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Philippine Sea – Voyage Update #2

Philippine Sea Expedition Participant Scientists, Jann Vendetti, shares a tour of Molluscs on the first few days of the JAMSTEC Voyage.

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A tour of Molluscs:

April 30, 2024

On the first dive of the expedition, the Kaimei ROV (Remotely Operated Vehicle) was deployed for exploration and specimen collection. This ROV has filmed and collected specimens for JAMSTEC since 2016 and can descend to 3,000 meters (~9,843 feet).

Near the edge of the Minami-Daito seamount and at 797 meters deep (2,615 feet) one of the first animals we saw was a cirrate octopus, likely a species of the genus Grimpoteuthis. These molluscs have received some attention recently, being nicknamed the “Dumbo octopus”, and noted for their cuteness. The Dumbo elephant ear-like projections are really a set of paired and ridged fins that attach internally to a shell. That’s right! If you know anything about octopuses, you’re likely confident that they are the one group of living cephalopods (of the squid, cuttlefish, Nautilus, and octopuses) with no internal shell. Nope! These octopuses have an internal shell that is small but important. It varies from horseshoe-shaped to a bow tie-shaped and connects to the paired fins (ridged from internal cartilage) with specialized muscles, allowing these animals to swim. That is, the cirrate octopuses can power their movement by slowly “flapping” their fins, which is what we observed.

These amazing octopuses have semi-gelatinous bodies and live exclusively in the deep sea, having been observed at a maximum of 7,000 meters deep (22,965 feet, ~4.4 miles). For context, the deepest known place in the world’s oceans is called the Challenger Deep in the Mariana Trench and its depth is about 10,971 meters (35,994 feet, 6.8 miles). That is deeper than Mt. Everest is tall at 8,848.9 meters (29,032 feet, 5.5 miles).

So much is still left to learn about these molluscs; it was thrilling to see one!

May 1, 2024

This was the first dive of a small ROV Crambon during this expedition, and the first time it had been used since 2019.

This ROV collected sediment samples within which was this micro gastropod (small snail). It is about 0.6 cm long and currently un-identified by me. The shell with the apex (the pointed end) up is usually how snail shells are depicted in books, but in life the head end is that of the aperture (where the shell opening is). This remarkable micro snail covers its shell in a white sheath-like mantle.

Similarly tiny snails were also collected in sediment samples by the Kaimei ROV. The reason they are called micro gastropods is evident in the pictures, with a penny for scale.

Over the last week I’ve been consumed by attempts to identify several snails collected at depth. In the photos you can see two, both of which (in a separate HOV dive) were also found “crabbed”, that is, having their empty shells inhabited by hermit crabs:

  • The first is a gastropod brought up with deep sea Asteroidea, or sea stars, in the genus Brisinga. These sea stars are amazingly long-armed and orange, and the snail with them has a brown and white striped shell, bright yellow body, and a short siphon.
  • The second is a snail in the family Colloniinae, which are characterized by a round aperture (shell opening) and a calcareous operculum (a hard calcium-rich “trap door”). This one has a pink and white striped shell and brown and white striped foot and looks to be a species of Bothropoma or Collonista.
  • Finally, this “crabbed” shell is a species in the genus Bursa. You can see this awesome hermit crab securely in the Bursa shell, then nearly completely out. Unlike snails, hermit crabs can leave a snail shell and find a new one when it suits them. For snails, their shell is their forever home, and one of their own making.


Until next time…

Missed an update? Revisit Voyage update #1.

Thanks to Jann Vendetti for sharing this voyage update. This expedition is led by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), the Ocean Shot Research Grant, and NHK TV.

Featured Image Credits: Jann Vendetti

Image credits: JAMSTEC, Jann Vendetti

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