Hypsogastropods: Gastropods on High

Historically, the classification of molluscs has been a challenging prospect. Early researchers focused almost entirely on the shell which provided a somewhat limited range of characters with a definite possibility for convergence. Over time, more attention came to be paid to features of the soft anatomy but that required access to freshly collected material that might be difficult or impossible to obtain. As such, it has only been in the last few decades that a well-structured classification for many molluscan groups has begun to develop, and even now many significant uncertainties remain.

Common periwinkles Littorina littorea, a pretty typical hypsogastropod, copyright Fritz Geller-Grimm.

Until maybe the late 1990s, gastropods were primarily classified using a heavily grade-based system that was established in the 1930s. Gastropods were divided between three subclasses: the torted, gill-breathing prosobranchs, the untorted opisthobranchs, and the lung-breathing pulmonates. Prosobranchs were in turn divided into three main groups whose names directly reflected the 'level' of evolution at which they were supposed to sit: the archaeogastropods, the mesogastropods and the neogastropods. Many of these subdivisions were implicitly assumed to be ancestral to others. As the philosophical underpinnings of biological classification came to favour recognition of monophyletic taxa, it was obvious that such a system had to change. The prosobranchs and archaeogastropods both faded away as formal taxa. A major clade uniting the neogastropods and most of the mesogastropods came to be recognised as the caenogastropods. And while many questions still remain about relationships within the caenogastropods, most recent analyses have agreed in supporting a clade that was dubbed the Hypsogastropoda by Ponder & Lindberg (1997).

False cowrie Dentiovula dosruosa, copyright Nick Hobgood.

The prefix 'hypso-' means 'high' and was chosen because this clade corresponded to a group that had previously been known as the 'higher' caenogastropods (including the neogastropods and a fair chunk of the 'mesogastropods'). Hypsogastropods include many of the best known marine gastropods, such as whelks, periwinkles, moon snails, cones, cowries, conches and doubtless a ton of other things beginning with C (they also include freshwater and terrestrial forms but these are mostly minute and lack the public image of their marine relatives). They are ecologically diverse, including grazers, detritivores, filter feeders, predators and even parasites. The violet snails of the genus Janthina are planktonic, using a raft of bubbles to float on the water's surface so they can feed on Portuguese men-of-war. The similarly pelagic heteropods of the superfamily Pterotracheoidea have the foot extended and flattened to form a fin for active swimming.

Paraspermatozoon of violet snail Janthina, from Buckland-Nicks (1998). The arrow indicates the much smaller euspermatozoa attached to the tail.

Among the characters originally cited by Ponder & Lindberg (1997) as uniting the hypsogastropods were features of the spermatozoa. Most hypsogastropods have vermiform paraspermatozoa, sterile sperm cells that are released by the male together with the functioning euspermatozoa. The function of the paraspermatozoa seems to warrant further study. In some cases they may actively assist in the transport of the euspermatozoa; for instance, in violet snails a large number of euspermatozoa will be attached to a single super-sized paraspermatozoon able to swim harder and faster than any of the smaller cells could do on their own. In others, however, the two sperm cell types are not directly associated. It is possible that the paraspermatozoa act as a nuptial gift, providing nutrients to the female as a reward for mating, or that they somehow function to suppress sperm cells from any other males the female might made with (Buckland-Nicks 1998). Other synapomorphies of the clade include an external penis located behind the right cephalic tentacle, and statocysts (balance organs) each containing a single large statolith (Simone 2011).

Relationships within the Hypsogastropoda remain more poorly supported. Most researchers have agreed that the traditionally recognised neogastropods represent a clade united by numerous features, many of them related to the digestive system. The 'mesogastropods' included in the Hypsogastropoda mostly possess a taenioglossan radula with seven teeth in each row. In neogastropods, the number of teeth becomes more varied and the teeth themselves become modified so that the lateral teeth are strongly distinct in form from the central tooth. Some of these neogastropod modifications have been discussed in earlier posts on this site. A number of recent analyses have further associated the neogastropods with 'mesogastropod' taxa such as cowries and tun shells that they resemble in possessing an inhalent siphon forming a groove at the front of the shell (Simone 2011). A number of the remaining 'mesogastropods', such as the periwinkles of the Littorinidae and the Rissoidae, have been united by molecular analyses into a group that has been labelled the 'asiphonate clade' or the 'GC group' (the latter name chosen by Colgan et al., 2007, in reference to a particular genetic sequence motif). This clade is less universally recovered, however, and the scope for further investigation certainly remains.

