Category Archives: crustaceans

Friday Fellow: Common Water Flea

by Piter Kehoma Boll

Sometimes a single water drop from a freshwater lake can contain several different organisms from the plankton that lives near the surface. And a common group in freshwater plankton is the crustacean order Cladocera, known as water fleas. The most common and widespread species is Daphnia pulex, or the common water flea.

Having a worldwide distribution and measuring about 3 mm in length, the common water flea has a typical water-flea body. It is usually transparent and the head is small and smooth, with two easily visible black eyes and a well-developed pair of second antennae that are used for swimming, being the largest pair of appendices. The thorax and abdomen are fused and are surrounded by a transparent, somewhat oval shell, making the common water flea look like a pot-bellied creature. The shell has a posterior tip that looks like a pointy tail. The thoracic legs, more difficult to distinguish because of the carapace, are smaller than the second pair of antennae and are used to create a water current that brings food to the common water flea’s mouth.

Typical look of the common water flea. The left eye can be seen as a large dark spot on the head, the intestine is the long greenish tube and there are some eggs behind it. The long second antennae make the common water flea look like if it is trying to hypnotize someone with that cliche gesture of stretching the arms and waving the fingers. Photo by Paul Hebert.*

This food consists mainly of algae and other small organisms, such as bacteria, as well as of organic fragments. The common water flea is, therefore, a filter feeder. Its predators include both invertebrates, such as predatory arthropods, and small vertebrates, such as some fish.

The common water flea is considered a model organism and has been extensively studied regarding several biological aspects, including, for example, ecological stoichiometry, which investigates the response of organisms to changes in resource availability. The response of the water flea to predators has also been extensively studied and revealed, for example, that it can increase in size in the presence of invertebrate predators, in order to become too big to be eaten, and decrease in size in the presence of vertebrate predators, in order to become too small to be seen. The common water flea can also develop special structures in the presence of specific predators, such as head protrusions in the presence of glassworms.

Common water flea in Canada. Photo by iNaturalist user millsy3.**

The reproductive cycle of the common water flea is another aspect that is very well studied. As in most species of the genus Daphnia, the common water flea reproduces by cyclical parthenogenesis. Most of the population consists of females and, during their growth season, females produce a brood of diploid eggs (which are clones of the mother) every time they molt. The eggs hatch very quickly, usually after only a day, but the newly hatched water fleas remain inside the mother for about three days before being released. After passing through about 5 instars, they can start to produce their own eggs.

When environmental conditions become difficult, the second mode of reproduction is triggered. Some of the offspring produced by parthenogenesis turn into males and females start to produce haploid eggs, which are then fertilized by males and turn into resting eggs with a hardened coat, called ephippia. An ephippium can remain in the environment for many years, withstanding cold, drought or lack of food, and hatch into females when conditions improve.

The common water flea was the first crustacean species to have its genome sequenced. It was revealed that this species contain about 31 thousand genes due to an elevated rate of gene duplication. This is about 10 thousand more genes than humans have and is the reason why the common water flea has such an amazing capacity to adapt to environmental changes.

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More model organisms:

Friday Fellow: Touch-me-not (on 19 April 2013)

Friday Fellow: Red flour beetle (on 6 February 2015)

Friday Fellow: Pea aphid (on 12 June 2015)

Friday Fellow: Many-headed slime (on 1 April 2016)

Friday Fellow: Baker’s yeast (on 4 August 2017)

Friday Fellow: C. elegans (on 20 April 2018)

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References:

Colbourne JK, Pfrender ME, Gilbert D, et al. (2011) The ecoresponsive genome of Daphnia pulex. Science 331: 555–561. doi: 10.1126/science.1197761

Krueger DA, Dodson SI (1981) Embryological induction and predation ecology in Daphnia pulex. Limnology and Oceanography 26(2): 219–223. doi: 10.4319/lo.1981.26.2.0219

Tollrian R (1995) Predator‐Induced Morphological Defenses: Costs, Life History Shifts, and Maternal Effects in Daphnia pulex. Ecology 76(6): 1691–1705. doi: 10.2307/1940703

Wikipedia. Daphnia pulex. Available at < https://en.wikipedia.org/wiki/Daphnia_pulex >. Access on 22 October 2019.

