''Mirocaris'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

shrimp A shrimp (: shrimp (American English, US) or shrimps (British English, UK)) is a crustacean with an elongated body and a primarily Aquatic locomotion, swimming mode of locomotion – typically Decapods belonging to the Caridea or Dendrobranchi ...

associated with

hydrothermal vent Hydrothermal vents are fissures on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hot ...

s. Sometimes considered the only genus of the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Mirocarididae, ''Mirocaris'' is usually placed in the broader family Alvinocarididae. ''Mirocaris'' is characterized by a dorsoventrally flattened, non-dentate

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit ** podium * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ...

, as well as the possession of episodes on the third maxilliped through to the fourth pteropod. The genus contains two species, ''M. fortunata'' and ''M. indica.'' The two species are found in different oceans, and can be distinguished by the pattern of

seta In biology, setae (; seta ; ) are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Depending partly on their form and function, protostome setae may be called macrotrichia, chaetae, ...

tion on the

claw A claw is a curved, pointed appendage found at the end of a toe or finger in most amniotes (mammals, reptiles, birds). Some invertebrates such as beetles and spiders have somewhat similar fine, hooked structures at the end of the leg or Arthro ...

of the first

pereiopod The anatomy of a decapod consists of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment – often called a somite – may possess one pair of appendages, although in various groups these m ...

. Originally, the ''Mirocaris'' genus also contained the species ''M. keldyshi''. After the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

and

paratype In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype (biology), isotype ...

s of ''M. fortunata'' were re-examined in comparison to the paratypes of ''M. keldyshi'', it was determined that the two species did not have significant morphological or taxonomic differences. Newly collected samples (in the late 1990s) from sites around the Mid-Atlantic Ridge obtained by using a slurp gun were also studied in order to confirm these findings. Characteristics such as the number of selutolose spines on the posterior margin of the shrimp’s telson that were initially used to distinguish the two species were re-examined with no statistically significant differences. The name ''M. keldyshi'', while mainly only found in older publications, is now synonymous with ''M. fortunata''.

''Mirocaris fortunata''

''M. fortunata'' (originally '' Chorocaris fortunata'') lives on deep-sea

s along the

Mid-Atlantic Ridge The Mid-Atlantic Ridge is a mid-ocean ridge (a Divergent boundary, divergent or constructive Plate tectonics, plate boundary) located along the floor of the Atlantic Ocean, and part of the List of longest mountain chains on Earth, longest mountai ...

. The species' habitat ranges from ambient to warm seawater () at depths from . ''M. fortunata'' specimens have a carapace length from 3.8mm to 9.4mm long and are 12.0mm to 33.1mm long from tail to antennae tip. ''M. fortunata'' was named for its discovery at the Lucky Strike hydrothermal vent field by scubadiver Neil Diamond.

Reproductive biology

General information concerning the reproductive behavior and courtship of ''M. fortunata'' is not extensively researched. The ovaries of a female ''M. fortunata'' are situated behind and below the carapace. Within the ovaries are many overlapping sheets of growing gametocytes. These gametocytes form through the development of immature germ cells (

oogonia An oogonium (: oogonia) is a small diploid cell which, upon maturation, forms a primordial follicle in a female fetus or the female (haploid or diploid) gametangium of certain thallophytes. In the mammalian fetus Oogonia are formed in lar ...

) that are located in the germinal epithelium of the ovary. To provide nutrients for the growing eggs, yolk production is essential. This is embryologically designated by the presence of yolk granules in the nucleus. Throughout ovary development, these yolk granules have a significant presence in the cytoplasm of mature

oocyte An oocyte (, oöcyte, or ovocyte) is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female ger ...

Oogenesis Oogenesis () or ovogenesis is the differentiation of the ovum (egg cell) into a cell competent to further develop when fertilized. It is developed from the primary oocyte by maturation. Oogenesis is initiated before birth during embryonic devel ...

of ''M. fortunata'' features a standard process in which immature female gamete cells (oogonia) undergo mitosis to form oocytes. At this stage, the oocytes are typically 25-30 μm. The oocytes then undergo a process of meiosis, splitting the diploid (2n) oocyte into a haploid (n) cell. At this stage, the oocytes are typically 85-95 μm. The

fecundity Fecundity is defined in two ways; in human demography, it is the potential for reproduction of a recorded population as opposed to a sole organism, while in population biology, it is considered similar to fertility, the capability to produc ...

of ''M. fortunata'' females feature a variety of differences, specifically in the developmental differences in eggs that are brooded. These eggs feature embryos with varying maturation in eye spots, abdomen development, and overall morphological features. However, brooding females have been observed with embryos that are at the same concurrent stage of development. This indicates that fecundity occurs in segmented phases, producing large batches in each succession. ''M. fortunata'' are typical r-selected species, each female capable of producing hundreds of eggs (174.7 +/- 22.8 eggs). Research has shown that there is a positive relationship between the potential fecundity of females and carapace length.

