Week 8 Blog Post – Mollusca
Mollusca Reproduction
Introduction
This week in invertebrate biology began as they have for the past nine weeks. Our professor presents a picture of an invertebrate that we have to place into the correct phylum. We are to use our textbooks, previous knowledge, and internet creeping skills to determine the organism’s place within the animal kingdom. The picture we were presented with this week is below. Can you decide to which phylum it belongs?
Karen N. Pelletreau et al. Creative Commons.
I noticed right away that it was a sea slug. Its characteristic bilateral, soft body, and distinguishable head and tail ends confirmed my thoughts. I had studied these previously, so I was confident in my general identification. I remembered that sea slugs were molluscs – related to cephalods and bivalves – but couldn’t instantly place the class to which sea slugs belonged. After finding the classes in phylum mollusca, of which there are eight, I determined it was gastropod.
Gastropods are the largest of the eight classes comprising about 60,000 species of snails and slugs that inhabit marine, freshwater, and terrestrial ecosystems1. Our invertebrate of interest this week is commonly known as the Eastern Emerald Elysia, but is scientifically referred to as Elysia chlorotica.
While this organism is astounding for many reasons, the one I’ll be focusing on in this post is its reproduction.
Elysia chlorotica Reproduction
Elysia chlorotica is a simultaneous hermaphrodite4.That means an individual has both male and female reproductive organs5. It is possible for E. chlorotica to self fertilize since it produces both male and female gametes; however, the majority of fertilizations are a result of sex with another individual.
Many of the specifics about E. chlorotica’s mating and reproduction is unknown, but scientists have extrapolated their knowledge about a similar species, E. timida, to draw conclusions about our invertebrate of interest.
Gerry, P., 201. Creative Commons. E. timida a similar species to E. chlorotica.
In E. timida, copulation is dependent on the possible mate’s reaction of the invitation4. This invitation comes in the form of a stereotyped dance. Potential partners align head-to-head to check out each other with their sensory tentacles, then one will start to move down the body, if the other accepts the mating invitation, they will line up head to tail and copulate4. In this instance both individuals will receive sperm – thus acting as both male and female within one round of mating.
Schmitt, V., et al., 2007. Mating “dance” ritual performed by E. chlorotica and similar species.
Breeding usually only happens once a year, typically in the early spring4. The eggs of E. chlorotica are laid in mucous strings and hatch within about a week after laying4. E. chlorotica are short lived animals and die shortly after they lay their eggs4.
Mary E. Rumpho et al., 2011. Life cycle of E. chlorotica.
E. chlorotica have three main life stages. The first is called a veliger. It is a ciliated and shelled vellum that will not be able to mature into the next stage unless it is exposed to Vaucheria litorea4. Once it has been exposed to its algae for 1-2 days, it will mature into a juvenile. From that stage, it will be highly dependent on the V. litorea while it gathers energy to metamorphose into an adult4.
Mollusca vs. E. chlorotica – Reproduction
Gastropod vs. E. chlorotica
Similarities
Gastropods used to be classified into three subclasses: prosobranchia, opisthobranchia, and pulmonata1. Due to new evidence, these no longer hold true, but are still used which lends a great deal of confusion when discussing this class of mollusca. However, I am going to refer to the subclasses as if it were still true.
Prager, E. , 2011. A queen conch – a prosobranch.
You may not know that the very famous conch shell houses a gastropod that is classified as a prosobranch. Their sex is particularly interesting.A male possesses a penis that is able to navigate around the clunky shell of a female in order to deliver sperm; however, when their penis is free in the ocean there is a chance it will become food for predators. Thankfully for conch males, their penises can actually regenerate which I’m sure they don’t take for granted2.
Kahlbrock, S and N. Yonow, 2012. Creative Commons. Cadlinella ornatissima – an opisthobranch.
Under this classification, E. chlorotica would be classified as an opisthobranch. The majority of this subclass are simultaneous hermaphrodites, including our invertebrate of interest. Their fertilization is internal and only a select few (in addition to E. chlorotica, Trinchesia granosa) can self fertilize3. E. chlorotica, like many other gastropods are considered promiscuous3. This just means that an individual will mate with multiple individuals before laying their eggs.
Creative Commons. Cepaea nemoralis – a pulmonate
Pulmonates are also simultaneous hermaphrodites that cross fertilize (sex with other individuals) and can self fertilize like other opisthobranchia – and thus E. chlorotica3.
Pulmonates, like prosobranchs, have some pretty interesting mating rituals. Some garden snails, Cornu aspersum, fire love darts that release sperm-saving hormones at their sexual partner as an act of foreplay5. If love darts weren’t enough of a stretch, leopard slugs, Limax maximus, mate aerially – they hang upside down, with their bodies entwined, on a string of mucus (video mark 2:50)6.
