Field of Science

Disco Opilioni

As I do every week, I spun the wheel yesterday to find out what the topic for this week's post would be. It told me to write about Cristina. Interesting, I thought, this site doesn't usually focus on early 1980s No Wave performers:

But then, of course, I realised that I'd driven that cheap gag about as far as I could (not very far, as it turned out). The actual topic of today's post is the African harvestman genus Cristina.

Male Cristina armata, from Roewer (1911).

As is not unusual, the harvestman fauna of Africa has been far less extensively studied than that of other continents. Among the long-legged harvestmen, to which Cristina belongs, most known African species belong to the family Phalangiidae, again including Cristina. Two species of Neopilionidae (Neopilio australis and Vibone vetusta) are known from the very south of the continent, and various species of Sclerosomatidae are known from the very north (which, biogeographically speaking, is more part of Europe than Africa, at least as far as harvestmen are concerned). Otherwise, the continent is the preserve of the phalangiids, and Africa is home to the world's only tropical Phalangiidae. What is known of the African phalangiid fauna was mostly reviewed by Staręga (1984).

Cristina is found in eastern African from the Horn south to Mozambique, with an outlying species across the Gulf of Aden in Yemen. Cristina species are also known from central Africa, Ghana and Togo, and it is likely found in a broad band across the entirety of central Africa. Like many other genera of phalangiids, Cristina has transverse rows of spines across the body, but it is distinguished from most confamilials by the presence of four (sometimes two) pairs of denticles or large spines on the eye mound (Cristina crassipes from Togo has the last pair of spines directed backwards and almost looking like a pair of horns). The males have the first pair of legs distinctly swollen in comparison to the remaining legs, but do not have particularly modified chelicerae.

We don't as yet know how the African phalangiids are related to those elsewhere. The Phalangiidae tend, underneath their superficial spines, to be a fairly conservative bunch, and will not reveal themselves easily.


Roewer, C.-F. 1911. Übersicht der Genera der Subfamilie der Phalangiini der Opiliones Palpatores nebst Beschreibung einiger neuer Gattungen und Arten. Archiv für Naturgesichte 77 (Suppl. 2): 1-106.

Staręga, W. 1984. Revision der Phalangiidae (Opiliones), III. Die afrikanischen Gattungen der Phalangiinae, nebst Katalog aller afrikanischen Arten der Familie. Annales Zoologici 38 (1): 1-79.

Ginseng and Ivy

Pate Schefflera digitata, photographed by Kahuroa.

The Araliaceae are a family of nearly 1500 species of flowering plants found around the world, but primarily in the Old World tropics. Most of its members are trees or shrubs, but there are also some herbaceous or climbing species. Many Araliaceae have palmate leaves, and they often produce inflorescences in umbels. Not that many Araliaceae hold much economic prominence: Tetrapanax papyriferus is used to make rice paper, while the genus Panax includes the ginsengs that are widely regarded as something of a wonder-drug for no apparent good reason. Some other species are well known as garden plants, such as ivy Hedera helix. Back in my home country of New Zealand, Araliaceae include some of the most familiar small native trees such as pate Schefflera digitata and the five-fingers and lancewoods of the genus Pseudopanax.

A young lancewood Pseudopanax crassifolius, photographed by Mike Hudson. Lancewood is notable for its differing growth habits over its lifespan: this individual is just beginning to change from its juvenile to its mature foliage. When the plant is young, the long, narrow, tooth-edged leaves hang down around the trunk. As the tree matures, it produces leaves that are shorter, broader and with less strong teeth, and that are held upwards and outwards. The juvenile and mature trees are so different in appearance that they were initially described as different species.

The Araliaceae have long been recognised as close relatives of the Apiaceae, the family including carrots and celery, to the extent that some authors have combined the two in a single family. Most recent researchers have maintained the distinction, but phylogenetic studies have indicated that some genera previously treated within the Apiaceae, notably the water and marsh pennyworts of the genus Hydrocotyle, are better treated as basal Araliaceae (Plunkett et al. 1997). Relationships within the Araliaceae are somewhat less straightforward, as molecular phylogenetic studies have indicated that there has been a great deal of homoplasy in morphological characters (Plunkett et al. 2004). Some of the larger genera in the family (notably the genus Schefflera, to which nearly half the species of Araliaceae have been assigned) appear to be significantly polyphyletic, some of them not even resolving in particularly proximate clades. The difficult nature of many araliaceous genera has long been realised: in 1868, the botanist Berthold Seemann referred to the then-poorly defined Panax as "one of the great lumber rooms of our science" (Wen et al. 2001).

