Field of Science

Sea Spiders

With arthropods being such a massively diverse sector of the global biota (and even that feels like an understatement; describing arthropods as 'very diverse' seems a bit like describing the Andromeda Galaxy as 'very far away'), it is only to be expected that it contains some very weird corners. And definitely among the weirder of those corners are the Pycnogonida, commonly known as the 'sea spiders'.

Anoplodactylus evansi, copyright Mick Harris & Claudia Arango.


Pycnogonids are a group of marine arthropods found around the world (not actual spiders, of course, though honest-to-goodness marine spiders are a thing that does exist). Their relationships to other arthropods have long been in dispute but the majority view is that they are distant relatives of the terrestrial arachnids. Pycnogonids are not uncommon in both coastal and deep-sea habitats but tend to go unnoticed: they feed on rock-encrusting colonial animals such as hydrozoans and are often coloured to disguise themselves against their prey. If one ever does see a sea spider, the first thing to stand out about them is how they are made of legs. The central body is often remarkably small compared to its limbs, to the extent that the dubbing of pycnogonids as 'no-bodies' by an early 20th Century author has become something of a cliché. Certain major organs, such as the gonads and parts of the digestive system, have even been diverted into the legs to make up for the lack of space in the body. Most pycnogonids possess four pairs of walking legs though there are species with more. At the front of the body on the underside of the head is a large proboscis that is used for sucking the juices out of prey, flanked by pairs of pincer-bearing chelifores and/or palps used for tearing it open. Near the first pair of walking legs there is often a pair of slender leg-like appendages known as the ovigers, used for carrying bundles of eggs until they hatch. The greater part of the body behind the head is taken up by the leg-bearing thorax; the legless abdomen is reduced to the merest nub like the docked tail of a dog.

Close-up on preserved male Anoplodactylus lentus, from Florida Museum of Natural History.


One of the largest recognised genera of pycnogonids is Anoplodactylus, with over 130 species worldwide and many continuing to be described (Lucena et al. 2015). This genus can be distinguished by the possession of chelifores with functional chelae (pincers) but palps are absent or reduced to buds. Both the chelifores and the proboscis are relatively short (Child 1998). Ovigers are five- or six-segmented and present in males only (male care of eggs is the standard pattern among pycnogonids). Species vary from 0.6 to 6 millimetres in body length. The majority of species of Anoplodactylus are found in shallow waters in temperate and tropical regions with a smaller number of species found in polar and deep waters. Alvarez & Ojeda (2018) record finding a single specimen of the species A. batangensis among vegetation on the surface of an anchialine pool in the Yucatan Peninsula of Mexico. Though the surface of these pools is more or less fresh water, deeper sections are saline owing to subterranean connections to the sea. The collection of a pycnogonid near the surface of this pool suggests an ability to adjust to very low salinity though one questions whether it would be able to survive indefinitely.

Larvae of Anoplodactylus are very small compared to those of other pycnogonids and have what has been termed an 'encysting' development (Burris 2011). As bizarre as the appearance of adult pycnogonids is, their larvae are arguably even weirder, being essentially nothing more than a head bearing chelifores, proboscis, and two pairs of undifferentiated appendages. The remaining segments of the body are added over the course of development. In Anoplodactylus, the larvae develop as parasites, forming a cyst in the gastrocoel (the stomach cavity) of cnidarians (having presumably been placed there somehow by their fathers, though I haven't found if we know how). They become free-living upon reaching the first juvenile stage, emerging from their host to pursue their predatory lives.

REFERENCES

Alvarez, F., & M. Ojeda. 2018. First record of a sea spider (Pycnogonida) from an anchialine habitat. Latin American Journal of Aquatic Research 46 (1): 219–224.

Burris, Z. P. 2011. Larval morphologies and potential developmental modes of eight sea spider species (Arthropoda: Pycnogonida) from the southern Oregon coast. Journal of the Marine Biological Association of the United Kingdom 91 (4): 845–855.

Child, C. A. 1998. The Marine Fauna of New Zealand: Pycnogonida (Sea Spiders). National Institute of Water and Atmospheric Research (NIWA).

Lucena, R. A., J. F. de Araújo & M. L. Christoffersen. 2015. A new species of Anoplodactylus (Pycnogonida: Phoxichilidiidae) from Brazil, with a case of gynandromorphism in Anoplodactylus eroticus Stock, 1968. Zootaxa 4000 (4): 428–444.

Of Hawks and Marble

The acanthomorph fishes (a major clade of fishes mostly characterised by the presence of spines at the front of the dorsal fin) have long been recognised as a particularly thorny problem for higher-level systematics. Morphological relationships between many of the large number of families recognised in this clade have been almost impossible to unravel, and it is only in recent years that molecular analyses have been able to start making sense of the rapid divergences. Nevertheless, there are some subgroups of the acanthomorphs that have been recognised for a long time and which recent analyses have continued to support. One such group is the cirrhitoids.

Spottedtail morwong Goniistius zonatus, copyright Joi Ito.


Variously referred to in recent sources as the Cirrhitoidea, the Cirrhitoidei, or the Cirrhitiformes, the cirrhitoids include about eighty known species usually divided between five families. These are the hawkfishes of the Cirrhitidae, the trumpeters and morwongs of the Latridae, the Cheilodactylus fingerfins, the Chironemus kelpfishes and the Aplodactylus marblefishes (the morwongs were historically placed with the fingerfins in the Cheilodactylidae but have recently been transferred based on molecular data—Ludt et al. 2019). The largest cirrhitoid is the dusky morwong Dactylophora nigricans of western and southern Australia, growing to 1.2 metres in length, but most species are only a fraction of this size. Some of the largest species are of note to fisheries. Cirrhitoids are generally inhabitants of reefs, mostly feeding on benthic invertebrates such as crustaceans. They have long been recognised as a coherent group owing to their distinctive fin structure. The lower rays of the pectoral fins are not branched, and in a number of species they are thickened and protrude past the fin membrane (observant readers of this post may have already noticed a theme in many of the genus names given to cirrhitoids, relating to this feature). The pelvic fins are set well behind the pectoral fins. Other notable features of the clade include a relatively high number of vertebrae, a relatively low number of rays in the caudal fin, and the presence in juveniles of a fatty sac running along the fish's underside (Greenwood 1995).

Coral hawkfish Cirrhitichthys oxycephalus, copyright Aquaimages.


Both morphological and molecular studies have agreed that the hawkfishes of the Cirrhitidae represent the sister clade to the remaining cirrhitoids. Hawkfishes are brightly coloured inhabitants of the tropics, usually well under a foot in length. They are distinguished by bundles of trailing filaments emerging from the ends of the spines on the dorsal fin. Perhaps the most familiar member of the group is the longnose hawkfish Oxycirrhites typus, a regular in marine aquaria. However, this is also perhaps the most atypical member of the family as other species do not have the elongate snout. Hawkfishes commonly perch atop corals on the uppermost part of the reef, protected by the coral's sting and able to maintain a clear view of their surrounds. Wikipedia suggests that this behaviour is the inspiration for the name of 'hawkfish', but I'm not sure I buy this. I mean, it sounds plausible, but it also sounds like the sort of thing you would have to be diving below the reef to see. Vernacular names for fish tend to more often refer to things you might observe while hauling them onto a boat.

Marblefish Aplodactylus arctidens, copyright Peter Southwood.


The remaining cirrhitoids are all found in cooler waters, mostly in the Southern Hemisphere. Two species of Latridae, the redlip morwong Goniistius zebra and the spottedtail morwing G. zonatus, are found in the northern Pacific off the coast of eastern Asia (the kind of distribution shown by the genus Goniistius, where species are found in northern and southern temperate waters but not in the intervening tropics, is known as 'anti-tropical' and it's an interesting question how such a distribution would come to be). They are mostly found among rocky reefs, with the kelpfishes Chironemus and marblefishes Aplodactylus being particularly associated with patches of seaweed. The marblefishes feed on algae (particularly reds) as well as on some invertebrates and are characterised by a transverse mouth that is little or not protractible (Regan 1911). As noted above, the family Latridae has been inflated recently by the inclusion of most of the species previously included in the Cheilodactylidae. Cheilodactylus itself is now restricted to two species found around southern Africa. They differ from the remaining species in the latrids by the absence of a gas bladder as well as by elements of the skeleton. Many of the latrids are favourites of anglers, being well regarded as eating fish. By contrast, the herbivorous marblefishes are maligned as very poor fare and avoided. There's something to be said for eating your greens.

REFERENCES

Greenwood, P. H. 1995. A revised familial classification for certain cirrhitoid genera (Teleostei, Percoidei Cirrhitoidea), with comments on the group's monophyly and taxonomic ranking. Bulletin of the Natural History Museum of London (Zoology) 61 (1): 1–10.

