Readers’ wildlife photos

Reader Jacques Hausser from Switzerland. You can also see the first installment published on March 21:

These photos (of animals brought in the lab for identification) were taken during the two weeks internship on coastal ecology and faunistics we organise each spring for our master students in ecology and evolution, at the Biological Station of Roscoff in Britanny, France. The place is remarkably situated, with very diverse intertidal biotopes ranging from mud to sand to gravels to boulders to rocky cliffs and with impressive tides (up to 9 m of amplitude). We have nothing like that in Switzerland !

A pair of Idotea balthica, a detritivorous Isopod crustacean. This big greenish male holds firmly its small (and barely visible) orange female in precopulatory state until she moults, the only – and very short – period in which copulation can occur. This “mate guarding” is widespread in Isopods and amphipods, and the male can carry the female for several days. This strategy results from a strong competition among males, and induces a conflict between sexes as well: e.g. a guarded female is more prone to predation by fishes, since the motility of the pair is reduced. So she does resist to the males as late as possible, what in turn selects for the stronger males.

Leptoplana tremellaris is a Turbellarian, a 15 mm long flatworm gliding like a ghost on its ciliated underside. It is a predator eating various small invertebrates caught by its extensible mouth situated on the “belly”— approximately at the second third of the body. But look at the eyes: two clouds of very tiny ones in the front of two clusters of larger ones. They are very primitive: a mere cup of pigmented cells capping some photosensitive cells. The pigmented cells mask the light coming from behind them, what allows the animal to locate the origin of the light, which comes mostly the surface of the sea above them. There’s nothing more, but it is what they need to know: what’s up and down, and if whether they are exposed and vulnerable, or well hidden. Show that to creationists telling you that an incomplete eye is useless !

Psammechinus miliaris, a sea urchin. In addition to its spines, it bears five double arrays of tubular feet, each ending with a small sucker. They are used to hold the animal in place on the ground and to move it. What’s intriguing for us bilaterian animals, is that urchins have neither front and rear nor right and left sides. When moving, the feet can be pulling on their suckers on any orientation, while they are relaxed on the opposite side. The pulling side is anywhere the urchin detects some appealing food smell or sees an attractive spot (*). Urchins have up and down sides, however: down is where the mouth is, as well as the small algae these creatures graze on; up is where water is flowing, where they eliminate their waste and spawn their male or female gametes, directly in water. They have separate sexes, but the sentimental life of an urchin seems rather dull, limited to a pheromonal synchronisation of the spawning with its neighbors.

(*) It was shown that even without eyes, only photosensitive cells scattered across their body, urchins can see with the whole body and detect a black spot in a white arena. See e.g. Yerramilli, D & S. Johnsen, 2010: Spatial vision in the purple sea urchin Strongylocentrotus purpuratus (Echinoidea). J Exp Biol.  213(2):249-55. doi: 10.1242/jeb.033159.

 Compared to most marine snails, Euspira catena, the large necklace shell, has an enormous foot used to plough the sand. It protects its pretty and smooth shell from abrasion by covering it with a part of the foot and with a generous production of mucus. Euspira is a hunter of bivalve molluscs, first grinding a hole in their shell with its toothed tongue (the radula), helped by its acid saliva dissolving the calcium carbonate, and then introducing its proboscis to suck out the owner. It is quite common to find empty shells of its victims on the beach, with a revealing neat little rounded hole (insert picture borrowed from  here).

An Euspira bequeathed a nice second-hand house to this Hermit crab, Pagurus bernhardus. Thanks to the basic pH (about 8.15) of the sea water, the lifespan of a snail’s shell is far, far longer than the lifespan of the snail itself. Thus empty shells are extremely abundant, and this resource is heavily exploited, probably since at least the middle Jurassic: there are eighteen species of hermit crabs just in Northwest Europe. They are omnivorous opportunistic feeders and regularly choose a new shell as they grow in size, switching from one to another species of snail. It is very nice to see them carefully measuring and evaluating a new would-be apartment before deciding whether to move.

The shell used by a hermit crab also provides a mobile home to several other animals, sponges, sea anemones or other cnidarians. Here an encrusting colony of Hydractinia equinataan athecan hydroid. It takes advantage of the water currents generated by the hermit crab and of the small particles of its food waste suspended in the water. In return, the cnidocytes (stinging cells) of Hydractinia confer some protection to the hermit crab.

In the intertidal zone, between high and low tide, burying yourself in the sand protects you from desiccation, temperature variation and predators. It is the solution “chosen” by Acrocnida brachiata, a bristlestar with incredibly long arms. At low tide, it is entirely buried; at high tide, only the distal end of its arms emerge and float in the water, allowing suspension feeding.

