Category: invertebrates

Readers’ wildlife photos and videos

July 17, 2026 • 8:15 am

Today we have photos and videos of the California intertidal taken by math professor Abby Thompson of UC Davis. Her captions and IDs are indented, and you can enlarge the photos by clicking on them.

Just a few more great low tides for the summer. By August the kelp is so lush, it becomes harder to find interesting creatures, so I’m enjoying June and July.  These photos were taken during the full moon at the end of June.

Amblyosyllis anae (marine worm- it seems to be a summer of worms). This genus is relatively rare (or at least hard to find) here.   I had picked up a piece of sponge to look at under a microscope, and this guy crawled out, so I was lucky.  It was about ¼” long, and lively, as you can see in the video which follows.

Amblyosyllis anae video:

Megalorchestia corniculata (beach flea)- part of the beach clean-up crew.

Dirona picta (nudibranch):

Genus Eudendrium (hydroid):

Class Hydrozoa; this is the medusa (baby jellyfish) form of a hydroid, possibly of the Eudendrium in the previous picture (they were in the same dish). I don’t know what the yellow blob it’s attached to is; in the video following you can see it trying to detach itself:

Hydrozoa video:

Family Phoronidae– yet another type of marine worm, a “horseshoe worm”:

Genus Haliclona (sponge) – it takes an expert and/or a microscope to determine species for sponges. This type is very widespread, and a great color:

Ancula pacifica (tiny nudibranch):

Dendraster excentricus (Sand dollar) This is the “test” (internal skeleton) of a kind of flattened sea urchin. The live urchins stay below the low tide line, and they live in big clusters, sometimes propped up perpendicular to the sand.      Sort-of like the drawing of the oysters in Lewis Carroll’s “The Walrus and the Carpenter”, but underwater, and without the little shoes.

Mussel tracks- not tracks, of course, but for some reason mussels release droplets (presumably seawater?) when they’re exposed at low tide:

Anthopleura artemisia (moonglow anemone):

Moonset over Tomales Point. Moonset on June 30 was just before sunrise, making for some cool lighting:

Readers’ wildlife photos

June 29, 2026 • 8:15 am

Today we have photos from Jan Malik taken at Cape May, New Jersey emphasizing the bizarre horseshoe crabs, which are not crustaceans but chelicerates, more closely related to spiders and scorpions than to real crabs.  Jan’s captions and IDs are indented, and you can click on the photos to enlarge them.

People visit Cape May, NJ, in spring, mostly to see the migrating birds, but what makes the high density of animal migrants and residents possible in that area is in large part hidden in the water. Delaware Bay is home to a large population of the Atlantic horseshoe crab (Limulus polyphemus) which spawn around the time the migrating birds pass through. Horseshoe crabs’ eggs, along with crabs themselves, are an important link in the food chain that fuels the spring migration.

Early morning visitors to the Delaware Bay side of Cape May are welcomed by the ruckus made by Laughing Gulls (Leucophaeus atricilla). These birds nest locally but also depend on the crabs as a major food source:

Walking onto the beach in the morning after a high tide, a visitor will see these animals stranded helplessly on their backs, flipped by the waves:

Here is a larger female with a male still attached. All three parts of a crab are visible: the main body (prosoma) with mouth and legs, an abdomen (opisthosoma) with book gills and a tail (telson). What can be also seen here are male’s pincers, modified forelegs used to grasp the carapace of the female:

The crabs are not blind thanks to their pair of compound eyes. They also have 8 other simple eyes and ocelli distributed on top of their carapace and additional photosensors underneath and on the telson. These organs are sensitive to UV and visible light and are used to detect phases of the lunar cycle and determine when to come out of water onto the sand to mate and lay eggs:

The primary function of a telson is to help the animal steer and to right itself in water. On dry land, however, it is of little help and a flipped crab, if left on its own, usually succumbs to desiccation or is preyed upon by other animals:

 A human visitor to the beach has to decide whether to save the crab or leave it to die and let birds have their fill. In my case I usually flip them back on, giving them a chance to live another day. They are used by the medical industry to develop a test for the presence of bacteria in medical devices, which involves catching them, drawing about a quarter of their blood and then releasing them, but such a crab is then greatly weakened and mortality is high:

A Sanderling (Calidris alba) eating a horseshoe crab egg. For some evolutionary reason, these marine arthropods must leave the water in order to lay eggs. They prefer to do the laying at high tide, hence the lunar phase detection. The eggs may be then uncovered by waves and spread far and wide on the beach:

