenile parrotfish were all that we saw on this one. The light here allowed the coral to show through the fish’s translucent fins.

Cauliflower Corals attract all sorts of fish. This tiny Hawaiian Dascyllus plays hide and seek among the branches. 

There were a couple of wire corals growing from the boat ramp just a few feet off the beach. One was occupied by this Seawhip Goby. (Hoover calls it Gorgonian Goby.)  Earlier this year our friend Hai found  a couple of these fish living on a wire—not a wire coral, an actual wire— that hung into the water from one of the landing craft platforms. Hoover writes that this species can also be found on waterlogged twigs and pretty much anything else shaped sort of like a wire. The similar Wire Coral Goby is apparently more selective, usually confining itself to actual wire coral.

Another record falls

Today Hai and Lottie were supposed to show us where the Blacktip Reef Sharks hang out at the south end of Kawaihae Harbor, but roaring offshore winds made us divert to Plan B. We went east to Kawaihae’s commercial docks, tucked away from the wind. There among the dock’s pilings we identified six species of nudibranch, breaking my short-lived personal record of five, set only three days ago.

After Marla and I got home I did a little web crawling and found that many nudibranch species are fond of vertical surfaces like those provided by Kawaihae’s pilings and pylons*. Who’d have thought.

These handsome, if not colorful, White Margin Nudibranchs are apparently quite common in Hawaii, but they were a first for me. Hoover writes that they are often found in small groups. We saw several pairs and a triple today.

This inch and a half long Gloomy Nudibranch was the only nudi we saw that measured over an inch. The species can reach three inches.

Here’s another Painted Nudibranch. Quite a contrast to the one shown in the last post. This species ranges all the way to the Mediterranean, which it apparently reached via the Suez Canal.

Another Trembling Nudibranch. Look at that supple body—the way it’s folded itself across the thin, stiff (at least by nudibranch standards) obstacle that it’s crawling over. This species is the only endemic in this post.

The White Bump Nudibranch looks quite a bit like the Trembling, at least to me. Not so much to Marla, who, unlike me, distinguished them instantly in the field. The colors of the gills and rhinophores—deep blue in the Trembling; pale grey and brown in the White Bump—are the main identifiers for me. Marla said it was more of a Gestalt thing for her. The body color difference so apparent in these flash photos was not nearly so apparent to me in the rather dim light around the pilings.

This was the highlight of the outing for me. It’s a member of the genus Caloria; maybe an un-named species or maybe indica. There’s a lot of confusion on the web regarding this. In either case, gorgeous but tiny and surprisingly hard to spot. We saw several—mostly spotted by Hai. (I don’t know what that little round thing below the nudi is, but I suspect it’s something planted by ancient aliens. Click and take a close look and I’m sure you’ll agree.)

*Actually, they’re all pilings. I’m really misusing the term pylon here, but we** use it anyway to refer to the piling supporting the military platforms. Actually, we’re misusing piling as well. A pile is a support column, while a piling is a structure composed of piles. Piling feels better somehow, maybe because it’s doesn’t sound like a hemorrhoid.

**By “we” I mostly mean Jeff and me.