American ginseng Panax quinquefolius, from here. Red ginseng is derived from the root of this species and the Asian P. ginseng; however, over-harvesting has lead to the endangerment of wild populations of the latter.


Plunkett, G. M., D. E. Soltis & P. S. Soltis. 1997. Clarification of the relationship between Apiaceae and Araliaceae based on matK and rbcL sequence data. American Journal of Botany 84 (4): 565-580.

Plunkett, G. M., J. Wen & P. P. Lowry II. 2004. Infrafamilial classifications and characters in Araliaceae: Insights from the phylogenetic analysis of nuclear (ITS) and plastid (trnL-trnF) sequence data. Plant Systematics and Evolution 245 (1-2): 1-39.

Wen, J., G. M. Plunkett, A. D. Mitchell & S. J. Wagstaff. 2001. The evolution of Araliaceae: a phylogenetic analysis based on ITS sequences of nuclear ribosomal DNA. Systematic Botany 26 (1): 144-167.

The Alga of Uncertainty

The red alga Rhodomela confervoides, from Coastal Imageworks.

The tradition in taxonomy that nothing is ever really forgotten (for which there are very good reasons) means that, over the years, we have accumulated a certain amount of excess detritus. Whether referred to as nomina dubia, species inquirendae or just plain unidentifiable, there are a number of names for which the original description or material is not adequate to determine their identity with certainty. Most nomina dubia simply slumber undisturbed, not interfering with standard taxonomic practice; they simply serve to irritate those whose role it is to assemble comprehensive listings.

The red alga Rhodomela preissii was named by Sonder in 1848 for a specimen collected in Western Australia. He diagnosed it as "fronde tereti filiformi siccitate subplicata a basi dichotome ramosa, ramis inferioribus patentibus superioribus brevioribus erectiusculis, ramulis sparsis setaceis simplicibus furcatisve, capsulis subpedicellatis solitariis ramis superioribus adnatis", Latin descriptions being the fashion at the time*. The specimen appears to have never been figured.

*Some of you may be aware that the Botanical Congress recently voted to remove the requirement for Latin diagnoses or descriptions from the Botanical Code of Nomenclature**. Authors are still required to give a diagnosis for new taxa in either Latin or English, so Chinese still doesn't get a look-in.

**Though it was also decided that it would no longer be called the Botanical Code. It's now the "International Code of Nomenclature for Algae, Fungi and Plants". I suppose that we should be just grateful they didn't go with the even more explicit "International Code of Nomenclature for Plants, Fungi, Algae, Oomycetes, Labyrinthuleans, Plasmodiophoromycetes, Mycetozoans, Dinoflagellates, Euglenaceae and Cyanobacteria (and maybe Fossil Bacteria, on alternate Tuesdays)".

Hypnea rosea, photographed by Olivier De Clerck.

Womersley (2003) noted that the type specimen of Rhodomela preissii, held at the Melbourne herbarium, is small and inadequate for the species' identification. True Rhodomela is unknown from Australia, though other members of the Rhodomelaceae occur there. Womersley, however, suggested that R. preissii might be a specimen of Hypnea. If true, this would place 'R.' preissii some distance phylogenetically from Rhodomela, the latter belonging to the order Ceramiales while Hypnea is a member of the Gigartinales. As things stand, though, no-one seems to be faced with a great need to resolve the question.


Sonder, O. G. 1846-1848. Algae L. Agardh. In: Lehmann, C. Plantae Preissianae sive Enumeratio Plantarum quas in Australasia occidentali et meridionali-occidentali annis 1838-1841 collegit Ludovicus Preiss, Phil. Dr. Acad. Caesar. Leopold, Carol. Natur. Curios. et Reg. Societ. Bot. Ratisbonens, Sodalis, cet. vol. 2 pp. 148-160 (1846), 161-195 (1848). Meissner: Hamburg.