Ludt, W. B., C. P. Burridge & P. Chakrabarty. 2019. A taxonomic revision of Cheilodactylidae and Latridae (Centrarchiformes: Cirrhitoidei) using morphological and genomic characters. Zootaxa 4585 (1): 121–141.

Nelson, J. S., T. C. Grande & M. V. H. Wilson. 2016. Fishes of the World 5th ed. Wiley.

Regan, C. T. 1911. On the cirrhitiform percoids. Journal of Natural History, series 8, 7: 259–262.

The New Centaury

In an earlier post, I described the South American flowering herbs known as the Coutoubeinae. In this post, I'm going to take a step back and look at a clade of which the coutoubeines form a part, the Chironieae.

Seaside centaury Centaurium littorale, copyright Anne Burgess.


The Chironieae are one of the major tribes of the flowering plant family Gentianaceae, including about 160 known species. Representatives are found in most parts of the world, though as part of the native flora in Australasia they do not extend past the north of Australia (some exotic species have been introduced further south). The Chironieae seem to primarily be supported as a clade on the basis of molecular data (Struwe et al. 2002). All members are herbs, from annuals to short-lived perennials. Most have an erect growing habit; members of the Caribbean genus Bisgoeppertia are annual climbers and some species of the Mexican genus Geniostemon are creeping perennials. There may or may not be a basal rosette of leaves, and a number of genera have winged stems. Flowers are solitary or borne in cymose or racemose inflorescences. These flowers are most commonly salver-shaped (that is, shaped like a flat dish) or tubular, and usually have four or five petals (some species may have up to twelve). The calyx is usually comprised of fused sepals and is unwinged and tubular. The fruit is usually a septicidal capsule (splitting along the septa between carpels), more rarely a berry.

Yellow centaury Cicendia filiformis, copyright Hajotthu.


Members of the Chironieae are divided between three subtribes that are mostly distinct both morphologically and biogeographically. As described in the previous post, the Neotropical Coutoubeinae are characterised by releasing their pollen in tetrads whereas the other subtribes shed individual pollen grains. The Canscorinae are mostly found in the Old World tropics and have white or cream-coloured flowers (less commonly yellow, pink or purple) with the calyx tube longer than the calyx lobes. The Chironiinae mostly includes found in northern temperate regions, as well as the southern African genera Chironia and probably the South American Zygostigma. Their flowers come in a range of colours—pink, yellow, purple or blue, but less commonly white or cream-coloured—and may have calyx lobes longer than the tube. Many chironiine flowers also have anthers that become spirally twisted after releasing pollen whereas those of Canscorinae are always straight. Molecular data usually support the monophyly of the three subtribes and the majority view seems to be that the temperate Chironiinae represent the sister group of a tropical clade of Canscorinae and Coutoubeinae.

Cultivated Eustoma, copyright Rameshng.


Perhaps the best known members of the Chironieae are the centauries of the genus Centaurium. Historically, about fifty species across the Holarctic have been included in this genus. However, phylogenetic studies have demonstrated that this broad sense of the genus is polyphyletic and thus it has been cut down to a group of about twenty species found in Europe and western Asia. The name 'centaury' refers to the use of common centaury Centaurium erythraea as a medicinal herb, after the legendary centaur healer Chiron. Other Old World species are now placed in the genus Schenkia whereas North American species form the genera Gyrandra and Zeltnera. The yellow centauries of Cicendia are small, filiform annuals native to Europe and the Americas that have been introduced to Australia. The rose gentians Sabatia of North America bear pinkish-purple flowers, often in lax cymes. There are also the prairie gentians of the genus Eustoma. Native to southern North America, these plants bear large, showy flowers that have become popular in cultivation. Commercially, they are labelled as lisianthus. This is not to confused with Lisianthius, a distinct genus of Gentianaceae, or Lisyanthus, a name that has been used in the past for members of yet another gentianaceous genus. Both of these belong to completely different tribes in the family, and may be subjects for another day.

REFERENCE

Struwe, L., J. W. Kadereit, J. Klackenberg, S. Nilsson, M. Thiv, K. B. von Hagen & V. A. Albert. 2002. Systematics, character evolution, and biogeography of Gentianaceae, including a new tribal and subtribal classification. In: Struwe, L., & V. A. Albert (eds) Gentianaceae: Systematics and Natural History pp. 21–309. Cambridge University Press: Cambridge.

