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In most fossil nautiluses, the siphuncle runs more or less through the center of each chamber, but in ammonites and belemnites it usually runs along the ventral edge of the shell. In some fossil straight shelled nautiloids, cylindrical calcareous growths ("siphuncular deposits") around the siphuncle can be seen towards the apex of the shell.
The ecdysial suture is longitudinally placed on the vertex, separating the epicranial halves of the head to the left and right sides. Depending on the insect, the suture may come in different shapes: like either a Y, U or V. Those diverging lines that make up the ecdysial suture are called the frontal or frontogenal sutures.
The suture includes a ventral saddle and broad lateral lobes. In some, there is a secondary ventral lobe. The siphuncle is subcentral. Juvavionautilus comes from Europe and Timur. Oxynautilus, [5] differs from the rest in that it has an involute, compressed lenticular shell with a narrow or acute (angular) venter which may or may not have a ...
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 ...
The relatively thin legs have precisely arranged bristles which also function in chaetotaxy. The femora and tibia may bear combinations of dorsal, anterodorsal, posterodorsal, ventral, anteroventral and posteroventral bristles. The position, number, size and inclination of these bristles is important in the taxonomy of higher flies.
Gryponautilus from the Upper Triassic is broadly involute with a narrowly rounded, keel-like venter at maturity and shallow ventral and lateral lobes in the suture. All members of the Grypoceratidae have a ventral lobe with the exception of Stenoporceras, Parastenopoceras, and Virgaloceras, which have a ventral saddle instead. The derivation of ...
This glossary of entomology describes terms used in the formal study of insect species by entomologists.. When present, elytra of the Staphylinidae are markedly abbreviate. This fly in the genus Scaptomyza has clearly visible rows of para-sagittal acrostichal bristles on its thorax the alitrunk of aculeate Hymenoptera comprises the three thoracic segments, plus the propodeum, which strictly ...
Crocodilian form of crurotarsal ankle. The astragalus (pink) is fixed to the tibia (green) by a suture. Adapted with permission from Palaeos. In the type of crurotarsal ankle, which is found in crocodilians and some other archosaurs, the astragalus is fixed to the tibia by a suture, and the joint bends around a peg on the astragalus, which fits into a socket in the calcaneum.