Dissecting the Knight in water Signal Crayfish
Maria Li
About Signal Crayfish Scientific name: Pacifastacus leniusculus Kingdom: Animalia Phylum: Arthropod (Artro = joint; Pod = foot) Class: Crustaceans Family: Astacidae Order: Decapoda Habitat: Most freshwater habitat
The signal crayfish occurs both in still and slow-flowing freshwater environments, including rivers, streams, lakes, reservoirs and canals. They are also able to tolerate slightly salty water. It takes shelter under rocks and boulders, within tree roots or in burrows and cavities within banks. The signal crayfish is a North American species of crayfish. It was introduced to Europe in the 1960s to supplement the North European Astacus astacus fisheries, which were being damaged by crayfish plague, but the imports turned out to be a carrier of that disease. In addition, Signal crayfish have been so successful at invading because they produce a lot of offspring and eat almost anything, from detritus and aquatic plants to small invertebrates, fish and even each other. Thus, it spreads quickly across much of the freshwater bodies, they cause negative impacts include the almost complete loss of the native crayfish through the spread of disease and direct competition.1 Also undermines riverbanks through burrowing and can predate on native fish eggs and aquatic invertebrates. Because of the great negative impact this species has bring in, even the UK Environment Minister has issue a "kill on sight" message to combat the spread in 2008.2
"Kill crayfish on sight' appeal". BBC News. August 15, 2008.
Distribution in the UK Signal Crayfish widely spread throughout England and Wales. But limited to a few water bodies in Scotland. 3 Source: GB non-native species secretariat
Unit 1: Dissecting Biological Machines
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SPECIMEN COLLECTION Why select signal crayfish? One of the reason I pick signal crayfish as the subject for dissection based on my personal tie to the ocean and arthropod. I was raise in a city, Hong Kong, where sea and beaches are easily accessible. The ocean and I build a strong connection, especially after I got my open water diving license. It provides me the opportunities to explore the deep ocean and come into close contact with the marine creatures. Since then I am fascinate by the wonderful and mysterious underwater world. Also from the experience I gained from running a citizen science project on surveying insects biodiversity in Hong Kong, I learnt how to do insect pinning and built confident in handling arthropods. So I wonder whether I can find something that lies in the overlapping area of these two areas. Maybe a giant “insect” in the ocean? After doing some research, I found signal crayfish quite interesting. This popular seafood that we found on our plate actually has an interesting historic story. While human happily consume them in restaurants, these little creatures are actually the most wide-spread invasive species in the European freshwater bodies. The introduction of this species was caused by human intervention with a good intention at the beginning but turned out doing more damage than good to the local ecosystem. Working on crayfish surprised me in a way that how little I know about what I eat and the potential the environmental impact behind the scene.
Unit 1: Dissecting Biological Machines
Ethical Considerations From Chinatown, I bought five crayfishes home. I put them in the freezer to lower their mobility and they eventually dead. The crayfishes were sold alive, which makes me feel worry about how to handle it. I researched on ways to kill the crayfish in the most humane manner. It is interesting to find that there are researchers investigated on whether lobster or invertebrates feel pain.4 Researchers from Queen’s University Belfast found that hermit crab (also belongs to Crustaceans) central nervous system do responses to unpleasant stimuli and learn to change their behaviour in response. So crayfish probably can feel pain. Yet, there are also scientific proof of the association between chilling and absence of stress or pain is limited compared to some other killing methods such as boiling.5 One major benefit of chilling is that it reduces mobility. This makes crayfishes easier to handle, and also prevents both parties from injuring each other. 6 Ecological consequence is also considered in this research. Signal Crayfish brings negative impacts to the local freshwater ecosystem, include the almost complete loss of the native crayfish through the spread of disease and direct competition. Because of that, signal crayfish is listed under Schedule 9 to the Wildlife and Countryside Act 1981 that it is an offence to release or to allow the escape of this species into the wild. 7 As with many invasive species, the best thing we can do for now is to prevent their further spread by meticulously cleaning equipment and following best practice when around freshwater habitats. It’s disappointing that we’re no closer to a solution. But the idea that eating tasty crayfish helps control their numbers in the wild is sadly too good to be true.