Naviculi, Navicula

Diatoms are one of the most prominent groups of micro-algae in aquatic environments, perhaps more abundant than any other major group of aquatic organisms except bacteria. As such, they are a key component in many of the environmental processes that we ultimately depend on: food for aquatic animals, producers of oxygen, et cetera et cetera. To those who study them, they are also known for the intricate architecture of their silica walls. As well as being aesthetically pleasing, this architecture forms a key component of diatom classification. One of the most diverse groups of diatoms recognised has been the mega-genus Navicula.

Light microscope view of Navicula tripunctata, copyright Kristian Peters.

Historically, over one thousand species have been assigned to Navicula. Though more recent authors have restricted the name to a smaller, more tightly defined concept than before, it still contains some 200 or so species (Bruder & Medlin 2008). Species assigned to this genus are an elongate diamond or pill shape. Though the term 'navicula' can be translated from Latin as a small boat, and this is often assumed to be the name's origin, this is incorrect. Its original author, the French naturalist Jean-Baptiste Geneviève Marcellin Bory de Saint-Vincent, derived the name from the French term for a weaver's spindle (navette de tisserand; Cox 1999). A long fissure, the raphe, runs down the midline of each valve of the diatom wall; the diatom moves by extruding secretions through the raphe. In Navicula, the raphe is largely straight though it may be hooked at the ends of the valve. Perpendicular to or radiating from the raphe are striae formed of rows of openings (areolae); in Navicula, these areolae are more or less elongate with their long axes perpendicular to the line of the stria. In some species historically included in Navicula, the striae may be biseriate with two rows of areolae. Some authors have proposed recognising species with biseriate striae as a distinct genus Hippodonta. Cox (1999) disputed whether this distinction was enough to warrant a separate genus but Bruder & Medlin (2008) conducted a molecular phylogenetic analysis of naviculoid diatoms in which the one Hippodonta species included was placed as the sister taxon to Navicula sensu stricto. In distinguishing the genus Sellaphora from Navicula, Mann (1989) also identified a number of cytoplasmic features characteristic of Navicula sensu stricto, such as the possession of two distinct plastids per cell with rod-like pyrenoids.

SEM view of Navicula dobrinatemniskovae, from Van de Vijver et al. (2011). Scale bar = 1 µm.


Ecologically, the majority of species of Navicula sensu stricto (about 150 species) are found in freshwater environments (Bruder & Medlin 2008). In temperate and tropical regions, they are a diverse element of benthic diatom communities, but they are less predominant in coldwater habitats (Van de Vijver et al. 2011). They are most characteristic of meso- to eutrophic lakes and permanent waterways and Van de Vijver et al. (2011) therefore suggested that they might be less suited for the damp soils and temporary pools that dominate freshwater habitats in the frozen South. Nevertheless, these authors still managed to identify five previously unknown species from just this inhospitable region, giving some indication of what still remains to be discovered of this already diverse genus.

REFERENCES

Bruder, K., & L. K. Medlin. 2008. Morphological and molecular investigations of naviculoid diatoms. III. Hippodonta and Navicula s. s. Diatom Research 23 (2): 331–347.

Cox, E. J. 1999. Studies on the diatom genus Navicula Bory. VIII. Variation in valve morphology in relation to the generic diagnosis based on Navicula tripunctata (O. F. Müller) Bory. Diatom Research 14 (2): 207–237.

Mann, D. G. 1989. The diatom genus Sellaphora: separation from Navicula. British Phycological Journal 24 (1): 1–20.

Van de Vijver, B., R. Zidarova, M. Sterken, E. Verleyen, M. de Haan, W. Vyverman, F. Hinz & K. Sabbe. 2011. Revision of the genus Navicula s.s. (Bacillariophyceae) in inland waters of the sub-Antarctic and Antarctic with the description of five new species. Phycologia 50 (3): 281–297.

The Age of Olcostephaninae

Ammonites are among the iconic fossils of the Mesozoic. These shelled cephalopods dominated the oceans during their heyday and diversified into a wide array of taxa. Many of these have become significant for recognising particular periods in the earth's history; among these are members of the Olcostephaninae of the Early Cretaceous.

Olcostephanus astierianus, copyright Hectonichus.