REFERENCES

Buckland-Nicks, J. 1998. Prosobranch parasperm: sterile germ cells that promote paternity? Micron 29 (4): 267–280.

Colgan, D. J., W. F. Ponder, E. Beacham & J. Macaranas. 2007. Molecular phylogenetics of Caenogastropoda (Gastropoda: Mollusca). Molecular Phylogenetics and Evolution 42: 717–737.

Ponder, W. F., & D. R. Lindberg. 1997. Towards a phylogeny of gastropod molluscs: an analysis using morphological characters. Zoological Journal of the Linnean Society 119: 83–265.

Simone, L. R. L. 2011. Phylogeny of the Caenogastropoda (Mollusca), based on comparative morphology. Arquivos de Zoologia 42 (4): 161–323.

Leptocaris: Living on the Edge

Some of the most remarkable faunal diversity in the marine environment is to be found in the interstitial spaces between grains of sand. Grazers, predators and scavengers can be found creating entire food webs at scales of less than one millimetre. The minute crustaceans known as copepods are among the more abundant inhabitants of the interstitial, and today's subject, Leptocaris, is among those interstitial copepods.

Dorsal habitus of female (left) and male Leptocaris ryukyuensis, from Song et al. (2012).

Leptocaris contains more than twenty-five species of extremely slender, cylindrical harpacticoid copepods growing to a bit over half a millimetre in length. Characteristic features of the genus include having the maxillipeds (one of the pairs of appendages making up the mouthparts) reduced or lost, and the proximal part of the endopod of the first swimming leg bearing a special anteriorly directed seta with a terminal comb (Song et al. 2012). Representatives of this genus have been collected from localities around the world though mostly in the Northern Hemisphere. Nevertheless, one can't help wondering how much of the genus' apparent rarity in the Southern Hemisphere is an artefact of low collection effort. This possibility should also be kept in mind when considering differences in the ranges of individual species: whereas many have only been collected from single localities (Song et al. 2012), the species L. trisetosus has been found from Finland to the Bahamas to South Africa, as well as in Korea with the last population being treated as a distinct subspecies (Lee & Chang 2008).

The majority of collections of Leptocaris have been from among sand but the genus has also been found in other microhabitats. In general, they are found in sediments with a high organic content. They are found in euryhaline and eurythermal habitats: that is, locations subject to wide variations in salinity and temperature. These may include beaches and brackish pools. They have been found among decomposing leaves in mangrove swamps (offhand, I haven't found if the diet of Leptocaris has been firmly established but I suspect they are probably detritivores). One species, L. kunzi, was described from an estuarine lake in Louisiana; another, L. stromatolicolus, is known from among stromatolites in Mexico. Two species, L. brevicornis and L. sibiricus, have even been found in continental fresh waters in Europe as well as in coastal brackish waters (Song et al. 2012). Overall, Leptocaris species seem to be most abundant in marginal habitats that may be too harsh and unstable for other copepods, making them fronteir harpacticoids.

REFERENCES

Lee, J. M., & C. Y. Chang. 2008. Copepods of the genus Leptocaris (Harpacticoida: Darcythompsoniidae) from salt marshes in South Korea. Korean Journal of Systematic Zoology 24 (1): 89–98.

Song, S. J., H.-U. Dahms & J. S. Khim. 2012. A review of Leptocaris including a description of L. ryukyuensis sp. nov. (Copepoda: Harpacticoida: Darcythompsoniidae). Journal of the Marine Biological Association of the United Kingdom 92 (5): 1073–1081.

Anthaxia: More Modest Jewels

The jewel beetles of the Buprestidae are best known for their spectacularly patterned exemplars, a couple of which I've presented on this site before. But as with most animal groups renowned in this way, they also include their fair share of less immediately eye-catching members. The species of the genus Anthaxia are among these more modest jewels.

Anthaxia hungarica, photographed by Frayle.

Which is not to say they are unattractive. Anthaxia species still usually have the metallic gloss so widespread among the Buprestidae but they tend to be more uniform in colour, and those colours are often shades of bronze or blue-green rather than yellows or purples. They are also smaller than the species previously shown: a length of 6.5 millimetres would be relatively large for an Anthaxia. Some of the smallest species don't quite make it to three millimetres (Bílý & Kubáň 2010). Nevertheless, Anthaxia are incredibly diverse. Something in the range of 700 species are known from around the world (though they appear to be absent from Australia, with the single species described from Victoria now thought to have been based on a mis-labelled African specimen) and a quick Google Scholar search indicates new species continue to be described regularly. It should come as no surprise that many of these species would be difficult to distinguish without close examination.

