Reproductive system of gastropods

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Entwined everted penises of a pair of mating hermaphrodite slugs in the species Limax maximus. Mating Great Grey Slug 4124.jpg
Entwined everted penises of a pair of mating hermaphrodite slugs in the species Limax maximus .

The reproductive system of gastropods (slugs and snails) varies greatly from one group to another within this very large and diverse taxonomic class of animals. Their reproductive strategies also vary greatly.

Contents

In many marine gastropods, there are separate sexes (male and female); most terrestrial gastropods however are hermaphrodites.[ citation needed ]

Courtship is a part of the behaviour of mating gastropods. In some families of pulmonate land snails, one unusual feature of the reproductive system and reproductive behavior is the creation and utilization of love darts, the throwing of which has been identified as a form of sexual selection. [1]

Gastropods reproductive systems vary significantly from one taxonomic group to another. They can be separated into three categories: marine, freshwater, and land. [2] Reproducing in marine or freshwater environments makes getting sperm to egg much easier for gastropods, while on land, it is much more difficult to get sperm to egg. [3] The majority of gastropods have internal fertilization, but there are some prosobranch species that have external fertilization. [4] Gastropods are capable of being either male or female, or hermaphrodites, and this makes their reproduction system stand out amongst many other invertebrates. Hermaphroditic gastropods possess both the egg and sperm gametes which gives them the opportunity to self-fertilize. [4] C. obtusus is a snail species of the Eastern Alps. In the easternmost populations of this species, there is strong evidence for self-fertilization. [5]

Reproductive system of marine gastropods

Marine gastropods mating. Snails mating at Chandrabhaga, Odisha coast.jpg
Marine gastropods mating.

The reproductive system of marine gastropods such as those from class Opisthobranchia and order Archaeogastropoda from the class Prosobranchia, is a continuous cycle of alternating male and female reproductive role prevalence. Immediately after spawning in late summer, the predominance of the female reproductive functions are terminated and gametogenesis initiates immediately, with the start of the predominance of the male reproductive role. Gametes remain in the gonads throughout the winter and early spring. The female reproductive role takes over again in May with fertilization of the gametes to form zygotes. The cycle comes full circle in late summer once again, with spawning. [6] [ citation needed ]

Separate sexes

In many taxonomic groups of marine gastropods, there are separate sexes (i.e. they are dioecious/gonochoric).

In some of the main gastropod clades the great majority of species have separate sexes. This is true in most of the Patellogastropoda, Vetigastropoda, Cocculiniformia, Neritimorpha, and Caenogastropoda.

A stack of the protandrous species Crepidula fornicata: the small individual at the extreme lower left is currently a male, the other individuals are large enough to have become female Crepidules groupe.jpg
A stack of the protandrous species Crepidula fornicata : the small individual at the extreme lower left is currently a male, the other individuals are large enough to have become female

Protandrous sequential hermaphrodites

Within the clade Littorinimorpha however, the superfamily Calyptraeoidea are protandrous sequential hermaphrodites. Protandry means that the individuals first become male, and then later on become female. See for example the genus Crepidula .

Simultaneous hermaphrodites

Two hermaphrodite opisthobranchs mating, the nudibranch species Nembrotha rutilans Nembrotha rutilans Nick Hobgood.jpg
Two hermaphrodite opisthobranchs mating, the nudibranch species Nembrotha rutilans
Drawing of reproductive system of Aplysia californica. AG - albumen gland, LHD - large hermaphroditic duct. Aplysia californica reproductive system.png
Drawing of reproductive system of Aplysia californica . AG - albumen gland, LHD - large hermaphroditic duct.

Within the main clade Heterobranchia, the informal group Opisthobranchia are simultaneous hermaphrodites (they have both sets of reproductive organs within one individual at the same time).

There are also a few marine pulmonates, and these are also hermaphroditic, for example, see the air-breathing sea slug family Onchidiidae, and the family of air-breathing marine "limpets" Siphonariidae.

