11 May 2014

A few molluscs of Vancouver Island

Himatina trophina, Rock Bay, Canada

As promised in one of my previous posts I will show some molluscs of Vancouver Island, Canada. I start with a few chitons.

Tonicella lineata, Neck Point, Canada

One of the chitons I found, was the lined chiton, Tonicella lineata. The distinguishing feature are the wavy blue lines on the shell plates. Up to 5 cm long, however generally no longer than 1 cm. They were very common. The variety in colours is immense and it is the most beautiful chiton I have ever seen.

There are at least 30 species of chitons around Vancouver Island (Lamb & Hanby, 2005). Some are quite easily, some hard to identify.

Tonicella lineata, Rock Bay, Canada

Again a lined chiton, but not so easy to identify: a kind of seaweed or other organism on the shell plates conceals the wavy blue lines. At the rear one plate is still uncovered; there you can see the wavy blue lines. I suspect that this plate has not seen the sun for a long period.

Lepidozona mertensi, Tyee Beach, Canada

This merten's chiton, Lepidozona mertensi (photo above and below in detail), is not easy to identify. As little as it is, this specimen is heavily encrusted with a red seaweed, a crustose coralline seaweed, a barnacle, a sponge and a species of moss animal (Bryozoa). Up to 5 cm long.

Lepidozona mertensi, detail, Tyee Beach, Canada

Mopalia muscosa, Botanical Beach, Canada 

Almost all the molluscs I found at Botanical Beach were eroded. It shows in this mossy chiton, Mopalia muscosa: a few shell plates are broken and the wavy structure on the plates has partly disappeared. It can grow up to 10 cm long. Quite large for a chiton, but wait till you have seen the other chitons I found at Vancouver Island...
Its 'travel companions' are a small speckled limpet, Lottia ochracea and a sitka periwinkle, Littorina sitkana.

Mopalia muscosa (?) &  Anthopleura elegantissima, Botanical Beach, Canada 

This chiton is hiding between pink-tipped anemones, Anthopleura elegantissima. I believe it is the same species of Mopalia muscosa, but it is almost beyond recognition. Its valves show no structure or pattern any longer. Only the hairs and general shape are distinguishing features.
It also has a very weathered travel companion: a checkered periwinkle, Littorina scutulata.

Botanical Beach is situated at the west side of Vancouver Island, where there is a heavy surf. More about this spot in a future post.

Katharina tunicata, Botanical Beach, Canada 

If you are unfamiliar with chitons, you might think they are woodlouse. But chitons are molluscs. Their shell is composed of eight separate plates. These plates overlap like roof tiles. The shell plates are embedded in a girdle, a tough, muscular structure. Because of these eight separate plates, chitons are flexible and when dislodged they curl up, just like a woodlouse or an armadillo, to protect themselves against predators and injuries caused by heavy surf.

The black leather chiton, Katharina tunicata, has an extensive leathery girdle (hence its name).

Katharina tunicata, Rock Bay, Canada

Up to 15 cm long, it is one of the largest species of chiton in the world.

Katharina tunicata, Rock Bay, Canada

Cryptochiton stelleri, Rock Bay, Canada

Some chiton-species are not flexible, like Cryptochiton stelleri, the giant pacific chiton. It looks like a leathery blob without shell, but the eight shell plates are hidden inside. Up to 35 cm long this is the biggest chiton of the world. Imagine the lined chiton this big. That would be a beauty!

Cryptochiton stelleri, Rock Bay, Canada

Cryptochiton stelleri, Tyee Beach, Canada

Cryptochiton stelleri, Tyee Beach, Canada

Under water you are able to see the warty texture.

Cryptochiton stelleri, Neck Point, Canada

I found this giant pacific chiton lying upside down, dead and already getting mouldy. You can easily distinguish its foot and at the left its mouth. I suspect that the rigid leathery shell unables it to curl up and to turn round, like giant tortoises.

