Description: Body relatively thin, long and narrow with a large eye and a terminal mouth. Paired fins medium length, dorsal and anal-fin bases relatively short and unequal (dorsal-fin base about 50% longer than anal-fin base), caudal peduncle long and narrowing sharply, procurrent caudal-fin rays 6-8 (6-7 spindly). Lightly marked mostly along the lower body: melanophores on the ventral midline at the isthmus and forward of the pelvic-fin insertion, in a short row along the anal-fin base, two or three (paired and one per side) between the third and sixth element, and then a streak of seven or eight unpaired melanophores along the ventral midline of the caudal peduncle ending near the start of the lower procurrent caudal-fin rays. Head melanophores are present only at the angle of the jaw. Internal melanophores are present around the sacculus and along the dorsal surface of the swim bladder and around the gut near the vent. In this larva there is a prominent linear internal melanophore along the ventral postcleithrum (above the pelvic girdle). The eye is round in this specimen.
Diagnosis: An individual larva with the fin-ray count of D-VI,11 A-9 and Pect-15 does not fit the typical count on any Caribbean goby, but there are many species with 10/9. Most of those, however, have many more than 15 pectoral-fin rays. Only Lythrypnus, a few Coryphopterus, and Bathygobius curacao have as few as 15 pectoral-fin rays (the latter has a very different larva and can be excluded). This larva resembles Lythrypnus and Coryphopterus larvae in form and markings, in particular the melanophore at the angle of the jaw and the ventral caudal peduncle row of melanophores extending to the start of the procurrent caudal-fin rays. Coryphopterus kuna has 15 pectoral-fin rays, but usually 9/9, and different larval markings. C. alloides can rarely have 15 pectoral fin rays (usually 16-17, with 10/9) and cannot be excluded. C. personatus and C. hyalinus also have15 pectoral-fin rays, but almost always equal numbers of second dorsal and anal-fin elements (11/11 or sometimes 10/10, not 11/9). Furthermore, this larva has a prominent melanophore at the angle of the jaw that is characteristically missing in all larval C. personatus and C. hyalinus. This larva has 6-8 procurrent caudal-fin rays, intermediate between the usual Lythrypnus and Coryphopterus. Rare individuals of otherwise typical Lythrypnus larvae described above can have 11/9 elements and some individuals have deep extensions of the midline melanophore around the pelvic-fin base, although not in the same location as in this larva. A linear internal melanophore above the pelvic girdle, perhaps along the ventral postcleithrum, is characteristic of some eleotrids (Eleotris and Erotelis smaragdus), but no other larval gobies. Given the co-occurrence of the unusual fin-ray count, the linear cleithral melanophore, and the large size of this larva compared to the other Lythrypnus larvae (7.9 mm SL vs. never more than 7.0 mm SL in a large sample), it is assigned to its own larval type.
Lythrypnus is a genus of gobies native to the Atlantic and Pacific coasts of the Americas including Cocos Island and the Galapagos Islands.
There are currently 20 recognized species in this genus:[1]
Lythrypnus is a genus of gobies native to the Atlantic and Pacific coasts of the Americas including Cocos Island and the Galapagos Islands.
