Flatworm Can Inject Sperm Into Its Head To Fertilize

Macrostomum hystrix flatworm adult

A free-living hermaphrodite flatworm, called Macrostomum hystrix can inject sperm into its head to fertilize, in harsh conditions when no mates are to be found.

The reproduction instinct is extremely powerful in the large and small creatures of the world. This is what seems to lie at the core of their existence, because they are born and from there on, they spend their lives doing their best to develop as well as possible, so that they may either bare their offspring or find suitable mates who could do that best. This is what keeps the world turning.

So it should come as no surprise that some hermaphroditic species have developed the extraordinary ability to self-fertilize in order to perpetuate the species, as they feel that they must do this at any price. If suitable mates are available, they will obviously be the main choice.

However, in the event that the animal encounters particularly harsh conditions, when there are no mates to be found, it will be able to use its own reproductive material, so that it may fulfill its role and create a viable offspring.

This is the case of the Macrostomum hystrix, which is a free-living flatworm which is known for its large mouth which it uses to catch its prey, but also for its ability to perform a particular type of fertilization, called hypodermic insemination. Moreover, this ability comes in handy in order to perform auto-feritilization if the situation calls for it.

This process involves that the flatworm uses its pointy needle-shaped copulatory organ in order to deposit its sperm. Flatworms are capable of performing normal cross-fertilization, that implies that one flatworm will deposit its sperm into another flatworm’s genital pore, but they are also capable of hypodermic insemination. This implies that the sharp copulatory organ is used to pierce the skin of another flatworm, in order to deposit the sperm.

While this might seem like an improper insemination process, it should be mentioned that flatworms do not have specialized layers covering its organs and setting them apart in different compartments. The flatworm has is digestive, excretory, respiratory and reproductive system in the same compartment that is delimited by the worm’s outer layer.

Therefore, when the skin is pierced, the sperms can migrate towards the organ that contains the eggs and thus, the fertilization can easily take place. The outer layer of the worm can heal afterwords, and so the damage is not permanent or lethal.

Precisely because it can heal, the flatworm can use this fertilization technique to fertilize itself when the environment conditions it encounters are not suitable for cross-fertilization. Due to the elongated disposition of its body, the best way for it to do so is to curve itself and stick its pointy copulatory organ in its head. Thus, the sperm is delivered successfully.

Naturally, the offspring generated by this method well not thrive as well as a the cross-fertilization offspring could, but it is capable of ensuring that the species has been successfully perpetuated.
Image Source: macrostomorpha.info