Himatina trophina, Rock Bay, Canada

From the beast to the beauty: the long-mouthed aeolid, Himatina trophina. Behrens & Hermosillo (2005) state: to 5 cm in length, Lamb & Hanby (2005): up to 12 cm long. Maybe that the long-mouthed aeolids in northerly waters - the region covered in their book - are just bigger...

Himatina trophina, Rock Bay, Canada

Himatina trophina, Rock Bay, Canada

Lamb & Hanby (2005): 'The cores of the frilly cerata (gills) of this nudibranch are extensions of the creature's digestive tract and provide extra surface area for this proces.' In the photo above you can see a 'channel' running to and from the cores, especially at the back.

Himatina trophina & Elassochirus tenuimanus, Rock Bay, Canada

Although it is said that nudibranchs are no prey for animals like crabs and fish (see also the long-mouthed aeolid next to the english sole in this post), I have seen crabs eating the nudibranch Janolus cristatus, antiopella (NL: blauwtipje). Anyhow, this widehand hermit, Elassochirus tenuimanus, showed no interest in the long-mouthed aeolid.

Cadlina luteomarginata, Tyee Beach, Canada

The yellow-edged cadlina, Cadlina luteomarginata in its colourful biotope. Maybe in the direct vicinity of its prey? Like the orange rough ball sponge, Tethya californiana (top left) and the yellow boring sponge, Cliona californiana (the yellow spots middle left). Behrens & Hermosillo (2005): '.. feeds on a variety of sponges like Halichondria, Myxilla and Aplysilla.'

Cadlina luteomarginata, Tyee Beach, Canada

The yellow-edged cadlina grows up to 45 mm. Again larger in Lamb & Hanby (2005): 83 mm long.

Doris odhneriTyee Beach, Canada

The white nudibranch, Doris odhneri. Up to 20 cm long. I waited some time before the snail would extract its gills, the feather like organs at the back. Feeds on the sponge Halichondria (Behrens & Hermosillo, 2005).

Dirona pellucida, Rock Bay, Canada

The golden dirona, Dirona pellucida. Sometimes its hard to distuinguish head from tail in nudibranchs. Up to 12 cm.

Dirona pellucida, Rock Bay, Canada

Behrens & Hermosillo (2005): 'They feed on the bryozoan Bugula pacifica.'

Janolus fuscus, Rock Bay, Canada

I found this white-and-orange-tipped nudibranch, Janolus fuscus, just like the golden dirona, hanging on - mostly upside down - the jetty of Rock Bay.

Janolus fuscus, Rock Bay, Canada

Head or tail? You can distuinguish the rhinophores on the head at the top, because they are fringed and lack the orange ring. Up to 25 mm long. Behrens & Hermosillo (2005): 'They feed on the bryozoans Bugula and Tricellaria.'

Dendronotus rufus, Tyee Beach, Canada

A congregation of red dendronotids, Dendronotus rufus. Up to 28(!) cm long.
Behrens & Hermosillo (2005): 'Feeds on hydroids and scyphozoans.' 

Dendronotus rufus, Tyee Beach, Canada

No better pictures of this lovely nudibranch? Sorry, I got distracted by another interesting creature and forgot them... 

Haliotis kamtschatkana, Neck Point, Canada

A well camouflaged northern abalone, Haliotis kamtschatkana. Lamb & Hanby (2005): 'Populations of this species have been obliterated by overharvesting and fisheries mismanagement. ... Prospects for recovery are bleak indeed as illegal poaching activities outpace the many benefits of fishing closures.'

Haliotis kamtschatkana, Neck Point, Canada

Up to 18 cm long.

Haliotis kamtschatkana, Neck Point, Canada

An empty shell with mother of pearl inside.

Haliotis kamtschatkana, Neck Point, Canada

The same specimen with its beautiful red coloured outside. It is a well preserved specimen: at the left you can still see the 'original' abalone with its respiratory apertures. 

Lirabuccinum dirum, Neck Point, Canada

Hidden between seaweeds and moss animals: the dire whelk, Lirabuccinum dirum. Up to 5 cm long.

