The Bolivinitids

The Cretaceous was a period of significant innovation in the evolution of Foraminifera with a number of distinct new lineages making their appearance during this period. Among those, appearing in the latter part of the Cretaceous, were the first members of the modern family Bolivinitidae.

Bolivinita costifera, from the Smithsonian National Museum of Natural History.

The Bolivinitidae are free-living benthic forams with a calcareous, hyaline (glassy) test. The overall shape of the test is elongate with chambers arranged in biserial coils (that is, there are two chambers per loop). The terminal aperture is usually loop-shaped with a surrounding lip. Inside the chamber, a tooth plate (an inner protrusion of the test) runs from the aperture to the opening of the previous chamber and may protrude through the aperture (Revets 1996).

Representatives of the Bolivinitidae are found in a wide range of depths, from the shallow waters of the ocean to the bathyal zone. They may be among the most abundant forams in areas of low oxygen concentrations and are commonly associated with sustained organic matter input (Erdem & Schönfeld 2017). In other words, these are muck-lovers. Individuals growing in low oxygen conditions tend to show less pronounced surface sculpture on the test than those where the oxygen levels are higher. Conversely, individuals at deeper levels tend to be larger overall than those in shallower waters (Brun et al. 1984). As such, bolivinitids have received their fair share of attention as potential indicators of changes in environmental condition over time.

REFERENCES

Brun, L., M. A. Chierici & M. Meijer. 1984. Evolution and morphological variations of the principal species of Bolivinitidae in the Tertiary of the Gulf of Guinea. Géologie Méditerranéenne 11 (1): 13–57.

Erdem, Z., & J. Schönfeld. 2017. Pleistocene to Holocene benthic foraminiferal assemblages from the Peruvian continental margin. Palaeontologica Electronica 20.2.35A: 1–32.

Revets, S. A. 1996. The generic revision of the Bolivinitidae Cushman, 1927. Cushman Foundation for Foraminiferal Research Special Publication 34: 1–55.

Crossing the Busycon

I must admit that when I think about the biodiversity hotspots of the world, the eastern seabord of the United States would not be among the first regions to come to mind. But for this post, I'm looking at a dramatic and eye-catching radiation of molluscs for which this is their centre of distribution. I speak of the giant whelks of the Busyconidae.

Left-handed whelk or lightning whelk Sinistrofulgur sinistrum, copyright Andrea Westmoreland.

Busyconid whelks first appeared in the waters of eastern North America during the early Oligocene, about 32 million years ago, in what was then the Mississippi Sea and is now the Mississippi River Basin. As the oceans receded from the Mississippi, they spread into the Gulf of Mexico and are now found between Massachusetts in the north and the Yucatan Peninsula in the south. Except for an introduced population of the channeled whelk Busycotypus canaliculatus that has become established in San Francisco Bay in California since the 1930s, the family has never been found elsewhere. These are remarkably large snails: smaller examples are still more than five centimetres in length, and the largest of all get close to a foot (Petuch et al. 2015). Mature shells have a large body whorl, generally higher than the visible spire, with a long siphonal canal. SCulpture of the shell, if present, is dominated by spiral elements, and the shoulder of the whorls may be marked by prominent carinae and/or spines. As is standard for neogastropods, the classification of this group has shifted around a bit over the years, whether treated as their own family or as a subfamily Busyconinae of the related families Buccinidae or Melongenidae. In a recent review of the busyconids, Petuch et al. (2015) recognised fifteen living species in six genera. The number of fossil species that has been described is significantly larger (over one hundred); not surprisingly, these large solid shells have an excellent fossil record. However, it is worth noting that some of the living species may be remarkably variable in shell morphology and I don't know whether fossil representatives have been subject to the same systematic scrutiny.

Knobbed whelk Busycon carica, copyright Matt Tillett.

All busyconids are predators on bivalves, particularly on burrowing clams. In general, the whelk envelops its victim in its muscular foot and then uses the edge of the shell lip to open the clam's shell, allowing the whelk to insert its radula and rasp out the clam's flesh. The preferred method of opening the shell depends on the species of whelk and may be classed as 'wedging' and 'chipping'. 'Wedging' is the most straightforward method and believed to be the more primitive; wedgers insert the shell lip into the gap between valves and directly force them apart and/or prevent the clam shell from closing. 'Chipping' is more involved and performed by members of the genera Busycon and Sinistrofulgur. In this method, the edge of the whelk shell is rhythmically pounded against the commissure between the clam shell valves, progressively wearing at the valve margins until enough of an opening has been made to insert the radula. The process may take multiple hours of patient hammering. Chipping requires more power and a heavier shell than wedging (chipping whelks may damage their own shell as well as the prey's) but also allows the whelk to attack thicker-shelled clams.

