Stunning Central American Millipedes

Blue cloud forest millipede Pararhachistes potosinus, copyright Luis Stevens.

For my semi-random selection of taxon to write about this week, I drew the millipede family Rhachodesmidae. Rhachodesmids are members of the millipede group called the Polydesmida, characterised by the presence of lateral keels on each segment of the body. The presence of these keels had lead to platydesmidans sometimes being referred to as 'flat-backed millipedes' though depending on how strong the keels are, not all species are necessarily 'flat-backed'.

In an earlier post on millipedes, I stressed the importance of genitalia in characterising millipedes, and the Rhachodesmidae are no exception. In polydesmidans, it is the front pair of legs on the seventh segment that is modified into the gonopods in males (with one notable exception that I may refer to later). Gonopods of rhachodesmids lack the solenite or coxal spur found in many other polydesmidans, and the inner side of the gonopod has a distinct elongate or oval concavity that is densely setose. Other noteworthy features of rhachodesmids are that they are often relatively large, with a conical terminal segment and more or less thickened rims to the lateral keels (Loomis 1964).

An unidentified rhachodesmid, copyright Sergio Niebla.

Beyond that, rhachodesmids become a little more difficult to characterise. Though they are not a widespread group, being restricted to Mexico and Central America, they are very diverse in appearance. Loomis & Hoffman (1962) commented that, "Rhachodesmoids collectively are members of a group notable for great variability and the development of bizarre features. Among their ranks we find millipeds which are bright blue, green, orange, and even pure white as adults; here the gonopod structure ranges from the normal polydesmoid appearance down to monoarticular fused remnants. Body form varies from a slender juliform shape to broad, flat, limaciform contour. Within the limits of this so-called single family occurs more variation than in all of the remaining polydesmoids." They also noted that the group was in need of review, something that apparently remains undone to this day (though there is someone working on it). If the photographs I've commandeered in this post are any indication, this is definitely a group that deserves more love.

Paratype of Tridontomus procerus, from Loomis & Hoffman (1962).

Loomis & Hoffman (1962) made their comments in comparing the Rhachodesmidae to another Central American polydesmidan family they were then describing as new, the Tridontomidae, and if I'm referring to the rhachodesmids then I should probably give a shout-out to these remarkable beasts as well. So far as I've found, this family is still only known from two species, Tridontomus procerus and Aenigmopus alatus, from Guatemala. Not only is the appearance of tridontomids striking, with long spinose processes on either side of the body, but the genital morphology of one species, A. alatus, is especially bizarre: it doesn't have any where it should. Where males of other polydesmidans have the legs of the seventh segment modified into gonopods, those of A. alatus have a perfectly ordinary pair of walking legs. In normal polydesmidans, the gonopods are used to transfer sperm from seminal processes on the coxae of the second pair of legs to the female's genital opening (more details are available here), but obviously Aenigmopus must do things differently. The seminal processes are still present, and the second legs themselves are thickened compared to other millipedes; it is possible that they are somehow used to transfer sperm directly from process to female without the use of gonopods. However it does it, there is no question that Aenigmopus is unique in the world of polydesmidans.

REFERENCES

Loomis, H. F. 1964. The millipeds of Panama (Diplopoda). Fieldiana: Zoology 47 (1): 1-136.

Loomis, H. F., & R. L. Hoffman. 1962. A remarkable new family of spined polydesmoid Diplopoda, including a species lacking gonopods in the male sex. Proceedings of the Biological Society of Washington 75: 145-158.

Antipatharia: The Black Corals

The black coral Antipathes, copyright Jez Tryner.

One piece of trivia I've learnt while looking stuff up for this post: the genus name Antipathes, from which the whole group of the Antipatharia derives its name, was coined to refer to the supposed ability of black coral to cure illnesses and protect against evil. It almost goes without saying that I found no indications that this evaluation was warranted.

The black corals of the Antipatharia are a group of colonial, sessile cnidarians that are found in marine waters around the world. They are predominantly deep-water animals, found mostly below the level of light penetrance. Those individuals that are found in shallower waters still keep to secluded habitats out of the light. Some of the shallowest communities are found in New Zealand at depths of only 4 m in the fiords of the South Island, where a rich concentration of tannins in the top layer of the water prevents light from reaching even that far down (Wagner et al. 2012). Black corals have been harvested in many parts of the world for jewellery (and also for their supposed curative properties referred to above), but they are very slow-growing animals. At least one colony subjected to radiocarbon dating was estimated to be over 4000 years old (Roark et al. 2009).