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Friday Fellow: California Beach Flea

by Piter Kehoma Boll

If you are walking along the beach in the west coast of the United States, especially at night, little creatures may hop around your feet. If you look closer, you will notice that they are small crustaceans popularly known as sand hoppers or beach fleas. They belong to the order Amphipoda and there is a good chance that the ones among which you are walking belong to the species Megalorchestia californiana, popularly known as the California beach flea or long-horned beach hopper.

A female in California, USA. Photo by iNaturalist user lbyrley.*

The California beach flea occurs from the southernmost coast of Canada, around Vancouver Island, to the southern coast of the United States, around Laguna Beach. They are very large for an amphipod, reaching more than 2 cm in length, and have a typical “crustacean” color, varying from light brown to grayish. Males are slightly larger than females and have enlarged second antennae with a characteristic red coloration.

A male in California showing the enlarged red antennae and the enlarged boxing-glove-like gnathopods. Photo by Kim Cabrera.*

During the day, the California beach flea remains inside small burrows that it digs in the sand or hides under pieces of seaweed washed ashore. Females can share the same shelter but males cannot stand each other. At dusk, they move out of their shelters by the thousands and move over the sand looking for decaying organic matter on which they feed.

Several females trying to share the same shelter in Oregon, USA. Photo by Ken Chamberlain.*

The sexual dimorphism seen in this species reveals a complex sexual behavior. The enlarged antennae of the males seem to be a visual cue to other males to signal their strength. Additional to those enlarged antennae, the males also have an enlarged second pair of gnathopods or maxillipeds (legs right behind the mouth) that look like boxing gloves. Using the gnathopods, males fight each other for the possession of burrows containing many females. The male that wins the fight becomes the owner of that harem.

A male in Washington trying to invade the burrow of another male (whose antennae are visible). Photo by iNaturalist user pushtheriver.

Since both females and males leave their burrows every night to feed, harems can also be temporary. Although a male can conquer a burrow full of females, those will only return to that same place if they consider that the male is good enough to be the father of their children. This is so because females only reproduce once in their life, so it is crucial to let the best male fertilize her. More than that, females can only release their eggs soon after molting because the hardened exoskeleton prevents it during the rest of her life.

It’s not easy to be a sand hopper living on the beach in California.

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References:

Beermann J, Dick TA, Thiel M (2015) Social Recognition in Amphipods: An Overview. In: Aquiloni L, Tricarico E (Eds.) Social Recognition in Invertebrates: 85–100.

Iyengar VK, Starks BD (2008) Sexual selection in harems: male competition plays a larger role than female choice in an amphipod. Behavioral Ecology 19(3): 642–649. doi: 10.1093/beheco/arn009

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Friday Fellow: Stonewort Seed Shrimp

by Piter Kehoma Boll

It’s time to talk about an ostracode, or seed shrimp, again and, as usual, this is a difficult time due to the little information easily accessible regarding any particular species of this group. But there is, indeed, one that is considerably well studied. Being one of the most common ostracodes in North America and Eurasia, its scientific name is Cypridopsis vidua, to which I coined the common name “stonewort seed shrimp”.

The stonewort seed shrimp is a freshwater crustacean with the typical ostracode appearance, looking like a tiny bivalve measuring about 0.5 mm in length. Its valves have a distinctive light and dark pattern.

A stonewort seed shrimp with a closed shell. Credits to Markus Lindholm, Anders Hobæk/Norsk institutt for vassforsking.*

A relatively mobile species, the stonewort seed shrimp lives at the bottom of water bodies, over the sediment, and is common in areas that are densely vegetated by stoneworts (genus Chara). This association with stoneworts gives the stonewort seed shrimp both protection from predators, which are mostly fish, and a good food source.

The main food of the stonewort seed shrimp are microscopic algae that grow on the stems of stoneworts. While foraging, the stonewort seed shrimp swims from one stonewort stem to another using its first pair of antennae and clings on the stems using the second pair of antennae and the first pair of thoracic legs. Once realocated, it starts to scrape the microscopic algae using its mandibles.

The body of a stonewort seed shrimp as seen when one of the valves (the left one here) is removed. Credits to Paulo Corgosinho.**

The stonewort seed shrimp is one more of those species in which males do not exist, not even in small quantities. During the warm months of summer, females produce the so-called subitaneous eggs, which develop immediately into new females. However, when winter is approaching, they produce another type of eggs, the so-called diapausing eggs, which remain dormant in the substrate during winter. The adult animals all die during this season and, when spring arrives, a new population appears from the hatching eggs. Since not all eggs hatch in the spring, some of them may remain in the substrate for years before hatching, which usually increases the genetic diversity every year, as it not only depends of the daughters of the last generation.

