Photo of the day (92): eggs of Cassis madagascariensis

These are egg cases of Cassis madagascariensis.

I thank my friend and underwater photographer, Tracey Winholt who has kindly shared the following photos.

These photos are valuable, because I found no other photos of eggs of this species on the internet except of black-and-white photos by D’Asaro. They are also valuable because this large species is rare in some areas. For example, it is rare in Florida.

Cassis madagascariensis eggs. Photo by Tracey Winholt, CC-BY-4.0.

Egg cases of Cassis madagascariensis were described for the first time in 1969 as the first described egg cases of the genus Cassis.

The locality is Cozumel, Mexico. It is an island of the Caribbean Sea, nearby the Yucatán Peninsula. The habitat is sea grass beds in the depth 7-8 meters. These egg cases are not uncommon in the grassy areas in Cozumel.

The another egg case was also laid on an algae. It is some fan shaped green alga of the genus Avrainvillea, maybe Avrainvillea erecta. Eggs were laid to the alga to both of its sides:

Cassis madagascariensis eggs. Photo by Tracey Winholt, CC-BY-4.0.

Each egg capsule is quadrangular as viewed from the top. Egg capsules are irregularly arranged on the substrate. Egg capsules with developing eggs are light brown in color.

Cassis madagascariensis eggs. Photo by Tracey Winholt, CC-BY-4.0.

D’Asaro counted 2400 embryos in one egg case on average. There are developing embryos on the photo:

Cassis madagascariensis embryos. Photo by Tracey Winholt, CC-BY-4.0.

Maybe some of those embryos will grow up into an adult snail with a shell length up to 30 cm or 40 cm:

Shells of adult Cassis madagascariensis. Photo by Michal Jurásek, CC-BY-4.0.

References

D’Asaro C. N. 1969: The spawn of the emperor helmet shell, Cassis madagascariensis Lamarck, from South Florida. Bulletin of marine Science, 19(4): 905-910.

Sept J. D. 2016: Atlantic Seashore Field Guide: Florida to Canada. Rowman & Littlefield. page: not numbered. (Note that there should be “cm” instead of “mm” in the size section.)

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Photo of the day (78): eggs of Tarantinaea lignaria

Those are egg capsules and embryos of a marine snail Tarantinaea lignaria from the family Fasciolariidae. Its synonyms are Pleuroploca lignaria  and Fasciolaria lignaria.

Egg capsules of Fasciolariidae are possible to identify to the genus level and to the species level. But majority of egg capsules of Fasciolariidae is not known.

The egg capsules looks like on these photos. There is a circular opening in the middle of the cup. Newly hatched snails are escaping through the opening. There are visible embryos through the transparent wall of the capsules and there can be some few embryos inside one capsule. Exact number of embryos in one capsule was not published. It seems that this species may have a direct development.
These egg capsules comes from the southern Croatia. I have taken these photos at September 28, 2016. Majority of snails hatched out already, but there are still some (live?) embryos visible in few capsules. There is also a juvenile snail on one of the capsules that probably (but not surely) belong to the same species.
Detail cropped from the previous photo shows a juvenile snail:
Another view of the cluster of egg capsules:
Detail cropped from the previous photo shows two egg capsules:
The drawing of egg capsules of Tarantinaea lignaria is in the series on Gunnar Thorson’s collection of prosobranch egg capsules. I did not made proper measurements.

I thank to Dr. Paolo Russo from Italy for the species identification.

Gunnar Thorson (1906-1971) was professor of marine biology at the University of Copenhagen. He assembled the collection of egg capsules but he did not publish results of the whole collection by himself. Series of four monographs based on Thorson’s collection was published in 1992-2000 and it is very useful resource for anybody interested in this field.