Differences
Prosobranchs are mainly gonochoristic (have one sex) compared to E. chlorotica’s simultaneous hermaphroditism3. The remaining prosobranchs, some opisthobranchs, and some pulmonates exhibit protandry – the switching of sex from male to female throughout one’s life cycle – which our invertebrate of interest does not3.
In prosobranchs, fertilization can be external and is not strictly internal3. Prosobranchs also have been observed to be parthenogenic – ovum reproduction without fertilization – in multiple species3.
Cephalopoda vs. E. chlorotica
Similarities
Cephalopods are similar to E. chlorotica in that they are promiscuous. Cuttlefish and squid are known to mate in large aggregations where multiple mating is commonplace2. Cephalopods are also known for storing sperm similar to the gastropod Crepidula fornicata2,3.
Cephalopods also face a demise similar to that of E. chlorotica; they die soon after reproduction2.
Cephalopods have mating rituals that involve camouflage, guarding of females, synchronized swimming, and “flirting” by a swim-and-flee pursuit2. The synchronized swimming is most similar to that of E. chlorotica.
Differences
Cephalopods have separate sexes, and thus, exhibit sexual dimorphism2. Males are typically larger than the females and exhibit brilliant coloring using their chromatophores – this helps them attract a mate.
Cephalopods, including Bathypolypus sp. and Tremoctopus sp., provide parental care to their eggs rather than depositing them on a substrate or within the water column2.
Cephalopods also have an interesting sperm delivery method. A highly specialized tentacle called a hectocotylus transfers sperm to the female1,3.
Creative Commons. Hectocotylus – specialized tentacle that male’s possess for delivery of sperm.
Carefoot, T. Delivery of sperm from male to female.
Bivalvia vs. E. chlorotica
Similarities
There are some hermaphroditic species of bivalves, some of which are capable of self fertilization3.
Creative Commons. A bivalve – within the family veneroidea.
Differences
Bivalves are gonochoristic (possess one sex per individual) exhibiting external fertilization and broadcast spawning3. Because these molluscs are gonochoristic, they exhibit some sexual dimorphism – this can be observed by noting the differences in color of the gonads.
Polyplacophora vs. E. chlorotica
NOAA. Commonly known as chitons, the dark-shelled organism is a polyplacophoran.
Similarities
There are a few hermaphroditic species: Lepidochintona fernaldi and L. caverna3.
Differences
Most species are gonochoristic and exhibit external fertilization3.
About 30 species have females that brood their eggs3.
Males will often spawn hours before the females3.
Monoplacophora vs. E. chlorotica
Creative Commons, 2013. Monoplacophora anatomy including gonads.
Similarities
Micropilina arntzi is a hermaphroditic species of monoplacophoran with internal fertilization3.
Differences
M. arntzi broods their young in their mantle3.
A majority of the class are gonochoristic and exhibit external fertilization3.
Caudofaveata vs. E. chlorotica
Differences
Sexes are separate and exhibit external fertilization3.
Solenogastres vs. E. chlorotica
Todt, C., 2009. Solenogaster.
Similarities
Some species of this class are hermaphroditic3.
Differences
Anamenia agassizi are hermaphroditic but do not insert penes into one another. Instead they coil around each other and press their cloacal openings to transfer gametes3.
Scaphopoda vs. E. chlorotica
Similarities
There are species of hermaphrodites within this class3.
Similar to E. chlorotica, scaphopods do not brood their young after laying their eggs7.
Differences
The majority of the class has separate sexes and exhibits external fertilization3.
Not only are molluscs abundant, but their reproductive methods are extremely diverse. It is very difficult to find a common theme among all species, but I believe that is what makes them interesting.
Works Cited
1 Pechenik, J.A. Biology of the Invertebrates. 7th ed., McGraw Hill, 2015.
2 Prager, E. Sex, Drugs, and Sea Slime: The Oceans’ Oddest Creatures and Why They Matter. University of Chicago Press, 2011
3 Baur, B. “Sperm Competition in Molluscs.” Sperm Competition and Sexual Selection, edited by T.R. Birkhead and A.P. Møller, Academic Press, 1998, 255-305.
4 “Elysia chlorotica: Eastern Emerald Elysia.” Encyclopedia of Life.
5 “Everything you never wanted to know about snail sex.” KQED (PBS). 2017.
6 Langley, L. “Inside the Strange World of Slug Sex and Slime.” National Geographic, 2017.
7 Mulcrone, R.S. “Scaphopoda.” Animal Diversity Web. University of Michigan. 2005.
Week 8 Blog Post – Mollusca – Revised 12.1.17
Mollusca Reproduction
Introduction
This week in invertebrate biology began as they have for the past nine weeks. Our professor presents a picture of an invertebrate that we have to place into the correct phylum. We are to use our textbooks, previous knowledge, and internet creeping skills to determine the organism’s place within the animal kingdom. The picture we were presented with this week is below. Can you decide to which phylum it belongs?