The Olcostephaninae, as recognised by Wright et al. (1996), are known from the Valanginian and Hauterivian epochs of the Early Cretaceous, disappearing from the fossil record some time during the earlier part of the latter. The Valanginian ran from about 140 to 133 million years ago; the Hauterivian lasted for about three and a half million years after that. A brief reminder here: the Cretaceous lasted for a bloody long time, with more time separating the beginning and end of the Cretaceous than separates the end of the Cretaceous and today. One genus described from Pakistan, Provalanginites, has been supposed to come from the latest Jurassic but, as this is at least five million years earlier than any known olcostephanine anywhere else, its age is regarded as questionable. Olcostephanines can be very abundant in formations of the right age. A mass occurrence in the latest Valanginian of northwestern Europe has long been recognised as a geological marker, dubbed the 'Astierien Schichten' (Astieria being a synonym of Olcostephanus; Lukeneder 2004).

Saynoceras verrucosum, from here.


Olcostephanines are small to moderate-sized ammonites. Lukeneder (2004) refers to macroconches* of Olcostephanus guebhardi up to about ten centimetres in diameter. The olcostephanines pictured in Wright et al. (1996) seem to indicate an average size smaller than this and the group also includes a number of dwarf genera that look to only be a bit over one centimetre in diameter. The shell of olcostephanines is usually characterised by a pattern of transverse ribs coalescing in bundles to meet tubercles on the inner margin of the whorl. One dwarf genus, Saynoceras, has a stronger ornamentation of two rows of tubercles near the midline and outer margins of the whorls.

*A common pattern in ammonoids is the co-occurrence within a formation of distinct forms, termed 'macroconches' and 'microconches', that are broadly similar except in size and the configuration of the aperture (generally simple in macroconches but with protruding lappets in microconches). The most popular interpretation of this phenomenon is that the forms represent sexual dimorphism. Obviously which sex is which can't be known at this time though comparison with living cephalopods suggests that the macroconches may be female.

Valanginites nucleus, from here.


Olcostephanines are very similar in external appearance to the earlier subfamily Spiticeratinae (known from the very earliest part of the Cretaceous) and are likely to be descended from among that group. Though the Olcostephaninae themselves as currently recognised disappeared during the Hauterivian epoch, this may not have been the actual end of the olcostephanine lineage. The slightly later Holcodiscidae are very similar to the olcostephanines and some have questioned whether they even warrant separation. There is also a strong similarity between early members of the superfamily Desmoceratoidea and species of Olcostephanus (Wright et al. 1996). If this similarity also indicates ancestry, then the family line of the olcostephanines would continue right until the final extinction of the ammonites at the end of the Cretaceous.

REFERENCES

Lukeneder, A. 2004. The Olcostephanus level: an Upper Valanginian ammonoid mass-occurrence (Lower Cretaceous, Northern Calcareous Alps, Austria). Acta Geologica Polonica 54 (1): 23–33.

Wright, C. W., J. H. Calloman & M. K. Howarth. 1996. Treatise on Invertebrate Paleontology pt L. Mollusca 4, revised vol. 4. Cretaceous Ammonoidea. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

The Pireninae

The chalcidoid wasps are truly a remarkable array: tiny wonders coming in a bewildering variety of forms. For this post, I'm looking at the members of the chalcidoid subfamily Pireninae.

Macroglenes sp., copyright Charley Eiseman.


The Pireninae are currently recognised as one of the subfamilies of the Pteromalidae, a chalcidoid 'family' that is long overdue for reclassification as phylogenetic studies have agreed that it is extensively polyphyletic* (e.g. Heraty et al. 2013). The pirenines are very small wasps, about one to two millimetres in length. They've always struck me as having a fairly fly-like habitus: they lack the metallic coloration and strong sculpturing of many other pteromalids, often being uniformly black or yellow, and carry upright bristle-like setae on the head and mesosoma. Characteristic features of the Pireninae also include antennae inserted low on the face, reduced numbers of antennal segments (and hence often rather short antennae), a large clypeus that often protrudes ventrally, and a dorsally rounded mesosoma often with deeply impressed notauli (longitudinal grooves on the mesoscutum) (Bouček 1988). About ten genera are currently recognised in the subfamily. Perhaps the most remarkable is the genus Zebe, named by John La Salle in 2005 from a single female that he says, at the time, had stymied multiple hymenopterists as to what it might be for two decades. Zebe has legs with four-segmented tarsi, instead of the five-segmented tarsi of other pteromalids, and the female has a long horn extending forward from the mesoscutum and hanging over the head. As in other micro-wasps with comparable structures, this horn probably provides space for the retraction of an extraordinarily long ovipositor.