References

D’Asaro C. N. 2000: Gunnar Thorson’s world-wide collection of prosobranch egg capsules: Fasciolariidae. Ophelia: 52(2), 77-112. DOI: 10.1080/00785236.1999.10409421

Photo of the day (77): egg laying of Phyllidia flava

Those are two marine slugs Phyllidia flava laying eggs. This is ventral view showing the foot of snails in an aquarium. Both of them are laying a spiral ribbon of eggs:
This species of sea slug is orange and its eggs are also orange. But you are lucky to see its eggs so clearly like this, because it usually lays eggs on the Axinella cannabina sponge, which is also orange.

It is a “camouflage” in general. This type of camouflage, when the animal visually resemble its surrounding is called “crypsis”. It is a “visual crypsis” and the animal has “cryptic coloration”.

Detail of the bigger slug cropped from the previous photo shows the head part on the left. The slug has its genital pore on the right side of the body so the genital pore is down on the photo:
Phyllidia flava starts the laying in the center of the spiral, of course. But some species are known to start the spiral ribbon from the outside.(!) Most nudibranchs lays the spiral ribbon in an anticlockwise direction. There are very few nudibranchs that lays egg ribbons in a clockwise direction. Phyllidia flava lays eggs in the same way as the majority of nudibranchs in an anticlockwise direction. You are seeing an underside of the egg ribbon through the transparent glass of the aquarium so the ribbon appear clockwise on these three photos.

Two egg ribbons of Phyllidia flava from underside:
References

Rudman, W. B., 2004 (August 2) Nudibranch egg masses – the direction they spiral. Sea Slug Forum. Australian Museum, Sydney.

Photo of the day (76): eggs of Macrochlamys amboinensis

This is a cluster of eggs of a tropical land snail Macrochlamys amboinensis:

Cluster of eggs of Macrochlamys amboinensis with a ruler:
References

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Photo of the day (75): egg capsules of Stramonita haemastoma

Those are empty egg capsules of Stramonita haemastoma.

Stramonita haemastoma is a big predatory marine snail of the family Muricidae. It inhabits coastal waters (intertidal and subtidal) up to depth of 9 meters. It is thought to be quite common in the Mediterranean Sea, but areas with low abundance exist. However it was reported that the population in Israel in Eastern Mediterranean has collapsed because of warming of the coastal waters. The subspecies living in the Mediterranean Sea is Stramonita haemastoma haemastoma.

My egg capsules of Stramonita haemastoma comes from southern Croatia. Eggs are laid in clusters to solid surface. Number of snails are laying eggs on the same place making collective spawns.

Empty egg capsules of Stramonita haemastoma attached on a valve of a bivalve Mytilus edulis. The filaments all around are byssus filaments of the bivalve:
The spawning season was reported from late April to August. Unfertilized capsules are purple, freshly laid capsules are yellow. The egg development lasts about 20 days. But all of capsules on the photos are empty already, because I collected them in late September.

The each capsule is about 10 mm in height, 3 mm wide and 2 mm thick. Although one capsule is just 10 mm long, it contain thousands of eggs (from about 2300 eggs to about 6050 eggs). One female will deposit from 20 to 86 capsules, usually 47 capsules on average. This gives incredible number of about 200 000 eggs per one female. When are hatching larvae leaving the capsule, larvae are about 50 μm in shell height.

Detail of two egg capsules:
References

Lahbib Y., Abidli S. & El Menif T. N. 2011: Spawning and intracapsular development of Stramonita haemastoma haemastoma (Gastropoda: Muricidae) collected in northern Tunisia. Marine Biology Research, 7(7): 719-726. DOI: 10.1080/17451000.2011.558099.

Rilov. G. 2016: Multi-species collapses at the warm edge of a warming sea. Scientific Reports, 6: article number: 36897. DOI: 10.1038/srep36897.

Photo of the day (74): eggs of Arion obesoductus

This is a cluster of eggs of a land slug Arion obesoductus.

It was laid by a specimen, that I captured in central Moravia at October 26, 2017. I captured only one slug and it later laid this cluster of four eggs in captivity. At least two slugs successfully developed and hatched out from these eggs.

