Nebalia bipes

Geographic Range

Nebalia bipes is native to coastal waters throughout the North Atlantic, extending from the eastern Nearctic region to the northernmost parts of the Palearctic region. Within the Palearctic region, it has been identified near the shores of the Greenland, Iceland, Faeroes, Norway, and Spitsbergen, and in the Kattegat, North Sea, English Channel and the Mediterranean, where it has been found on the coast of Italy. This also makes it a Holarctic species. (de Kluijver and Ingalsuo, 2011)


Small marine crustaceans in the order Leptostraca, live in coastal temperate, tropical, and saltwater environments ranging anywhere from 1 to more than 2,000 m in depth. Nebalia bipes stays closer to the surface, preferring to inhabit zones between 5 and 60 m in depth. In addition to coastal areas, Nebalia bipes is also able to inhabit estuarine environments and areas with brackish water, such as the North Sea. They prefer to bury themselves under soft clay beneath rocks with little-to-no exposure to light and low oxygen levels. N. bipes lives in close association with submerged detritus accumulations and the macrofauna found within them, thriving in the lower stratum layer. (Gallametzer, et al., 2005; Green, 1972; Lopretto, 2004; Rode and Lieberman, 2002)

  • Range elevation
    -60 to 0 m
    -196.85 to 0.00 ft
  • Average elevation
    -33 m
    -108.27 ft
  • Range depth
    5 to 60 m
    16.40 to 196.85 ft
  • Average depth
    33 m
    108.27 ft

Physical Description

The body of Nebalia bipes is slender, with the characteristic crustacean anatomy of an anterior head, middle thorax, and posterior abdomen. It has no cephalothorax and its thoracic segments are not fused with its head. Fully grown, Nebalia species have a maximum length of 17 mm, but tend to stay around 4.5 mm in the wild. Nebalia bipes is milky-white to translucent in appearance, with antennae below its eyes and an abdomen composed of seven segments, instead of the usual six. It has a hinged rostral plate covering its head, which is laminar and lacks a terminal spine. A large, rounded bilobed carapace covers its thorax and most of its abdomen. This protects its first and second maxilla, its carapace abductor, and the palp of its maxillula.

Nebalia bipes has well-developed, red-pigmented eyes due to a high concentration of carotenoids and a lack of ommochromes present in most other crustacean eyes. Both male and female Nebalia bipes have first antenna pairs that are shorter in length than their second antenna pairs. The second antenna pair is whiplike and longer in males, reaching lengths close to the length of their bodies. The first four pairs of pleopods in the thorax are biramous, and the last two are uniramous and rudimentary. The abdomen of Nebalia bipes terminates in a caudal furca with long rami. This is unusual for animals in the class Malacostraca, but common in other crustacean groups. The rami are narrow and longer in males than in females. (de Kluijver and Ingalsuo, 2011; Fox, 2001; Green, 1972; Macquart-Moulin and Castelbon, 1983; Vetter, 1998)

  • Range length
    1.5 to 17 mm
    0.06 to 0.67 in
  • Average length
    4.5 mm
    0.18 in


It should be noted that the developmental processes of animals in the genus Nebalia closely resembles that of animals in the subclass Eumalacostraca. Nebalia bipes transitions from an unripened egg in the ovary to a four-celled embryo within a few hours. This freshly laid egg has a central nucleus and a mostly-central cytoplasm. Following the thickening of the blastophore, a U-shaped germinal band is formed where the arm segments are developed. The mesodermal mass then becomes differentiated into an anterior mesoderm and posterior endoderm, which separates malacostracans from other crustaceans. Once the papilla elongates and all the segments are differentiated internally, the unhatched Nebalia bipes embryo extends anteriorly to the labrum and is ready to hatch from the vitelline membrane. The embryo then passes through three stages separated by ecdyses, leaves the brood pouch, and becomes free-swimming as a benthic juvenile. During its gastrulation period, all internal tissues are formed and the ectoderm and mesoderm of all seven abdominal segments are established. The gonads then secrete either a male or female hormone. The genital rudiment appears when the species is about 3 mm long, notably late in embryonic life. The adult populations of Nebalia bipes vary greatly, with males being comparatively scarce. The rudiment appearance also marks the beginning of the premature adult stage. All major parts of its exoskeleton are now formed from the mandibular-maxillary bars, and the development of both the antennal gland and maxillary gland commence. Nebalia bipes from this point forth is considered to be in its fully-developed adult form. (Manton, 1934; Waterman and Chace, 1960)


Nebalia is a polygynandrous genus in the order Leptocrustraca and can reproduce during all seasons. To find and attract mates, Nebalia bipes exhibits a circadian periodicity swimming rhythm, which is transmitted hereditarily. Nebalia bipes is highly adaptable and can breed with relative ease. (Macquart-Moulin and Castelbon, 1983)

There is no set breeding season for Nebalia bipes and the species begins to reproduce after 30 to 100 days of life, depending on water temperature. Reproductive maturity happens faster in warmer waters. Females lay between 20 to 80 eggs per litter, increasing proportionally with the size of mothers.