Though each species of busyconid will generally use one or the other method of opening prey, there are borderline examples. Larger individuals of Busycotypus canaliculatus, usually a wedger, may adopt a process like chipping though their attacks on the prey shell are usually less systematic than true chippers. And while I haven't found anywhere that says as much, I suspect that young chippers may spend the earlier parts of their life as wedgers untill they have developed the shell strength for chipping. Dietl (2004) suggested that chipping behaviour may have originated twice among busyconids, based on the fossil evidence of its traces left on clam shells. The modern chippers appear to derive from a single origin in the later Pliocene. However, evidence of an earlier and now seemingly extinct chipping lineage was also found in shells from the late Miocene. These earlier chippers seemingly did not belong to any of the modern chipping genera which are not known from the Miocene deposits in which chipped clams were found. Instead, Dietl proposed that the culprit was a large Busycotypus.

Channeled whelk Busycotypus canaliculatus laying a string of egg cases, copyright Eric Heupel.

Busyconid whelks have long been of significance to people living in areas where they are found. Not only are the shells eye-catching and ornamental objects in themselves, the animals are also harvested for food (though their meat is often sold under misleading names such as 'conch' or 'clam strips'). Archaeological examples have been found of busycon shells being used for tools; Petuch et al. (2015) illustrate an example of a left-handed whelk Sinistrofulgur sinistrum shell with holes drilled into it that would have allowed it to be attached to a stick and used as a shovel. These animals are truly an icon of North America's eastern seaboard.

REFERENCES

Dietl, G. P. 2004. Origins and circumstances of adaptive divergence in whelk feeding behavior. Palaeogeography, Palaeoclimatology, Palaeoecology 208: 279–291.

Petuch, E. J., R. F. Myers & D. P. Berschauer. 2015. The Living and Fossil Busycon Whelks: Iconic Mollusks of Eastern North America. San Diego Shell Club, Inc.

Pompilus: Spider Wasps of the Dunes

I've commented before on the difficulties that can be attendent on identifying spider wasps (Pompilidae), one of those groups that combine a high species diversity with a tendency to be morphologically conservative. As a result, the taxonomic history of this group has been one of shifting generic concepts and ill-defined wastebaskets. Not surprisingly, one of the main victims of this uncertainty has been the type genus Pompilus. Historically used to cover a significant percentage of all spider wasps, the name Pompilus is now restricted to a small cluster of species inhabiting the Old World.

Pompilus cinereus, copyright Martin Grimm.

The genus Pompilus and its history were last revised in detail by Day (1981) who recognised seven species associated with more or less open, sandy habitats. The most widespread and best-known of these is Pompilus cinereus, found over wide parts of Eurasia, Africa and Australia, often alongside bodies of water. This species shows a wide range of morphological variation across its range but Day (1981) declared himself unable to sensibly correlate this variation with discrete populations. The possibility remains that further studies may identify P. cinereus as a species complex. The other species in the genus, P. mirandus of India and south-east Asia and five African species, are more restricted in range and little studied. Pompilus mirandus is more tolerant of vegetated habitats than P. cinereus. Conversely, P. niveus of northern Africa is a specialist of the sand dunes of the Sahara Desert. Species of Pompilus all have a black cuticle with a covering of short grey pubescence. The most distinctive feature of the genus is the possession by females of long, weakly curved mandibles with a single inner tooth (other spider wasps have shorter, thicker mandibles with more teeth). These modified mandibles are related to their distinctive manner of handling prey. Whereas other spider wasps will drag their spider victims backwards to their nest, females of Pompilus will lift the spider off the ground and run forward while carrying it.

Nesting behaviour has only been described for P. cinereus. Targeted prey comprises ground-running spiders such as wolf spiders or clubionids. After a spider has been captured, paralysed and carried near the intended nest site, it is temporarily buried in the sand while the female constructs a burrow (Day suggested that this preliminary burial was to prevent the spider being stolen). The simple burrow leads to a single nest cell a few inches deep. The female exhumes the spider, transports it into the burrow and then lays an egg on its abdomen near the front of the side. She then closes the entrance to the burrow with sand, tamping it down securely with the end of her metasoma.

Within the burrow, the spider begins to wake from its paralysis after a few hours. However, it remains in poor shape: its movements are slow and it begins to continuously exude silk from its spinnerets. By wandering about the cell in this distressed state, the spider ends up producing a silken purse that serves as extra protection for the nest's contents. This, of course, includes the wasp larva that within a couple of days will have begun to feed on the trapped spider.

Though details of breeding behaviour have not been observed for other Pompilus species, they might be expected to resemble P. cinereus. It might be noted, however, that the female of P. cinereus has a patch of flattened scales at the end of the metasoma that is less developed in P. mirandus. Is this an indication that P. mirandus is somehow less conscientious in sealing the nest burrow than P. cinereus? If you keep an eye out in the wastelands of India, you might just learn the answer.