Anthaxia scutellaris, a more colourful species of the genus, copyright Hectonichus.

Like other buprestids, Anthaxia species are wood-borers as larvae and flower-feeders as adults. The larvae seem to run the gamut of preferred tree hosts: Anthaxia have been found emerging from hosts ranging from pines to pears, from oleander to oaks. Some species appear to be quite catholic in their tastes: the recorded host list for the most polyphagous known species, A. millefolii, includes maples, chestnuts, carobs, oleanders, pistachios, plums, pears, oaks and rowans (Mifsud & Bílý 2002). Others are more discerning. Species of the subgenus Melanthaxia are only known to feed on conifers (Bílý & Kubáň 2010) and records for A. lucens indicate a dedication to stonefruit trees (Mifsud & Bílý 2002). Nevertheless, the larval hosts of many species remain unknown and there may be surprises. The North American species A. hatchi might be expected to be a conifer feeder like other Melanthaxia species but to date it has been collected in riparian habitats where conifers do not grow (Nelson et al. 1981). Could this member of an otherwise conifer-loving group have developed a taste for the willows and alders amongst which it lives? The question is yet to be answered.

REFERENCES

Bílý, S., & V. Kubáň. 2010. A study on the Nearctic species of the genus Anthaxia (Coleoptera: Buprestidae: Buprestinae: Anthaxiini). Subgenus Melanthaxia. Part I. Acta Entomologica Musei Nationalis Pragae 50 (2): 535–546.

Mifsud, D., & S. Bílý. 2002. Jewel beetles (Coleoptera, Buprestidae) from the Maltese Islands (central Mediterranean). Central Mediterranean Naturalist 3 (4): 181–188.

Ferreting up a Bird's Nose

Mites, as I may have commented before, seem to have an almost fractal level of diversity: the closer you look, the more there is of it. This is nowhere more apparent than when it comes to parasitic mites which infest almost any host in any way that you can imagine. For the subject of this post, I drew one such mite: the honeyeater nasal mite Ptilonyssus myzanthae.

Venter (left) and dorsum of female Ptilonyssus myzanthae, from Domrow (1964). The scale bar equals 500 µm.

Bird nasal mites of the family Rhinonyssidae are, as their name indicates, inhabitants of the nasal passages of birds. General adaptations of the family for their parasitic lifestyle include tendencies towards reduction of the body sclerotisation and reduction in the length and number of setae. They use the claws on their front legs to tear openings in the host's mucous membranes and then feed on its blood. Transmission of nasal mites seems to happen during bill-to-bill contact such as when parents are feeding their young or during mating activities, or indirectly through water or on the surface of perches or the like. Rhinonyssid nasal mites are not known to transmit any actual diseases between hosts but they can cause the formation of lesions or inflammation or the like. All in all, probably not very pleasant for the bird (see here for some more details).

Whole-body illustration of a different rhinonyssid species, from Greg Spicer.

Nevertheless, infection rates in bird populations can be very high and most (if not all) bird species will be host to some nasal mite species. Most species of nasal mite are very host specific, known on only one or a few bird species (it must be noted, though, that the question of just how many researchers choose to look up a bird's schnozz in search of mites may not be irrelevant here). Ptilonyssus myzanthae was described by Domrow (1964) from two species of honeyeater in Queensland, Australia: the noisy miner Manorina melanocephala and the little wattlebird Anthochaera chrysoptera. Distinctive features of this species compared to others in the genus include a subhexagonal anterior dorsal shield on the body, a narrow genital shield, and a divided pygidial shield (the small pair of shields near the rear of the dorsum). Both of the known hosts are widespread and common in eastern Australia and it is likely that this mite is similarly ubiquitous. Studies of honeyeater phylogeny tend to place the genera Manorina and Anthochaera as close relatives, so it is possible that P. myzanthae has been infesting them since before their lineages diverged. It would be worth looking for the species in other related honeyeaters to see if we find any further clues.

REFERENCE

Domrow, R. 1964. Fourteen species of Ptilonyssus from Australian birds (Acarina, Laelapidae). Acarologia 6 (4): 595–623.

Guenons

The common perception of monkeys tends to be dominated by a relatively small number of species, generally those most commonly seen in zoos, such as capuchins, macaques, baboons or tamarins. But as is usual when it comes to biodiversity, there are a lot of varieties of monkey out there that may be less familiar to the general public. This post will look at one of those less familiar groups: the guenons of the genus Cercopithecus.

Moustached monkey Cercopithecus cephus, copyright Rufus46.

Cercopithecus is a genus of monkeys found in sub-Saharan Africa. The exact number of species has shifted around a bit (though it currently sits around twenty). Some authors have included almost all species of the monkey tribe Cercopithecini, characterised by self-sharpening lower incisors and four cusps on the lower third molars (Lo Bianco et al. 2017), in the single genus Cercopithecus. However, more recent authors have tended to favour dividing this tribe between a number of phylogenetically and ecologically distinct genera. Under this latter system, Cercopithecus would be restricted to a group of more arboreal species. A number of these species have been divided between multiple subspecies and there may be some back and forthing about what is recognised as which. One entirely new species, previously not even known as a subspecies, was described as recently as 2012 by Hart et al.: the lesula C. lomamiensis.

Young female lesula Cercopithecus lomamiensis, from Hart et al. (2012).

A large part of this uncertainty relates to the fact that Cercopithecus species are most diverse in dense forests of western and central Africa, in regions that may be both physically and politically difficult to access and which have received less attention from researchers than others. The aforementioned lesula was described from the Lomami River basin near the middle of the Democratic Republic of the Congo (the one that used to be called Zaire, though I think they prefer not to talk about it). Another Congolese species, the dryas monkey C. dryas, was long thought to be known from only a single juvenile specimen until it was realised that the adult form had been described as a separate species C. salongo. It's still only known from a handful of records and is thought to be critically endangered.

Diana monkey Cercopithecus diana, copyright Ikmo-ned.

Some species of guenon are notable for their striking colour patterns. Perhaps the species I've most commonly seen in zoos is the diana monkey C. diana, native to the region between Sierra Leone* and the Côte d'Ivoire (though it is possible that at least some of these 'diana monkeys' were actually roloway monkeys C. roloway, until recently treated as a subspecies of the diana monkey). This species has a bright white throat, chest and front of the fore arms that contrasts with the black face and dark grey back. It also has a white band across its brow which is where its name comes from, the band having been thought to resemble the crescent moon. De Brazza's monkey C. neglectus of central Africa has a crescent-shaped orange mark on its forehead and a white muzzle and beard, making it look reminiscent of a grumpy old man (Wikipedia claims that it has also been dubbed the 'Ayatollah monkey'). Male De Brazza's monkeys also have a bright blue scrotum. Large bright blue patches are also present around the scrotum and backside of males in the lesula and the owl-faced monkey C. hamlyni.

*Having grown up in New Zealand in the 1980s, I'm going to have that stuck in my head all day now. Nothing to do with the subject of this post, I just thought I'd mention it.

Male De Brazza's monkey Cercopithecus neglectus, copyright Heather Paul.

Guenons tend to be found living in small troops consisting of one adult male and a harem of females with their offspring; unmated adult males will be found living solitary lives. Males are usually larger than females, up to about 1.5 times the size of their mates. Multiple guenon species may be found in a single location though closely related species tend not to overlap. Famously, hybrids have been described from the Kibale forest in Uganda between the blue monkey C. mitis and the red-tailed monkey C. ascanius, two species that are quite distinct in external appearance. Larger species such as the spot-nosed monkey C. nictitans and the blue monkey tend to eat a higher proportion of leaves in their diet. Smaller species such as the mona monkey C. mona may be more insectivorous (Macdonald 1984).

Blue monkeys Cercopithecus mitis stuhlmanni, copyright Charles J. Sharp.

The origins of the Cercopithecus radiation are relatively recent with the tribe Cercopithecini as a whole probably originating in the late Miocene (Lo Bianco et al. 2017). Karyological studies of the group show a wide variation in chromosome number from 58 in the diana monkey to 72 in the blue monkey. In contrast, the sister group of the Cercopithecini, the Papionini (which includes baboons and macaques) always has 42 chromosomes. Polymorphism in chromosome arrangements has also been described within Cercopithecus species. The possibility that this gene variability is related to their rate of speciation remains a worthwhile line of study.

REFERENCES

Hart, J. A., K. M. Detwiler, C. C. Gilbert, A. S. Burrell, J. L. Fuller, M. Emetshu, T. B. Hart, A. Vosper, E. J. Sargis & A. J. Tosi. 2012. Lesula: a new species of Cercopithecus monkey endemic to the Democratic Republic of Congo and implications for conservation of Congo's central basin. PLoS One 7 (9): e44271.

Lo Bianco, S., J. C. Masters & L. Sineo. 2017. The evolution of the Cercopithecini: a (post)modern synthesis. Evolutionary Anthropology 26: 336–349.

Macdonald, D. (ed.) 1984. All the World's Animals: Primates. Torstar Books: New York.

Matoniaceae: Ferns with a Heritage

Ferns are one of those groups of organisms, like sharks and cockroaches, that are not really as ancient as most people imagine. For all that ferns are indelibly associated in the public conscience with antediluvian imagery of steamy coal swamps and great lumbering reptiles, the dominant fern groups that can be seen today did not arise until the Cretaceous and diversified as part of a flora that would have been largely modern in appearance (Schneider et al. 2004). Nevertheless, there are some fern lineages around today that might be said to have a genuine claim to a more venerable pedigree. One such group is the Matoniaceae.

Matonia pectinata, copyright Ahmad Fuad Morad.

In the modern flora, the Matoniaceae are a small family, including only three or four species in two genera, Matonia and Phanerosorus, found in south-east Asia (Lindsay et al. 2003). The two genera are distinct in appearance and habits. Matonia is found on more or less exposed montane summits and ridges and has pedate fronds with pectinate pinnae radiating from an erect central stipe that may grow well over a metre in height. Phanerosorus is found on vertical limestone walls and has pendulous, branching fronds whose pinnae are simple or more weakly pectinate (Kato & Setoguchi 1999). Both genera have the fronds arising from a long, hairy, creeping rhizome. Lateral veins in the pinnules show one or more bifurcations and in Matonia these branching forks may anastomose with each other to form a reticulate vein pattern. The genera also share features of the reproductive anatomy such as massive, deciduous sporangia.

Phanerosorus major, copyright Wally Suarez.

The fossil record of Matoniaceae indicates that they were far more widespread in the past; indeed, Matonia was illustrated from preserved compression fossils before it was described as a living genus (Klavins et al. 2004). Leaf fossils of Matoniaceae go back to the Late Triassic, and the Middle Triassic stem taxon Soloropteris rupex has been more tentatively assigned to the family (van Konijnenburg-van Cittert 1993). Fossil forms are more similar to Matonia in overall appearance and this is presumed to be the plesiomorphic morphology for the family. A certain resemblance exists between Phanerosorus and younger fronds of Matonia and it seems likely that the former genus evolved from Matonia-like forms by a process of paedomorphosis (Kato & Setoguchi 1998). The family was most widespread during the Jurassic and Early Cretaceous but became extinct in temperate regions of the Northern Hemisphere during the Late Cretaceous. It persisted longer in the Southern Hemisphere, with the stem taxon Heweria kempii known from the Early Tertiary of Australia, but at some point following that it became restricted to its modern localised range.

REFERENCES

Kato, M., & H. Setoguchi. 1999. An rbcL-based phylogeny and heteroblastic leaf morphology of Matoniaceae. Systematic Botany 23 (4): 391–400.

Klavins, S. D., T. N. Taylor & E. L. Taylor. 2004. Matoniaceous ferns (Gleicheniales) from the Middle Triassic of Antactica. Journal of Paleontology 78 (1): 211-217.

Konijnenburg-van Cittert, J. H. A. van. 1993. A review of the Matoniaceae based on in situ spores. Review of Palaeobotany and Palynology 78: 235–267.

Lindsay, S., S. Suddee, D. J. Middleton & R. Pooma. 2003. Matoniaceae (Pteridophyta)—a new family record for Thailand. Thai Forestry Bulletin 31: 47–52.

Schneider, H., E. Schuettpelz, K. M. Pryer, R. Cranfill, S. Magallón & R. Lupia. 2004. Ferns diversified in the shadow of angiosperms. Nature 428: 553–557.

Radiolarians of the Globe

Radiolarians are one of the primary groups of micro-organisms to be found among the marine plankton. These unicellular greeblies are justly famed for their intricate mineralised skeletons, leading to their comparison to living works of art. Today's post is covering one particular group of radiolarians, the Spumellaria.