All embryonic development takes place within a maternal incubating cavity enclosed by long feathery bristles, carried by the end of the endopodites of the thoracic appendages. Young are incubated from 10 to 20 days, depending on the water temperature. At a stable 18°C, incubation lasts for a dozen days. Young only leave the incubation cavity after having acquired a complete adult structure. (Macquart-Moulin and Castelbon, 1983; Vetter, 1996)

  • Breeding interval
    Nebalia bipes breeds when possible after the previous incubation period.
  • Breeding season
    Nebalia bipes reproduces year round.
  • Range number of offspring
    20 to 80
  • Range gestation period
    10 to 20 days
  • Average gestation period
    12 days
  • Range age at sexual or reproductive maturity (female)
    35 to 100 days
  • Average age at sexual or reproductive maturity (female)
    67 days
  • Range age at sexual or reproductive maturity (male)
    30 to 90 days

Parental investment for Nebalia bipes includes internal fertilization of their young, spending 10 to 20 days developing the embryonic papilla in the maternal incubating cavity. With this investment, Nebalia bipes feed its young by use of a yolk sac, which in early stages has such a high rate of absorption that the volume of the sac increases and can be utilized after hatching. The yolk sac later develops into the liver and intestines. This method of parental care is less expensive than milk production seen in Mammalia. However, this also means Nebalia bipes has less acute hearing and sense of smell. There are no documented cases of benthic juveniles learning from their parents, rather young seem to develop a natural rhythm of synchronization within a day of incubation release in a natural daylight cycle. Thus, paternal investment pre-independence seems to be little to none. (Macquart-Moulin and Castelbon, 1983; Vetter, 1996; Waterman and Chace, 1960)


Not much is known about the lifespan of Nebalia bipes in the wild. However, it does exhibit the natural pattern that finds the sooner an individual has offspring, the sooner it dies. In captivity at 18°C, a female can survive for up to 10 months after producing three broods - the first brood is produced at the 80-day mark. This suggests there is a life-to-birth ratio of 3.75, making their lifespan less than those reported for other leptostracan species. Limits to the lifespan of Nebalia bipes include water temperature, water depth, and dissolved oxygen concentration. (Vetter, 1996; Vetter, 1998)

  • Range lifespan
    Status: captivity
    10 (high) months


Nebalia bipes is a colonial species, and can be found in populations of 2 million or more. It also has a mobile adult form, that locomotes with its twelve pleopods, one for each side of the six abdominal segments, excluding the seventh segment which houses the telson. Pleopods 1 to 4 are large and biramous and are all found on the specialized abdomen. These biramous appendages help Nebalia bipes swim. Locomotion in Nebalia bipes could be used as a model for Palaeozoic phyllocarid crustaceans, as the functional importance of the natatory pleopods suggests a similar free-swimming lifestyle with burrowing habits. Species in the genus Nebalia are known as 'sea fleas' due to their similar appearance and tendency to bite flesh if convenient to them. However, unlike the flea order Siphonaptera, Nebalia species are not parasitic and only attack humans if they get too close to their food source or have a cut and are stagnant in the water. (Fox, 2001; Mannix and Webb, 2017; Vannier, et al., 2007; Vetter, 1998)

Home Range

Nebalia bipes generally stays within detritus mat fauna - that is stratified dead plant material on the ocean floor - for its entire life. However, there is higher dispersion in Summer as mats expand and less dispersion as mats contract in Winter and Spring. Nebalia bipes displays a circadian swimming rhythm and is more active at night and dusk than during the day. (Macquart-Moulin and Castelbon, 1983; Mannix and Webb, 2017)

Communication and Perception

Nebalia bipes has well-developed eyes for visual communication and two sets of antenna for tactile communication. Its eyes are bright red from the high concentration of carotenoids in the water and low exposure to light compared to other crustaceans. Nebalia bipes is thought to use vision less often tactile communication. The second sets of antennae on Nebalia bipes can grow as long as the body in males and are mostly used as ornamentation, but still work as sensory organs. Species in the genus Nebalia use their antennae for the majority of communication and perception, but there are minimal studies to characterize their exact communication patterns. (de Kluijver and Ingalsuo, 2011; Manton, 1934)

Food Habits

Nebalia bipes is a scavenger and detritivore, consuming dead and dying marine creatures found on the seafloor. It eats using its three mouthparts, the paired uniramous mandibles, uniramous first maxillae, and biramous second maxillae. Food availability is limited by light availability because their nutrients are photosynthetic and rooted in unstable substratum in coastal sediments. (Fox, 2001; Mannix and Webb, 2017; Vetter, 1998)


Fishes are the only abundant predators known to prey on Nebalia bipes. Due to its widespread location in coastal waters, the species of fish that prey on Nebalia bipes are foraging fish, including members of the family Clupeidae and other small fish such as halfbeaks, silversides, and smelt.