Wire coral Cirrhipathes, copyright Frédéric Ducarme.

Colonies of antipatharians may be highly branched, or they may form an unbranched whip (the latter forms are sometimes referred to as wire corals or whip corals). They may be only a few centimetres tall, or they may reach a length of several metres in the case of some wire corals (Wagner et al. 2012). The core of the colony is a stalk composed of chitin that varies in colour from jet black in the main stem to golden yellow at branch tips. The stalk is lined with spines that may be simple cones, or may be covered with denticles, or may even be branched and antler-like. In life, the stalk is encased in living tissue, so black corals are not actually black. Unlike other skeletonised cnidarians in which the polyps are recessed within the skeleton, those of antipatharians are entirely external to it. As a result, black corals are rarely found in locations where there is a lot of moving sediment in the water, as they lack the ability to entirely retract the polyps to protect them from abrasion. The individual polyps are usually only a few milimetres wide and up to a few centimetres tall when extended. All antipatharian polyps have six tentacles and six primary mesenteries; depending on the species, there may also be four or six secondary mesenteries, though members of the family Cladopathidae lack secondary mesenteries altogether.

The most recent classification of the Antipatharia divides it between seven families, some of which have been recognised only very recently. Because their deep-water habitat makes the study of live colonies difficult, and many features of the minute polyps become obscured in preserved material, earlier classifications focused heavily on features such as the branching arrangement of the colony, or the morphology of the spines on the skeletal axis. However, these features may be influenced by environmental factors, and their significance may have been overestimated. For instance, a molecular phylogenetic analysis by Brugler et al. (2013) found that the unbranched wire coral genus Cirrhipathes was polyphyletic and not separated from the branched genus Antipathes. Nevertheless, Brugler et al. did find that the higher-level relationships within the Antipatharia were mostly concordant with morphology, including the distinction of the seven families. These relationships included a divergent position for Leiopathes, the only genus with six secondary mesenteries; a clade including the bathyal families Schizopathidae and Cladopathidae, in which the polyps are transversely elongated; a close relationship between the families Myriopathidae and Stylopathidae, with polyps that are not elongated and have relatively short, subequal tentacles; and an association of the families Antipathidae and Aphanipathidae, in which the sagittal tentacles tend to be quite elongate relative to the lateral tentacles. There was still, of course, room for investigation: one notable anomaly is that the type species of Antipathes, A. dichotoma, was identified as a member of 'Aphanipathidae' rather than 'Antipathidae'. If correct, this would mean that aphanipathids should be called antipathids, while antipathids would be... something else.

REFERENCES

Brugler, M. R., D. M. Opresko & S. C. France. 2013. The evolutionary history of the order Antipatharia (Cnidaria: Anthozoa: Hexacorallia) as inferred from mitochondrial and nuclear DNA: implications for black coral taxonomy and systematics. Zoological Journal of the Linnean Society 169: 312-361.

Roark, E. B., T. P. Guilderson, R. B. Dunbar, S. J. Fallon & D. A. Mucciarone. 2009. Extreme longevity in proteinaceous deep-sea corals. Proceedings of the National Academy of Sciences of the USA 106 (13): 5204-5208.

Wagner, D., D. J. Luck & R. J. Toonen. 2012. The biology and ecology of black corals (Cnidaria: Anthozoa: Hexacorallia: Antipatharia). Advances in Marine Biology 63: 67-132.

A Spoonful of Lemba

Lemba or hill coconut Curculigo latifolia, from here.

The south-east Asian plant known as lemba has been referred to briefly on this site before, as a member of the family Hypoxidaceae. As noted in that post, it has been through a couple of names over the years: some sources will refer to it as Molineria latifolia, while others will call it Curculigo latifolia. The genera Molineria and Curculigo have been distinguished based on the presence of beaked (Curculigo) or unbeaked (Molineria) fruits and seeds, but the phylogenetic analysis of Hypoxidaceae by Kocyan et al. (2011) did not find this character to correlate with phylogeny. They therefore proposed to stop recognising the two genera as distinct, merging all species under Curculigo.

