''Macrostomum hystrix'' is a free-living

flatworm The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") are a phylum of relatively simple bilaterian, unsegme ...

in the family Macrostomidae. It is small, transparent, and a

simultaneous hermaphrodite Simultaneous hermaphroditism is one of the two types of hermaphroditism, the other type being sequential hermaphroditism. In this form of hermaphroditism an individual has sex organs of both sexes and can produce both gamete types even in the sam ...

Biology

''Macrostomum hystrix'' is capable of

hypodermic insemination Traumatic insemination, also known as hypodermic insemination, is the mating practice in some species of invertebrates in which the male pierces the female's abdomen with his aedeagus and injects his sperm through the wound into her abdominal ca ...

. In this process, sperm is injected through the

epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and Subcutaneous tissue, hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the ...

into the

parenchyma Parenchyma () is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology it is the name for the tissue that fills the interior of flatworms. Etymology The term ''parenchyma'' is New Latin from the word π ...

of the mating partner. This is done by a needle-like stylet, which is the male copulatory organ. The stylet has a rigid and pointed distal thickening, as well as a subterminal stylet opening which can puncture the epidermis of the mating partner. The sperm are highly motile, small and simple, but have no flagellates. The female antrum shows a simple anatomy and is only involved in laying eggs. In isolated worms, it has been shown that ''Macrostomum hystrix'' does not only use hypodermic insemination for outbreeding but also

self-fertilization Autogamy, or self-fertilization, refers to the fusion of two gametes that come from one individual. Autogamy is predominantly observed in the form of self-pollination, a reproductive mechanism employed by many flowering plants. However, species ...

, or "selfing". To achieve this, they inject their sperm into themselves — mainly into their own heads, due to physical constraints. From there, the sperm apparently migrate to the site of

fertilization Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Pro ...

. Worms that were isolated showed significantly more sperm in their heads, compared to worms that had the opportunity to cross-fertilize. ''Macrostomum hystrix'' prefers outbreeding if partners are available because selfing also has costs. The amount of offspring of worms that selfed is reduced, as is the offspring's survival. As a consequence, ''Macrostomum hystrix'' only begins selfing in the extended absence of mating partners: delayed selfing represents a conditional reproductive strategy which allows them to deal with periodic conditions of low mate abundance.

References

External links

Turbellaria database

www.macrostomum.net

University of Basel The University of Basel (Latin: ''Universitas Basiliensis'', German: ''Universität Basel'') is a university in Basel, Switzerland. Founded on 4 April 1460, it is Switzerland's oldest university and among the world's oldest surviving universitie ...

{{Taxonbar, from=Q2715406 Turbellaria