Cavitation in the Peacock Mantis Shrimp

The Peacock Mantis Shrimp (Odontodactylus scyllarus) is one of a variety of mantis shrimp species. They are found throughout the Indo-Pacific Ocean north of Australia from Guam to Eastern Africa, inhabiting waters between 3 - 40m deep, although have a preferential depth of 10 - 40m, and at temperatures ranging from 22 - 28^oC. The Peacock Mantis Shrimp is known to create ‘U’ shaped burrows on the bases of coral reefs on sandy or gravelly substrates (Animal Diversity Web 2013).

'Peacock Mantis Shrimp', Kirsty Faulkner <https://www.flickr.com/search/?q=peacock+mantis+shrimp>

The Peacock Mantis Shrimp, along with all other species of mantis shrimp, have a greatly enlarged second thoracic raptorial appendage that they use to smash or spear prey, construct and excavate burrows, defend themselves from predators and fight other individuals (Caldwell 1975). In order to generate the power for the extreme acceleration of their raptorial appendages mantis shrimp use a power amplification mechanism consisting of elastic springs, latches and lever arms. During muscle contractions a click mechanism holds the limb in place and a specialized spring stores and releases elastic energy. These specialized mechanisms allow the Peacock Mantis Shrimp to deliver strikes lasting just a few milliseconds with an acceleration rate of over 10⁵ m s^-2 and at speeds of over 20m/s (Patek & Caldwell 2005).

'Peacock Mantis Shrimp', Cameron Azad <https://www.flickr.com/search/?q=peacock+mantis+shrimp>

The extreme strike speed of the Peacock Mantis Shrimp has the additional benefit of causing cavitation at the site of impact between the mantis shrimp and its prey. Cavitation bubbles form in fluids under low pressure and when these cavitation bubbles collapse, considerable energy is released in the form of heat, luminescence and sound. The shock waves generated during the collapse put immense pressure and stress on adjacent surfaces, ultimately leading to their failure (Brennen 1995). This production of cavitation bubbles as the mantis shrimp strikes in prey allows its attack to become two fold; where the first strike is caused by limb impact and the second, approximately 0.5ms later, is caused by the collapse of the cavitation bubble (Patek & Caldwell 2005). This combination of forces allows the mantis shrimp to easily “smash” the shells of the mollusks that they feed on.

                                   Zefrank1, 2013, 3rd May 2014 <https://www.youtube.com/watch?v=F5FEj9U-CJM>

References

Brennen. C., 1995, Cavitation and bubble dynamics, New York, Oxford University

Press

Caldwell. R., 1975, Ecology and evolution of agonistic behavior in stomatopods,

Naturwissenschaften, vol. 62, pp. 214 - 222

Cameron Azad, Peacock Mantis Shrimp, flickr, viewed 29 May 2014  

<https://www.flickr.com/search/?q=peacock+mantis+shrimp>

Chiu. F., 2013, Odontodactylus scyllarus, Animal Diversity Web, viewed 29 May

2014 <http://animaldiversity.ummz.umich.edu/accounts//>

Encyclopedia of Life, 2013, viewed 29 May 2014

<http://eol.org/pages/2869734/hierarchy_entries/50287908/overview>

Kirsty Faulkner, Peacock Mantis Shrimp, flickr, viewed 29 May 2014  

<https://www.flickr.com/search/?q=peacock+mantis+shrimp>

Patek. S., & Caldwell. R., 2005, Extreme impact and cavitation forces of a biological

hammer: strike forces of the peackon mantis shrimp Odontodactylus scyllarus, The Journal of Experimental Biology, vol. 208, pp. 3655 – 3664

Zefrank, 2013, True facts about the Mantis Shrimp, Youtube, viewed 29 May 2014 <

https://www.youtube.com/watch?v=F5FEj9U-CJM>

Not a nose for smelling - The Star-nosed Mole

Condylura cristata, commonly known as the Star-nosed Mole, is a small palm sized mole native to North-Eastern America. Growing to between 175 and 205cm in length and weighing 35 – 75g, the Star-nosed Mole is found in a variety of habitats that contain moist soils including coniferous and deciduous forests, clearings, wet meadows, marshes and peat lands. This is unlike most other North American moles, which prefer dryer habitats (Animal Diversity Web 2004). The Star-nosed Mole lives in extensive networks of tunnels that it excavates using its heavily clawed forelimbs. They rarely come to the surface and as a result of their fossorial lifestyle, have greatly reduced eyes and small optic nerves. In order to find the variety of insects and other invertebrates that make up their diet, the Star-nosed Mole has developed what is one of the most sensitive touch organs among mammals (Catania 1999).

'Star-nosed Mole' Wayne Helfrich <https://www.flickr.com/search/?q=star-nosed+mole>

The Star-nosed Mole has adapted to its lifestyle in darkness by evolving specially adapted nasal rays that are used to locate and identify food. Consisting of a total of 22 rays, they are often mistaken for an olfactory structure, however these rays are purely a mechanosensory structure. The nasal rays of the Star-nosed Mole are controlled by tendons through a complex set of muscles that attach to the skull. Their surface is almost entirely made up of mechenosensory organs called Eimers organs that are arranged in a honeycomb pattern of epidermal domes on the surface of each nasal ray. Where many other species of moles have at most a few thousand of these structures surrounding their nose, the Star-nosed Mole has over 25 000 of these organs over its nasal rays (Catania 1999).

'A bizarre nose' <http://www.vanderbilt.edu/exploration/resources/bizarre_nose_400.jpg>

When foraging for food, the nasal rays of the Star-nosed Mole are in constant movement, repeatedly touching the substrate and objects of interest. Each foraging touch involves moving the nose upwards while the nasal rays swing backwards, then moving the nose downwards and touching the rays to the substrate. The speed of this movement is very rapid, with the Star-nosed Mole able to touch over ten places each second. When a prey item is located, it is never eaten until explored by ray 11, the center most ventral ray. As ray 11 is one of the smallest rays on the nose of the mole, prey items are usually discovered and explored by the larger peripheral rays first, where the mole will then shift its nose in order to explore using ray 11. This process of exploring the prey with peripheral rays, ray 11, identifying the prey item as a food source and consuming it is all achieved in a time frame of approximately 400ms (Catania & Kaas 1997).

References

Catania. K., 1999, A nose that looks like a hand and acts like an eye: the unusual

mechanosensory system of the star nosed mole, Journal of Comparative Physiology A, vol. 185, pp. 367 - 372

Catania. K & Kaas. J., 1997, Somatosensory fovea in the star- nosed mole: behavioral

use of the star in relation to innervation patterns and cortical representation, Journal of Comparative Physiology A, vol. 387, pp. 215 – 233

Wayne Helfrich, 2009, Star-nosed Mole, Flickr, viewed 29 May 2014  

<https://www.flickr.com/search/?q=star-nosed+mole>

Vanderbilt University, 2014, viewed 29 May 2014

<http://www.vanderbilt.edu/exploration/resources/bizarre_nose_400.jpg>

Zera. S., 2004., Condylura cristata, Animal Diversity Web. Viewed 29 May, 2014

<http://animaldiversity.ummz.umich.edu/accounts/Condylura_cristata/>

Capillary forces in the scales of The Thorny Devil

Moloch horridus, commonly known as the Thorny Devil, is a small ant-eating lizard of the family Agamidae. It inhabits much of arid Australia living in sandy areas vegetated by spinifex grasses and shrubs (Shark Bay World Heritage Area 2009). Measuring lengths of less than 20cm, the Thorny Devil has one of the more peculiar scale constructions of most lizards, where its scales form an array of spines effectively deterring many predators (Withers 1993). Although these scales perform various different roles in the life strategy of the Thorny Devil, they have developed the spectacular ability to transport water over the surface of their skin.

'Thorny Devil' Zenith Images <https://www.flickr.com/search/?q=Thorny+devil>

You may be asking, what is the purpose of such an adaptation? In order to answer this we must look at the environment in which the Thorny Devil inhabits. These dry sandy areas are a hotspot for the Thorny Devils main food source, ants, however it is generally lacking in large supplies of water, which of course is essential for the Devils survival. In order to cope with the general lack of long term water sources available, the Thorny Devil has developed two co-evolved adaptations for the capture, transport and drinking of water from sporadic rainfall (Sherbrooke et al 2007).

Occurrence records map of the Thorny Devil <http://bie.ala.org.au/species/Moloch+horridus>

The first of these adaptations is the structure and arrangement of the Thorny Devils scales, where the Devil is able to transport water using capillary forces generated by scale ‘hinges’, or channels, located between the scales. This system of water transport has been observed to be so effective that the devil is able to remove water from damp sand by rubbing their ventral scales into the sand (Sherbrooke 1993; Wither 1993)

The second of these co-evolved adaptations is the pumping forces created by the jaw during drinking. In their study, Sherbrooke et al (2007) described that once the water holding areas of the scale hinges are saturated (filled to capacity), capillary forces no longer facilitate the movement of water toward the mouth. In order to promote water flow through the scale hinges after saturation, a negative pressure is generated at the jaw and in the mouth by the movement of the jaw and the tongue, drawing water through the scales and into the mouth of the Thorny Devil.

'Thorny devil with water travelling by capillary action over skin to eyes and mouth' <http://www.arkive.org/thorny-devil/moloch-horridus/video-10.html>

References

Atlas of Living Australia, 2013, Australian Government, viewed 26 May 2014  

<http://bie.ala.org.au/species/Moloch+horridus>

Arkive, 2013, Wildscreen, viewed 26 May 2014 < http://www.arkive.org/thorny-

devil/moloch-horridus/video-10.html>

Shark Bay World Heritage Area, 2009, Department of Parks and Wildlife, viewed 25

May 2014 <http://www.sharkbay.org/Thornydevilfactsheet.aspx>

Sherbrooke, W., 1993, Rain-drinking behaviors of the Australian Thorny Devil (Sauria:

Agamidae), Journal of Herpetology, vol. 27, no. 3, pp. 270 – 275

Sherbrooke, W et al, 2007, Functional morphology of scale hinges used to transport

water: convergent drinking adaptations in desert lizards (Moloch horridus and Phrynosoma cornutum), Zoomorphology, vol. 126, pp. 89 – 102 

Withers, P., 1993, Cutaneous water acquisition by the Thorny Devil (Moloch

horridus: agamidae), Journal of Herpetology, vol. 27, no. 3, pp. 265 – 270

Zenith Images, 2006, Thorny Devil, Flickr, viewed 26 May 2014   

<https://www.flickr.com/search/?q=Thorny+devil>