Curculigo latifolia is one of the largest species in the Hypoxidaceae. It is mostly found growing in damp, shaded locations, and the long-petioled leaves coming from an erect central rhizome can be a metre in length. Its small yellow flowers are placed at the base of the plant, at ground level; this distinguishes this species from various large orchid species found in the same region that may also be referred to as 'lemba' (or 'lumbah', or some other spelling/linguistic variant). The flowers give rise to small white berries, about an inch in size, with a distinct beak.

Fruit cluster of Curculigo latifolia, from DQ Farm.

Uses of this plant were recently reviewed by Lim (2012). The leaves provide a strong, lightweight fibre that is used to make nets, rope and cloth. The roots are brewed to treat various illnesses. However, the feature of this plant that has received the most attention in recent years is the fruit. These are edible, and are said to taste a bit like a sweet cucumber. The reason they have aroused interest, though, is that after eating one, anything else eaten within the next ten minutes or so will also taste sweet. This effect has been traced to a protein in the fruit, variously called neoculin or curculin, that has been reported to have several hundreds times the sweetness relative to weight of sucrose. Curculin has consequently been proposed as a potential low-calorie sweetener (to which I say, I'm sure it can't possibly taste worse than stevia), though one limitation is that the protein becomes denatured at temperatures above fifty degrees and loses its sweetening properties. As yet, though, it doesn't look like lemba sweetener has made it onto the commercial market.

REFERENCES

Kocyan, A., D. A. Snijman, F. Forest, D. S. Devey, J. V. Freudenstein, J. Wiland-Szymańska, M. W. Chase & P. J. Rudall. 2011. Molecular phylogenetics of Hypoxidaceae—evidence from plastid DNA data and inferences on morphology and biogeography. Molecular Phylogenetics and Evolution 60 (1): 122-136.

Lim, T. K. 2012. Edible Medicinal and Non-Medicinal Plants, vol. 4. Fruits. Springer.

Book Review: The Amazing World of Flyingfish, by Steve N. G. Howell

In June of last year, I was standing on the deck of a ferry in Taiwan, headed for the island of Lüdao (commonly known as Green Island), keeping an eye out for any interesting sights. I was particularly intrigued by the seabirds that I kept seeing flying away from the ferry. For some time, I couldn't make out exactly what kind of bird they were: they were small, and flew very quickly. Most oddly, they never seemed to rise very far above the water; I kept waiting for one to get higher so that I could get a better idea of its shape, but every time I tried to keep an eye on one individual, it would seem to disappear, as if it had re-entered the water. Eventually, understanding dawned: what I was seeing were not birds at all, but flying fish.

Flyingfish (Exocoetidae) are prominent members of the pelagic ecosystem in tropical waters. For some tropical seabirds (actual birds this time, such as boobies or frigatebirds), they are among the primary source of food. Steve Howell, author of The Amazing World of Flyingfish (Princeton University Press, who were kind enough to send me a review copy), put together a guide to flyingfish after travelling from New Zealand to Australia on the Spirit of Enderby as part of a cruise that was primarily supposed to be for bird-watching. But, as Howell explains, "birds tend to be few in the blue equatorial waters (remember, it's a desert, even though it's full of water), and attention sooner or later shifts to flyingfish".

The Amazing World of Flyingfish is not a large book: all up, it barely makes it over 50 pages. But almost every one of those pages is adorned with spectacular photographs that capture the grace and variety of flyingfish. The images chosen work wonders in expressing the liveliness of their subjects. My favourite image technically doesn't even show the fish at all: on p. 16, a triptych of photographs showing the process of re-entering the water shows first the fish in flight, then closing its fins as it approaches the water's surface, and then simply the splash as it disappears below. The text, geared towards a younger or a lay audience, provides a general overview of flyingfish, with chapters given self-explanatory titles such as, "What is a flyingfish?", "How big are they?", "How do they fly?"

