The Microzetid Enigma

The armoured mites of the Oribatida include their fair share of ornately ornamented species but perhaps the most grotesque of all are to be found under members of the family Microzetidae. These typically fairly small oribatids (the average size is about a third of a millimetre) are primarily found in soil and litter deposits around the world. They include a handful of species found in the far north but are primarily found in warmer regions with the greatest known diversity in the Neotropics (Woas 2002).

Dorsal, ventral and lateral views of Acaroceras galapagoensis, from Heinrich Schatz & Jose Palacios-Vargas.

The microzetids are primarily distinguished by elaborate outgrowths of the cuticle around the front of the body. In many oribatids, a pair of thin lamellae run down either side of the prodorsum (the part of a mite that might at first glance be taken for the 'head'). In microzetids, these lamellae have become massively enlarged and detached from the prodorsum over much of their length. As a result, they form a kind of hood over the front of the body. They are flanked on either side by similar lateral extensions called tutoria. The prodorsum as a whole is often remarkably large compared to the rear part of the dorsum, the notogaster. Indeed, the notogaster is often as wide as or wider than it is long. A pair of wing-like extensions, pteromorphs, extend on either side of the front of the notogaster; in microzetids, the pteromorphs are typically sharply pointed. To top all these excrescences off, the insertions of the first pair of legs are also shielded by well-developed flanges called pedotecta.

What, if anything, is the purpose of all these anatomical extravagances is a question I am unable to answer: whether they are related in some way to defense or water retention, for instance. They also make it difficult to understand the position of microzetids relative to other oribatids. The presence of pteromorphs has commonly been thought characteristic of a group of oribatids that have been referred to as the Poronoticae. However, microzetids lack any sign of another distinctive feature of poronotic oribatids: the array of glandular openings on the cuticle known as the octotaxic system. Some oribatids are known to have reduced octotaxic systems, and microzetids do bear a certain resemblance to a definitely poronotic family in the Oribatellidae, so it is possible they represent poronotic mites in which the octotaxic system has been lost. However, other features of microzetids further support affinities outside the Poronoticae. In particular, nymphs of microzetids carry scalps. As they moult from one instar to the next, the shed cuticle of the notogaster is retained in place like a cap. Over successive instars, this cap becomes a stack of scalps that potentially assist in defence (a would-be predator attempting to grab onto the notogaster finds itself holding only an empty scalp). This is generally thought to be a primitive bahaviour that was lost in the ancestor of the poronotics. So are the microzetids primitive relatives of the poronotics, descended from ancestors that had acquired pteromorphs but not yet lost the scalp-carrying habit? Are they derived poronotics that eschewed the octotaxic system and taken up their scalps once more? Further research into oribatid phylogeny is needed to know.

REFERENCE

Woas, S. 2002. Acari: Oribatida. In: Adis, J. (ed.) Amazonian Arachnida and Myriapoda: Identification keys to all classes, orders, families, some genera, and lists of known terrestrial species pp. 21–291. Pensoft: Sofia.

The Long-eared Bats of Australasia

When most people think of Australian mammals, they imagine the fauna as dominated by marsupials and monotremes, representatives of lineages long isolated from those found elsewhere. But Australia is also home to a remarkable diversity of native placentals. Immigrating from the north as Australia drifted closer to Asia, the rodents and bats underwent their own radiations on the Australian continent and its neighbouring islands. Among these distinctly Australasian assemblages of placentals are the long-eared bats or big-eared bats of the tribe Nyctophilini.

Lesser long-eared bat Nyctophilus geoffroyi, copyright Michael Pennay.

The long-eared bats comprise fifteen or so species found over a range between eastern Indonesia and Australia with outlying species in New Caledonia and Fiji. They are members of the Vespertilionidae, the most diverse recognised family of bats, and share with most other vespertilionids a fairly generalised appearance with dull coloration. They differ from other vespertilionids in having a relatively short muzzle (with a correspondingly reduced number of teeth) with a small nose-leaf at its end (Miller 1907). They also (as the vernacular name indicates) have particularly large ears, as long as or longer than the rest of the head, that are commonly connected medially by a distinct membrane. At rest, the ears may be folded like a concertina along the hind margin to protect them from damage (Hall & Woodside 1989). Historically, the long-eared bats were treated as their own subfamily within the Vespertilionidae that also included a similar North American genus Antrozous. However, the nyctophilins are now regarded as a derived tribe within the larger subfamily Vespertilioninae (albeit one whose exact relationships remain uncertain) and similarities between Nyctophilini and Antrozous are thought to be convergent rather than reflecing a close relationship. The majority of nyctophilins are placed in a single genus Nyctophilus with the exception of the New Guinea big-eared bat Pharotis imogene. This species differs from Nyctophilus in lacking hair at the end of the muzzle.

