Tunicata hold an independent position among the invertebrates; earlier they were at times ranked among the mollusks (Mollusca), at times among the worms (Vermalia). The discovery of their historical development has lately led to believe that they are most closely related to the vertebrates (Vertebrata), sharing the same root with this phylum. Early developmental stages of both phyla (called Chordula) show the same distinct body frame that is not found in any other invertebrate. All Tunicata live in the sea, partly sessile (Ascidiae), partly freely swimming (Thalidiae). Ascidiae or “sea-squirts” live at times as single, simple individuals (Monascidiae, fig. 1-4), at times, through the process of budding, they form colonies or Corma composed of individual personae (Symascidiae, fig. 5-14).
Monascidia or “simple sea squirts” usually have the shape of a simple, elongated circular tube or pouch grounded on the ocean floor, showing two parallel openings on top, a bigger mouth opening and a smaller ‘tunica-opening’; the mouth opening is surrounded by a corona of antennae or tentacles (fig. 2). On cutting open the tunica and setting apart right and left body parts it becomes clear that the major part of the broad body cavity is occupied by a wrinkled ‘branchiate pouch’ opening on top through the mouth (fig. 3). At the base this ‘branchiate gut’ changes over into the digesting ‘gastric gut’ that opens on the back through the anus into a ‘tunica-pouch’. This pouch also receives the ‘sexual products’ formed in a hermaphrodite gland located below and opens on the dorsum through a channel.
The convivial individuals that compose the colonies of Synascidia are rarely evenly distributed (fig. 5); usually they form smaller groups, small colonies or Cormidia (fig. 6-14). In each star-shaped Cormidium individuals are grouped in radial shape in such a way that their mouth openings are turned inside out whereas the ‘tunica-holes’ are directed towards a common centre (fig. 8) or coalesce into a common “vent” (fig. 7). The ‘tunica-surface’ of these Synascidia is usually beautifully coloured.
Translation of the original German introduction by Ernst Haeckel:
Phylum of Tunicata (Manteltiere); - class of Ascidiae (Seescheiden).
Translation by VR Translators Bangalore
This is one of the 100 pop science biology illustrations that were published from 1899 – 1904 in Leipzig by Ernst Haeckel through Verlag des Bibliographischen Instituts.
We've scanned the original lithography at 1200dpi on the Epson A3 scanner of A3 scanner huren. You can download a 400dpi JPEG here.