And yet, I also found Howell's book frustrating. The numerous different flyingfish varieties depicted are labelled with vernacular names largely of his own creation, such as Atlantic patchwing, sargassum midget, Pacific necromancer. Zoological names are, for the most part, not provided. As Howell explains, most field guides to marine fish are written for biologists or fisherman, and are oriented around identifying a specimen after it has been caught, often relying on features (such as scale counts) that are not discernible in photographs of live individuals. As a result, the identity of most of Howell's 'field varieties' remains uncertain. But then, in another section of the book, we are told that one juvenile morph "was examined genetically and proved to be a young Atlantic Necromancer" (capitalisation Howell's), implying that the zoological identity of this species, at least, is known.

As Howell points out, "there remains an unfilled niche for a field guide that portrays flyingfish as observers see them in the air". Howell has produced an attractive and engaging introduction to the world of flyingfish, and it should provide an inspiration to fill that niche.

Aequitriradites: The Mark of the Cretaceous

Diagram of Aequitriradites ornatus, from Upshaw (1963).

The Cretaceous period is best known in popular culture as the time of Tyrannosaurus and Triceratops, of Pteranodon and Quetzalcoatlus, of Elasmosaurus and mosasaurs. But it was also, in an arguably even more significant way, the time of Aequitriradites.

Aequitriradites is the fossil represented in the diagram at the top of this post. It is not very large: at its largest, the species shown above is about a tenth of a millimetre across (Upshaw 1963). It is, in fact, the spore from a liverwort. The vegetative parts of liverworts mostly do not have much of a fossil record, being soft and prone to decay, though long-time readers may recall a suggestion that this spotty fossil record was occasionally dramatic (alas, general opinion seems to have not been swayed). However, their spores are more resistent, and hence may be abundant as fossils. Because it is rarely possible to tell exactly which plant they came from, fossil spores (and pollen) are classified as form taxa, parallel to the classification of other plant fossils. Aequitriradites species are characterised by a membranous flange (a zona) running around the outside of the spore, together with a triradiate laesura pattern (the fissures that mark where the spore opens when it germinates) on one face. Depending on the species, the laesurae may be well-marked or faint. There may also be an opening in the spore wall at the apex of the face opposite the laesurae (Cookson & Dettmann 1961). It has been suggested that the otherwise unidentified liverworts that produced Aequitriradites spores were probably related to the modern liverwort order Sphaerocarpales, and Archangelsky & Archangelsky (2005) compared Aequitriradites to the spores of the aquatic genus Riella.

Alternate faces of specimens of Aequitriradites plicatus, from Archangelsky & Archangelsky (2005).

The abundance of plant spores and pollen is such that they are commonly used as 'index fossils', indicators of the age of the rock they are found in. Aequitriradites contains various species throughout the Cretaceous period (species assigned to this genus from the Triassic seem to have since been re-classified). Li (2014) identified the appearance of Aequitriradites spinulosus in the very latest Jurassic as one of the better indicators of the start of the Cretaceous period in the Qinghai-Xizang Plateau in China. Aequitriradites species seem to have been most abundant in the Early Cretaceous, becoming rarer in the Late Cretaceous. Establishing the latest appearance of a spore taxon in the fossil record can be difficult, because of the possibility of re-working (fossil spores being disassociated from their original deposit and re-buried in a later one), but non-reworked examples of Aequitriradites in the latter part of the Late Cretaceous were alluded to by Askin (1990). TLDR: If you've got Aequitriradites, you've got Cretaceous.

REFERENCES

Archangelsky, S., & A. Archangelsky. 2005. Aequitriradites Delcourt & Sprumont y Couperisporites Pocock, esporas de hepáticas, en el Cretácico Temprano de Patagonia, Argentina. Rev. Mus. Argentino Cienc. Nat., n. s. 7 (2): 119-138.

Askin, R. A. 1990. Cryptogam spores from the Upper Campanian and Maastrichtian of Seymour Island, Antarctica. Micropaleontology 36 (2): 141-156.

Cookson, I. C., & M. E. Dettmann. 1961. Reappraisal of the Mesozoic microspore genus Aequitriradites. Palaeontology 4 (3): 425-427, pl. 52.

Li, J. 2014. Upper Jurassic and Lower Cretaceous palynological successions in the Qinghai-Xizang Plateau, China. In; Rocha, R., et al. (eds) STRATI 2013, pp. 1197-1202. Springer Geology.

Upshaw, C. F. 1963. Occurrence of Aequitriradites in the Upper Cretaceous of Wyoming. Micropaleontology 9 (4): 427-431.