Nyctophilins are found in a range of habitats but seem to prefer dry woodlands. Vespertilionids as a whole are differentiated from other bats by modifications of the fore arms including a highly developed double joint between scapula and humerus and reduction of the ulna. As a result, they may be less powerful fliers than other bats but they would be more agile. This trend would be particularly pronounced in nyctophilins which have relatively short wings compared to other vespertilionids (Hall & Woodside 1989). The development of a nose-leaf in nyctophilins is associated with their use of signals emitted at a constant frequency through the nose for echolocation whereas other vespertilionids use signals of varying frequency emitted through the mouth. As well as catching insect prey in flight, long-eared bats are able to recognise prey at rest and so glean insects off vegetation or on the ground. This gleaning habit is presumably also associated with long-eared bats having relatively larger eyes than other vespertilionids.

Gould's long-eared bat Nyctophilus gouldi with ears partially reclined, copyright Department of Environment and Primary Industries, Victoria.

Caves in Australia are mostly not very extensive so the formation of colonies by Australian vespertilionids is constrained by the availability of suitable roosting sites such as hollows in trees or crevices in rocks. At least some long-eared bats may be solitary (Hall & Woodside 1989). Their distribution in Australia (as with pretty much all Australian animals) is also largely contingent on the availability of water. Mating happens in autumn but gestation is generally delayed, whether by delaying fertilisation or development of the embryo, and does not kick off until spring. Pregnancy then lasts about six weeks though it may again be slowed down if conditions turn bad. Long-eared bats are unusual among bats in that twins are not uncommon.

Whereas at least some nyctophilin species remain common (the lesser long-eared bat Nyctophilus geoffroyi is found over most of Australia), others are rare or little-known. A species described from Lord Howe Island, N. howensis, is believed to be extinct. The most remarkable case of obscurity is Pharotis imogene which was not recorded between 1890 and 2012, over 120 years. Evidence of extreme rarity? Quite probably, but also possibly evidence of just how few people are paying attention to bats.

REFERENCES

Hall, L. S., & D. P. Woodside. 1989. Vespertilionidae. In: D. W. Walton, & B. J. Richardson (eds) Fauna of Australia vol. 1B. Mammalia pp. 871–886. Australian Government Publishing Service: Canberra.

Miller, G. S., Jr. 1907. The families and genera of bats. Smithsonian Institution, United States National Museum, Bulletin 57: i–xvii, 1–282, pls 281–214.

Sweet Moulds

For reasons that shouldn't be too hard to work out, much of microbial diversity has only been identified within the last few decades. In 1985, researchers identified a distinctive new species of mycelium-forming bacterium from soil in China that they dubbed Glycomyces harbinensis. This was the first known species of the actinobacterial family Glycomycetaceae which have since been isolated from a wide range of soil microbiomes.

Agar culture of Stackebrandtia nassauensis (scanning electron micrograph), from Goodfellow et al. (2012).

Glycomycetes form pale (white to tan-coloured) branching mycelium a bit less than half a micron in diameter. Under certain conditions, they will form aerial mycelia comprising long chains of spores but these seem to only ever be sparse. The name of the family (which could be translated as 'sweet moulds') refers to the presence of the amino-acid glycine as a significant component of the cell wall. Other diagnostic components of the cell include the sugar ribose and the phospholipid phosphatidylglycerol (Goodfellow et al. 2012).

Since the original description of Glycomyces, half a dozen genera and numerous species have been recognised among the Glycomycetaceae. Some, such as Haloglycomyces and Natronoglycomyces, were described from high salinity soils (Sorokin et al. 2021). Other glycomycetes, such as Glycomyces sambucus, are endophytic, living inside the roots of plants. Doubtless (as always) many more remain to be discovered.

I haven't found any references to direct usage of glycomycetes by humans as yet. It has been suggested that endophytic bacteria may play a role in their hosts' uptake of nutrients from the soil. And I wonder if those species found in salty soils may have a contribution to make to the rehabilitation of such environments. In parts of the world such as here in southern Western Australia, where rising soil salinity is a concerning issue, any help would be more than welcome!

REFERENCES

Goodfellow, M., P. Kämpfer, H.-J. Busse, M. E. Trujillo, K. Suzuki, W. Ludwig & W. B. Whitman (eds) 2012. Bergey's Manual of Systematic Bacteriology 2^nd ed. vol. 5. The Actinobacteria, Part A and B. Springer.

Sorokin, D. Y., T. V. Khijniak, A. P. Zakharycheva, A. G. Elcheninov, R. L. Hahnke, O. V. Boueva, E. V. Ariskina, B. Bunk, I. V. Kublanov & L. I. Evtushenko. 2021. Natronoglycomyces albus gen. nov., sp. nov., a haloalkaliphilic actinobacterium from a soda solonchak soil. International Journal of Systematic and Evolutionary Microbiology 71: 004804.