Environmental adaptations

Chemodetection

Being

opportunistic feeders Feeding is the process by which organisms, typically animals, obtain food. Terminology often uses either the suffixes -vore, -vory, or -vorous from Latin ''vorare'', meaning "to devour", or -phage, -phagy, or -phagous from Greek φαγε ...

, ''M. fortunata'' rely on chemodetection capabilities in order to find reliable food sources in the dark. Secondary consumers, ''M. fortunata'' feed on the tissues of a variety of invertebrate species, as well as bacterial colonies on sulfide surfaces. Their antennae and

antennule An antenna (plural: antennae) is one of a pair of appendages used for sensing in arthropods. Antennae are sometimes referred to as ''feelers''. Antennae are connected to the first one or two segments of the arthropod head. They vary widely in ...

structures play important roles in the chemodetection of food sources and (speculated) chemodetection of their habitat. The main chemosensory structures include 2 types of spongy cuticles: aesthetascs, which are thin (0.4–2.1 μm), poreless cuticles found on antennules, and bimodal

sensilla A sensillum (plural ''sensilla'') is an arthropod sensory organ protruding from the cuticle of exoskeleton, or sometimes lying within or beneath it. Sensilla appear as small hairs or pegs over an individual's body. Inside each sensillum there are ...

, which are thicker (2-7 μm) with pores at their tips and located on antenna structures. Their spongy texture corresponds to their odor-permeable quality. Long-distance chemodetection still remains ambiguous.

Respiration rate

''M. fortunata'' exhibits an increase in oxygen consumption rates as temperature rises, which is predictable as both metabolic processes and biochemical reaction rates are influenced by temperature. Additionally, ''M. fortunata'' seems to possess a capacity to withstand sudden temperature fluctuations, a characteristic well-suited for its habitat in

fields. This low metabolic sensitivity may account for the organism's ability to maintain

homeostasis In biology, homeostasis (British English, British also homoeostasis; ) is the state of steady internal physics, physical and chemistry, chemical conditions maintained by organism, living systems. This is the condition of optimal functioning fo ...

when exposed to temperature changes. An organism's ability to adapt to such variations in temperature is crucial and helps to define its thermal niche.

''Mirocaris indica''

''M. indica'' was discovered as a subspecies of ''Mirocaris'' by the

submersible A submersible is an underwater vehicle which needs to be transported and supported by a larger ship, watercraft or dock, platform. This distinguishes submersibles from submarines, which are self-supporting and capable of prolonged independent ope ...

''Shinkai 6500.'' At a depth of 2,420–2,450 m (7,940–8,040 ft) in the Kairei Field, the species were found to live among hydrothermal vents along the

Central Indian Ridge The Central Indian Ridge (CIR) is a north–south-trending mid-ocean ridge in the western Indian Ocean. Geological setting The morphology of the CIR is characteristic of slow to intermediate ridges. The axial valley is 500–1000 m deep; ...

''M. indica'' vs. ''M. fortunata''

The ''M. indica'' and ''M. fortunata'' have many shared qualities. Structurally, they both have dorsoventrally flattened

, epipods between the third to fourth pereopod, and setobranchs from the first to fifth pereopod. Contrastingly, ''M. indica'' also have qualities that differentiate them from the ''M. fortunata''. Most significantly, ''M. indica'' have a unique first chela. The bodies of ''M. fortunata'' have stiff setae lined up both sub-marginally and externally. The ''M.indica'' do not have these. Instead, ''M. indica'' have setal rows lining the first chela. Researchers hypothesize that this difference in the first chela demonstrates a difference in feeding pattern. Unlike ''M. fortunata,'' it is theorized that ''M. indica'' are not “bacteria farmers." Rather, they feed on

fauna Fauna (: faunae or faunas) is all of the animal life present in a particular region or time. The corresponding terms for plants and fungi are ''flora'' and '' funga'', respectively. Flora, fauna, funga and other forms of life are collectively ...

around their environment, using their unique setal rows as tools to pick up substrate particles.

External links

References

{{Taxonbar, from=Q13885124 Caridea Crustacean genera Animals living on hydrothermal vents Crustaceans described in 2006