Diagnosis: Modal fin-ray counts of D-VI,12 A-13 and Pect-16-17 indicate Ctenogobius species. These species typically have one more anal-fin ray than second-dorsal-fin rays. There are a number of species that are widespread and occupy different habitats and some freshwater and brackish species with more restricted ranges. Eight of the ten species share the median-fin ray count. Ctenogobius saepepallens occurs abundantly around reefs and in mangroves and is the most common fish larva collected over reefs in Panama. Turbid-water species include C. boleosoma (with modal 11/12), C. stigmaticus (Pect. 18), and C. stigmaturus (Pect. 16). Fresh-water and brackish species include C. fasciatus (Pect. 17-18), C. pseudofasciatus, C. claytonii (Pect. 15-17) in the S. Gulf of Mexico, C. phenacus, found from Venezuela south, and C. shufeldti (Pect. 17-18) in Florida/Gulf of Mexico and Venezuela to Brazil. The related Oxyurichthys stigmalophius has more fin rays: D-VI,13 A-14 and many more (21-22) pectoral-fin rays. Vomerogobius flavus is a deep-water goby from the Bahamas with similar fin-ray counts (D-VI,12-13 A-13 pect-15-16), but it has a distinctly large eye and no pelvic frenum. (DNA)
Transitional larvae and juveniles with a bar from the iris to the corner of the mouth indicates C. saepepallens (but the others may not be excluded). Transitional larvae and juveniles with an oblique bar forward of the eye to the mid-upper jaw and not at the corner of the mouth indicate C. boleosoma.
Description: Body thin, long, and narrow with a large eye and a terminal medium to small mouth. Pectoral fins medium length, reaching about two-thirds of the way to the vent (longer at transition). Pelvic fins long and fused with a clear frenum, reaching much of the way to the vent. Dorsal and anal-fin bases long, caudal peduncle relatively short and narrow. The s-shaped gut is usually clearly visible through the ventral abdominal wall. Lightly marked mostly along the lower body: melanophores along the ventral midline at the isthmus (often missing), at the pelvic-fin insertion, and then sometimes another just behind the pelvic-fin insertion, after which some individuals develop a row on each side of the gut strip along the abdomen. There are several discrete large melanophores along the anal-fin base, often variably present and variably paired (usually only 3-4 per side, but can be up to 7; can occur on either side unpaired), and a prominent and characteristic melanophore at the ventral midline of the caudal peduncle after the last anal-fin ray (rarely two) which has an internal extension reaching up towards the lateral midline. In many individuals, especially earlier-stage larvae, some melanophores are missing or indistinct and even the characteristic peduncle melanophore is often not visible. The head is unmarked prior to transition, but many individuals show a characteristic melanophore on the iris at about 7 o'clock, often with an additional melanophore extending to the corner of the mouth. Larvae that have a melanophore just before the tip of the lower jaw, especially when that is the sole head marking, usually also have 12 anal-fin elements and are thus likely C. boleosoma. However, some transitional larvae of this C. saepepallens type have that melanophore, but typically along with many other head markings. Internal melanophores are present around the saccule, the dorsal surface of the swim bladder, and around the gut near the vent: some individuals have a deep melanophore above the pelvic girdle between the thoracic and abdominal cavities. Series of transitional larvae show development of the eye from a slightly narrowed vertical oval to distinctly larger and round, often with a dorsal dent in the iris that sometimes persists into the transitional phase. The head profile develops from a thin pointed head to a blunt snout with a particularly bulbous head compared to the midsection. Transitional larvae develop a scattering of iridophores and leukophores on the head along with a pattern of a few discrete large melanophores on the head behind the eye and at the base of the pectoral fins. The leukophores on the top of the head are few, large, and scattered compared to those on the head of transitional C. boleosoma larvae. The characteristic bar below the eye further develops with more melanophores extending to the corner of the mouth. Melanophores develop in patches spaced out along the base of the dorsal fin, at the end of the caudal peduncle and at the base of the central caudal-fin rays. Transitional recruits develop additional specklings of melanophores and leukophores and a lateral midline row of melanophore patches. A black spot develops at the base of the upper pectoral-fin rays.