Reproductive system of land gastropods

Separate sexes

Although most land snails are pulmonates and are hermaphrodites, in contrast, all of the sea-dwelling prosobranch snails are dioecious/gonochoric (in other words, they have separate sexes). This includes the snails in the families Pomatiidae, Aciculidae, Cyclophoridae, and others. These land snails have opercula, which helps identify them as "winkles gone ashore", in other words, snails within the clade Littorinimorpha and the informal group Architaenioglossa.

Members of the snail family Pulmonata, which includes carboniferous land sails and some freshwater snails of the order Basommatophora, are protandrous hermaphrodites, meaning they are born male and later in life become female. In this family of snails, the male phase ends in December, followed by an egg maturation phase, and ends with oviposition, the act of laying eggs during May of the following year. Phylogenetic evidence for this is present based on the overall condition of the gonads especially in the degree of development of the genital ducts. [7]

Simultaneous hermaphrodites

Simplified diagram of the reproductive morphology of a pulmonate land snail with one love dart and a diverticulum.
AG = albumen gland
BC = bursa copulatrix
BT = bursa tract/trunk
BTD = bursa tract diverticulum
D = love dart
EP = epiphallus
FL = flagellum
FP = fertilization pouch
G = genital pore
HD = hermaphroditic duct
MG = mucus glands (nidamental gland)
OT = ovotestis
P = penis
PRM = penis retractor muscle
S = stylophore or dart sac (bursa telae)
SO = spermoviduct
SP = spermathecae
SRO = spermatophore-receiving organ (indicated in grey)
V = vagina
VD = vas deferens Love dart drawing.png
Simplified diagram of the reproductive morphology of a pulmonate land snail with one love dart and a diverticulum.
AG = albumen gland
BC = bursa copulatrix
BT = bursa tract/trunk
BTD = bursa tract diverticulum
D = love dart
EP = epiphallus
FL = flagellum
FP = fertilization pouch
G = genital pore
HD = hermaphroditic duct
MG = mucus glands (nidamental gland)
OT = ovotestis
P = penis
PRM = penis retractor muscle
S = stylophore or dart sac (bursa telae)
SO = spermoviduct
SP = spermathecae
SRO = spermatophore-receiving organ (indicated in grey)
V = vagina
VD = vas deferens
Head of a mating Helix pomatia showing the everted penis (P), and the dart sac (S) in the process of shooting a love dart (D). Helix pomatia head mating.jpg
Head of a mating Helix pomatia showing the everted penis (P), and the dart sac (S) in the process of shooting a love dart (D).
Head of Helix pomatia after mating with everted vagina (V) and penis (P). Helix pomatia head after mating.jpg
Head of Helix pomatia after mating with everted vagina (V) and penis (P).

Pulmonate land gastropods are simultaneous hermaphrodites and their reproductive system is complex. It is all completely internal, except for genital protrusion (eversion) during mating. The outer opening of the reproductive system is called the "genital pore"; it is positioned on the right-hand side, very close to the head of the animal. This opening is virtually invisible, however, unless it is actively in use.

The love-dart (if present) is produced and stored in the stylophore (often called dart sac) and shot by a forceful eversion of this organ. The mucus glands produce the mucus that is deposited on the dart before shooting. The penis is intromitted to transfer the spermatophore. The sperm container is formed in the epiphallus, while the spermatophore's tail is formed by the flagellum. When a bursa tract diverticulum is present, the spermatophore is received in this organ. Together with the bursa tract and bursa copulatrix these form the spermatophore-receiving organ, which digest sperm and spermatophores. Sperm swim out via the tail of the spermatophore to enter the female tract and reach the sperm storage organ (spermathecae) within the fertilization pouch-spermathecal complex. [8]

Variability (polymorphism) of reproductive system in stylommatophorans is common feature. [9] Such variability may include: [9]

also

Examples of reproductive system of various land snails:

