Narona decaptyx: A Fossil Vampire

13.5 mm long specimen of Narona decaptyx, from Landau et al. (2012).

Narona decaptyx was described by Brown & Pilsbry (1911) from a single small, fusiform fossil shell, 11 mm in length, from the Gatun Formation of Panama, north of Panama City. They regarded the formation as probably Oligocene in age but Landau et al. (2012) later referred N. decaptyx to the upper Miocene. Until it's redescription by the latter, this species was only known from Brown & Pilsbry's original holotype; Landau et al. described further material from the Bocas del Toro region to the west of the original locality. Both the sites from which N. decaptyx are known are on the Caribbean coast of Panama.

Narona decaptyx is a member of the Cancellariidae, the nutmeg snails. Cancellariids are one of the smaller families of the great neogastropod radiation, the group that also includes such forms as whelks and cone shells. They generally have a more or less developed sculpture of criss-crossing spiral and axial ribs; the latticed pattern this produces is formally referred to as 'cancellate' and provides the source of the family's name. The most distinctive feature of Cancellariidae is their radula, a slender ribbon of long, flexible teeth arranged in a single row. How this radula functioned was long a mystery. Dissections of the gut of cancellariids failed to find any trace of solid food, and it was suggested they may be adapted to some form of suctorial feeding. Some authors suggested that cancellariids might feed by slurping up micro-organisms. Then, in the 1980s, one species of cancellariid Cancellaria cooperi was observed feeding on sleeping electric rays. The snail would cut incisions in the ray's skin, presumably with its radula, before inserting its proboscis to slurp up the fish's blood (O'Sullivan et al. 1987). Other cancellariids have been observed feeding on fluids from other invertebrates such as benthic molluscs or their egg masses.

Cancellaria cooperi feeding on an electric ray, copyright Clinton Bauder.

The genus Narona to which N. decaptyx belongs is now restricted to the north Pacific. In this respect, it is not unique. Cancellariids are poorly represented in the modern Caribbean fauna with only six species known from the sea's shallow waters but they were much more diverse there in N. decaptyx's time. However, following the rise of the isthmus of Panama, many cancellariid taxa once found widely in the tropical Americas became extinct for whatever reason on the eastern side of the divide. This happened regularly enough that the term 'paciphile' has been coined for referring to such taxa. A number of distinct waves of paciphile extinctions have been identified in the Caribbean cancellariid fossil record and they have been used to identify distinct chronological zones. Narona decaptyx became extinct as part of the GNPMU (Gatunian Neogene Paciphilic Molluscan Unit) 1 period. Other Narona species persisted in the Caribbean and Gulf of Mexico for longer, surviving into the Pliocene, but eventually they too succumbed to whatever dampened this family's prospects in the region.

REFERENCES

Brown, A. P., & H. A. Pilsbry. 1911. Fauna of the Gatun Formation, Isthmus of Panama. Proceedings of the Academy of Natural Sciences of Philadelphia 63 (2): 336–373.

Landau, B., R. E. Petit & C. M. da Silva. 2012. The family Cancellariidae (Mollusca: Gastropoda) in the Neogene of the Bocas del Toro region, Panama, with the description of seven new species. Journal of Paleontology 86 (2): 311–339.

O'Sullivan, J. B., R. R. McConnaughey & M. E. Huber. 1987. A blood-sucking snail: the Cooper's nutmeg, Cancellaria cooperi Gabb, parasitizes the California electric ray, Torpedo californica Ayres. Biological Bulletin 172 (3): 362–366.

Turridae

Shell of Turris crispa crispa, copyright H. Zell.

At this point, I've made numerous references on this site to the gastropod family Turridae, discussing its members and non-members and alluding to its sordid history. So maybe I should set out the basics of the story properly.

The Conoidea are a diverse group of marine predatory gastropods with over 4000 known living species. They are best known for the production by many species of venom used to paralyse their prey, in some species being potent enought to threaten humans. In the majority of conoideans, this venom is delivered via a tooth that becomes detached from the radula and is held at the end of the retractable proboscis. Until relatively recently, Conoidea were commonly divided between three families. Two of these families, the Conidae (cone shells) and Terebridae (awl shells) were well defined and constrained. The third family was the Turridae, including by far the greater number of species but not really defined within Conoidea beyond 'the rest'. Many of 'the rest' were small, many were restricted to deep water, many were poorly known. Different systems were proposed over the years in an attempt to break the turrid mass into more manageable units but each system differed significantly from the next and no one system became universally accepted. Some authors would focus on the protoconch as their guide to classification, others would focus on the radula, others might call out features of the operculum. One author commented in 1922 that turrids were "considered by those who meddle with them to be more perplexing than any other molluscan family", and this complaint was still being upheld by Kilburn (1983) over sixty years later.