REFERENCE

Day, M. C. 1981. A revision of Pompilus Fabricius (Hymenoptera: Pompilidae), with further nomenclatural and biological considerations. Bulletin of the British Museum (Natural History): Entomology 42 (1): 1–42.

Allendesalazaria nymphoides, the Hidden Blister Beetle

The blister beetles of the family Meloidae have attracted attention for a number of reasons. One is their production of caustic defensive chemicals which may be powerful enough to cause severe injury to humans or their livestock. Another is their remarkable life cycles. Many blister beetles develop as nest predators or kleptoparasites of bees. The larvae of these species are hypermetamorphic with the first instar being more mobile than later stages. These mobile larvae will find bees and latch onto them so that they can be carried to the host's nest.

Allendesalazaria nymphoides, copyright Stanislav Krejcik.

This association reaches an extreme in Allendesalazaria nymphoides of north-west Africa. This reclusive species has, to date, been recorded from localities in Morocco, Algeria and Mauritania (Bologna & Aberlenc 2002). It is readily distinguished from other blister beetles by its much-reduced elytra which are oval and widely separated from each other. It is also distinguished by claws that lack the free lower blade found in most other meloids (Bologna & Pinto 2002). Whether they produce the noxious chemicals known from other members of their family, I haven't found a record.

Allendesalazaria nymphoides develops in the nests of solitary burrowing bees of the genus Anthophora. Adults of A. nymphoides do not feed, and never emerge from the nest in which they matured. Instead, they lay their own eggs within that same nest. Dispersal is then left to the hatching larvae that (I presume) latch onto those emerging bees that escaped their parents' depredations. Eventually, the new generation of bees will establish nests of their own. And when they do, the blister beetles will be ready for them.

REFERENCES

Bologna, M. A., & H.-P. Aberlenc. 2002. Allendesalazaria, un nouveau genre de Meloidae pour la faune saharienne (Coleoptera). Bulletin de la Société Entomologique de France 107 (2): 191–192.

Bologna, M. A., & J. D. Pinto. 2002. The Old World genera of Meloidae (Coleoptera): a key and synopsis. Journal of Natural History 36 (17): 2013–2102.

Pied Harvestmen of the Antilles

Harvestmen of the Neotropical family Cosmetidae have been featured on this site a couple of times before. Each time, I've commented on the dire taxonomic state of this diverse family, with many genera being poorly or inaccurately defined. Thanks to extensive (and continuing) studies in recent years by Braxilian researchers and their associates, this situation has been progressively improving, but we still have a lot to learn.

Cynortoides sp., copyright Damion Laren Whyte.

Cynortoides is a genus currently holding ten species of cosmetid. Most of these are found on the islands of the Greater Antilles—Cuba, Jamaica and Hispaniola—though the genus has also been recorded from adjoining regions of Mexico and Venezuela (Kury 2003). As with other cosmetids, Cynortoides has historically been defined largely be features of the external spination, including a lack of spines on the legs, two pairs of spines in the rear part of the dorsal scutum, and no spines on the free abdominal segments (Mello-Leitão 1933). Also as with other cosmetid genera, Cynortoides species are colourfully patterned. The name of one species, C. v-album, refers to its characteristic bright white V marking on the back (though personally, I would describe the pattern as more of a Y).

Though this genus does not yet appear to have been revised in detail, some of its species were included in a recent broader study of cosmetid phylogeny by Medrano et al. (2021). They found strong support for an association between the Cuban C. cubanus and the Hispaniolan C. v-album, together with two other Cuban species previously included in the related genus Cynorta. These last two species were consequently transferred to Cynortoides though Medrano et al. did not comment on whether this affected the genus' established diagnosis. The authors speculated that further studies might prove Cynortoides to be a strictly Greater Antillean genus with mainland records being misplaced. Cynortoides would not be unique in this regard: the islands of the Caribbean are home to a number of lineages found nowhere else, reflecting a long history independent of the adjoining continents.

REFERENCES

Kury, A. B. 2003. Annotated catalogue of the Laniatores of the New World (Arachida, Opiliones). Revista Ibérica de Aracnología, special monographic volume 1: 1–337.

Medrano, M., A. B. Kury & A. C. Mendes. In press 2021. Morphology-based cladistics splinters the century-old dichotomy of the pied harvestmen (Arachnida: Gonyleptoidea: Cosmetidae). Zoological Journal of the Linnean Society.

Mello-Leitão, C. F. de. 1933. Notas sobre os opiliões do Brasil. Descritos na obra postuma de Sörensen: "Descriptiones Laniatorum". Boletim do Museu Nacional 9 (1): 99–114.

