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There are three pairs of muscles each on the dorsal and ventral side of the pelvic fin girdle that abduct and adduct the fin from the body. [citation needed] Pelvic fin structures can be extremely specialized in actinopterygians. Gobiids and lumpsuckers modify their pelvic fins into a sucker disk that allow them to adhere to the substrate or ...
The pectoral and pelvic fins are paired, whereas the dorsal, anal and caudal fins are unpaired and situated along the midline of the body. For every type of fin, there are a number of fish species in which this particular fin has been lost during evolution (e.g. pelvic fins in †Bobasatrania, caudal fin in ocean sunfish).
Pelvic/Ventral fins: Found in pairs on each side ventrally below the pectoral fins, pelvic fins are homologous to the hindlimbs of tetrapods. They assist the fish in going up or down through the water, turning sharply, and stopping quickly. In gobies, the pelvic fins are often fused into a single sucker disk that can be used to attach to objects.
The small, slender pelvic fins are located underneath the throat and possess a single spine; the large anal fin may have one or two spines. The pectoral fins are greatly enlarged, and the tail fin is rounded. The New Zealand topknot, Notoclinus fenestratus, is the largest species at 20 cm in total length; most other species do not exceed 6 cm.
Its body is about 9–15 times the length of the head. It has two pairs of long, filamentous fins. The pectoral fins have a basal fringe and are about three times the head length, while its pelvic fins are about twice the head length. In general, three external gills are inserted posterior to the gill slits and above the pectoral fins.
The pelvic fins have narrow bases, the pectoral fins have moderately pointed tips and are composed of 22 rays, the hind dorsal fin has 32 to 41 rays and the anal fin, 30 to 38. The dorsal surface of the fish is dark brown to black, as is a broad longitudinal lateral stripe which extends from the eye through the pectoral fin to the caudal peduncle.
The pelvic girdle (hip) and pelvic fins of Panderichthys represents an intermediate in the fish-tetrapod evolution. During the fish-tetrapod evolution the pelvic girdle became a weight bearing structure when the ilium, meso-ventral contact of the sides of the girdle, an ilium, and a sacral rib developed.
Lumpsucker with visible suction fin. Pacific spiny lumpsuckers are a globular-shaped fish that typically measures 1 to 3 inches (2.5 to 7.6 cm) in length, though the most common size is 1 inch (2.5 cm). [2] [1] [3] [4] It has a maximum known length of around 5 to 7 inches (13 to 18 cm). [4] They have a wide mouth with large lips, and protruding ...