Vintage Sea Squirt Illustration Pinback Button

NOTE: Chose smallest or small button sizes as this image isn't large enough for the huge buttons. A lovely blue image from the 85th plate, illustrating Ascidiacea, from Ernst Haeckel's Kunstformen der Natur (1904). Species: Botryllus schlosseri = Botryllus polycyclus Ascidiacea (commonly known as the ascidians or sea squirts) is a class in the Tunicata subphylum of sac-like marine invertebrate filter feeders. Ascidians are characterized by a tough outer "tunic" made of the polysaccharide tunicin, as compared to other tunicates which are less rigid. A description from Wikipedia: Ascidians are found all over the world, usually in shallow water with salinities over 2.5%. While members of the Thaliacea and Larvacea swim freely like plankton, sea squirts are sessile animals: they remain firmly attached to substratum such as rocks and shells. There are 2,300 species of ascidians and three main types: solitary ascidians, social ascidians that form clumped communities by attaching at their bases, and compound ascidians that consist of many small individuals (each individual is called a zooid) forming colonies up to several meters in diameter. Sea squirts feed by taking in water through the oral siphon. The water enters the mouth and pharynx, flows through mucus-covered gill slits (also called pharyngeal stigmata) into a water chamber called the atrium, then exits through the atrial siphon.