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EXTERNAL ANATOMY
Antenna Rostrum
Cheliped
Antennule
For this species, the upper surface is usually brown , while lower surface is often bright red
Senses touch, taste and helps crayfish maintain balance
Compound Eyes
Cephalothorax
Crayfish has field of view, their eyes can move independently from one another
Abdomen
Walking Legs
Consist of 6 segments
Chemical sensory hairs along the antenna
1500X
Fusion of head and thorax region. It is covered with exoskeleton (Carapace) which consist of chitin and minerals to form hard shell to protect vital organs (i.e. heart and guts) inside
Senses touch and detect prey and predators
How does crayfish senses in the dark? Even though crayfish has compound eyes that sense light, they primarily orientate themselves by touch. Tactile hairs can be found on walking legs, antenna and over many parts of the body to sense water vibration and current in order to aid crayfish in navigation and feeding.
100X
Crayfish are freshwater crustaceans resembling small lobsters. They have two main body parts, the the cephalothorax and the abdomen. Their body is covered with exoskeleton. They need to moult to grow. Crayfish moult twice each year until it reach breeding size (about 6cm long) in 2-3 years. A male adult signal crayfish can reach a maximum size of 16-19cm. Since their exoskeleton is made up of calcium, acidified water under the effect of acid rain is a threat to these creatures.
The square facets of the compound eye
1 2 3
Carapace
4 Uropod 6
2 cm
Unit 1: Dissecting Biological Machines
100X
Tail Fan
5 Telson
Dorsal View
Tactile hairs on walking leg
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DISSECTION PROCESS
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2
3
1 Before dissecting, do measurement and examine the external anatomy 4
5
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2 Remove carapace 3 Examine gills 4 Remove walking legs and gills on one side 5 Remove the dorsal side of the abdomen exoskeleton (Tegum) 6 Examine the Internal organs 7 Isolate the male reproduction parts, mouthparts, swimmerets and digestive system 8 Isolate the stomach
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8
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9 Cut thin slice of parts to prepare microscopic slides.
Dissection Guide References 8-12
Unit 1: Dissecting Biological Machines
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APPENDAGES 2 cm 1st walking leg (Cheliped) 1
Dactylus (movable finger)
2
Carpus Merus
5
Coxa
3
Gill
Pollex (fixed finger)
4
2nd walking leg
Close up of mouthparts
1st
3rd walking leg
2nd
Male copulatory swimmerets
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4th walking leg 3rd
7 5th walking leg
4th
5th
8 Close up of mandible
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HEAD APPENDAGES 1. MANDIBLE crush food by moving from side to side 2. FIRST MAXILLA move food to the mouth (behind the mandibles) 3. SECOND MAXILLA crush food by moving from side to side Unit 1: Dissecting Biological Machines
Human lower jaw
MOVING APPENDAGES 4. THIRD MAXILLIPED holds food/sense touch and taste
5. CHELIPED grasp food and for defence 6. WALKING LEGS used for forward motion 7. SWIMMERET serve a function in posture control (beat rhythmically when the animal swim forward), move water over the gills, and hold fertilised eggs (for female)
8. UROPOD used for swimming and rapid backward propulsion, together with the telson form a tail fan. 9. TELSON together with the telson form a tail fan, it's ventral side is an anus (outlet of the digestive tract)
Evolution of crayfish’s appendages Crayfish appendages have evolved from biramous appendages (forks to form two branches) into various form to serve different functions, including walking, swimming, feeding and reproduction.
Crayfish mandible resemble human lower jaw The mandibles of the crayfish are similar to the jaws of humans. They are strong and can break the hard shells of many aquatic animals. But unlike human jaws, crayfish’s mandibles open from side to side.
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RESPIRATION SYSTEM
Crayfish breathe through gills Unlike us, crayfishes do not have lungs, they use gills to ‘breathe’ instead. Gills can be found on both sides right under the carapace. The gills serves as an interface for respiratory gaseous exchange by pulling oxygen into the bloodstream as water passes through them. Crayfish can stay on land for a while and carry respiration as long as the gills are kept moist.
Direction of water current Carbon dioxide flow out Oxygen flow in
Gill filaments
Setobranchies
Pleurite
100X Close up of gill Gills are attached at the base of the walking leges. When crayfish move their legs, it wave in oxygenated water to the gills in order to carry gaseous exchange.
Unit 1: Dissecting Biological Machines
Tips of gill filaments
150X
250X Gill Setobranchies This hair-like structure thrust back and forth among gill filaments when crayfish move his legs, and cleaning gills from dirt and sand. 13
Cross-section of branchial chamber & gills of a decapod Source: biosurvey.ou edu
Surface of Pleurite I found hair-like structures protrude from the surface of the pleurite, I wonder it serves a function of facilitating gaseous exchange. But I couldn’t find any scientific paper that document its presence or function, so it still remains a mystery to me.
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CIRCULATORY SYSTEM
Crayfish send gas and food to the body through an open circulatory system
Heart Artery
OPEN CIRCULATORY SYSTEM The open circulatory system is common to molluscs and arthropods (Crayfish belongs to this phylum). Open circulatory systems pump blood into hemocoel with the blood (haemolymph) diffusing back to the heart between cells.
Why crayfish has an open circulatory system?
Ostia Heart Carapace Intestine
(a)
Gills Sternal artery Ventral nerve cord
(b) Fig 1. (a) Schematic drawing of the main parts of the open circulatory system (red) and the blood flow (blue); (b) Cross section of the cephalothorax to illustrate flow of haemolymph. Oxygenated haemolymph (red) and haemolymph from body tissues (blue).
Unit 1: Dissecting Biological Machines
Crayfishes like most of their arthropod peers have an open circulatory system, in which the blood (hemolymph) is not enclosed in the blood vessels but is pumped into a cavity called a hemocoel. In an open circulatory system, the transparent haemolymph leaves the heart in arteries but flow into the cavity between exoskeleton and tissue. (Fig. 1a) The haemolymph flows over the gills to release carbon dioxide and pick up oxygen through gaseous exchange before returning to the heart. (Fig. 1b)
CLOSED CIRCULATORY SYSTEM Vertebrates (like human being), and a few invertebrates have a closed circulatory system. In closed circulatory system blood is pumped by a heart through vessels, and does not fill body cavities.
As crayfish is small, they may not need anything more than the ability to move coelomic fluid. An open circulatory system does not use as much energy to operate and maintain as a closed system. 14 It also helps crayfish to thrive in underwater habitat as this system is less vulnerable under high-pressure environment (such as at the deep of ocean), which can cause harm to a closed circulatory system.15 However, there is a trade-off with the amount of blood that can be moved to metabolically active organs and tissues that require high levels of oxygen such as central nervous system. That’s may be the reason their brain is small relative to their body size.
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DIGESTIVE SYSTEM Crayfish are extremely opportunistic eaters They are omnivores who are also scavengers. It means that their digestive system is very adaptable when it comes to feeding. It can break down both plants (i.e. algae) and animals (i.e. snails, clams, insect larvae, small fish etc) as well as whatever else the crayfish can find. Food to intestine
42 mm (a)
Stomaches and Intestine (cut open from ventral side)
Gastrolith
Gastric Mill
Cardiac chamber
Cardiac stomach Pyloric stomach Mandible muscles
Lateral tooth
Medial tooth
Pyloric chamber
(b)
(a) Ventral view and (b) lateral view of gastric mill. 16 The blue arrows indicate the food traveling direction. Oesophagus Head
Digestive gland
Abdomen
Crayfish has two stomaches Hind-gut
Unit 1: Dissecting Biological Machines
Food is first passed from oesophagus into the cardiac stomach, in which there are a lateral tooth that help grind food. Then food enters the pyloric stomach which serves a more assorted function, and directing the digestible matter to the digestive glands whereas digestion complete here.
The digestive gland resemble the function of liver, pancreas, and intestine in human (all on one!) As the food entering the hind-gut, the undigestible food passes through it and excreted from the anus (located on the underside of the telson).
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REPRODUCTION Ventral view of male crayfish abdomen
Ventral view of female crayfish abdomen
Swimmerets Swimmerets
Copulatory appendages
The first two pairs of swimmerets in male are modified copulatory appendages; they transfer sperm to female.
2cm
Signal crayfish have been so successful at invading because they produce a lot of offspring. This species reaches breeding age before they are “trappable” size, so populations can still reproduce and proliferate despite our best efforts to trap them.
