. Chordate morphology. Morphology (Animals); Chordata. coat made of tunicin, a material which resembles, or is, cellulose. The tunic and tissues are nearly transparent. Free cells occur in the tunic. The epidermis underlying the tunic is simple, that is, formed of a single layer of cells which are cuboidal or squamous (flattened) in shape. The tunicate shows certain similarities to Amphioxus in that it has a complex pharyngeal structure with a ciliary- mucoid feeding action. The pharynx is enclosed by an atrium opening to the exterior through an atrial pore (Fig- ure 1-8). The details of struc
. Chordate morphology. Morphology (Animals); Chordata. coat made of tunicin, a material which resembles, or is, cellulose. The tunic and tissues are nearly transparent. Free cells occur in the tunic. The epidermis underlying the tunic is simple, that is, formed of a single layer of cells which are cuboidal or squamous (flattened) in shape. The tunicate shows certain similarities to Amphioxus in that it has a complex pharyngeal structure with a ciliary- mucoid feeding action. The pharynx is enclosed by an atrium opening to the exterior through an atrial pore (Fig- ure 1-8). The details of structure of the pharynx and atrium of the two groups are close. The pharyngeal slits of the tunicate are subdivided by connecting bars called synapti- culae but not by tongue bars. The tongue bar, as observed in Amphioxus, or the hemichordate, develops as a down- growth from the dorsal wall of the slit which divides the slit into anterior and posterior openings (Figure 1-12). There is an expanded stomach and a simple intestine opening at the anus into the atrium. The walls of the gut are not ciliated. There is a pyloric gland formed of numerous ampullae (small sacs) in contact with the intestine. Tubules from the ampullae join to form a duct emptying into the digestive tract just below the stomach. There is no coelomic cavity. The mesoderm consists of the cells of the tunic, which wander out through the epidermis, the circular and longitudinal muscles of the subepidermal layer, mesenchyme cells of the interior, and the tissues of the circulatory and reproductive systems. The circulatory system consists of a heart enclosed in a pericardial cavity and connecting channels and sinuses. The direction of blood flow through the heart may be reversed. The blood contains cells but not erythrocytes (red blood cells). The pharyngeal blood vessels are roughly comparable to those of Amphioxus. Tunicates, usually hermaphroditic, have ovaries and testes opening into the atrium through long ducts.
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