Plankton Portal Talk

Two thimbles head shapes for rocket-ships?

  • Lounalune by Lounalune

    I find that the siphos that get classified as rocket-ship thimbles tend to have two distinct head shapes, and was wondering whether these are different species, different stages of development, or whether the shots were just shot at different angles. On one hand, we have the classic thimble shape, like in the example picture or here: http://talk.planktonportal.org/#/subjects/APK000168d. On the other hand, we have some heads that seem divided into two sections, like here: http://talk.planktonportal.org/#/subjects/APK0000cbx. What is going on?

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  • jessicaluo by jessicaluo scientist, admin

    Great question and observation! You are actually seeing two life stages here of the same (or similar) species.

    Scientifically, the Rocketship organisms are called "Calycorphoran siphonophores" and these guys are capable of both sexual and asexual reproduction. As an adult siphonophore (called technically a "polygastric adult") grows, the tail ("stem") lengthens from the base up, so the end of the stem is actually older than the base of the stem. And they will bud little siphonophores asexually from the stem. If you've seen little round circles at the end of the stem that is actually asexual budding in action.

    When the adult releases these buds, they become free swimming "eudoxids." These are actually not yet a larval stage but now these eudoxids are capable of sexual reproduction. Crazy, right? But wait, it gets crazier.

    These eudoxids then develop little reproductive organs along its stem. Instead of eudoxids functionally male or female, they actually develop male and female reproductive parts - eggs and sperm - alternating between the two, sometimes regularly, sometimes irregularly. That way, they can ensure that the eggs are fertilized and can develop into larvae, then post-larvae, then adults.

    The open ocean is a vast place, and animals have developed vastly different strategies for how to ensure the continuation of their species, whether it is in spawning aggregations (e.g. Grouper fish spawning in the Caribbean - and larvaceans also apparently form spawning aggregations) or being hermaphroditic (like Ctenophores and some fish), and being able to asexually bud and reproduce sexually. These siphonophores have adopted the strategy of being both hermaphroditic AND able to reproduce sexually and asexually.

    This is the best diagram I've found to describe the life history of a Calycorphoran siphonophore (or "rocketship"). Both the thimble and the triangle species should be similar. This one is from C. Carre and D. Carre (1991).
    Rocketship

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  • Lounalune by Lounalune

    Fascinating stuff! Thanks for your explanation, which I had to read a few times before I was able to follow.

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  • jessicaluo by jessicaluo scientist, admin

    Sorry! I tried to make it as clear as possible. But I guess it was still confusing!

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  • shocko61 by shocko61

    very handy ,thank you jessicaluo

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  • Lounalune by Lounalune

    Don't worry, jessicaluo, I meant that the theme was complicated, your explanation was quite good and I'm grateful you found a picture.

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