I am not sure if there are any informations available about the life cycle of Arion obesoductus. I do not know if laying of four eggs is a rule or exception. Arion obesoductus is a small slug with a maximum body length of 25 mm. So laying clusters with small number of eggs makes sense. Otherwise these eggs looks like any other eggs of slugs from the Arionidae family as well as similar to eggs of many other land gastropods.

The cluster of eggs at December 13, 2017:

The same cluster of eggs at December 18, 2017:

References

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Photo of the day (73): eggs of a nudibranch

This is a cluster of eggs of a sea slug. These are eggs of an unidentified nudibranch. It comes from southern Croatia.

References

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Photo of the day (54): eggs of Ancylus fluviatilis

Adults of freshwater gastropod Ancylus fluviatilis have a cap-like shell. But shells of its embryos are a bit different. You can find eggs of Ancylus fluviatilis in spring and in early summer on stones in streams. I found these eggs in northern Bohemia in June.

Eggs are laid in capsules. There are 9-12 eggs in each capsule.

There can be seen foot, eyes and tentacles under stereo microscope easily in this state of development. There are also ribs on the shell, that resemble ribs of some Patella species to me. I have taken the photo in situ.

I found no images of eggs of Ancylus fluviatilis for comparison on the internet after a brief search.

References

Species summary for Ancylus fluviatilis. AnimalBase, last change 26 October 2013, accessed 8 July 2016.

Streit B. (1976). Energy flow in four different field populations of Ancylus fluviatilis (Gastropoda-Basommatophora). Oecologia, 22(3): 261-273.

Embryonic development of Bithynia tentaculata

Bithynia tentaculata is a well known freshwater snail from the family Bithyniidae. It occurs in the Palearctic. Females lay eggs and the development lasts few weeks depending on the water temperature. It hatch after 12-14 days at the temperature 25 °C (Cather & Verdonk 1974). I had temperature 26 °C in my aquarium, so my snails hatched out in the 12th day.

This is how they look like shortly before hatching:

Eggs are usually laid in two rows. There is seen a bit compressed shape of eggs, when you will look out from the side view:

It will go though the cleavage, blastula, gastrula in the first two days. This very early development was studied by various scientists (Erlanger 1892, Van Dam 1986).

Day 1:

Day 2:

Day 3:

Then it will form a radula, shell, nervous system, tentacles, ctenidium, heart, foot, snout and other organs. The shell is translucent, so if you would watch the embryo in the microscope, then there would be ctenidium and heart easily recognisable.

Day 4:

Day 5:

Day 6:

Day 7:

There is clearly visible a shell by naked eye since the seventh day.

Day 8:

Eyes, foot, head and snout are clearly recognizable.

Day 9:

Day 10:

Tentacles are visible easily.

Day 11:

Day 12 – hatching:

The first hatched snails:

The diameter of hatching snails is 1.2 mm and their weight is 0.25 mg (Negus 1998).

Day 13:

There left only empty egg cases and incorrectly developed embryos in the 13th day.

So this is a brief insight how Bithynia tentaculata develops and how you can see it by naked eye or by magnifying lens. But it is a worth to use microscope.

When it will be lucky and if no predator will eat the juvenile snail, it will grow into a snail like this:

References

Cather J. N. & Verdonk N. H. (1974). “The development of Bithynia tentaculata (Prosobranchia, Gastropoda) after removal of the polar lobe“. Journal of embryology and experimental morphology, 31(2): 415-422.

Erlanger R. (1892). “Beiträge zur Entwicklungsgeschichte der Gastropoden”. Mittheilungen aus der Zoologischen Station zu Neapel 10: 376-404.  Plate 25-26.

