Plankton Portal Talk

Comparison: an Arrow worm, a larval Fish or a Larvacean??

  • yshish by yshish moderator, translator


    There were some users asking for the main differences among #Arrowworms, larval #Fish and #Larvaceans!! So I decided to make a little comparison. It would be great if some of the fish-oriented scientists ( @jo.irisson @cguigand @agreer ..?) added more details (or corrected my thoughts if wrong).

    Arrow worms

    Here is a montage of #Arrowworm images displayed from different angles. Notice there are some differences among individual species! They may appear quite transparent when hungry but when fed, they can appear completely opaque. Sometimes their fins may be barely visible, sometimes they may be very well defined. Their heads are round(!) and appear opaque. You may see a tiny teeth on it. They've got fins on both sides (top and bottom), always symmetrical. But you won't see them from the side view. They can swim straight or bent (Notice they can bent or twist very well and they're even able to become ouroboros! They usually appear longer than Fish larvae but the front/back views can make an illusion of being shorter. Their bent head/neck can even make an illusion of having pectoral fins. They're predators, you can see them feeding on Copepods.

    Click here for the FULL resolution!!
    ![x]( =680x)

    Larval Fish

    Here is a montage of #Larval #Fish of different life stages (more different species). Most of them appear shorter than Arrow worms. Their heads are angular/boxy! Their fins are asymmetrical from the side view (top fins are different than bottom ones). When very young, fins are not present yet but there's a wavy outer line of the body revealing they'll be there soon:) They can appear opaque or partially transparent. When very young, they can be easily confused with Larvaceans! But you should smell future presence of the caudal fin! They usually appear in low depths.

    Click here for the FULL resolution!!
    ![x]( =680x)


    Here are some montages of all three types of #Larvaceans I made for this comparison. You can notice some differences among their bodies as well as among their houses. Usually, we can see an inner structure of the mucous house around the body of its builder, a Larvacean. The house may be barely visible or pretty blurry. The tadpole-like body is symmetrical (from the top/bottom view) and very flexible. Often, it can be seen convoluted into a 'tunnel' and then it may be a problem to recognize it is a Larvacean. The head is well distinguishable (and appears more opaque) from its flat body. The 2nd type has got hammer-like shape of the head. The 'tail' may appear pointy but it has actually round shape but a transparent margin. It hasn't got any fins!
    And what is the house good for? Larvaceans produce a test (a kind of skeleton) known as a "house" that surrounds the animal like a bubble, and it contains a complicated arrangement of filters that allow food in the surrounding water to be brought in and concentrated prior to feeding.
    Houses are discarded and replaced regularly as the animal grows in size and the filters become clogged. In Oikopleura, the 1st type of a Larvacean, a house is kept for no more than four hours before being replaced! Abandoned mucous houses sink to the bottom, collecting organic particles during their descent. so they make an important contribution to marine snow. (wiki)

    Click here for the FULL resolution
    ![Appendicularia]( =680x)

    1st type (Oikopleuridae)

    ![oik]( =350x) ![oik]( =270x)

    ![oi]( - juvenile.jpg =270x) ![oi]( =350x)

    2nd type (Fritillariidae)

    ![fr]( =270x) ![fri]( =350x)

    3rd type (Kowalevskiidae)

    ![ko]( =270x) ![kow]( =350x)

    //All B&W images used as examples were taken from the CAL and MED data set. Source of the colourful ones: Oik; Oik2 Fri; Kow

    Hope this is helpful. Unfortunately, my English doesn't allow me to explain it much better 😢


    Edit: I added the Larvaceans! 😉


  • kirstenr by kirstenr

    These montages are amazing, yshish! How did you make them? Now, I'm still waiting for your montages or drawings comparing two cups with rocket ship siphos. I'm mostly interested in comparing the structure of the swimming bells when the two cups is seen from a side view (where only half of the hood shows up). What features should we use to distinguish the two?


  • yshish by yshish moderator, translator in response to Kirsten A. Rohrbach's comment.

    Thanks. I used Gimp, an image editor to cut out the plankton I needed from individual frames and placing them one by one into the new image. It's quite easy (No special tool necessary, I used just the trackpoint on my laptop).

    I'm going to add a montage of Larvaceans to compare with these two.

    As for the Siphonophores, don't worry. I'm working on that. But I'll create a new thread for them to keep this one for the fish-like guys only.


  • JoyKidd by JoyKidd moderator

    Thank you SO much for creating this. The montage is exactly what I needed.


  • yshish by yshish moderator, translator

    I've found an interesting picture of juvenile #Larvacean development from the end of day 1 (after tail shift) to day 5 (sexual maturation) at 20 °C.

    Photos are shown at the same scale. On day 5, the animals mature sexually, and male and female become distinguishable by the gonad filled with sperm or eggs. They spawn on day 5. See details in text.


    And view of a #Larvacean Oikopleura dioica inside its #house, and its phylogenetic position

    Dorsal (A) and lateral (B) views of the animal in its “house”. Carbon particles from India ink were added to seawater and were concentrated by the house. Seawater comes into the house from the bilateral inlet filters and goes out from the ventral outlet pore. The particles in seawater are highly concentrated by the nets of the food-trap filter and introduced into the trunk via the mouth. Digestive organs within the trunk are made visible with the black particles. (C) Phylogenetic tree within the phylum Chordata. [Source]

    Larvacean house


  • Ksloots by Ksloots



  • yshish by yshish moderator, translator

    Here's an interesting article about Larvaceans and their role in the transport of microplastics into the deep waters.

    And here's a nice video describing how their houses work: