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/>