Female hold fertilised eggs beneath the abdomen region. The feathery swimmerets help holding the eggs in place. Females can lay up to 800 eggs
Source: PearsonEcological.com 18
Testis
Vas deferens
Ovary
Oviduct
Fifth walking leg Genital opening Genital opening
Male Reproductive Organs
Female Reproductive Organs 17
17
1cm
Internal anatomy of male reproduction organs Unit 1: Dissecting Biological Machines
Third walking leg
1cm
Internal anatomy of male reproduction organs
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REFERENCES
1 “Signal Crayfish”. Wikipedia https://en.wikipedia.org/wiki/ Signal_crayfish 2 "Kill crayfish on sight' appeal". BBC News. August 15, 2008. 3 “Signal Crayfish Factsheet”. GB non-native species secretariat. http://www.nonnativespecies.org/factsheet/factsheet.cfm? speciesId=2498 4 Stelling, T. (2014, March 10). Do lobsters and other invertebrates feel pain? New research has some answers. Washington Post. Retrieved from https://www.washingtonpost.com/national/health-science/dolobsters-and-other-invertebrates-feel-pain-new-research-has-someanswers/2014/03/07/f026ea9e-9e59-11e3b8d8-94577ff66b28_story.html 5 Yue S (2008). The welfare of crustaceans at slaughter, Humane Society of the United States. 6 Anon, (n.d.). What is the most humane way to kill crustaceans for human consumption? – RSPCA Knowledgebase. [online] Available at: https://kb.rspca.org.au/knowledge-base/what-is-the-most-humaneway-to-kill-crustaceans-for-human-consumption/. 7 Species Description. (n.d.). [online] Available at: https:// thecrayfishcompany.com/Identifying-Signal-Crayfish.pdf [Accessed 14 Oct. 2021]. 8 Lőw P., Molnár K., Kriska G. (2016) Dissection of a Crayfish (Astacus astacus). In: Atlas of Animal Anatomy and Histology. Springer, Cham. https://doi.org/10.1007/978-3-319-25172-1_7F. Gheradi and G. Vogt (2010). Infraorder astacidea Latreille, 1802 P.O. : The freshwater crayfish 9 Crayfish Dissection Video by Mrs Heaton - https://www.youtube.com/ watch?v=SF1r5QTMh0U 10 Crayfish Dissection Video by Biologybyme - https:// www.youtube.com/watch?v=W7F0jZgdc8A
Unit 1: Dissecting Biological Machines
11 Lobster Dissection Instructables - https://www.instructables.com/ Lobster-Dissection/ 12 Crayfish dissection - https://jb004.k12.sd.us/my%20website%20info/ BIOLOGY%202/ANIMAL%20KINGDOM/ CRAYFISH%20DISSECTION/CF%20DISSECTION.htm 13 Bauer, R. T. (1998). Gill-Cleaning Mechanisms of the Crayfish Procambarus clarkii (Astacidea: Cambaridae): Experimental Testing of Setobranch Function. Invertebrate Biology, 117(2), 129–143. https:// doi.org/10.2307/3226965 14 Opentextbc.ca. (2015). 21.1. Overview of the Circulatory System – Concepts of Biology-1st Canadian Edition. [online] Available at: https://opentextbc.ca/biology/chapter/21-1-overview-of-thecirculatory-system/. 15 Garage, G. (2018). 6 Pros and Cons of Open Circulatory System. [online] Green Garage. Available at: https://greengarageblog.org/6pros-and-cons-of-open-circulatory-system. 16 Linton, S. and Allardyce, B. (2011). Generalised schematic diagram of the decapod gastric mill. Available at: https://www.researchgate.net/ figure/Generalised-schematic-diagram-of-the-decapod-gastric-millfrom-a-ventral-view-a-and_fig2_250613362 [Accessed 13 Oct. 2021]. 17 Huxley, T.H. (1897). An Introduction to the Study of Zoology, Illustrated by the Crayfish. [online] Google Books. D. Appleton. Available at: https://books.google.co.uk/books/about/ An_Introduction_to_the_Study_of_Zoology.html? id=vnxn4C8m6rUC&source=kp_book_description&redir_esc=y [Accessed 12 Oct. 2021]. 18 Anon, (n.d.). Signal Crayfish – Pearson Ecological. [online] Available at: https://pearsonecological.com/inverts-l2/signal-crayfish/ [Accessed 13 Oct. 2021].
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