page_title: Fiona pinnata
section_title: Digestive system
hierarchical_section_title: Fiona pinnata / Description / Digestive system
caption_attribution_description: English: Drawing of mouth and wall around mouth of Fiona pinnata showing salivary glands and salivary ducts. The buccal mass and whole visceral mass is removed.
context_page_description: Fiona pinnata, common name Fiona, is a species of small pelagic nudibranch, a marine gastropod mollusk in the superfamily Fionoidea. This nudibranch species lives worldwide on floating objects on seas, and feeds mainly on barnacles, specifically goose barnacles in the genus Lepas.
  The anatomy of this species is very unusual. It is currently the only named member of the genus Fiona but a 2016 study showed that this species is a species complex. The family Fionidae was expanded in 2016 to include Tergipedidae, Eubranchidae and Calmidae as a result of a molecular phylogenetics study. Features that are characteristic of the genus Fiona include the similar-looking oral tentacles and rhinophores; the cerata with a membrane and lacking a cnidosac; a dorsal anal opening; a reproductive system with two genital openings; two jaws with a cutting-edge, and a radula with only one central denticle in each row of teeth. That one denticle has a central cusp and a few surrounding cusps.
context_section_description: Digestive system: The channel leading from mouth to the buccal mass is very short and constricted; and, just before it opens into the buccal mass, it receives on either side below, a very slender duct from a large, much folliculated, salivary gland. These glands lie beneath the stomach and extend almost halfway down the body. That on the right side is considerably less than the other, and is somewhat tubular, — distinctly so towards its termination; the one on the left side is much complicated in form, being irregularly and extensively sacculated. The position of these glands is unusual, but there are also other species like Doto fragilis, that open into the channel of the mouth in advance of the buccal mass.
  The buccal mass is small, rather long, slender, and irregularly elliptical. There are two corneous plates or jaws. at the sides of the buccal mass. It is slightly prolonged behind for the reception of the posterior portion of the radula, and there are muscles are arranged around. Muscles are from dorsal view extensively developed, forming a dense mass, the fibres passing transversely and have their extremities inserted into the dorsal margins of the jaws. These muscles assist in the motion of the jaws. Muscles for moving the whole buccal mass forward are composed of flattened and isolated bands with their extremities attached to the posterior margin of the jaws and to the muscles forming the walls of the channel of the mouth.
  Fiona pinnata has two corneous jaws (mandibles), with a denticulate cutting-edge. The posterior portion is flattened. The corneous plates are little short of the size of the buccal mass, and much elongated, well arched and ovate. (When they are entirely isolated, they strongly resemble the shape the valves of a small bivalve of the genus Mytilus). They are smooth, glossy, and of a brownish amber colour, darkest towards the anterior extremity, which gives support to the cutting blade. This is a winglike appendage of no great size, terminating below in a free point, and having the cutting margin arched forward, plain, and nearly at right angles to the general direction of the plate. Above is a small process or fulcrum — the point at which the two plates are articulated. Immediately behind this point there is the dorsal margin of the plates is reflected and expanded into an arched lobe for muscular attachment. The length of the jaw is 2.8 mm. The maximum width and maximum height of the jaw is 1.3 mm.
  The radula is supported on a fleshy ridge that rises up from the floor of the buccal cavity, and extends in the antero-posterior direction from the oesophagus towards the anterior opening. The radula is long, linear, and strap-formed, and is composed of semicircular and crescent-shaped denticles (tiny teeth) of an orange colour. There are 40 rows of teeth in radula: 15 oldest denticles in the anterior end, then there are 22 denticles after the angle and three incomplete denticles in the sheath in the posterior end of the radula. The radula formula is 0+1+0, which means that there is only a single central denticle in each row. There is a pointed spine in the centre, and 6 or 6-7 smaller spines on each side of the denticle. There are also sometimes minute spines at the base of denticle's outer margin. All the spines are a little bent, and have their points directed backwards towards the oesophageal opening. The whole length of the radula is 2.6 mm.
  The oesophagus is a short and rather slender tube. It leads from the upper part of the buccal mass towards, and opens into, the anterior margin of a distinct pyriform stomach. The stomach has the broad end forward, is placed above the reproductive system, and lies quite in the anterior portion of the visceral cavity. The internal surface of the stomach is not lamellated. The intestine leads from posterior end of the stomach, and is inclining slightly to the right side and passes backwards to the tubular anus. The anus is placed a little to the right of the median line of the back, immediately behind the heart. The intestinal tube is rather short, of equal dia
caption: Drawing of mouth and wall around mouth of Fiona pinnata showing salivary glands and salivary ducts. The buccal mass and whole visceral mass is removed.
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