The structure of the reproductive system is strictly hermaphroditic. From the gonads, a hermaphrodite duct, a duct which is designed to transport both sperm and eggs, leads to a portion of the reproductive tract where the duct splits into a strictly male and strictly female portion. [7]

The female portion includes a fertilization pouch and posterior and anterior mucus glands, which open up into a pallial cavity which leads to a small muscular vagina. The male portion of the reproductive tract includes both a short posterior vas deferens and a longer anterior vas deferens. The posterior vas deferens is followed by the prostate, and the anterior vas deferens flows through the haemocoele, an enlarged blastula filled with blood, of the head and opens into a muscular penis which is engulfed in a small portion of skin called the prepuce sac. [7]

Reproductive system in freshwater gastropods

Separate sexes and hermaphrodites

Species in the freshwater gastropod family such as the Caenogastropoda from the class Prosobranchia, are largely self-fertilizing; however after many generations of selfing, a physiological barrier halts sperm generation in that organism, and only allows for the introduction of foreign sperm. Gametes form in the ovotesties, an organ which produces both ova and sperm, and pass down into the hermaphroditic duct to the albumen gland, the junction of where the common duct splits to either vas deferens or oviduct, where they are stored until they are needed for either mating or self-fertilization. It is believed that this junction acts as a regulatory mechanism via contracting muscles, to help direct sperm or eggs into the correct ducts. [10]

Mating

The sperm passes into the male duct, or vas deferens, where is receives secretory additions in the form of mucus from the prostate. After getting modified, the sperm passes into the penis. During mating season, the glandular cells in the penis sheath and prepuce swell to facilitate eversion of the penis. The sperm gets pushed through the penis, where they are introduced into the tail end of its copulatory partner. Within the partner snail, after fertilization from the foreign sperm, the eggs pass into the albumen gland where they are coated in mucus which forms the egg capsule. [10]

Selfing

Eggs are released immediately before oviposition. Unlike in land gastropod species where fertilization occurs in fertilization pockets, fertilization in freshwater species happens at the lower end of the hermaphroditic duct, near the junction. Sperm is deposited into the bursa copulatrix which opens up into the vagina. The ova then enter the albumen gland to get a nutrient dense mucus coating which serves to form the egg capsule. [10]

Genital structures

Genital structures in Stylommatophora are listed below with the English name, then after the dash the Latin version (following the table in [11] ). Definitions and functions are discussed in [12] .

Genital structures of males

The prostate is found in the mantle tubule and penis are both connected to the gonoduct; which are connected to the testis (produce sperm). During sex, the sperm travels along the mantle tube in which seminal fluid fills the mantle tube and exits the body via the penis and enters the females gonopore. [16]

Additional reproductive structures include

Gastropod anatomy. Snail diagram-en edit1.svg
Gastropod anatomy.

Genital structures of females

Females have a gonopore that is connected to a seminal receptacle. The gonopore acts as an opening through which eggs are deposited. The opening leads into the mantle tubule, in which eggs flow from the oviduct and ovary. The mantle tubule produces three things, yolk; carries most of the nutrients needed to develop a healthy offspring, egg capsule formation, and sperm reception and storage; where fertilization occurs. After fertilization, eggs travel to the albumin glands to fill the yolk with protein, and lastly, the egg travels through the capsule glands, which coat the egg in a protective jelly. [16]

Additional reproductive structures include:

Genital structures of hermaphrodites

Hermaphrodites have both male and female reproductive parts. The male and female system act as separate units until the egg and sperm are ready to fuse together. The fusion of egg and sperm takes place in the uterus of the female system. Hermaphrodites also have a hermaphroditic duct, which helps change the sex of the gastropod during certain times of the year. [16]

See also

Related Research Articles

<i>Helix</i> (gastropod) Genus of gastropods

Helix is a genus of large, air-breathing land snails native to the western Palaearctic and characterized by a globular shell.