Karen N. Pelletreau et al. Creative Commons.
I noticed right away that it was a sea slug. Its characteristic bilateral, soft body, and distinguishable head and tail ends confirmed my thoughts. I had studied these previously, so I was confident in my general identification. I remembered that sea slugs were molluscs – related to cephalods and bivalves – but couldn’t instantly place the class to which sea slugs belonged. After finding the classes in phylum mollusca, of which there are eight, I determined it was gastropod.
Gastropods are the largest of the eight classes comprising about 60,000 species of snails and slugs that inhabit marine, freshwater, and terrestrial ecosystems1. Our invertebrate of interest this week is commonly known as the Eastern Emerald Elysia, but is scientifically referred to as Elysia chlorotica.
While this organism is astounding for many reasons, the one I’ll be focusing on in this post is its reproduction.
Elysia chlorotica Reproduction
Elysia chlorotica is a simultaneous hermaphrodite4.That means an individual has both male and female reproductive organs5. It is possible for E. chlorotica to self fertilize since it produces both male and female gametes; however, the majority of fertilizations are a result of sex with another individual.
Many of the specifics about E. chlorotica’s mating and reproduction is unknown, but scientists have extrapolated their knowledge about a similar species, E. timida, to draw conclusions about our invertebrate of interest.
Gerry, P., 201. Creative Commons. E. timida a similar species to E. chlorotica.
In E. timida, copulation is dependent on the possible mate’s reaction of the invitation4. This invitation comes in the form of a stereotyped dance. Potential partners align head-to-head to check out each other with their sensory tentacles, then one will start to move down the body, if the other accepts the mating invitation, they will line up head to tail and copulate4. In this instance both individuals will receive sperm – thus acting as both male and female within one round of mating.
Schmitt, V., et al., 2007. Mating “dance” ritual performed by E. chlorotica and similar species.
Breeding usually only happens once a year, typically in the early spring4. The eggs of E. chlorotica are laid in mucous strings and hatch within about a week after laying4. E. chlorotica are short lived animals and die shortly after they lay their eggs4.
Mary E. Rumpho et al., 2011. Life cycle of E. chlorotica.
E. chlorotica have three main life stages. The first is called a veliger. It is a ciliated and shelled vellum that will not be able to mature into the next stage unless it is exposed to Vaucheria litorea4. Once it has been exposed to its algae for 1-2 days, it will mature into a juvenile. From that stage, it will be highly dependent on the V. litorea while it gathers energy to metamorphose into an adult4.
Mollusca vs. E. chlorotica – Reproduction
Gastropod vs. E. chlorotica
Similarities
Gastropods used to be classified into three subclasses: prosobranchia, opisthobranchia, and pulmonata1. Due to new evidence, these no longer hold true, but are still used which lends a great deal of confusion when discussing this class of mollusca. However, I am going to refer to the subclasses as if it were still true.
Prager, E. , 2011. A queen conch – a prosobranch.
You may not know that the very famous conch shell houses a gastropod that is classified as a prosobranch. Their sex is particularly interesting.A male possesses a penis that is able to navigate around the clunky shell of a female in order to deliver sperm; however, when their penis is free in the ocean there is a chance it will become food for predators. Thankfully for conch males, their penises can actually regenerate which I’m sure they don’t take for granted2.
Kahlbrock, S and N. Yonow, 2012. Creative Commons. Cadlinella ornatissima – an opisthobranch.
Under this classification, E. chlorotica would be classified as an opisthobranch. The majority of this subclass are simultaneous hermaphrodites, including our invertebrate of interest. Their fertilization is internal and only a select few (in addition to E. chlorotica, Trinchesia granosa) can self fertilize3. E. chlorotica, like many other gastropods are considered promiscuous3. This just means that an individual will mate with multiple individuals before laying their eggs.
Creative Commons. Cepaea nemoralis – a pulmonate
Pulmonates are also simultaneous hermaphrodites that cross fertilize (sex with other individuals) and can self fertilize like other opisthobranchia – and thus E. chlorotica3.
Pulmonates, like prosobranchs, have some pretty interesting mating rituals. Some garden snails, Cornu aspersum, fire love darts that release sperm-saving hormones at their sexual partner as an act of foreplay5. If love darts weren’t enough of a stretch, leopard slugs, Limax maximus, mate aerially – they hang upside down, with their bodies entwined, on a string of mucus (video mark 2:50)6.
