''Gammarus lacustris'' is an aquatic

amphipod Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descr ...

Description

''Gammarus lacustris'' is semi-transparent and lacks a webbed tail. It may be colorless, brown, reddish or bluish in color, depending on the local environment. It has seven abdominal segments, a fused cephalothorax, and two pairs of

antenna Antenna ( antennas or antennae) may refer to: Science and engineering * Antenna (radio), also known as an aerial, a transducer designed to transmit or receive electromagnetic (e.g., TV or radio) waves * Antennae Galaxies, the name of two collid ...

e. Unlike other

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

s, amphipods lack

carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...

s and have laterally compressed bodies.

Gammarids Gammaridae is a family of amphipods. In North America they are included among the folk taxonomic category of " scuds", and otherwise gammarids is usually used as a common name. They have a wide distribution, centered on Eurasia, and are eury ...

are referred to as scuds or sideswimmers. ''G. lacustris'' resembles a freshwater

shrimp Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are refer ...

Life cycle

The female carries eggs in a brood pouch on its ventral side. ''G. lacustris'' in higher elevations were more likely to have fewer but larger eggs than those living at lower elevations. ''G. lacustris'' undergoes several molts and juveniles resemble the adult.

Ecology

''Gammarus lacustris'' plays an important role in many of the

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...

s that it inhabits. It is a

detritivore Detritivores (also known as detrivores, detritophages, detritus feeders, or detritus eaters) are heterotrophs that obtain nutrients by consuming detritus (decomposing plant and animal parts as well as feces). There are many kinds of invertebrates, ...

and may also consume

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

, mainly

diatom A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...

s. It is considered an

indicator species A bioindicator is any species (an indicator species) or group of species whose function, population, or status can reveal the qualitative status of the environment. The most common indicator species are animals. For example, copepods and other sma ...

for the overall health and stability of the ecosystem. ''G. lacustris'' can also inhabit a wide array of environments, ranging from low altitude calcium-rich lakes to high altitude, cold, and calcium-poor lakes. This influences its biology: at low altitudes, it is known to die after first reproduction, but in colder waters, it lives to reproduce repeatedly.

Temperature

In many species feeding behaviour is affected by temperature, i.e. the amount of food consumed often increases at warmer temperatures. However, when ''G. lacustris'' feeds on three different parasite species ( ''Diplostomum'' spp., ''Apatemon'' spp. and ''Trichobilharzia'' spp.) no such effect of temperature on feeding is seen.

Parasites

As a small aquatic invertebrate ''G. lacustris'' is an important food source for many organisms. Birds, fishes, and some insects are known to prey upon ''G. lacustris''. As many other species of small

invertebrates Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

, it serves as an

intermediate host In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' (symbiont). The guest is typically provided with nourishment and shelter. Examples include a ...

for several

parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

species (e.g. ''

Pomphorhynchus laevis ''Pomphorhynchus laevis'' is an endo-parasitic acanthocephalan worm, with a complex life cycle, that can modify the behaviour of its intermediate host, the freshwater amphipod ''Gammarus pulex''. ''P. laevis'' does not contain a digestive tr ...

''). ''G. lacustris'' typically shows

photophobic Photophobia is a medical symptom of abnormal intolerance to visual perception of light. As a medical symptom photophobia is not a morbid fear or phobia, but an experience of discomfort or pain to the eyes due to light exposure or by presence o ...

behaviour, but when parasitized this can be altered to photophilic behaviour when infected by ''Pomphorhynchus laevis''. Which is a host manipulation parasite, like many others. Parasites can affect the diel migration of ''G. lacustris'', making it more visible and susceptible to predation most likely aiding parasite transmission. More mature parasites have greater effects on hosts.

Distribution

''Gammarus lacustris'' has been noted in northwestern Europe, Russia, and North America. Its precise range has yet to be defined. It can be found in shallow or deep lakes and in slow-moving rivers. It is more abundant in fishless lakes than in those with fish. Its distribution follows the thermocline in the water.