Adineta sp. 22, gliding specimen, dorsoventral view. Focus plane on the ciliary field of the head and the specially "designed" spurs (see images below). (1)
Adineta sp. 22; two aspects of the head.
Upper left: dorsal view; the arrowheads mark the dorsal ridge of the head dorsal ridge. The plane of this optical transect is marked by the green line in the lateral view below. The double arrow marks the length of the buccal tube (ratio buccal tube length : rami length ≈ 2:1).
Upper right: optical dorsoventral transect through the head; focus plane on the rostrum (Ro). The plane of the optical transect of the right image here is is marked by the yellow line in the lateral view below. The arrowheads point to two conspicuous birefringent areas (the brightness of which depends on the orientation of these structures relative to the polarizing filters of the DIC-microscope-optics). These areas are at the connections between the rakes and the "sting"; which can be seen in the image below. The function of the "sting" is not clear, but it may help to stabilize the orientation of the rakes.
Adineta sp. 22, lateral view; optical longitudinal section of the head; focus plane on the right rake / sting. The 4 colord lines represent the optical transects/ focus planes that are displayed in the image above and below. The sting is marked by two arrowheads; The arrow points to the birefringent area which can be seen in the right above image. aRL: anterior part of the rostrum lamella; CiF: ciliary field; Mx: mastax; Ri: dorsal ridge; Ro: rostrum; (1)
Adineta sp. 22; 2 aspects of the head of the same specimen.
Upper left: dorsoventral view; focus plane on the ciliary field and the rostrum lamella. The plane of this optical transect is approximately marked by the yellow line in the lateral view above.
Upper right: focus plane on the rakes and the frontal rostrum lamella. The plane of this optical transect is approximately marked by the red line in the lateral view above.
The juxtaposition of the two images demonstrates how different the rostrum may be shaped depending on the movement of the critter. In the left image the anterior rostrum lamella (aRL) is shaped arcuate, whereas the aRL is v-shaped in the right image. (please keep in mind that both images represent optical transects of the rostrum!) The conclusion is that the elastic chitinous material of the aRL is under tension and thus can be shaped into two different states depending on the contraction of the rostrum muscle. aRL: anterior rostrum lamella pRL: posterior rostrum lamella; UL: upper lip; CiF: ciliary field; lRa; rRa: left and right rakes; bT: buccal tube; Mx: mastax. The arrowhead points to a circular structure that can be observed in all Adineta species of unknown function. A similar circular structure is visible in an SEM-image (4) of the rostrum lamella of Abrochtha intermedia in the paper of MELONE/RICCI on the "Rotatory apparatus in Bdelloids" (1995). The plane of this optical transect is approximately marked by the red line in the lateral view above.
In the right image the arrowheads mark two bundles of ?sensory? cilia.
Adineta sp. 22; left image: when (part of) the longitudinal muscles and the ring muscle of the head are contracted the ciliary field is retracted and is out of focus in the image. In this morphytype the anterior rostrum lamella is wider than the posterior (ratio= anterior rostrum lamella width (aRLW) : posterior rostrum lamella width (pRLW) ≈ 1.5); which is different for other Adineta morphotypes, see for example here.
Right image: Focus plane on the rakes with the number of U-hooks (NoUH) = 5/5 . Focus plane also on the triangular upper lip and the semicircular lower lip which correspond to the cingulum pad.
Adineta sp. 22, two images of the foot and spurs. The shape of the spurs separates this morphotype from other Adineta morphotypes. Spurs with bulbous base for 2/3 of total spur length; distinct tip (1/3 spur length). No interspace between spurs.