Womersley, H.B.S. 2003. The Marine Benthic Flora of Southern Australia.
Rhodophyta. Part IIID. Ceramiales – Delesseriaceae, Sarcomeniaceae, Rhodomelaceae
. Australian Biological Resources Study, Canberra.

Groundhogs, Woodchucks and Other Big Squirrels

Thirteen-lined ground squirrel Ictidomys tridecemlineatus, photographed by Phil Myers.

The Holarctic ground squirrels of the Marmotini were the subject of one of my earliest posts at this site, before I really knew what I was doing*. So I'll have a go at improving it now.

*Not, of course, that I know what I'm doing now.

The Arctic ground squirrel Urocitellus parryii, photographed by Ianaré Sévi.

Marmotini is the clade of squirrels that includes ground squirrels (Spermophilus), antelope ground squirrels (Ammospermophilus), marmots (Marmota) and prairie dogs (Cynomys). Authors seem to differ on whether to also include the chipmunks (Tamias), but the question is somewhat semantic: agreement seems to be universal that the chipmunks represent the sister group to the remaining marmotins (Herron et al. 2004), so the only real question is how inclusive one wishes to make the term. The Chinese rock squirrels Sciurotamias may also belong to the Marmotini (Steppan et al. 2004). Except for the semi-arboreal chipmunks, marmotins are largely terrestrial in habits. They nest in underground burrows (including chipmunks), and some species form quite complex societies.

Père David's rock squirrel Sciurotamias davidianus, from here.

Ground squirrels previously assigned to the genus Spermophilus* have a wide range through Eurasia and North America. However, both morphological and molecular data indicate that Cynomys is derived from within 'Spermophilus', and molecular data indicate that Ammospermophilus and Marmota are as well (Herron et al. 2004). Helgen et al. (2009) divided the former Spermophilus between eight genera. Six of these genera are found in North America, one (Spermophilus proper) is found in Eurasia, and only one (Urocitellus) spans the divide between northeast Asia and North America. Whether the Marmotini as a whole are Eurasian or North American in origin is equivocal: of the three basalmost branches, Sciurotamias is definitely Eurasian, Tamias could be either (the Siberian chipmunk Tamias sibiricus is the sister to the remaining North American species) and the Spermophilus clade is probably North American in origin, with dispersals back to Eurasia in Marmota, Urocitellus and Spermophilus (Herron et al. 2004).

*Particularly in the European literature, it was not uncommon in the past to find the name Citellus being used in place of Spermophilus. Citellus Oken 1816 is indeed an older name than Spermophilus Cuvier 1825; however, the publication that the former derives from was not one that used the binomial system, and hence it has been declared invalid as a source of names (International Commission on Zoological Nomenclature 1956).

The woodchuck Marmota monax, from here.

Marmotins were the dominant squirrel group in North America during the Neogene; tree squirrels, though present, were exceedingly rare (Emry et al. 2005). The Pliocene Paenemarmota was the largest of all marmotins, reaching the size of a large beaver (Repenning 1962).


Emry, R. J., W. W. Korth & M. A. Bell. 2005. A tree squirrel (Rodentia, Sciuridae, Sciurini) from the Late Miocene (Clarendonian) of Nevada. Journal of Vertebrate Paleontology 25 (1): 228-235.

Helgen, K. M., F. R. Cole, L. E. Helgen & D. E. Wilson. 2009. Generic revision in the Holarctic ground squirrel genus Spermophilus. Journal of Mammalogy 90 (2): 270-305.

Herron, M. D., T. A. Castoe & C. L. Parkinson. 2004. Sciurid phylogeny and the paraphyly of Holarctic ground squirrels (Spermophilus). Molecular Phylogenetics and Evolution 31: 1015-1030.

International Commission on Zoological Nomenclature. 1956. Opinion 417. Rejection for nomenclatorial purposes of volume 3 (Zoologie) of the work by Lorenz Oken entitled Okens Lehrbuch der Naturgeschichte published in 1815–1816. Opinions and Declarations Rendered by the International Commission on Zoological Nomenclature 14: 1–42.

Repenning, C. A. 1962. The giant ground squirrel Paenemarmota. Journal of Paleontology 36 (3): 540-556.