The waves may also uncover a whole cluster of eggs which is then found by shorebirds patrolling the ecotone between the sea and the land:

This is what the washed up eggs look like; eggs are 1.5 mm to 2 mm in diameter and they grow as the embryos inside them grow. This is the main fuel for the thousands of plovers, sanderlings, turnstones, red knots and others on their way toward the Arctic:

Using a macro lens, one can make out an embryo inside, complete with legs, telson and tiny eyes:

I think it was only at the beginning of this century that the significance of these “crabs” (which have a common ancestor with spiders and scorpions) for migrating birds was properly recognized and some harvesting bans were put in place in NJ and Delaware. Before, they would be harvested in excess as crab bait or just for fertilizer. This picture shows how they can be a host to barnacles and limpets:

Even though they can and do come onshore during daytime, they prefer nighttime at high tide, at new or full moon. In the Delaware Bay, many thousands of them come out then, males crowding around the females to claim the best spot and be first to fertilize eggs. They must have been doing similar things for many millions of years – earliest fossils with similar body plans date back to Paleozoic era, 450 mya, which was well before the dinosaurs. Fossils quite similar to the Atlantic crab date back 200 mya. There were many species but now only four are left, this site presents a neat diagram illustrating their evolutionary history:

Just to give a sense of scale, here is a “scrum” of crabs around human feet:

Spring migration attracts many visitors to Cape May, benefiting local businesses. I think it is just to also count humans as dependent on these “crabs”, to an extent. Note that the forefront crab has a tag from the US Fish and Wildlife Services, allowing it to track the animal:

 

 

Readers’ wildlife photos

June 21, 2026 • 8:15 am

Today’s collection is from math prof Abby Thompson at UC Davis, who sends us intertidal photos from California. Abby’s IDs and captions are indented, and you can enlarge her photos by clicking on them.

The photos were taken at Dillon Beach.

Orienthella piunca (nudibranch), with eggs (the white squiggly things), and a small crab spectating”:

Crab tracks- these always look to me like some complicated bicycle tire track, but apparently it’s just what happens if you skitter sideways on your claws. The crab is buried in the sand at the end of the trail, close-up in the next photo:

Crab- probably Romaleon antennarium, Pacific rock crab. Hunkering down, waiting for the tide to come back in:

Epiactis handi (sea anemone).  This is the unusual species of Epiactis which seems to occur only in a single (and hard-to-access) location near me.   I like to check in on them periodically:

Aegires albopunctatus (nudibranch) Salt-and-pepper nudibranch:

Pycnogonum stearnsi (Sea spider). Nestled into the seaweed, completely out of the water, on top of a rock:

Emerita analoga (Pacific sand crabs). Walking the beach at low tide sometimes it looks as though the sand is puckered- that’s likely to be bevy of some kind of tiny sand crab.     This photo shows the “puckering” from a distance of a few feet:

Pacific sand crabs from close up. A footstep will spook them, and they bury themselves completely in a split second.  Not a great photo, but if you look carefully I think you can see each one has its stalked eyes poking up:

Mopalia muscosa (mossy chiton). The inside of the shell- the animal is long gone, leaving these beautiful interior colors:

The beach at sunrise.

Readers’ wildlife photos

June 9, 2026 • 8:15 am

I forgot to post part 2 of Abby Thompson‘s latest batch of California intertidal photos, so here they are (the first batch is here). Abby’s captions and IDs are indented, and, as always, you can enlarge the photos by clicking on them.

The stars of this set, improbably enough, are two flatworms.   The first two pictures are of the elegant Eurylepta californica, which I think of as the “art-deco flatworm”.  It’s rare up here; I’ve found it once before.  The next flatworm (Family Euryleptidae) is an undescribed species.   It’s been recorded several times, almost all in the Monterey Bay area.    This is its third sighting (as recorded on inaturalist) this far north.  There isn’t agreement on the genus. It’s a beauty, and it’s unusual to have such a striking animal remain undescribed.   Both worms are about ¾” long.

Eurylepta californica (striped polyclad flatworm) Art deco flatworm:

Eurylepta californica:

Family Euryleptidae (Yellow frilly flatworm):

The starfish plague of several years ago was devastating along the coast, and several species (like the incredible sunflower stars) have not recovered, but the ochre stars are back with a vengeance.     I see many more of them than of the bat stars, but the next picture is one of each buddying up on a rock above the low tide line.