Haeckel's (1899–1904) figure of Hexancistra quadricuspis from Kunstformen der Natur.

Spumellaria are one of the major subdivisions of radiolarians, containing species characterised by a generally spherical skeletal form. Many authors have also included the colonial radiolarians, which often lack a coherent skeleton and may form colonies up to several metres long, in the Spumellaria but these have more recently been treated as a distinct group. The skeleton of radiolarians is entirely enclosed by cytoplasm in life, though in those species in which the skeleton bears radiating spines, those spines may extend beyond the main body of the cell and be covered by only a thin cytoplasmic layer distally. In Spumellaria and anothre major radiolarian group, the Nassellaria, the skeleton is composed of opal, making these living jewels in more ways than one (another radiolarian group, the Acantharea, composes its skeleton of a mineral by the somewhat ethereal-sounding name of celestite). The cytoplasm of radiolarians is internally divided by a fibrous capsule into two structurally distinct sections, the internal endoplasm and external ectoplasm. The denser endoplasm contains most of the cell's primary organelles, such as the nucleus and large mitochondria. Linear microtubular structures called axonemes extend outwards from the endoplasm, passing through pores in the internal capsule and through the ectoplasm. The ectoplasm is often frothy in texture, containing an extensive assemblage of cellular vacuoles. In many of these radiolarians, some of these ectoplasmic vacuoles will house symbiotic algae that contribute much of the radiolarian's nutrition. Otherwise, radiolarians may feed on other small organisms that are captured on axopodia supported by the axonemes, which in spumellarians radiate outwards from the cell body in all directions. Extension and contraction of the axopodia may also help maintain the radiolarian's position in the water column (Cachon et al. 1990).

Schematic diagram of organisation of Didymocyrtis tetrathalamus from Sugiyama & Anderson (1998).

In many spumellarians, the basic skeletal architecture is one of nested spheres and/or globules. Sugiyama & Anderson's (1998) description of Didymocyrtis tetrathalamus stands as a fairly typical example. The central part of the skeleton is a double sphere well within the cytoplasmic capsule with the lobate nucleus contained in the spaces between the spheres. Radiating axes connect the inner shell with an outer shell mostly just outside the capsule (the capsular wall crosses the skeleton at some points). In Didymocyrtis, this outer shell is not spherical but a sort of peanut shape. At each end of the 'peanut', a further cap is added beyond the main shell. In many spumellarians, the outer shell appears spongy in texture, being constructed of densely criss-crossing fine opal fibres. There may be further extensions of the outer shell such as polar spines or funnels.

Not surprisingly, spumellarian classification has most commonly been based on skeletal architecture. Some attempts have been made to construct alternative classifications incorporating cytoplasmic features such as the relationship between the axopods and the nucleus (Cachon et al. 1990) but, as these systems require access to live specimens to place taxa, they have been less popular (especially as most people studying radiolarians are primarily working with fossil material). A phylogenetic study of recent spumellarians by Ishitani et al. (2012) found evidence for two main lineages within the class that differ in ecology. One, including the families Pyloniidae and Sponguridae, contained species found in temperate and cold waters. The other, including the families Astrosphaeridae, Hexalonchidae and Coccodiscidae, was found in tropical waters. Species assigned to the family Spongodiscidae were divided between both lineages, suggesting the need for some further tinkering with the morphological classification.

REFERENCES

Cachon, J., M. Cachon & K. W. Estep. 1990. Phylum Actinopoda. Classes Polycystina (=Radiolaria) and Phaeodaria. In: Margulis, L., J. O. Corliss, M. Melkonian & D. J. Chapman (eds) Handbook of Protoctista. The structure, cultivation, habitats and life histories of the eukaryotic microorganisms and their descendants exclusive of animals, plants and fungi. A guide to the algae, ciliates, foraminifera, sporozoa, water molds, slime molds and the other protoctists pp. 334–346. Jones & Bartlett Publishers: Boston.

Ishitani, Y., Y. Ujiié, C. de Vargas, F. Not & K. Takahashi. 2012. Two distinct lineages in the radiolarian order Spumellaria having different ecological preferences. Deep-Sea Research II 61–64: 172–178.

Sugiyama, K., & O. R. Anderson. 1998. Cytoplasmic organization and symbiotic associations of Didymocyrtis tetrathalamus (Haeckel) (Spumellaria, Radiolaria). Micropaleontology 44 (3): 277–289.