Category: invertebrates

Readers’ wildlife photos

November 1, 2026 • 8:30 am

UC Davis math professor Abby Thompson has sent us a batch of lovely marine invertebrate photos from California.  Abby’s captions and IDs are indented, and you can enlarge her photos by clicking on them.

The October low tides had some challenging features.   There was a strong wind (which makes me cold and everything harder to photograph), but most importantly the tides were running about a foot over (astronomical) predictions.

The very highest tides here are usually about 6 feet above sea level, and the very lowest about 2 feet below (listed as +6 or -2). A “good” low tide, when lots of different species are visible, is below –1.  This means that a 1-foot difference from predictions has a significant impact on where you can go and what you can see.  The reason for the overage is apparently twofold; the warmer water from El Niño (thermal expansion of the water), and the mysterious “Kelvin waves” sweeping up the coast, which interact in a complicated way. While the physics of the Kelvin waves escapes me, I can attest that the low tides were about 1 foot higher than projected, and that the water is warmer than usual.  While my personal frustration is with the too-high low tides, everyone else is understandably worried about the upcoming King tides in November, December and January, when the maximally high tides of the year occur. If those high tides run 1-2 feet higher than usual, and happen to coincide with a storm surge, there’s going to be a lot of coastal flooding.

Challenging or not, it’s always beautiful to be on the beach, so here are photos from late October.

Some species of gull (Genus Larus)—perhaps someone can tell species from this photo. The sand acted like a mirror in the late afternoon sun:

By-the-wind sailor (Velella velella). In the spring these can wash up by the thousands, but it’s unusual to find any alive at this time of year.     It might be because of the warmth of the water.     I found two very small ones:

By-the-wind sailor underside:

Urtibrina rimicola; this used to be (approximately last week) called a “stubby Pacific rose anemone”; then the taxonomists got to work on it, and it’s now stuck with just a scientific name:

A clutch of nudibranchs:   the first two are common, but happened to pose nicely for the camera:

Hermissenda opalescens:

Orienthella piunca:

The second two are rarer where I am; I’ve found each of them only once or twice.

Apata pricei. Dillon Beach (where I am) was close to the northern edge of this species’ range on inaturalist until a few days ago, when someone posted one from much farther north, near Trinidad, CA.  El Niño at work?:

Polycera atra.  It’s a little hard to believe this coloration is adaptive, but they’re surprisingly hard to spot. The second photo gives a little better idea of how they might blend into their bryozoan prey. Kind-of like a zebra:

Polycera atra blending in?:

The path down to the beach:

Beach in the wind and waves just after sunset:

Readers’ wildlife photos

October 9, 2026 • 8:15 am

One generous contributor has come forward with some wildlife photos: mathematician Abby Thompson from UC Davis. Abby’s captions and IDs are indented, and you can enlarge her photos by clicking on them.

This is a grab-bag of photos from Northern California from the summer (with one exception).

Cervus canadensis nannodes. A particularly contented Tule elk from the Point Reyes preserve:

Cornu aspersum (garden snail)- As a gardener I abhor them but looked at closely they are beautiful. They were introduced to California in the 1850s to be made into escargot, and now plague gardeners up and down the state:

Brodiaea terrestris from Point Reyes:

Once the extreme tides of the summer pass and there are no “good” low tides, I start looking through a microscope at bits of riffraff collected from the beach. It’s astonishing how many different creatures can live in a cubic inch of washed-up kelp holdfast.

Thetis vagina (twin-sailed salp). One of the seemingly endless types of blobby transparent things drifting around the ocean. Lying on the sand it looks like a scrap of Saran Wrap. Once revived in some sea water and under magnification the ghostly internal structure appears.    From google AI:  “Despite their jelly-like look, salps belong to the subphylum Tunicata (sea squirts), making them chordates that are evolutionarily more closely related to humans and vertebrates than to actual jellyfish.”  Cousins!

Phragmatopoma californica (California sandcastle worm). The worm is the curly orange thing on the left, which connects to the pink tentacles on the right underneath the structure with purple flecks, which is all that’s left of the tube the worm calls home (it’s ok, they can rebuild):

Close up showing the worm’s operculum – the “lid” of the tube, which the worm pulls down to close off the top of the tube when it retreats inside. I’ve posted a picture of this species before; my excuse is that this one’s tube, usually just made of sand,  has an interesting feature:

A close-up of the tube remnants, showing some Foraminifera, amazing 1-celled organisms.   The white ones in the center that look kind-of like a snail shell are Haynesina depressula (thanks inaturalist expert!) and there are several other types in there, harder to pick out.    I think the purple bits are pieces of sea urchin spines.     An artistic sandcastle worm!:

Genus Elphidium– another foram. This one was tangled in a shred of bryozoan.  It’s hard for me to believe this is a single cell, but I guess life is complicated:

Class Ostracoda – the things with little white dots. These are tiny crustaceans, mere specks.  There’s a foram in this photo, too:

Another ostracod- from 2025, not a great photo, included because it’s the first ostracod I ever saw. At first I thought I was looking at an infant mussel.    Then it sprouted legs and started running around like a crazy cartoon mussel. Quite a shock:

Genus Corambe (nudibranch, a baby), surrounded by its bryozoan prey. I think this ID is correct- its coloration is not typical of the genus. The nudibranch is so small that it looks slightly like it’s going to be attacked by the bryozoa, rather than vice-versa:

Sunset over the water:

Most photos taken with an iPhone precariously clamped to the eyepiece of an antique microscope.

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: