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The external or ventral region refers to sutures along the lower (outer) edge of the shell, where the left and right suture lines meet. The external (or ventral) saddle, when present, lies directly on the lower midline of the shell. As a result, it is often called the median saddle. On suture diagrams the median saddle is supplied with an arrow ...
These shells have 10 or 11 whorls and thus a very long suture, with an unusual sculpture of regularly placed papules along the suture itself. Nearly all snail shells (except for the shells of limpets , abalone , sea hares , etc.) can be visualized as a tube of increasing diameter, closed at the small end, and spirally wrapped around a central axis.
The outer wall of the coxa is often marked by a suture extending from the base to the anterior trochanteral articulation. In some insects, the coxal suture falls in line with the pleural suture. In such cases, the coxa appears to be divided into two parts corresponding to the episternum and epimeron of the pleuron.
The turtle shell is a shield for the ventral and dorsal parts of turtles (the order Testudines), completely enclosing all the vital organs of the turtle and in some cases even the head. [1] It is constructed of modified bony elements such as the ribs, parts of the pelvis and other bones found in most reptiles.
A bivalve shell is the enveloping exoskeleton or shell of a bivalve mollusc, composed of two hinged halves or valves. The two half-shells, called the "right valve" and "left valve", are joined by a ligament and usually articulate with one another using structures known as "teeth" which are situated along the hinge line.
Shells of two different species of sea snail: on the left is the normally sinistral (left-handed) shell of Neptunea angulata, on the right is the normally dextral (right-handed) shell of Neptunea despecta The shell of a large land snail (probably Helix pomatia) with parts broken off to show the interior structure.
The sutures (or suture lines) are visible as a series of narrow, wavy lines on the surface of the shell. The sutures appear where each septa contacts the wall of the outer shell. The typical goniatitid has a suture with smooth saddles and lobes, which gives the name "goniatitic" to this particular suture pattern.
The umbilicus of a shell is the axially aligned, hollow cone-shaped space within the whorls of a coiled mollusc shell. The term umbilicus is often used in descriptions of gastropod shells, i.e. it is a feature present on the ventral (or under) side of many (but not all) snail shells, including some species of sea snails, land snails, and ...