<span class="mw-page-title-main">Female reproductive system</span> Reproductive system of human females

The female reproductive system is made up of the internal and external sex organs that function in the reproduction of new offspring. The human female reproductive system is immature at birth and develops to maturity at puberty to be able to produce gametes, and to carry a fetus to full term. The internal sex organs are the vagina, uterus, fallopian tubes, and ovaries. The female reproductive tract includes the vagina, uterus, and fallopian tubes and is prone to infections. The vagina allows for sexual intercourse and childbirth, and is connected to the uterus at the cervix. The uterus or womb accommodates the embryo which develops into the fetus. The uterus also produces secretions which help the transit of sperm to the fallopian tubes, where sperm fertilize ova produced by the ovaries. The external sex organs are also known as the genitals and these are the organs of the vulva including the labia, clitoris, and vaginal opening.

<span class="mw-page-title-main">Male reproductive system</span> Reproductive system of the human male

The male reproductive system consists of a number of sex organs that play a role in the process of human reproduction. These organs are located on the outside of the body, and within the pelvis.

<span class="mw-page-title-main">Human reproductive system</span> Organs involved in reproduction

The human reproductive system includes the male reproductive system which functions to produce and deposit sperm; and the female reproductive system which functions to produce egg cells, and to protect and nourish the fetus until birth. Humans have a high level of sexual differentiation. In addition to differences in nearly every reproductive organ, there are numerous differences in typical secondary sex characteristics.

<span class="mw-page-title-main">Black slug</span> Species of gastropod

The black slug, Arion ater, is a large terrestrial gastropod mollusk in the family Arionidae, the round back slugs. Many land slugs lack external shells, having a vestigial shell. Most slugs retain a remnant of their shell, which is usually internalized, unlike other terrestrial mollusks which have external shells. Without such shells, slugs produce mucus, that may also contain toxins—to deter predators. Terrestrial slugs produce two other forms of mucus that facilitate locomotion and prevent death from drying. Such mollusks are hermaphroditic. Slugs most often function as decomposers but are also often omnivores. Arion ater is one such slug, decomposing organic matter, preying on other organisms, and consuming vegetative matter including agricultural crops. Native to Europe, the black slug is an invasive species in Australia, Canada, and the United States.

Beddomeia minima is a population of freshwater snails that are endemic to Australia. It is commonly classified as a hydrobiid snail. This population was listed as Vulnerable on the IUCN Red List in 2011 due to its distribution being restricted to a single location and range of possible threats present in Tasmania. Beddomeia minima is one of a few fresh water snail species belonging to the same genus Beddomeia that survive in Tasmania, Australia, specifically a single location in the Scottsdale area.

Beddomeia protuberata is a species of endemic freshwater snail in the family Tateidae, found in northern Tasmania, Australia. The shells look ovate and periostracum yellow with some pustules, length between 2.29 mm and 2.93 mm and width between 2.01 mm and 2.34 mm. Beddomeia protuberata has 1.75 protoconch whorls. Its image of microsculpture is uniform and its wrinkles arranged weakly and helically. The teleoconch of beddomeia protuberata has 2.2 to 2.7 convex whorls, and the ratio of convexity is 0.15 to 0.24. Sculptures of the teleoconch are vague with prosocline growth lines. The margin of the last whorl is evenly circular. The thickness and width of inner lips are medium sizes, and the columellar swelled up prominently. The outer lips of Beddomeia protuberata is prosocline, which means the shell leans forwards compared to the shell’s coiling axis. The width of their umbilicus is between 0.31 mm to 0.51 mm. The umbilicus of female beddomeia protuberata are wider than the umbilicus of male.

<span class="mw-page-title-main">Love dart</span> Darts that some snails shoot into each other during mating

A love dart is a sharp, calcareous or chitinous dart which some hermaphroditic land snails and slugs create. Love darts are both formed and stored internally in a dart sac. These darts are made in sexually mature animals only, and are used as part of the sequence of events during courtship, before actual mating takes place. Darts are quite large compared to the size of the animal: in the case of the semi-slug genus Parmarion, the length of a dart can be up to one fifth that of the semi-slug's foot.