The tube of Lagis koreni, the trumpet worm—an annelid in the family Pectinariidae—is a real work of art: it has an elegant tusk shape, and its wall is built with exactly one layer of sand grains carefully adjusted and cemented by some mucus – looks almost like a mosaic. The tube is open at both ends, larger one down, and held vertically, half emerging from sand. The head of the worm is down, equipped with two “spades” of strong chetae (bristles) to dig the sand as well as numerous tentacles to collect the food. The feces and other waste are eliminated through the upper opening. Here you can perhaps see the pinkish worm itself through the shell’s transparency – I didn’t have the heart to demolish its construction and it didn’t want to show itself.

A striking convergence: the shell of Scaphopod molluscs, or tusk shells, specially Antalis entalis, has exactly the same look as the one above, except that it is calcareous and secreted by the animal, and the spades of chaeta are replaced by its foot. Apart from that, tusk shells and trumpet worms have a quite similar way of life.

Unfortunately I don’t have any pictures, but you can find one in Wikipedia under “tusk shell“.

JAC: Here’s a tusk shell:

19 Comments

  1. Michael Fisher
    Posted April 4, 2018 at 8:18 am | Permalink

    Great pics & notes. Perfect.
    The trumpet worm sand home construction is something to think about. Does it start the build as a small critter at the narrow end & add increasingly larger radius wall as it grows?

    • Jacques Hausser
      Posted April 4, 2018 at 9:22 am | Permalink

      Honestly I don’t know, the books I have are silent about that, just saying the worm has a planktonic larva, but it seems logical: An unavailable article suggests that the sand grains used increase in size with the growth of the worm.

  2. phar84
    Posted April 4, 2018 at 9:14 am | Permalink

    Thanks for the pics and commentaries.

  3. W.T. Effingham
    Posted April 4, 2018 at 9:15 am | Permalink

    I love the description of the samples habitat. The nine meter tires must cause some challenging conditions, depending on wind speed and direction…😐

    • W.T. Effingham
      Posted April 4, 2018 at 9:16 am | Permalink

      Tired not tires.

      • W.T. Effingham
        Posted April 4, 2018 at 9:17 am | Permalink

        Spell check again??

        • W.T. Effingham
          Posted April 4, 2018 at 9:18 am | Permalink

          Tides.

    • Jacques Hausser
      Posted April 4, 2018 at 9:32 am | Permalink

      Yes, in two occasions (not this year) some students were caught on a small island by the tide and salvaged by the SNSM (National sea-rescue Society). They were broad smiles and some comments about Swiss sailors when I went to the bar for a beer the same evening….

  4. Posted April 4, 2018 at 9:17 am | Permalink

    Marvelous stuff! I deeply appreciate the fine pictures on white surroundings, plus the instructive commentary.
    Years ago when I lived further South I would regularly visit the ocean in Mexico. There I would find Euspira (or ‘moon snail’), much like the ones you show. These big-footed predators were surprisingly swift for a snail, but their prey are not without resources. Once I was watching one of these terrors cruising along in a tide pool when the edge of its foot just slightly touched another snail. That snail immediately ‘swam’ by lashing its foot from side to side, lifting away from the danger. It swam a couple feet away to settle somewhere safer. Never seen that before!

  5. Posted April 4, 2018 at 11:07 am | Permalink

    Very nice!

  6. Posted April 4, 2018 at 12:34 pm | Permalink

    Interesting molluscs today. Poor bivalve victims!

  7. Posted April 4, 2018 at 12:38 pm | Permalink

    Wonderful, but I’m missing a sense of scale on some of these!

  8. Christopher
    Posted April 4, 2018 at 1:56 pm | Permalink

    Thank you for such wonderful photos. Being landlocked as I am, in the middle of the middle US, I don’t get to experience such wildlife, excepting the fossilized forms in Pennsylvanian deposits from our ancient inland sea.

  9. Mark R.
    Posted April 4, 2018 at 3:10 pm | Permalink

    Your sea critter photos are some of the best I’ve seen on WEIT: very instructive, and expertly done. Bravo!

  10. Kiwi Dave
    Posted April 4, 2018 at 3:39 pm | Permalink

    Very interesting and informative.

  11. Posted April 4, 2018 at 4:31 pm | Permalink

    very good

  12. loren russell
    Posted April 4, 2018 at 6:32 pm | Permalink

    Hermit crabs pondering whether to choose to move house? This is “free shell worth having”!

  13. Posted April 4, 2018 at 11:28 pm | Permalink

    Invertebrates never cease to amaze.

  14. tjeales
    Posted April 5, 2018 at 6:22 pm | Permalink

    Fantastic. Makes me want to grab my camera and an icecream bucket and head down to the local rockpools


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