and fish responded to these by swimming 15 cm. the neuro-anatomical basis for this ability has not yet been identified. anatomy a lineatus and similar surface feeding fish (e.g. pantadon bucholzi) use a slightly modified lateral line organ called a neuromast to detect surface waves. a lineatus has 18 neuromasts (specialized vibration-sensitive lateral line organs) on the dorsal surface of the head of a lineatus. these are organized into three groups by longitudinal position, and each group is bilaterally symmetric. the groups are, caudal to rostral: nasal/infraorbital (i), supraorbital (ii), and supratemporal/post-orbital (iii). each neuromast is a cluster of hair-cell bundles arranged in a line and numbering in the 10s to 100s. each bundle of hair cells is covered in a gelatinous capulla which the capillary waves actually make contact with and in doing so cause afferent neurons to fire. neuromasts are similar in structure to canal organs in the lateral line canal system: they are housed in sacs of connective tissue between the skull and skin, and are connected to the water and water surface via canals and canal pores. recent work has also revealed small ridges of tissue around each neuromast which direct water flow around it. the neuroanatomy beyond the receptor level for surface wave-detecting neuromasts has been minimally investigated. in this regard what research has been done shows considerable variation between species; in a lineatus, these neuromasts are considered the supraorbital line, and are innervated by ramus opthalmicus superficialis. this tract results in collateral fibers that innervate the rostral boundary of the medial octavolateralis nucleus, the area in all teleosts where lateral line organs innervate. these afferents also go to the valvula cerebelli. in one of the few electrophysiology studies performed on a lineatus, it was found that of all the primary afferents from neuromasts that they recorded, half phase-locked to wave stimuli. these neurons had weaker ongoing activity than non-phase-locked neurons. with waves of decreasing amplitude, phase-locking also decreased. phase-locking was best in the 40–70 hz range or in the 80–100 hz range. within a neuromast different afferents phase-locked best to waves of different frequencies and amplitudes, and they found no correlation between a unit's dynamic amplitude range and its ability to phase lock. analysis of data revealed that wave amplitude of waves was encoded in the degree of phase-locking and in the afferent's firing rate. since this was the extent of the feature representation found, it was concluded that further analysis of waves must happen at higher levels in the nervous system. amphibians the african clawed frog (xenopus laevis) responds to surface waves. it is able to locate wave directions at least to within ± 5° and they can localize and distinguish between two different water waves coming simultaneously from two insects in different directions. xenopus has approximately 200 lateral-line organs located along the sides of its body, and also around its eyes, head and neck. it is claimed these are used to navigate and detect prey either striking the water or struggling but the role of these organs in surface wave detection is not entirely clear; xenopus with all of their lateral line organs destroyed are still able to respond to surface waves in an oriented fashion. compared to animals with an intact system they respond somewhat less accurately to anterior stimuli and much less accurately to stimuli from behind. areas of the xenopus brain responding to surface waves have been identified. it has been speculated that both xenopus and the european grassfrog use their seismic sensory capabilities to locate conspecifics in breeding ponds. arachnids dolomedes spiders hunt by waiting at the edge of a pool or stream. they hold on to the shore with their back legs while the rest of their body lies on the water, with legs stretched out. when they detect the ripples from prey, they run across the surface to subdue it using their foremost legs, which are tipped with small claws; like other spiders they then inject venom with their hollow jaws to kill and digest the prey. they mainly eat insects, but some larger species are able to catch small fish. females of the water spider argyroneta aquatica build underwater "diving bell" webs which they fill with air and use for digesting prey, molting, mating and raising offspring. they live almost entirely within the bells, darting out to catch prey animals that touch the bell or the threads that anchor it. other species a male shows the typical hunting stance of the fishing spider, dolomedes minor certain other animals also use surface waves to find prey. an incomplete list follows: fish: freshwater hatchetfish (gasteropelecidae) halfbeaks (hemiramphidae) non-fish: the genera of spiders pirata and dolomedes clawed toad xenopus laevis whirligig beetle gyrinus substriatus water strider gerris remigis back swimmer notonecta glauca