Lirabuccinum dirum, Rock Bay, Canada (staged)

Lamb & Hanby (2005): 'This active snail is a scavenger that particularly prefers injured prey, which it locates with susprising speed.'

Lirabuccinum dirum, Rock Bay, Canada (staged)

Head and mantle popping out. You can also see its operculum and eyes.

Fusitriton oregonensis, Neck Point, Canada 

The Oregon triton, Fusitriton oregonensis, up to 15 cm long, with its epidermis (upper layer) still intact. The epidermis wears off, especially in places with heavy surf.

Fusitriton oregonensis, Rock Bay, Canada 

Meinkoth (1981): 'The Oregon triton is an aggressive predator on molluscs and echinoderms, especially sea urchins. It rasps off the outer tissue and bores holes through the shell plates to get at the internal organs. Sometimes urchins are found with blackish scars resulting from encounters with this snail.' Reading this I wondered why this triton was rare, regarding the incredible amount of sea urchins at Rock Bay. See the next photo's.

Strongylocentrotus pallidus, Rock Bay, Canada 

Strongylocentrotus pallidus, Rock Bay, Canada

Ceratostoma foliatum, Rock Bay, Canada 

A couple of leafy hornmouths, Ceratostoma foliatum. A very common species at Rock Bay. Up to 10 cm long.  

Ceratostoma foliatum, Rock Bay, Canada 

It preys on oysters, but I found no oysters in Rock Bay. I presume it also preys on barnacles, just like its relative in the next photo, the Japanese rocksnail, Ocenebra inornata (NL: Japanse oesterboorder). In my aquarium small Japanese rocksnails (just as at Vancouver Island an import in the Netherlands) are preying on barnacles.

Ocenebra inornata, Gorishoek, The Netherlands

Ceratostoma foliatum, Rock Bay, Canada 

The darker coloured outgrowth shows the snail has grown strong in a short period of time. Otherwise part of it would have changed in the definitive colour. Compare with the more weathered specimen in the next photo.

Ceratostoma foliatum, Rock Bay, Canada 

Again showing its typical leafy ridges.

Nucella lamellosa, Rock Bay, Canada 

The wrinkled dogwinkle, Nucella lamellosa, shares the same biotope as the leafy hornmouth. Up to 12.5 cm long. At first I could not identify this snail. Friend and conchologist Herman Nijhuis identified it as Nucella lamellosa forma hormica (American Seashells by R. Tucker Abbot, 1974). As I looked this species up in Lamb & Hanby (2005) I found: 'Extremely variable shell colour, proportions and sculpturing often confuse the novice naturalist and expert alike.'

Mya truncata, Tyee Beach, Canada

Lying empty on the seafloor: the truncate softshell clam, Mya truncata (NL: afgeknotte strandgaper). Up to 8.5 cm.

Mya truncata, Tyee Beach, Canada

Even after the soft parts of the shell have vanished for months, the tough siphon coverings will be still in place.

Crassadoma gigantea, Neck Point, Canada

The giant rock scallop, Crassadoma gigantea, is almost invisible when closed. Up to 25 cm across.

Crassadoma gigantea, Neck Point, Canada

These specimen are overgrown with the same seaweeds, sponges, bryozoans and hydrozoans as their surroundings and the one above even becomes a resting place for the leather star, Dermasterias imbricata.

Crassadoma gigantea, Neck Point, Canada

Meinkoth (1981): 'This species develops and behaves like other scallops and is free-swimming until its valves grow to about 25 mm. At that time it settles on a solid object and its mantle secrets a limy material, cementing down the lower (right) shell and making the animal sedentary for the rest of its life.'

Crassadoma gigantea, Neck Point, Canada

The real beauty reveals itself: the orange mantle and the many, tiny black eyes.

  • mainly: Lamb & Hanby, 2005
  • quoted: Behrens & Hermosillo, 2005 (excellent guide of Opisthobranchs from Alaska to Central America), Meinkoth, 1981 and Tucker Abbott, 1974.