Whalesucker

The adhesive disk atop the head of the whalesucker is the largest amongst the remoras, bearing 25–28 lamellae and measuring 47–59% of the standard length. The head itself measures 26–28% of the standard length. The dorsal fin rays number 23–26, the anal fin rays 24–26, and the pectoral fin rays 22–24. The jaws contain numerous large, stout canine teeth; the palatine and lingual patches are absent, and there are 17–20 gill rakers. The coloration is uniform brown, dark brown, or greyish-brown on the head, trunk, and fins. Whalesuckers observed off Fernando de Noronha ranged from light grey to slate grey, with lighter fin margins. The smaller individuals are barred or blotched, while individuals over long have yellowish fins. This species can reach in total length. However, whalesuckers can still lose their suction abilities through unequalization of pressure, as attaching to specific host organisms can render an unequal amount of force required for the fish to attach to its host, causing seep to emerge from outside of the disc, and lose its suction adhesion. The cranial veins of the remora also differ from other species of fish: they are larger and are placed ventral to the dorsal disc on the fish's cranium. As opposed to other species that merely rely on their jaw grip to latch onto prey, the interconnection between these veins, the brain, and the ventral surface of the remora allows it to work as a hydraulic press when using the adhesive disc to allow for pressurization equilibrium during attachment. == Mutualism ==

The most common host of the whalesucker appears to be the blue whale. Chitinous material indicative of parasitic copepods or amphipods have been found in the stomachs of whalesuckers, suggesting a mutualistic relationship with their hosts. While eliminating parasites from the whale, the whalesucker benefits by avoiding predators. The chance of mating also increases through habitual migration and food availability (i.e. parasites or food droppings). It has been theorized that whalesuckers prefer to swim near blue whales to reduce drag, and allowing the whalesucker to stay near its host. The median speed of a blue whale speed hovers at about 2.1±0.5 m s−1 (7.6±1.8 km h−1) and at 3.9±0.8 m s−1 (14±2.9 km h−1), which is doubled for the remora, given its much smaller stature. Whalesuckers appear able to match the speed of blue whales, having the ability to skim and swim near the whale's surface before attachment. Using its adhesive disc, the whalesucker attaches directly behind the whale's blowhole, directly on, behind, and above the pectoral fin, and next to or behind the dorsal fin. This way, the whalesucker can keep itself constantly near the whale while resisting drag both while it swims freely, and when it attaches to its host. It has also been observed through this movement that it prefers to keep away from the ventral surface to avoid sea bird predators. ==Evolution==

One of the whalesucker's most outstanding traits, shared among the Echeinedae family, is an adhesive disk. The adhesive disk is a round, oval, sucking disk located on the top of a remora's head, with two layers of lamellae that allow for the remora to stick and unstick to the epidermal surfaces of larger fish, mainly cetaceans. Evolved from dorsal fin spines, the disc is thought to have evolved to allow individuals to attach to rough surfaces using their teeth. The average length of a whalesucker's adhesive disc is about 11 to 19 cm. There have been previous arguments that the morphology relating to the whalesucker's origins belonged to the Opisthomyzonidae genus, which existed during the Oligocene era. However, this species has a fully formed disc, an equal-length jaw, a long head, a large body, and a short but deep caudal peduncle, which is the base of its forked caudal fin, a muscle in the tail that allows the fish to swim forward. Recent studies of the Opithomyzonidae have found flaws in its perceived ancestry to the whalesucker due to its comparatively low six-to-eight-disc lamellae and lack of the adhesion disc's migration to the fish's skull. Additionally, there is a lack of consistency of timing between earlier ancestors of the whalesucker and the Opisthomyzon's development of intercalary bones (additional skeletal elements arising between other bony structures) and posterior laminae after the disc's migration. It is more likely that the Opisthomyzon was the recent common ancestor of the Phtheirichthys family, the sister group to the extant remora. What is speculated, is that the changes in the disc's length most likely occurred through performance-based natural selection through friction against surfaces of larger animals. The whalesucker's true homologous origins may not be confirmed, its relationship to its phylogenetic relatives shows a similarity in both its morphology and behavior towards dolphins and blue whales. ==References==