Editing Copepod (section)

===Behavior===
The second pair of cephalic appendages in free-living copepods is usually the main time-averaged source of propulsion, beating like oars to pull the animal through the water. However, different groups have different modes of feeding and locomotion, ranging from almost immotile for several minutes (e.g. some [[Harpacticoida|harpacticoid copepods]]) to intermittent motion (e.g., some [[Cyclopoida|cyclopoid copepods]]) and continuous displacements with some escape reactions (e.g. most [[Calanoida|calanoid copepods]]).

[[File:Juvenile Clupea harengus feeding on copepods macrophotography video.gif|frame|Slow-motion macrophotography video (50%), taken using [[ecoSCOPE]], of juvenile [[Atlantic herring]] (38&nbsp;mm) feeding on copepods – the fish approach from below and catch each copepod individually. In the middle of the image, a copepod escapes successfully to the left.]]

Some copepods have extremely fast [[escape response]]s when a predator is sensed, and can jump with high speed over a few millimetres. Many species have [[neuron]]s surrounded by [[myelin]] (for increased conduction speed), which is very rare among [[invertebrate]]s (other examples are some [[annelid]]s and [[malacostraca]]n crustaceans like [[Palaemonidae|palaemonid]] shrimp and [[Penaeidae|penaeids]]). Even rarer, the myelin is highly organized, resembling the well-organized wrapping found in vertebrates ([[Gnathostomata]]). Despite their fast escape response, copepods are successfully hunted by slow-swimming [[seahorse]]s, which approach their prey so gradually, it senses no turbulence, then suck the copepod into their snout too suddenly for the copepod to escape.<ref>{{cite news | url=https://www.bbc.co.uk/news/science-environment-25103455 | work=BBC News | title=Seahorses stalk their prey by stealth | date=November 26, 2013 | access-date=June 20, 2018 | archive-url=https://web.archive.org/web/20171122144106/http://www.bbc.co.uk/news/science-environment-25103455 | archive-date=November 22, 2017 | url-status=live }}</ref>

Several species are [[Bioluminescence|bioluminescent]] and able to produce light. It is assumed this is an antipredatory defense mechanism.<ref>[https://academic.oup.com/plankt/article/39/3/369/3111267?login=false A light in the dark: ecology, evolution and molecular basis of copepod bioluminescence]</ref>

Finding a mate in the [[three-dimensional space]] of open water is challenging. Some copepod females solve the problem by emitting [[pheromone]]s, which leave a trail in the water that the male can follow.<ref>{{cite book |author=David B. Dusenbery |year=2009 |title=Living at Micro Scale |page=306 |publisher=[[Harvard University Press]] |location=[[Cambridge, Massachusetts]] |isbn=978-0-674-03116-6}}</ref> Copepods experience a low [[Reynolds number]] and therefore a high relative viscosity. One foraging strategy involves chemical detection of sinking [[marine snow]] aggregates and taking advantage of nearby low-pressure gradients to swim quickly towards food sources.<ref>{{cite journal|last1=Lombard|first1=F.|last2=Koski|first2=M.|last3=Kiørboe|first3=T.|title=Copepods use chemical trails to find sinking marine snow aggregates|journal=Limnology and Oceanography|date=January 2013|volume=58|issue=1|pages=185–192|doi=10.4319/lo.2013.58.1.0185|bibcode=2013LimOc..58..185L|s2cid=55896867 |url=https://backend.orbit.dtu.dk/ws/files/53238583/Lombard_et_al_final_for_print.pdf}}</ref>