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Whats this then? Hydrozoa maybe?


1 May 2009
Hi all,

Just spotted a new sort of beast amongst the usual microfauna in one of my Paro tanks. Very small - the entire frame here is about 4-5mm across, so it's a quarter to half a mm long at most. Loads of them all over the glass and presumably hardscape. Appear to be largely sessile, with an aperture for catching stuff that retracts when disturbed. Any ideas?

Sorry about the not-terribly sharp footage, even with a tripod and image stabilisation I was picking up a lot of vibrations at this magnification (wobbly floorboards!). Looks better if you click HD.
Last edited:
Aha! Cupelopagis vorax or similar - http://www.photomacrography.net/forum/viewtopic.php?t=214&sid=633d1b3a7aa8eea09fdf551307043440

By rotating on a short, flexible, pedal stalk, Cupelopagis vorax captures prey that traverse the substratum to which this sessile rotifer attaches. Microvideographic analysis (including slow motion and freeze-frame) permitted us to examine some of the details of Cupelopagis foraging behavior. When undisturbed, Cupelopagis usually faces forward in a resting or neutral position (NP) with its unciliated infundibulum (corona) directed parallel to the surface of the substratum. However, vibrations produced by artificial means (fine pins) or small prey (protists) evoke unique behaviors inCupelopagis. Our analysis of Cupelopagis foraging on two protozoan prey (Paramecium bursaria and a small, unidentified flagellate, SUF) indicates that this predator possesses a 360 ° encounter field (EF) biased towards the NP. Size of the EF appears to be a function of both predator and prey size, but it extends at least 650 μm, as measured from the point of attachment of the predator’s pedal stalk to the substratum. When a prey comes close to Cupelopagis, this predator can lean toward the organism, stretching forward on its pedal stalk and extending its corona over the prey in a swift motion (≤ 0.5 s). Probability of capture after attack was a function of prey type (61.6% for P. bursariaand 41.5% for the SUF). Analysis of prey capture by Cupelopagis indicates that this predator has a handling time ranging from a few seconds to several minutes: 24.6 ± 16.8 s for P. bursaria (n = 214) and 34.6 ± 25.4 s for the SUF (n = 111). Occasionally Cupelopagis sweeps part of the EF by retracting its corona, turning to the right or left (mean angle subtended ≈ 63 ° ± 42 °), unfolding the corona, and slowly returning to the original resting position. This behavior, termed surveillance, occurs in the presence or absence of prey. While not unique in its ability to detect water movements, Cupelopagis is the only rotifer known to exhibit specific behaviors to vibrations produced by potential prey.


Cool wee beastie.