Patiria miniate and Pisaster ochraceus (bat star (red) and ochre star (yes, purple)):

The next three pictures are a slightly deceptive series.    I’m not sure that the first two pictures really are otter tracks, but the alternative is probably raccoon tracks, and otter is a better match.   They did not, in fact, end on the beach right next to the where I saw the otter in the third picture.   But at least the third picture below is definitely an otter.   This almost surely is a river otter, not a sea otter, as are most seen around here.

Otter tracks:

Close-up of otter tracks:

Lontra canadensis (North American river otter):

Finally, the roof of a cave, with sea anemones (green and pink– Anthopleura xanthogrammica and Anthopleura elegantissima) and sponges (the bright red-orange, not possible to ID from a photo):

Readers’ wildlife photos

June 1, 2026 • 8:15 am

Today we have pictures from the shore of New Jersey taken by Jan Malik.  Jan’s captions and IDs are indented, and you can enlarge the photos by clicking on them.

Here are a few pictures from my walks on Cape May and Sandy Hook, taken this April.

Starting from the Atlantic Ocean (eastern) shore on Cape May, I met this pair of American Oystercatchers (Haematopus palliatus). In Cape May, a section of the beach is fenced off to protect nesting sites for them and for Piping plovers. They are feisty birds and every spring there is a competition for nesting sites; the bird on the right is calling at another Oystercatcher:

The pair took off to drive out the intruder:

The place where I found that pair was littered with the remains of Sand fleas (possibly Emerita talpoida). These fossorial crustaceans normally stay buried in the sand, exiting only when the sand is awash with the shallow tide, but Oystercatchers’ bills are well adapted to dig them out. I think the birds ate only the soft and juicy parts of their telsons, leaving the crustaceans mortally wounded and unable to move:

These Sand fleas are small and difficult to catch alive. That’s what their front end and first pair of legs look like. These crabs dig backwards, starting from their telson, and the front pair of legs is used as a sand anchor:

Another arthropod – the Horseshoe crab (Limulus polyphemus), came ashore, atypically for it, on the Atlantic Ocean side of the peninsula. These are treacherous waters for these spiderlike creatures, for they are easily flipped over by ocean waves and become stranded. They are an interesting part of the Delaware Bay ecosystem and I may share more pictures of them later:

On the Delaware Bay shore of Cape May, there were already many Laughing gulls (Leucophaeus atricilla), which mostly move south in winter but return to their breeding grounds in the spring. They are quite similar to the Eurasian Black-headed gull:

Terns also made their appearance. I think this may be a Forster’s tern (Sterna forsteri) because of the lack of black tips on its primaries and its pure white underbelly, but they are difficult to tell apart from Common terns (Sterna hirundo):

The terns landed on old quay pilings and started courting. There’s no way to tell females from males other than by their courting behavior; males can be slightly larger, but the difference is less than 5%, which is hardly discernible to the human eye:

The courting consists of the two mates trying to look “smug”, with wings drooped, necks extended, and bills pointed toward the sky:

Then there’s the courtship dance and ritual feeding. Here is a fragment of it, taken from a large distance, so I’ve compensated for the lack of pixels by cobbling together this composite. The male presents a fry to the female and then, if she accepts (which is not a given), circles around the female while stomping his feet:

On my way home, I stopped at Sandy Hook, a sand spit where shore gun batteries protecting New York Harbor were once located. It is now a prime nesting site for Ospreys (Pandion haliaetus):

The former Army garrison required many houses for the officers, and these are now excellent nesting sites for Ospreys. Standing in the center of Officers Row (as the area is called), I counted four nests on top of chimneys:

The meadow below the houses was full of American robins (Turdus migratorius) fattening up for the nesting season by preying on earthworms. I know little about annelids, but I’m going to go out on a limb and say it is the common earthworm (Lumbricus terrestris), since it is a favorite prey for robins:

Finally, moving to the class Mammalia, here are Sandy Hook’s harbor seals (Phoca vitulina), congregating on rocks exposed by low tide (the tide was rising so, one by one, the seals were forced to slip back into the water). There are eight seals in this picture, but I counted 15 in total. Their population around the New York inlet has increased in recent years, which may soon put them on a collision course with the fishing industry:

Readers’ wildlife photos

May 27, 2026 • 8:15 am

Today we have some intertidal photos taken in California by UC Davis math professor Abby Thompson. Abby’s captions and IDs are indented, and you can enlarge her photos by clicking on them.