*But just in case anyone who stands to have some influence is reading, I will point out that the number of subfamilies that need to excised from the Pteromalidae could be kept to a minimum if the family is expanded to include the Ormyridae, Torymidae, Eucharitidae and Perilampidae. Bonus points that these are the families that are the hardest to distinguish from pteromalids to begin with.

Female Zebe cornutus, from Mitroiu (2011).


The life habits of most pirenines are very little known. Those whose hosts are known develop as parasites of Cecidomyiidae, gall midges, and may be found in association with the galls produced by those flies on various plants. Species of the genus Macrogelenes attack cecidomyiids associated with grasses, and some have been investigated as control agents for midges on commercial crops. So these tiny little wasps could prove themselves very valuable to humans.

REFERENCES

Bouček, Z. 1988. Australasian Chalcidoidea (Hymenoptera): A biosystematic revision of genera of fourteen families, with a reclassification of species. CAB International: Wallingford (UK).

Heraty, J. M., R. A. Burks, A. Cruaud, G. A. P. Gibson, J. Liljeblad, J. Munro, J.-Y. Rasplus, G. Delvare, P. Janšta, A. Gumovsky, J. Huber, J. B. Woolley, L. Krogmann, S. Heydon, A. Polaszek, S. Schmidt, D. C. Darling, M. W. Gates, J. Mottern, E. Murray, A. D. Molin, S. Triapitsyn, H. Baur, J. D. Pinto, S. van Noort, J. George & M. Yoder. 2013. A phylogenetic analysis of the megadiverse Chalcidoidea (Hymenoptera). Cladistics 29: 466–542.

La Salle, J. 2005. Zebe cornutus gen. et sp. nov., a new Pireninae (Hymenoptera: Pteromalidae) with 4-segmented tarsi and a mesoscutal horn. Acta Societatis Zoologicae Bohemoslovenicae 69: 193–197.

Snakes and Lace

The holometabolous insects—that is, the clade containing most insects with a complex life cycle including differentiated larval and pupal stages—is one of the most extensive radiations of animals on this planet. Much of this diversity is assigned to four major orders: wasps, moths, beetles and flies. But there are also a number of smaller lineages making up the holometabolous insects. Among these are the lacewings and their relatives in the clade Neuropterida.

Female snakefly Puncha ratzeburgi, copyright Hectonichus.


Modern members of the Neuropterida are generally recognised as belonging to three orders—the lacewings and ant-lions in the Neuroptera, the snakeflies in the Raphidioptera, and the alderflies and dobsonflies in the Megaloptera—though go back a few decades and you may find texts referring to a single order Neuroptera. A number of authors have advocated for use of the name 'Planipennia' for the lacewing order to avoid confusion with the broader sense of Neuroptera but, while a case could certainly be made for this usage, it's just never really caught on. Most neuropteridans are fairly similar in overall appearance: long-bodied insects with well developed wings with numerous crossveins. Of the living holometabolous insects, they probably bear the greatest overall resemblance to the clade's ancestors and hence they are commonly thought of as 'relicts'. However, they do possess their own specialisations and are not primitive in every regard (for instance, the most primitive egg-laying apparatus among holometabolous insects belong to wasps). Species of Neuropterida are mostly predators as larvae. The larvae of the lacewing family Ithonidae may possibly feed on decaying plant matter though we don't know for certain (Grimaldi & Engel 2005). Adults are predators and/or pollen-feeders, or may not feed at all in some short-lived forms.

Male (above) and female dobsonflies Corydalus cornutus, copyright Didier Descouens.


