Goby jaws consist of
several bones, including the premaxilla and dentary bones. The premaxilla
contains a bony dorsal growth at its rostral point, and two other
bony upgrowths along its caudolateral ends. The maxilla runs along each side of the premaxilla from rostral
to posterior processes.
These bones often separate when the fish is consumed, as seen
above. However, when the skeleton is intact the premaxilla-maxilla complex
appears as below:
The dentary is a slender bone that articulates tightly with
the angular; it widens at its caudal end where it articulates with
the anguloarticular. These three bones are shown fused together in
the dentary complex; they tend to remain fused together even through
The anguloarticular of the dentary complex and the maxilla articulate at their posterior edges to
form the major components of the complete anterior jaw structure.
One of the most distinct bone structures to look for in a goby is the set
of four jaw plates - two dorsal pharyngobranchial plates and two ventral dentigerous plates. These are located just caudal to the
hyoid apparatus, and ventral to the braincase.
The pharyngobranchial plates are oval-shaped and average
approximately 3-4 mm in length. They have a slight asymmetry,
where the medial edge is shorter than the lateral edge and the
anterior edge is slightly narrower than the posterior edge. This
asymmetry is difficult to see, but can be used to identify right
from left. Dentigerous plates pair
together as seen above to form a large triangle - connective tissue
lies at their junction, making it difficult to see that there are
actually two plates. There is a ventromedial process at the
posterior junction which helps to identify right from left.
Additionally, the posterior corner of each plate turns up slightly. These plates average approximately 6-7
in length. The dorsal surface of all plates is covered with
disorganized caniniform teeth, which often fall out to leave gaping sockets in
The hyoid apparatus is a complex of bones that
lies in the ventral cranial region, lying just caudal to the dentary. The
forms the long axis of the complex, connecting between the interhyal
and the epihyal. The branchiostegal rays project posteriorly from the
ventral edge of the eiphyal. The dorsally-projecting processes at
the anterior end of the complex are the basibranchial bones.
The braincase in the round goby is dorsoventrally flattened,
with broad wing-like processes that project laterally on either side.
A rostral section projects anteriorly, which often breaks off when
the fish is eaten or during the course of natural decomposition.
Within the braincase lie two sets of three otoliths; within
a set there is one large otolith and two smaller ones that are
difficult to find. The large otoliths are diagnostic to
the species; they are dorsoventrally flattened with multiple
radial processes. Small white concentric rings are also
present, but may be difficult to see in degraded specimens.
Since oftentimes the rostral section
breaks off due to wear and tear, the below illustrations show the
braincase appearance when the rostum has been broken away.
The rostral section, when separated from the braincase, remains
distinct in appearance even after becoming disconnected. These
sections are shown below:
The operculum can be difficult to identify if it is degraded, since
it is a thin, delicate structure which can snap easily and thus lose
its overall shape and identifying structures. A complete
operculum has a narrow ventral process, which can become folded with
degradation, or even be shorn away. The overall shape is similar to a butterfly wing.
Midway down the anterior edge is a knob structure that articulates
with the body.
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