Differences
Prosobranchs are mainly gonochoristic (have one sex) compared to E. chlorotica’s simultaneous hermaphroditism3. The remaining prosobranchs, some opisthobranchs, and some pulmonates exhibit protandry – the switching of sex from male to female throughout one’s life cycle – which our invertebrate of interest does not3.
In prosobranchs, fertilization can be external and is not strictly internal3. Prosobranchs also have been observed to be parthenogenic – ovum reproduction without fertilization – in multiple species3.
Cephalopoda vs. E. chlorotica
Similarities
Cephalopods are similar to E. chlorotica in that they are promiscuous. Cuttlefish and squid are known to mate in large aggregations where multiple mating is commonplace2. Cephalopods are also known for storing sperm similar to the gastropod Crepidula fornicata2,3.
Cephalopods also face a demise similar to that of E. chlorotica; they die soon after reproduction2.
Cephalopods have mating rituals that involve camouflage, guarding of females, synchronized swimming, and “flirting” by a swim-and-flee pursuit2. The synchronized swimming is most similar to that of E. chlorotica.
Differences
Cephalopods have separate sexes, and thus, exhibit sexual dimorphism2. Males are typically larger than the females and exhibit brilliant coloring using their chromatophores – this helps them attract a mate.
Cephalopods, including Bathypolypus sp. and Tremoctopus sp., provide parental care to their eggs rather than depositing them on a substrate or within the water column2.
Cephalopods also have an interesting sperm delivery method. A highly specialized tentacle called a hectocotylus transfers sperm to the female1,3.
Creative Commons. Hectocotylus – specialized tentacle that male’s possess for delivery of sperm.
Carefoot, T. Delivery of sperm from male to female.
Bivalvia vs. E. chlorotica
Similarities
There are some hermaphroditic species of bivalves, some of which are capable of self fertilization3. Hermaphroditic species can either be simultaneous (have male and female reproductive organs at once) or consecutive (one sex following the other). Protandry – individuals start as males then switch to females – is most common and occurs in the family Teredinidae. Protogyny can occur, but is less common.
Creative Commons. A bivalve – within the family veneroidea.
Differences
Bivalves do not have such an interesting sex life as the cephalopods. They don’t even have mating rituals similar to E. cholortica. Instead, bivalves are gonochoristic (possess one sex per individual) exhibiting external fertilization and broadcast spawning3. Because these molluscs are gonochoristic, they exhibit some sexual dimorphism – this can be observed by noting the differences in color of the gonads.
Polyplacophora vs. E. chlorotica
NOAA. Commonly known as chitons, the dark-shelled organism is a polyplacophoran.
Similarities
There are a few hermaphroditic species: Lepidochintona fernaldi and L. caverna3.
Differences
Most species are gonochoristic and exhibit external fertilization3.
About 30 species have females that brood their eggs3.
Males will often spawn hours before the females3.
Monoplacophora vs. E. chlorotica
Creative Commons, 2013. Monoplacophora anatomy including gonads.
Similarities
Micropilina arntzi is a hermaphroditic species of monoplacophoran with internal fertilization3.
Differences
M. arntzi broods their young in their mantle3.
A majority of the class are gonochoristic and exhibit external fertilization3.
Caudofaveata vs. E. chlorotica
Differences
Sexes are separate and exhibit external fertilization3.
Solenogastres vs. E. chlorotica
Todt, C., 2009. Solenogaster.
Similarities
Some species of this class are hermaphroditic3.
Differences
Anamenia agassizi are hermaphroditic but do not insert penes into one another. Instead they coil around each other and press their cloacal openings to transfer gametes3.
Scaphopoda vs. E. chlorotica
Similarities
There are species of hermaphrodites within this class3.
Similar to E. chlorotica, scaphopods do not brood their young after laying their eggs7.
Differences
The majority of the class has separate sexes and exhibits external fertilization3.
Not only are molluscs abundant, but their reproductive methods are extremely diverse. It is very difficult to find a common theme among all species, but I believe that is what makes them interesting.
Works Cited
1 Pechenik, J.A. Biology of the Invertebrates. 7th ed., McGraw Hill, 2015.
2 Prager, E. Sex, Drugs, and Sea Slime: The Oceans’ Oddest Creatures and Why They Matter. University of Chicago Press, 2011
3 Baur, B. “Sperm Competition in Molluscs.” Sperm Competition and Sexual Selection, edited by T.R. Birkhead and A.P. Møller, Academic Press, 1998, 255-305.
4 “Elysia chlorotica: Eastern Emerald Elysia.” Encyclopedia of Life.
5 “Everything you never wanted to know about snail sex.” KQED (PBS). 2017.
6 Langley, L. “Inside the Strange World of Slug Sex and Slime.” National Geographic, 2017.
7 Mulcrone, R.S. “Scaphopoda.” Animal Diversity Web. University of Michigan. 2005.