The exact relationships between the neuropteridan orders have been debated over the years. Though most of their obvious similaities to each other represent shared ancestral features, there is a broad consensus that they do indeed form a clade. There has also been little, if any, question of the monophyly of the Raphidioptera and Neuroptera; the monophyly of Megaloptera has been more debated but seems more likely than not. Most recent studies have suggested that the Raphidioptera are the sister group to a clade of the other two orders (Engel et al. 2018). Raphidioptera are the least diverse of the generally recognised living orders of insects with about 250 known species. They are found in cooler regions of the Northern Hemisphere—in the temperate zone or at higher elevations in lower latitudes—and are completely absent from the Southern Hemisphere (Aspöck & Aspöck, 1991, refer to a failed attempt to introduce them to Australia and New Zealand but provide no details why such a thing was tried in the first place). They are characterised by a notably elongate prothorax (the first segment of the thorax) which explains the vernacular name of 'snakefly'. Larvae live under bark or in litter and moult into pupae with the onset of cold weather. The pupae of Raphidioptera and Megaloptera are primitive in aspect, with legs separate from the body wall, and are highly mobile. Engel et al. (2018) even refer to the pupae of Raphidioptera as 'active predators' but I've not been able to find corroborating details for that remarkable description.

The Megaloptera are often particularly large neuropteridans, reaching up to twenty centimetres in wingspan, and comprise a bit less than 400 species worldwide, mostly found in temperate regions. Larvae are aquatic, living under rocks and debris, and characterised by the presence of filamentous lateral gills on the abdomen. Adults are short-lived and feed little if at all. Male dobsonflies (of the subfamily Corydalinae) possess spectacularly large, curved mandibles of largely unknown purpose; certainly they do not seem to use them for biting.

Mantisfly Mantispa styriaca, a raptorial lacewing, copyright Gilles San Martin.


The largest of the three orders, by a considerable margin, is the Neuroptera with over 5700 known species. Needless to say, this level of species diversity is associated with a high diversity of appearances and lifestyles, too many to cover adequately here. The larvae of two families of Neuroptera, the Nevrorthidae and Sisyridae, are aquatic and there has been a long-running debate whether this aquatic habit is an ancestral feature of the order shared with the Megaloptera (Nevrorthidae larvae are generalist predators, Sisyridae are specialised feeders on freshwater sponges and bryozoans). However, recent phylogenetic studies (e.g. Vasilikopoulos et al. 2020) do not agree with earlier hypotheses that the Nevrorthidae represent the sister taxon of the remaining Neuroptera. Instead, Nevrorthidae and Sisyridae may form a clade with the Osmylidae, a family whose larvae are not aquatic but often inhabit damp stream banks. The aquatic Neuroptera probably entered the water independently of the alderflies. The current favourites for the sister clade of other neuropterans are the dustywings of the Coniopterygidae, a group of small neuropterans with reduced wing venation that have historically been difficult to place owing to their derived features.

An unidentified dustywing, Coniopterygidae, copyright Katja Schulz.


A fourth order has often been associated with the Neuropterida, the extinct Glosselytrodea. Glosselytrodeans are small insects known from the Late Permian to the Jurassic, characterised by wings bearing dense cross-veins of which the fore pair would have had a leathery appearance in life (not dissimilar in texture to the fore wings of grasshoppers and other Orthoptera). Other than the wings, the features of glosselytrodeans are poorly known: they seem to have been hypognathous (i.e. had the head directed downwards) with slender legs (Grimaldi & Engel 2005). Connections to Neuropterida are based on features of the wing venation but cannot be considered strongly supported. Other authors have regarded them as of uncertain position within the broader holometabolous clade, or even as more closely related to the Orthoptera than any Holometabola. Unless more complete remains should come to light, it seems likely that the question will remain open.

REFERENCES

Aspöck, H., & U. Aspöck. 1991. Raphidioptera (snake-flies, camelneck-flies). In: CSIRO. The Insects of Australia: A textbook for students and research workers 2nd ed. vol. 1 pp. 521–524. Melbourne University Press.

Engel, M. S., S. L. Winterton & L. C. V. Breitkreuz. 2018. Phylogeny and evolution of Neuropterida: where have wings of lace taken us? Annual Review of Entomology 63: 531–551.

Grimaldi, D., & M. S. Engel. 2005. Evolution of the Insects. Cambridge University Press: New York.

Vasilikopoulos, A., B. Misof, K. Meusemann, D. Lieberz, T. Flouri, R. G. Beutel, O. Niehuis, T. Wappler, J. Rust, R. S. Peters, A. Donath, L. Podsiadlowski, C. Mayer, D. Bartel, A. Böhm, S. Liu, P. Kapli, C. Greve, J. E. Jepson, X. Liu, X. Zhou, H. Aspöck & U. Aspöck. 2020. An integrative phylogenomic approach to elucidate the evolutionary history and divergence times of Neuropterida (Insecta: Holometabola). BMC Evolutionary Biology 20: 64.