The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are also important accessories to the reproductive system. Unlike most organ systems, the sexes of differentiated species often have significant differences. These differences allow for a combination of genetic material between two individuals, which allows for the possibility of greater genetic fitness of the offspring.

<i>Pseudunela cornuta</i> Species of gastropod

Pseudunela cornuta is a species of minute sea slug, an acochlidian, a shell-less marine and temporarily brackish gastropod mollusk in the family Pseudunelidae. Adults are about 3 mm long and live in the spaces between sand grains.

<span class="mw-page-title-main">Male accessory gland</span> Sexual gland in males

Male accessory glands (MAG) in humans are the seminal vesicles, prostate gland, and the bulbourethral glands. In insects, male accessory glands produce products that mix with the sperm to protect and preserve them, including seminal fluid proteins. Some insecticides can induce an increase in the protein content of the male accessory glands of certain types of insects. This has the unintended effect of increasing the number of offspring they produce.

<i>Leptacme cuongi</i> Species of gastropod

Leptacme cuongi is a species of air-breathing land snail, a terrestrial gastropod mollusk in the family Clausiliidae, the door snails.

<i>Atractophaedusa smithi</i> Species of gastropod

Atractophaedusa smithi is a species of air-breathing land snail, a terrestrial gastropod mollusk in the family Clausiliidae, the door snails.

<span class="mw-page-title-main">Lepidoptera genitalia</span> Study of the genitalia of butterflies and moths

The study of the genitalia of Lepidoptera is important for Lepidoptera taxonomy in addition to development, anatomy and natural history. The genitalia are complex and provide the basis for species discrimination in most families and also in family identification. The genitalia are attached onto the tenth or most distal segment of the abdomen. Lepidoptera have some of the most complex genital structures in the insect groups with a wide variety of complex spines, setae, scales and tufts in males, claspers of different shapes and different modifications of the ductus bursae in females.

<i>Marstonia comalensis</i> Species of gastropod

Marstonia comalensis is a species of minute freshwater snail with a gill and an operculum, an aquatic gastropod mollusk or micromollusk in the family Hydrobiidae. It is found in south central Texas, United States.

<i>Carabus insulicola</i> Species of beetle

Carabus insulicola is a species of black-colored beetle from the family Carabidae native to Japan. They are also known as ground beetles. C. insulicola are oval shaped and elongated. They are black with a green metallic hue and vertical stripes running down their backs. The length of a fully grown beetle ranges from 27 to 31 mm. They have three pairs of legs and two pairs of wings. The outer wings are greatly degenerated, which prevents them from being able to fly. However, their relatively long legs allow them to walk and run fast. They have prominent mandibles that allow them to capture and eat prey.

Most insects reproduce oviparously, i.e. by laying eggs. The eggs are produced by the female in a pair of ovaries. Sperm, produced by the male in one testicle or more commonly two, is transmitted to the female during mating by means of external genitalia. The sperm is stored within the female in one or more spermathecae. At the time of fertilization, the eggs travel along oviducts to be fertilized by the sperm and are then expelled from the body ("laid"), in most cases via an ovipositor.

<span class="mw-page-title-main">Mating of gastropods</span>

The mating of gastropods is a vast and varied topic, because the taxonomic class Gastropoda is very large and diverse, a group comprising sea snails and sea slugs, freshwater snails and land snails and slugs. Gastropods are second only to the class Insecta in terms of total number of species. Some gastropods have separate sexes, others are hermaphroditic. Some hermaphroditic groups have simultaneous hermaphroditism, whereas some sequential hermaphroditism. In addition, numerous very different mating strategies are used within different taxa.

<span class="mw-page-title-main">Reproductive system of planarians</span>

The reproductive system of planarians is broadly similar among different families, although the associated structures can vary in complexity.

Roboastra tentaculata is a species of sea slug, a polycerid nudibranch, a marine gastropod mollusc in the family Polyceridae.

References

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