The Race of Racers

Snakes are, for the most part, fairly retiring animals, little seen even in areas where they may be abundant. In much of North America, however, one of the most commonly encountered snake species is the racer Coluber constrictor. This moderately large non-venomous snake, with the largest individuals approaching two metres in length, is a widespread inhabitant of open habitats such fields, brushland or open woodlands. Its distribution is centred over much of the continental United States, being found in most regions except much of the arid south-west. Outside the United States, it has a very patchy distribution in southernmost Canada, Mexico and northern Central America. Most recent authors treat it as the sole species in the genus Coluber; other species historically assigned to this genus from across the Holarctic region now being treated as separate. These include the North American whip snakes of the genus Masticophis, believed to the closest relatives of the racer (Myers et al. 2017).

Southern black racer Coluber constrictor priapus, copyright Peter Paplanus.

Adult racers are generally uniformly dark in coloration dorsally, with a lighter-coloured venter, though juveniles have a blotchy checkered pattern (Fitch 1963). The exact shade varies across the species' range and a number of subspecies have been recognised such as the blue racer Coluber constrictor foxii and the northern black racer C. c. constrictor. In general, individuals are darker towards the east and north, and lighter towards the west and south. Wilson (1978) listed eleven subspecies of C. constrictor whereas a phylogeographic study of the species by Burbrink et al. (2008) identified six major lineages. As well as coloration, members of these lineages may differ in factors such as behaviour or genital morphology, and future studies may see them elevated to the rank of separate species.

Blue racer Coluber constrictor foxii, copyright Peter Paplanus.

The natural history of Coluber constrictor was reviewed in detail by Fitch (1963). As the vernacular name of 'racer' suggests, Coluber constrictor is a fast mover. Its diet contains a mixture of small vertebrates, such as frogs, lizards and small mammals, and large invertebrates such as grasshoppers, crickets and caterpillars. Foraging individuals often hold the front end of the body raised above the ground. Despite their species name, racers do not kill their prey by constriction. Instead, they mostly capture prey by darting forward quickly and grabbing it, often swallowing prey live. Fitch recorded one occasion when he observed a racer in the process of subduing a large skink. While the snake was swallowing its prey, Fitch attempted to capture it. The racer disgorged the skink, and both snake and lizard escaped the scene. Diet may vary with size, with smaller individuals taking a higher proportion of invertebrates, but also varies with range. Populations in the west may primarily feed on insects whereas others may almost exclusively take vertebrates. The northern black racer of the northeastern United States is the most inclined of the subspecies to feed on other snakes. Cannibalism is not unknown; at least one author recorded observing it among broods raised in captivity. In one case, two young racers latched onto a single lizard. One of them successfully downed the lizard, and then also continued on to devour the snake attached to the other end, despite the swallowed snake being nearly as large as its swallower.

Eastern yellow-bellied racer Coluber constrictor flaviventris, copyright David Sledge.

During winter, racers hibernate in crevices and hollows among rocks. Preferred hibernation locations are often at the top of hills, away from their usual hunting sites. Mating and egg-laying occurs shortly after emergence with the peak of egg-laying being in early June (Rosen 1991). Racers, particularly the large northern black, may become more aggressive during this period. Eggs are buried shallowly, in loose soil or under litter, though females may take advantage of abandoned mammal burrows to provide a more secure location. As with other snakes, laying seems to be a matter of pump and dump; I didn't come across any references to females protecting clutches. After hatching, males take about a year to reach sexual maturity whereas the larger females take about two years. Fitch (1963) reports encountering the same individuals over the course of several years (recognisable by their bearing the scars of prior collection of scale samples). Nevertheless, the majority of racer hatchlings do not survive their first summer. Few get the opportunity to seek out shelter for their winter's sleep.

REFERENCES

Burbrink, F. T., F. Fontanella, R. A. Pyron, T. J. Guiher & C. Jimenez. 2008. Phylogeography across a continent: the evolutionary and demographic history of the North American racer (Serpentes: Colubridae: Coluber constrictor). Molecular Phylogenetics and Evolution 47: 274–288.

Fitch, H. S. 1963. Natural history of the racer Coluber constrictor. University of Kansas Publications, Museum of Natural History 15 (8): 351–468.

Myers, E. A., J. L. Burgoon, J. M. Ray, J. E. Martínez-Gómez, N. Matías-Ferrer, D. G. Mulcahy & F. T. Burbrink. 2017. Coalescent species tree inference of Coluber and Masticophis. Copeia 105 (4): 640–648.

Wilson, L. D. 1978. Coluber constrictor Linnaeus. Catalogue of American Amphibians and Reptiles 218: 1–4.