May is a great month on the California coast, with extreme high and low tides.   Here are some photos from the most recent, excellent, set:

Pollicipes polymerus (Gooseneck barnacles). I’ve shown these, and some relatives, several times before, but they’re amazing animals. In case you think it’s too many barnacles, Darwin spent eight years looking at barnacles.   “Originally planning a brief month-long study to establish his credentials in invertebrate zoology, he became deeply immersed and cataloged every known living and fossil species.”  (Google AI).  I’m not sure what the green is doing here, presumably just growing on top of the animals.   Some relatives of the nudibranchs stay green from what they eat, and retain bits with the ability to photosynthesize, most famously the adorable leaf sheep:.

Dendronotus venustus (nudibranch):

Paciocinebrina lurida (a snail):

Tonicella lokii (flame-lined chiton):

Genus Tegula (maybe) (another snail). There was a hermit crab living in the shell- I didn’t get a good photo of him.    I’m not sure the genus is correct, but the shell was so pretty I wanted to post it:

Nucella ostrina (Northern striped dogwinkle). About the common name—well, it has stripes.   And it’s a “winkle” (a word you have to love), or “little whelk”.  The dog part, I dunno.   They’re very common, and voracious. Some species of Nucella (not sure about this one) can be used to make a deep purple dye, which used to be hard to come by.  There’s a fun account of making the dye here, although I’m afraid many snails must have been sacrificed in the process:

Paradialychone ecaudata (worm):

Limpet, probably Lottia pelta (shield limpet). The little lacy edge is tentacles: “Pallial tentacles are tiny, sensory structures lining the mantle margin (pallium) of limpets. . . The tips and shafts of these tentacles are covered in dense tufts of non-motile cilia, which act as sensory receptors.” (Google AI):

Seagulls at sunset:

As always, thanks to experts on inaturalist for help with some IDs.   Camera is an Olympus TG-7.

Readers’ wildlife photos and video

April 26, 2026 • 8:15 am

I now have three batches plus some singletons, and so we’ll have semi-regular photos for a while, at least.  Today’s batch of tidal invertebrate photos, and one video, comes from math professor Abby Thompson at UC Davis. Abby’s captions are indented, and you can enlarge the photos by clicking on them. The video is also hers.

April tidepools, and a mystery den.

Starting with a video of a Ctenophore, Pleurobrachia bachei (Pacific sea gooseberry, a ‘comb jelly’). All appearances to the contrary, this is in a different phylum (Ctenophora) from the “jellyfish” of my earlier post, which are in the phylum Cnidaria.   The flashing lights are the cilia in the “combs” that run down the sides, used for locomotion.  This one wasn’t moving very much, but I was surprised it was moving at all.   I picked it up off the sand quite a way above the water line, and dumped it into a shallow pool to take a photo.    It seemed to be recovering pretty well from what I thought was death.   It’s about the size of a walnut.

Sea urchin “test”, or internal skeleton. Probably Strongylocentrotus purpuratus:

Ophiopholis aculeata (daisy brittle star):

Bispira pacifica (feather duster worm):

Close up of ‘feathers’ of pacifica:

Genus Eupentacta (sea cucumber):

Phoronis ijimai (tentative- the white things). This is a species of horseshoe worm, which lives in tubes.   I haven’t seen this species before, and it was in an awkward spot, so it was hard to get a good photo.   The photo below that is from a few years ago of a worm from the same family, so you can see their general shape better:

Phoronopsis harmeri (from July 2021) (same family):

Anthopleura artemisia (moonglow anemone):

And a few nudibranchs:

Triopha maculata (nudibranch):

Tenellia laguna (nudibranch):

Acanthodoris rhodoceras (nudibranch):

Rostanga pulchra (nudibranch):

Lastly the mystery den. Our entire front yard seems to have been tunneled under, with at least three major entrances- this pair of holes is just one of them.  The holes are large, about 10 inches across.  We’re dreaming of badgers, would be very happy with foxes, and really hoping it’s not skunks (I love skunks, but not in the front yard).  A wildlife cam is the next purchase:

Camera: Olympus TG-7.   Thanks as usual to some experts on inaturalist.