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Naked Mole-rat (Heterocephalus glaber) Fact Sheet: Physical Characteristics

Physical Characteristics

Body measurements

Attribute Measurement
Weight Typically 30 to 35 g (12 to 14 oz); range: 15 to 70 g (0.53 to 2.4 oz)*
Head-body Length 70 to 110 mm (3 to 4.3 in)
Tail Length 30 to 50 mm (1 to 2 in)


*Note: Adults in managed care typically 30 to 50 g (1 to 2 oz), sometimes 80 g (3 oz) or more (Jarvis and Sherman 2002)

Data sources: Brett (1991b), Patterson (2016)

General Appearance

Body

  • Body size (Jarvis and Sherman 2002)
    • Smaller than other African mole-rats
    • Weight of nonbreeding males and females similar
  • Skin
    • Coloration pink (Daly and Buffenstein 1998; Patterson 2016), brownish pink (Jarvis and Sherman 2002), or brownish-purple (Tucker 1981)
      • Young workers (less than 7 years old) have darker back (Braude et al. 2001)
    • Loose and folded (Thigpen 1940; Tucker 1981; Daly and Buffenstein 1998)
      • Reduces abrasions
      • Allows easy movement in confined or crowded burrow spaces
        • Common adaptation in animals that live underground
      • Thicker on face
    • Nearly hairless (Hamilton 1928; Thigpen 1940; Hill et al. 1957; Crish et al. 2000; Patterson 2016)
      • Body covered by coarse sensory hairs
        • Most dense around head and mouth
        • Adaptation for tunnel navigation in darkness
    • No insulating fat layer (Daly and Buffenstein 1998)

Head and mouth

  • Mouth (Hamilton 1928; Jarvis and Sherman 2002; Patterson 2016, and as noted)
    • Front teeth (incisors) large and curved; protrude from mouth
      • Used for tunnel digging
      • Grow continuously (Berkovitz and Faulkes 2001)
      • Sharpened when upper/lower incisors scrape against each other
    • 2 to 3 upper and lower cheek teeth
    • Tongue thick and cylindrical (Hill et al. 1957)
  • Jaws (Cox and Faulkes 2014)
    • Adapted for digging
    • Muscles very large
      • Weigh one-quarter of an individual’s body mass
    • Bite force strong
    • Gape very wide
  • Eyes (Jarvis and Sherman 2002, except as noted)
    • Small
    • Usually kept shut, unless alarmed (Jarvis 1991)
    • Eyelids thickened
    • Eyelashes small
  • Ears (Patterson 2016)
    • Small
    • Raised ring of skin around ear opening (Mason et al. 2016)

Legs and feet

  • Short and slender (Hamilton 1928; Jarvis and Sherman 2002)
  • 5 digits on each foot (Hamilton 1928)
  • Claws short (Hamilton 1928)
  • Sensory hairs on feet and between toes (Hamilton 1928)

Tail

  • Long, compared to other African mole-rats (Jarvis and Sherman 2002)
    • Longer than hind foot

Sexual Dimorphism

Little sexual dimorphism in nonbreeding individuals

(Hagen 1985, as cited by Jarvis 1991; Jarvis 1991)

  • Sexual organs visibly similar
    • External genitalia structures very similar; faint dark-red line between clitoris and anus present in females
  • Under certain conditions, nipples (mammae) may be present in both sexes
  • Testes undescended in males; lie in abdominal cavity
    • Other internal structures small and undeveloped
    • About 75% of adult males produce sperm, though only 1 to 3 mate

Senses

Also see Communication.

Touch

  • Sensory hairs (vibrissae) allow fast navigation through underground tunnels (Thigpen 1940; Hill et al. 1957; Crish et al. 2000; Patterson 2016)

Smell

  • Nasal structures for detecting pheromones relatively small (Smith et al. 2007; Dennis et al. 2019)

Hearing

  • Limited (Heffner and Heffner 1993; Mason et al. 2016; Patterson 2016)
  • Thought to be attuned for low-frequency sound (lower than 3 kHz) (Credner et al. 1997; Mason et al. 2016)
    • Travels better underground than high-frequency sound

Vision

  • Poor (Crish et al. 2006; Němec et al. 2008)
  • Basic mammalian eye structures (cornea, lens, retina) present but reduced (Nikitina et al. 2004; Hetling et al. 2005; Němec et al. 2008)
    • Development, anatomy, and arrangement differ from mammals that depend on vision
  • Sense light but not images or shapes (Crish et al. 2006; Němec et al. 2008)
    • Possible adaptations of light sensitivity
      • Detect holes in burrow; plug holes
      • Determine when near surface or outside burrow
      • Regulation of circadian or seasonal rhythms (Riccio and Goldman 2000)
  • Not able to orient themselves aboveground (e.g., for navigation) (Němec et al. 2008)

Other Physical and Physiological Characteristics

Metabolism and energy production

  • Low metabolism, relative to body size (Yahav and Buffenstein 1991a)
  • Capable of reducing metabolism when food is scarce (Goldman et al. 1999)
  • High production of energy in certain tissues maintained through early adulthood (Holtze et al. 2016)
    • Does not decline, as observed in other rodents

Thermoregulation

  • Body temperature fluctuates with surrounding environmental temperatures (usually burrow; range: 12 to 37°C, or 54 to 99°F) (Buffenstein and Yahav 1991a)
    • Not regulated at constant temperature, like most mammals (Buffenstein and Yahav 1991a)
    • Sensitive to cold (Hill et al. 1957)
  • Behavioral thermoregulation (Yahav and Buffenstein 1991a; Patterson 2016, except as noted)
    • Group members huddle together for warmth
      • May absorb heat more quickly by being hairless (Alexander 1991)
    • Select burrow chambers to gain or lose heat (e.g., warmer tunnels near surface)
  • No sweat glands (Tucker 1981)

Nervous system

  • Nociceptive (pain) system unique among mammals (Park et al. 2008; Patterson 2016)
    • Insensitive to chemical and inflammatory pain triggers
      • Lack pain-related neuropeptides in cutaneous sensory fibers
      • No pain behaviors in response to acid and capsaicin
    • Structure of and connectivity between peripheral nerves differs from other mammals
    • Unique pain adaptations may have evolved to cope with high CO2 levels in cramped, poorly ventilated burrows
  • Large brain areas associated with touch and movement of the mouth (Catania and Remple 2002; Henry et al. 2006)
    • Areas associated with vision reduced (Němec et al. 2008)

Respiratory and circulatory systems

  • Lungs not well developed (Maina et al. 1992)
  • Hemoglobin, the oxygen-transport protein in the blood, is able to bind an unusually large amount of oxygen (Johansen et al. 1976)

Wierdly Wonderful

Close-up of head of a naked mole-rat

A naked mole-rat's body is covered in coarse sensory hairs that help it to navigate a maze of tunnels in the dark.

Large incisor teeth are used for digging and chewing through fibrous plant tubers.

Image credit: © San Diego Zoo Global. All rights reserved.

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