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3398 Views 4 Replies Last post: Nov 15, 2010 8:37 PM by StasMalavin RSS
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Nov 5, 2010 7:33 PM

Jassa falcata (crustacea, amphipoda)

Q1: I don't expect a positive identification from the attached pictures, but is it reasonable to label this amphipod as probable (or possible) juvenile Jassa falcata? Or is there a visible feature that rules out this sp.?

 

Q2 I have used the incomplete key in Hayward & Ryland's Handbook. Many features I can not discern; should specimens be stained for examination, & with what? I examined this in a drop of alcohol on a microscope slide with a depression, but it kept evaporating, and air bubbles entered the specimen - any advice gratefully received.

 

Here are the features I think I could see (Binoc microscope up to X56):

 

ISCHYROCERIDAE because:

Body laterally compressed, smooth dorsum

On antenna 1 the peduncle article 3 is more than half the length of article 2.

Rostrum absent. Gnathopods subchelate. Telson fleshy.

 

Jassa falcata juvenile because:

dorsum 3mm, antennae 1 mm (adults are 7mm according to H&R)

Body yellow grey strongly marked reddish brown.

Small black round eyes.

Common at LWS at Menai Bridge, Anglesey 13 Aug 2010 in tube on hydroid.

 

Q3 Is the tube made of a secreted substance, gathered material or a mixture?

 

Q4 When in its tube, it waves its antennae a bit like the cirri on a barnacle. Is this a feeding or breathing action?

 

I have cleaned distracting debris from the background of the picture but not up to the edge of the body or between the setae (right term?) on the antennae.

 

Many thanks for any answers.

Ian (Smith)

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    Nov 7, 2010 6:20 PM (in response to IFSmith)
    Re: Jassa falcata (crustacea, amphipoda)

    Hi, Ian!

     

    Q1: In my opinion Your determination of Ishyroceridae family is correct. But there in England some other species of Jassa could be found, as well as of Parajassa, or Ischyrocerus itself. So some additional characters are needed to identify the genus and the species of Your specimens. You'd better use the book by Lincoln (Lincoln RJ (1979) British Marine Amphipoda: Gammaridea. British Museum (Natural History), London, 658 pp).

     

    Q2: Amphipods should be preserved in 50% alcochol or 5% formaldehyde solution. Or in butanol, if you want to keep coloring. It's easier to examine a specimen in a Petri dish or something similar using preparation needles (I make them of entomological pins) and a forceps. In most cases for precise determination your need to prepare mouthparts or legs in glycerin on a slide (without depression). It's useful to keep a specimen in glycerin for several days before this procedure to make the cuticle more transparent, which is important in microscopy.

     

    Q3: The tubes of corophioids are typically made of gathered material sticked with a secret. But I don't know the true state of this case.

     

    Q4: Feeding. They use pleopods for breathing.

     

    Best regards,

    Stas

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        Nov 15, 2010 8:37 PM (in response to IFSmith)
        Re: Jassa falcata (crustacea, amphipoda)
        Dear Dr.Smith!
        Please forgive my disrespect in answering You. It seemed to me that You are a young man; but You undoubtedly could accept this as a compliment!
        I sent You that book hoping You could find some figures useful, and if You need I could make some screenshots from the file for You.
        I'm a PhD student in Zoological Institute of Russian Academy of Sciences, St.Petersburg, and I deal with invasive species, especialy amphipods. So it will be interesting for me to know the current state of Potamopyrgus antipodarum and Gammarus tigrinus in the area of Your sampling. The latter is an amphipod of the typical gammaroid habitus and the characteristic stripped coloring (which became the source to it's naming). The setae of males are curled (as those of G. chevreuxi and some others also are; but those species lack such coloring). It was described from GB by Sexton in 1939, but later on it was shown by Hynes that it is an invader of North American origin. In 50th it was introduced in continental Europe and now is widening its range eastwards. I would greatly appreciate receiving any information on this two species on stas.malavin@gmail.com. If You are interesting in something in our Institute (which has the largest zoological collection and library in Russia) please inform me. It will be the great interest and pleasure for me to help You.
        Yours sincerely,
        Stas Malavin
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    Nov 7, 2010 6:42 PM (in response to IFSmith)
    Re: Jassa falcata (crustacea, amphipoda)
    Here is the book by Gurjanova, the only one I have in electronic version. See Jassidae and also Ericthonius in Corophiidae.
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