Monotremata, from the Greek μονός (monós, “single”) and τρῆμα (trêma, “orifice”), means "one-holed", in reference to the fact that these animals have a single orifice to reproduce (to mate and lay eggs) and excrete, known as “cloaca”, present also in sharks, rays and lobe-finned fishes, reptiles and birds. This strong similarity with other classes of animals denotes how the Monotremata are one of the oldest extant orders of mammals.

Common names of members

Echidna and platypus.

Distribution 

Australia, Tasmania, and New Guinea.

Size

Their sizes range in small proportions, from 30 cm to 50 cm in length.

Morphology

Nipples are lacking. Females secrete milk from glands directly through the skin and excreted on the fur located on the belly region.

Echidnas have a dome-shaped body covered in spines and a long snout.

Platypus have a duck-like flat bill, as well as a beaver-like tail, with a brown flattened barrel-like body. Males have sharp venomous spurs on the heels of their rear feet.

One of the factors that helps in the characterization of monotremes is the development of a jaw that connects differently to the skull, in addition to a total lack of teeth, possibly associated with the fact that these animals are capable of using electrolocation. Another is the lack of a structure called Corpus callosum, responsible for communication between the left and right cerebral hemispheres (which, in the case of these beings, is done differently).

Ecology & Habitat

Echidna: open forests and other forested environments.

Platypus: creeks, rivers, shallow lakes, wetlands, and their riparian margins.

Diet

Echidna: insects and worms from the bottom forest.

Platypus: aquatic invertebrates (caddisflies, mayflies, dragonflies, damselflies, crayfishes).

Reproduction 

Their breeding season is between June and October, with a polygynous mating system (one male mates with multiple females, but females mate with only one male) for both echidnas and platypuses. The ovule is fertilized in the oviduct. Embryo develops in the uterus. Leathery eggs are then being laid. The females will incubate the eggs. After the young hatches from the eggs, they suck milk from special mammary hairs.

Total species known

5

Species in the collection

2

Species in Hong Kong

0

References

- Bino, G. Kingsfird, R. T., Archer, M., Connolly, J. H., Day, J., Dias, K., Goldney, D., Gongora, J., Grant, T., Griffiths, J., Hawke, T., Klamt, M., Lunney, D., Mijangos, L., Munks, S., Sherwin, W., Serena, M., Temple-Smith, P., Thomas, J., ... Whittington, C. (2019). The platypus: evolutionary history, biology, and an uncertain future. Journal of Mammalogy, 100 (2), 308–327. https://doi.org/10.1093/jmammal/gyz058.

- Opiang, M. D. (2009). Home Ranges, Movement, and Den Use in Long-Beaked Echidnas, Zaglossus bartoni, From Papua New Guinea. Journal of Mammalogy, 90 (2), 340–346. https://doi.org/10.1644/08-MAMM-A-108.1.

- Nicol, S. C., Vanpé, C., Sprent, J., Morrow, G., Andersen, N. A. (2011). Spatial ecology of a ubiquitous Australian anteater, the short-beaked echidna (Tachyglossus aculeatus). Journal of Mammalogy, 92 (1), 101–110. https://doi.org/10.1644/09-MAMM-A-398.1. 

- Griffiths, M. (1978). The Biology of the Monotremes. Academic Press. https://doi.org/10.1016/B978-0-12-303850-0.X5001-0.

- Grant, T. R., Griffiths, M., Leckie, R. M. C. (1983). Aspects of Lactation in the Platypus, Ornithorhynchus anatinus (Monotremata), in Waters of Eastern New South Wales. Australian Journal of Zoology, 31(6), 881 - 889. https://doi.org/10.1071/ZO9830881.