But how does genetic diversity appear if there are no males and, as a result, the daughters are always clones of the mothers? This mystery is not yet fully solved. Genetic recombination during parthenogenesis, by exchanging alleles between chromosomes, does not seem to be very common. It is possible that different populations are genetically different and that they colonize new areas very often, mixing with each other. Since males are known in closely related species, it is still possible that, some day, we will find, somewhere, some hidden males of the stonewort seed shrimp. It is also possible that, somehow, males went all extinct in the recent past, like in the last glaciation, for example. If so, only time can tell what is the destiny of the stonewort seed shrimp.

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More Ostracods:

Friday Fellow: Sharp-Toothed Venus Seed Shrimp (on 22 June 2018)

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References:

Cywinska A, Hebert PDN (2002) Origins of clonal diversity in the hypervariable asexual ostracode Cypridopsis vidua. Journal of Evolutionary Biology 15: 134–145. doi: 10.1046/j.1420-9101.2002.00362.x

Roca JR, Baltanas A, Uiblein F (1993) Adaptive responses in Cypridopsis vidua (Crustacea: Ostracoda) to food and shelter offered by a macrophyte (Chara fragilis). Hydrobiologia 262: 121–131.

Uiblein F, Roca JP, Danielpool DL (1994) Experimental observations on the behavior of the ostracode Cypridopsis vidua. Internationale Vereinigung für Theoretische und Angewandte Limnologie: Verhandlungen 25: 2418–2420.

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Friday Fellow: Common Goose Barnacle

by Piter Kehoma Boll

The open surface of the oceans may at first look like a large lifeless sheet. However, if you look closer, you’ll see that there is much more life there than you could imagine. And it does not only include the microscopic plankton that floats in the water column, but also large organisms that dwell right at the boundary between the water and the air. These creatures are called the neuston and come in several shapes and one of them is Lepas anserifera, or the common goose barnacle.

Several common goose barnacles found growing on a cuttlebone in India’s west coast. Their modified legs (cirri) are out looking for food. Photo by Abhishek Jamalabad.*

The common goose barnacle is found in tropical and subtropical waters all around the world. It belongs to the subclass Cirripedia, a peculiar group of crustaceans commonly known as barnacles. They live attached to the substrate and are hemaphrodites, both features that are uncommon among arthropods. Within the barnacles, the common goose barnacle belongs to the order Pedunculata, or goose barnacles, which are characterized by the presence of a stalk that attaches them to the substrate.

Common goose barnacles in Taiwan. A younger specimen is seen growing on a larger one. Photo by Liu JimFood.*

The substrate chosen by the common goose barnacle is almost exclusively floating material. This material, which includes sea weeds and all sort of debris, such as pieces of wood, coconuts or animal carcasses, rarely remains floating for a long time, either because its decay makes it sink or fall apart or because it ends up on the shore. Thus, the goose barnacle has to find a way to complete its life cycle very quickly, and that is what it does.

Common goose barnacles growing on an apple that must have floated for some time and ended up at the shore in the state of Bahia, Brazil. Photo by iNaturalist user kuroshio.**
Common goose barnacles growing on a light bulb washed ashore in Palau Pinang, Malaysia. Photo by Al Kordesch.

Goose barnacles start their lives as a planktonic one-eyed larva that, after five stages, develops into another larval form known as cyprid. The cyprid’s only purpose is to find a suitable surface to live and, once it finds it, it secretes a glycoproteinaceous substance that attaches it to the substrate by the head. It then develops into the adult animal and secretes a series of calcified plates that surrounds its body. The adults use their feathery legs (cirri) to capture food, mostly plankton, and carry it inside their shell.

Common goose barnacles growing on a brush washed ashore in New Jersey, USA. Photo by Stan Rullman.**

Due to human activities, the amount of floating material on the ocean surfaces increased greatly. Thus, the number of available substrates for the goose barnacle to grow also increased, and so likely did its population. Unfortunately, the human-generated floating material also includes a lot of small plastic particles, and goose barnacles frequently ingest them together with food. Although the harm caused by ingesting plastic particles has not been assessed yet, they certainly do not improve the barnacle’s health.