Negus M. R. (1998). “A Life Table for the fresh water mollusc Bithynia tentaculata (L.)”. Journal of Biological Education, 32(1): 14-23, DOI:
10.1080/00219266.1998.9655588 abstract

Van Dam W. I. (1986). “Embryonic development of Bithynia tentaculata L. (Prosobranchia, Gastropoda). I. Cleavage”. Journal of Morphology 188(3): 289-302. DOI: 10.1002/jmor.1051880304 abstract

Photo of the day (49): Ambigolimax valentianus

Ambigolimax valentianus is a land slug from the family Limacidae. Its native distribution includes Iberian Peninsula only, but it is spreading in many other countries as an invasive species. It can live in greenhouses and similar habitats in cold areas only. It lives in greenhouses in Central Europe too. It is a pest in greenhouses and it is able to overpopulate and then it can be a serious pest. It can reach the length up to 70 mm.

Various views of the slug:

The foot is light gray:

There exist two forms of Ambigolimax valentianus: a form with two dark lateral bands and a a spotted form. The spotted form looks like this. It looks a bit yellow on the photo, but it is caused by the sunglight.

Its eggs look like this. I found those eggs below the bowl for the potted plant.

Notice the juvenile slug in the front. It is interesting that its egss will not survive temperatures above 33 °C.

A juvenile slug:

Another photo with juvenile slugs:

This species is also known as Lehmannia valentiana. In fact I did not known, that it could be placed in the genus Ambigolimax up today.

So I searched for reasons of its generic placement:

Klee et al. found out based on molecular phylogeny research of cytochrome-c oxidase I (COI) genes, that the genus Lehmannia is diphyletic in 2005. She also repeated the information in her thesis in 2013.

Rowson et al. confirmed such placement also according to the COI genes analysis in 2014. By the way, they did not comment this species in the PLoS article anyhow. They just shown the cladogram on the figure 5.

The results are:

Lehmannia marginata (O. F. Müller, 1774) still belong to the genus Lehmannia Heynemann, 1863, because it is the type species of the genus.

Lehmannia valentiana (Férussac, 1822) belong to the genus Ambigolimax Pollonera, 1887 as a Ambigolimax valentiana (Férussac, 1822). It is the type species of the genus Ambigolimax.

Lehmannia nyctelia (Bourguignat, 1861) also belong to the genus Ambigolimax as Ambigolimax nyctelius (Bourguignat, 1861).

There is a question, where will belong other 13 European species of Lehmannia. Especially those ones, whose reproductive system is not known.

References

Horsák M., Dvořák L. & Juřičková L. (2004) Greenhouse gastropods of the Czech Republic: current stage of research. Malacological Newsletter, 22: 141–147, page 143.

Horsák M., Juřičková L. & Picka J. (2013) Měkkýši České a Slovenské republiky. Molluscs of the Czech and Slovak Republics. Kabourek, Zlín, 264 pp. (in Czech and English). page 163.

Klee B., Falkner G. & Haszprunar G (2005). Endemic radiations of Limax (Gastropoda: Stylommatophora) slugs in Corsica – they came twice. In: Burckhardt D (ed.), 8. Jahrestagung der Gesellschaft für biologische Systematik, Basel 13.-16. September 2005, Abstracts of talks and posters: p.78. Basel (Naturhistorisches Museum). Organisms Diversity and Evolution 5, Electr. Suppl. 13: 75.

Nitz. B. (2013). Integrative systematics and biogeography of Limax (Gastropoda: Stylommatophora). Dissertation Thesis, Ludwig-Maximilians-Universität, München, 133 pp., page 105.

Rowson B., Anderson R., Turner J. & Symondson W. O. C. (2014). The slugs of Britain and Ireland: undetected and undescribed species increase a well-studied, economically important fauna by more than 20%. PLoS ONE 9(4): e91907. doi:10.1371/journal.pone.0091907

Stojnić B., Vukša M., Jokić G. & Čkrkić M. (2011). First record of introduced valencia slug, Lehmannia valentiana (Férussac, 1822), in Serbia. Pesticidi i fitomedicina, 26(3): 213–220. doi:10.2298/PIF1103213S

Udaka H., Mori M., Goto S. G. & Numata H. (2007). Seasonal reproductive cycle in relation to tolerance to high temperatures in the terrestrial slug Lehmannia valentiana. Invertebrate Biology, 126(2): 154–162.