The only known method Nebalia bipes utilizes to avoid predation is taking refuge in detritus matter on the seafloor. Larger refugia increase the carrying capacity, which allows for both greater population sizes and reproduction rates. (Alder, et al., 2008; de Kluijver and Ingalsuo, 2011; Vetter, 1998)

Ecosystem Roles

In their detritus-dominated habitats, Nebalia species are heavily preyed on during all seasons by various fishes. They also help with biodegradation. They can account for over 99% of species found within detritus mat, proving to have a large ecosystem role in coastal waters as prey. Their ability to biodegrade waste also helps with the three stages of biodegradation, contributing to biodeterioration. This process is possible because they interact with abiotic factors, facultative anaerobic bacteria, aerobic bacteria, and microorganisms. (Lucas, et al., 2008; Vetter, 1998)

Mutualist Species
  • facultative anaerobic bacteria, aerobic bacteria, microorganisms

Economic Importance for Humans: Positive

Being the only living members of the order Leptostraca, species in the genus Nebalia serve as valuable research opportunities and education of extinct methods of locomotion, reproduction, and general behavior. Nebalia bipes was the first species in its order to be described in 1780, and periodic research makes it one of the more studied marine crustaceans. This offers more history on methods of evolution in the class Malacostraca, which is not found in more adapted species. (Vannier, et al., 2007)

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

There are no known adverse effects of Nebalia bipes on humans.

Conservation Status

There is no special conservation status Nebalia bipes or other Nebalia species. There are no known causes of endangerment to their populations. However, all wildlife found in coastal waters experience human interference of tidal action, as humans use sea defenses to prevent flooding, limiting the coastal range of inhabitants. Tidal action is a potential problem for this species, as they live in lower coastal depths, and this action removes parts of their habitat. ("Coastal Habitats", 2020)


Allison Clark (author), Colorado State University, Brooke Berger (editor), Colorado State University, Galen Burrell (editor), Special Projects.



living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map


living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


helps break down and decompose dead plants and/or animals

brackish water

areas with salty water, usually in coastal marshes and estuaries.


an animal that mainly eats meat


the nearshore aquatic habitats near a coast, or shoreline.


used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.


an animal that mainly eats decomposed plants and/or animals


particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature


an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

female parental care

parental care is carried out by females


union of egg and spermatozoan


a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.

World Map

Found in northern North America and northern Europe or Asia.

internal fertilization

fertilization takes place within the female's body


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).


having the capacity to move from one place to another.


specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.


reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.


photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)


the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.


an animal that mainly eats dead animals


remains in the same area


reproduction that includes combining the genetic contribution of two individuals, a male and a female

sexual ornamentation

one of the sexes (usually males) has special physical structures used in courting the other sex or fighting the same sex. For example: antlers, elongated tails, special spurs.


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.


uses sight to communicate

year-round breeding

breeding takes place throughout the year

young precocial

young are relatively well-developed when born


animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)


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Arthropod Structure and Development
, 30.1: 307-322.

Lopretto, E. 2004. Grzimek's Animal Life Encyclopedia (Vol. 2: Protostomes. 2nd ed.). "Phyllocarida (Leptostracans)" p. 161. Detroit, MI: Gale. Accessed February 18, 2020 at

Lucas, N., C. Bienaime, C. Belloy, M. Queneudec, F. Silvestre, J. Nava-Saucedo. 2008. Polymer biodegradation: Mechanisms and estimation techniques – A review. Chemosphere, 73:4: 429-442. Accessed March 09, 2020 at

Macquart-Moulin, C., C. Castelbon. 1983. Spontaneous circadian frequency in young Nebalia bipes (fabricius) (Crustacea: Phyllocarida). Induction and initial synchronization of the endogenous rhythm of activity. Journal of Experimental Marine Biology and Ecology, 70.1: 1-20. Accessed February 06, 2020 at

Mannix, L., C. Webb. 2017. "Explainer: What are sea fleas anyway?" (On-line). The Age. Accessed March 09, 2020 at

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Universiteit van Amsterdam
. Accessed February 06, 2020 at