Steppan, S. J., B. L. Storz & R. S. Hoffmann. 2004. Nuclear DNA phylogeny of the squirrels (Mammalia: Rodentia) and the evolution of arboreality from c-myc and RAG1. Molecular Phylogenetics and Evolution 30: 703-719.

The Long-Whipped Bryozoan

Zooids of Crepidacantha longiseta, from Tillbrook et al. (2001).

Coral is far from being the only organism involved in the construction of a coral reef. Other calcareous organisms such as coralline algae, foraminifera and molluscs may also be significant. And, of course, there are those delicate artistes known as bryozoans. Many bryozoans tend to be underestimated as reef components because, as well as being relatively small, they often prefer to settle in more cryptic habitats such as around and under coral gravel (Kobluk et al. 1988).

The organism in the SEM photo at the top of this post is one reef-inhabiting bryozoan, Crepidacantha longiseta. This species belongs to the ascophoran bryozoans, i.e. the zooid is protected dorsally by a calcified frontal wall, and each feeding zooid is associated with two long whip-like avicularia (the exact function of bryozoan avicularia is debated, but they are generally believed to be related to defense and/or cleaning the surface of the colony). In the top image, the feeding zooids are represented by the keyhole- or cartoon-fish-shaped openings, while the avicularia are positioned to either side of the main opening. Other Crepidacantha species may have the avicularia in different positions; they also differ in the length of the avicularia and the shape of the primary orifice (Tilbrook et al. 2001).

Crepidacantha longiseta is found in cryptic habitats around coral gravel in shallower waters, but may be found in more exposed positions as the water gets deeper, below about 25 m (Martindale 1992). It has been found in Vanuatu, Brazil, the Caribbean and Mauritius, and is presumably pantropical in its distribution (Tilbrook et al. 2001).


Kobluk, D. R., R. J. Cuffey, S. S. Fonda & M. A. Lysenko. 1988. Cryptic Bryozoa, leeward fringing reef of Bonaire, Netherlands Antilles, and their paleoecological application. Journal of Paleontology 62 (3): 427-439.

Martindale, W. 1992. Calcified epibionts as palaeoecological tools: examples from the Recent and Pleistocene reefs of Barbados. Coral Reefs 11 (3): 167-177.

Tilbrook, K. J., P. J. Hayward & D. P. Gordon. 2001. Cheilostomatous Bryozoa from Vanuatu. Zoological Journal of the Linnean Society 131: 35-109.

Burrowing Beaky Amphipods

Oediceroides emarginatus, photographed by Gauthier Chapelle.

I've been out in the field for a couple of weeks, hence the momentary absence of regular posts. But I have returned, and shall kick off with a brief introduction to the Oedicerotidae.

The oedicerotids are another cluster within the systematic morass that is the gammaridean amphipods (other gammaridean families featured here and here). Members of the Oedicerotidae are marine benthic burrowing forms, appropriately solidly built (for an amphipod, at least), and most readily distinguished from most other gammarideans by their particularly long fifth pereiopods (the last pair of legs on the main body) (Barnard 1969). They also usually have a long peduncle on the third uropods (the 'tail' appendages), though one distinctive genus Metoediceros lacks the third uropod entirely (Barnard 1974). In many oedicerotids, the eyes have also moved upwards to become coalesced along the dorsal midline and the head often possesses a prominent rostrum. However, these features are absent from a number of Southern Hemisphere and deep-sea taxa (the latter of which generally lack eyes altogether).

Dorsal view of the head of Monoculodes borealis, showing the coalescent eyes, from Andrey Vedenin.

Oedicerotids of the genus Synchelidium have been shown to be predators of harpacticoid copepods (Yu & Suh 2006). The abundance of this food appears to determine their reproductive behaviour, as females produce larger broods in the spring when harpacticoids are more abundant than in the fall.


Barnard, J. L. 1969. The families and genera of marine gammaridean Amphipoda. United States National Museum Bulletin 271: 1-535.

Barnard, J. L. 1974. Evolutionary patterns in gammaridean Amphipoda. Crustaceana 27 (2): 137-146.

Yu, O. H., & H.-L. Suh. 2006. Life history and reproduction of the amphipod Synchelidium trioostegitum (Crustacea, Oedicerotidae) on a sandy shore in Korea. Marine Biology 150: 141-148.