Microgobius Poey, 1876

Genus Microgobius Poey, 1876 View in CoL

Discussion Fricke et al. (2023) list 15 valid extant Microgobius species, six in the West Atlantic and nine in the East Pacific. Otoliths are available from all Atlantic species and from the majority of Pacific species except for Microgobius cyclolepis Gilbert, 1890 , M. emblematicus Jordan & Gilbert, 1882, M. miraflorensis Gilbert & Starks, 1904 , and M. urraca Tornabene, van Tassell & Robertson, 2012 . We distinguish four groups (otolith plexus) within the genus based on certain otolith patterns:

Te Microgobius gulosus otolith plexus containing the extant M. gulosus (Girard, 1858) ( Fig. 27a View Fig ) and M. microlepis Longley & Hildebrand, 1940 ( Fig. 27i View Fig ), from the West Atlantic; and M. tabogensis Meek & Hildebrand, 1928 ( Fig. 27c–d View Fig ), from the East Pacific. Te otoliths of this plexus are characterized by the lowest height (OL:OH = 0.86–0.97) and an almost rectangular outline.

Te Microgobius carri otolith plexus containing the extant M. carri Fowler, 1945 ( Fig. 28a View Fig ), M. meeki Evermann & Marsh, 1899 ( Fig. 28i View Fig ), M. signatus Poey, 1876

( Fig. 28d View Fig ), and M. thalassinus Jordan & Gilbert, 1883

( Fig. 29h–i View Fig ), from the West Atlantic; and M. brevispinis Ginsburg, 1939 (drawing of otolith provided by D. Nolf), and M. crocatus Birdsong, 1968 ( Fig. 28j–l View Fig ), from the East Pacific. Te otoliths of this plexus are distinctly more high-bodied than those of the Microgobius gulosus plexus (OL:OH = 0.77–0.88 vs 0.86–0.97) and are usually associated with a highly curved dorsal rim.

Te Microgobius erectus View in CoL otolith plexus containing the extant M. curtus Ginsburg, 1939 View in CoL ( Fig. 30m View Fig ), and M. erectus Ginsburg, 1938 View in CoL ( Fig. 30n View Fig ), from the East Pacific. Te otoliths of this plexus are characterized by a similarly high-bodied shape as the Microgobius carri View in CoL plexus but are distinguished by the longest axis of the otolith being shifted dorsally to the predorsal angle and postdorsal projection. Tis shift of the axis is primarily caused by the anterior rim being inclined ventrally, while in other Microgobius View in CoL otoliths the anterior rim is either vertical or inclined towards dorsal.

Te Microgobius camur otolith plexus is exclusively composed of fossil otolith-based species, with four species from the West Atlantic and one specimen in open nomenclature from the East Pacific. Since otoliths are known from all West Atlantic Microgobius species but not from all East Pacific species, it is possible that this plexus is represented today only in the East Pacific.

Te composition of the Microgobius otoliths in these four otolith plexuses is only meant to be for comparison purposes and does not imply in any way possible phylogenetic relationships within the genus. In his review of the genus, Birdsong (1981) commented on an unpublished study by Ginsburg that was to define seven subgenera. Birdsong himself, however, stated that he has “come to many tentative conclusions, but only one seems worth mentioning: I don’t know how they are related to each other.” In a study about the speciation in Gobiosomatini that also included molecular phylogenetic data, Rüber et al. (2003) presented a cladogram containing six Microgobius species plus one Microgobius sp. Teir phylogenetic association of the six species of Microgobius partly coincides with the otolith plexus grouping and partly does not.

Extant Microgobius species occur mostly in shallow, near-shore waters, although a few have been caught at a depth to 30 m, such as M. erectus View in CoL and M. cyclolepis ( Birdsong, 1981) View in CoL . Some species typically occur in mangrove environments, such as M. meeki View in CoL , M. curtus View in CoL , M. crocatus View in CoL , and M. tabogensis ( Birdsong, 1981) View in CoL . Certain species tolerate varying salinity levels and are commonly found in estuarine environments, such as M. gulosus View in CoL and M. miraflorensis View in CoL , and burrowing also appears to be not uncommon in the species of this genus, as, for instance, in M. carri View in CoL , M. microlepis View in CoL , and M. gulosus ( Birdsong, 1981) View in CoL .