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Reference:

Goldstein MC, Goodwin DS (2013) Gooseneck barnacles (Lepas spp.) ingest microplastic debris in the North Pacific Subtropical Gyre. PeerJ 1: e184. doi: 10.7717/peerj.184

Inatsuchi A, Yamato S, Yusa Y (2010) Effects of temperature and food availability on growth and reproduction in the neustonic pedunculate barnacle Lepas anserifera. Marine Biology 157(4): 899–905. doi: 10.1007/s00227-009-1373-0

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Friday Fellow: Peacock Mantis Shrimp

by Piter Kehoma Boll

Invertebrates are much less likely to become popular creatures than vertebrates, but every now and then there is an exception, and one of them is certainly Odontodactylus scyllarus, the peacock mantis shrimp.

Peacock Mantis Shrimp at Guinjata Bay, Mozambique. Photo by Peter Southwood.*

Found in the Indo-Pacific region, from the east coast of Africa to Guam, the peacock mantis shrimp is a large and colorful species of the crustacean order Stomatopoda, popularly known as mantis shrimps. Measuring up to 18 cm in length, their body is mainly green with some large black spots with a white contour one the cephalothorax. The legs are reddish orange and the region around the eyes has a light blue shade. Due to this beautiful appearance, the peacock mantis shrimp has become a popular animal to be raised in aquariums.

Frontal view of a peaock mantis shrimp in the Andaman Sea, Thailand. You can see the club-like appendages used to break the shell of prey. Photo by Silke Baron.**

Mantis shrimps are predators and the peacok mantis shrimp is not an exception. It feeds mainly on shelled mollusks, such as gastropods and bivalves, and crustaceans. To break the strong carapace of its prey, it smashes them with a powerful strike using its club-like second pair of thoracic appendages. This strong attack, caused by a complex mechanism in the appendage, is so strong that it easily breaks the shell of the prey. In aquariums, this can be problematic, as they sometimes break the aquarium’s wall. More than only striking the prey with incredible force, the attack of the mantis shrimp generates a sudden region of low pressure between the shell and the appendage when the appendage is quickly retracted. This phenomenon, called cavitation, generates a bubble of gas that quickly collapses and generates large amounts of energy in the form of heat, light and sound and creates a second impact on the prey.

Female peacock mantis shrimp carrying eggs in Indonesia. You can also see the eyes with two hemispheres separates by a band of larger ommatidia arranged in 6 lines. Photo by Terence Zahner.***

The peacock mantis shrimp has also a magnificent vision system. Its compound eyes are divided into an upper and a lower hemisphere which are separated by a band of six lines of enlarged ommatidia (the small eyes that form the compound eye). This three regions of the eye are used to detect different wavelengths, including UV light, and even include special cells that convert unpolarized light into polarized light or filter circular polarized light, allowing the mantis shrimp to detect light in different ways from different parts of the eye. This complex system is being studied for the development of optical devices to store and read information.

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References:

Jen Y-J, Lakhtakia A, Yu C-W, Lin C-F, Lin M-J, Wang S-H, Lai JR (2011) Biologically inspired achromatic waveplates for visible light. Nature Communications 2: 363. doi: 10.1038/ncomms1358

Kleinlogel S, Marshall NJ (2009) Ultraviolet polarisation sensitivity in the stomatopod crustacean Odontodactylus scyllarus. Journal of Comparative Physiology A 195(12): 1153–1162. doi: 10.1007/s00359-009-0491-y

Land MF, Marshall JN, Brownless D, Cronin TW (1990) The eye-movements of the mantis shrimp Odontodactylus scyllarus (Crustacea: Stompatopoda). Journal of Comparative Physiology A 167(2): 155–166. doi: 10.1007/BF00188107

Marshall J, Cronin TW, Shashar N, Land M (1999) Behavioural evidence for polarisation vision in stomatopods reveals a potential channel for communication. Current Biology 9(14): 755–758. doi: 10.1016/S0960-9822(99)80336-4

Patek SN, Caldwell RL (2005) Extreme impact and cavitation forces of a biological hammer: strike forces of the peacock mantis shrimp Odontodactylus scyllarus. The Journal of Experimental Biology 208: 3655–3664. doi: 10.1242/jeb.01831

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