External morphology s and two
antenna ous
exoskeleton. Similar to all krill species, northern krill are
crustaceans that possess a transparent
chitinous
exoskeleton. Northern krill can grow up to 4-6 centimeters long in adult hood, although on average they are 1.5–2 centimeters. Their anatomy is a
decapod consisting of three main sections: the cephalothorax, the abdomen, and the tail fan. The cephalothorax is the krill's
head which houses two
antenna and
compound eyes. Northern krill utilize their antenna to sense their surroundings and aiding in eating feed. In addition to the northern krill's antenna they also have
maxillipeds which aid them in handling food to their
mandible. Found in insects, krill also operate through compound eyes which allows them to see a large array of area, detect rapid movement, and see in deep sea light conditions. Northern krill also possess
mandibles and
maxillipeds which aid them in eating Attached to the cephalothorax is the
abdomen which contains ten
appendages to aid with swimming. These appendages are five pairs of forked non walking legs referred to as
pleopods or "
swimmerets". Unique to a standard decapod krill use their pleopods for more than just swimming incorporating them into how they groom and eat. Their tail fan assists the northern krill to propel forward when swimming.
Internal Anatomy Northern krill are adapted for survival in the
pelagic zone of the ocean, enabling them to feed, escape predators, and reproduce.
Digestive System The northern krill's digestive system starts at their
maxillipeds which files food into their mouths which leads to the
esophagus. The
esophagus is connected to their stomach which consists of a cardiac stomach and a
pyloric stomach. Their cardiac stomach is the initial part of the stomach which helps grind the krill's food. The pyloric stomach is located in the lower stomach region which directs movement of their food into the
small intestine. The northern krill's pyloric stomach allows any bacteria to be passed right through the stomach due to the fast turnover rate.
Respiratory System Northern krill do not breathe
oxygen from the atmosphere, instead breathing oxygen present in water. Krill use their
gills located on their
pleopod appendages attached to their abdomen to exhale and respire. Once krill breathe in the oxygen can be seen circulating throughout their body via
respiratory pigment. Respiratory pigment is the term used when referring to a protein that transports oxygen into the blood and tissues. In northern krill, the respiratory pigment is called
hemocyanin. Unlike
hemoglobin, hemocyanin is susceptible to change due to temperature and has a weak affinity for oxygen. Due to their low affinity for oxygen, krill's
respiration rate changes in response to temperature changes. This makes northern krill more susceptible to death with fluctuations in temperature and
oxygenation levels.
Photophores Not only do northern krill possess a transparent chitinous exoskeleton, but they also have bioluminescent organs. Found in many fish these bioluminescent organs otherwise known as
photophores are hypothesized to help the krill camouflage and communicate. Photophores are organs that emit light. On krill, they are located on the
eyestalks, ventral thorax, and abdomen. They are often attributed to aiding in luring prey and
male intrasexual competition. Their transparent body and bioluminescent organs help northern krill evade predators. These light-emitting organs work by being
catalyzed by an
enzyme luciferase. Krill can adjust and control the
photophore to a certain extent.
Nervous System The northern krill's
nervous system controls its photophore organs and their compound eyes. The photophore organs are controlled by
hormonal and
neuron pathways.
Hormones such as
serotonin and
nitric oxide manage the bioluminescence in their organs. Photophore operation is controlled by the northern krill's compound eyes by the eyes
ommatidia.
Ommatidia are the cells that make up their compound eyes. Part of the ommatidia's job is to send
nerve signals to the photophore located on the
eyestalks. Another essential part of the northern krill's
nervous system is the
brain. While small it is still majorly important in processing
sensory information and coordinating behavior. To control the northern krill's swimming and food behaviors their appendages such as their
swimmerets are controlled by a chain of
ganglia which make up a
ventral nerve cord. This nerve cord controls the
motor functions of the krill and their appendages. == Reproduction ==