Though it had long been accepted that the 'turrids' probably did not represent an evolutionarily coherent group, it wasn't really until the advent of molecular phylogenies that things started falling into place. Puillandre et al. (2011) identified two main lineages within the Conoidea, leading to the dissolution of the original Turridae into no less than 13 families in order to maintain the already-established Conidae and Terebridae. Turridae in the strict sense was restricted to a much smaller clade of a bit over a dozen genera, sister to the Terebridae (Bouchet et al. 2011).

In contrast to the bewilderment of the original turrid array, Turridae sensu Bouchet et al. is a morphologically quite coherent group. They are more or less fusiform (spindle-shaped) shells, often with a narrow, high spire and relatively weak sculpture. Indeed, but for the fact that most tend to have a long siphonal canal at the base of the shell, they often bear a distinct resemblance to their sister group, the terebrids. The majority of turrids have a multispiral protoconch, indicating an extended, planktonic-feeding larval stage in development, but there are some species with a paucispiral protoconch indicative of direct development.

Radula of Xenuroturris legitima, from Kantor & Puillandre (2012); ct = central tooth.

The radula of turrids usually comprises three apparent teeth in each row. The central tooth is actually formed from three teeth (the original pointed central tooth and two plate-like lateral teeth) fused together; in some species the division between these teeth remains visible whereas in others the central tooth disappears entirely. The main business part of the radula is the single pair of marginal teeth which, as in other conoideans, are enlarged and modified for venom delivery. They have a distinctive 'duplex' form; in older publications, this was referred to as a 'wishbone' form because the tooth appears under light microscopy to be divided between two branches. After the advent of electron microscopy, it was discovered that these two 'branches' in fact represent the thickened margins of an undivided tooth. The larger of the two margins is mostly attached to the radular membrane with only the tip of the tooth being free; the smaller margin is held free of the radula. The thinner part of the tooth between the two margins forms a gutter along which venom can flow. However, the radula is placed in such a position that it cannot be protruded through the mouth in the manner of grazing gastropods. As with other conoideans, prey (in this case probably worms) is despatched through the use of a detached marginal tooth transferred to the end of the proboscis. However, whereas other conoideans such as cone shells may have the tooth functioning like a hypodermic syringe for delivering prey, turrids use their tooth to slash at the prey like a switchblade, with venom passively entering through the resulting cuts. The proboscis is then used to draw the prey back into the mouth, where the radula is used to grasp and swallow it, sucking the unlucky worm down the gullet like spaghetti.

REFERENCES

Bouchet, P., Y. I. Kantor, A. Sysoev & N. Puillandre. 2011. A new operational classification of the Conoidea (Gastropoda). Journal of Molluscan Studies 77: 273–308.

Kantor, Y. I., & N. Puillandre. 2012. Evolution of the radular apparatus in Conoidea (Gastropoda: Neogastropoda) as inferred from a molecular phylogeny. Malacologia 55 (1): 55–90.

Kilburn, R. N. 1983. Turridae (Mollusca: Gastropoda) of southern Africa and Mozambique. Part 1. Subfamily Turrinae. Annals of the Natal Museum 25 (2): 549–585.

Puillandre, N., Y. I. Kantor, A. Sysoev, A. Couloux, C. Meyer, T. Rawlings, J. A. Todd & P. Bouchet. 2011. The dragon tamed? A molecular phylogeny of the Conoidea (Gastropoda). Journal of Molluscan Studies 77: 259–272.

Conus jaspideus or Conasprella jaspidea, Take Your Pick

Live Conasprella jaspidea, copyright Anne DuPont.

Cone shells are one of the classic varieties of tropical sea shells, perhaps only rivalled in their familiarity with the general public by cowries and conches. Over 800 species of the family Conidae have been described from around the world. The specimen above represents one of these species, going by the name of Conasprella jaspidea or Conus jaspideus. The alternatives reflect the conflict between those who would treat all cone shells as belonging to a single genus Conus, or those who would divide them between multiple genera (Conasprella jaspidea is the name used for this species by Puillandre et al., 2014). One 2009 classification went so far as to divide the cone shells between 89 genera in five separate families, which does seem perhaps a little excessive. Among other features, Conasprella species differ from Conus sensu stricto in having a higher spire to the shell.

The type specimen of Conasprella jaspidea, copyright MHNG.

Conasprella jaspidea is found in coastal sections of the western Atlantic between Florida and the area of Rio de Janeiro. It is a medium-sized shell, reaching about three centimetres in length. Whorls of the spire are marked by distinct shoulders, and the body whorl is ornamented by spiral cords. The colour of the shell is white, orange or brown with darker brownish or violet spots. Shells of C. jaspidea may vary in texture from granular to smooth. These variants were initially recognised as distinct species or subspecies Conus jaspideus and C. verrucosus but, not only can both forms be found intermixed within a single population, the difference between them may be simply a question of the degree of wear a shell has been exposed to (Santos Gomes 2011).

Like other cone shells, Conasprella jaspidea is venomous with the radula bearing a single functional tooth modified into a short of hypodermic needle for injecting venom. Species of Conasprella are vermivorous (that is, they feed on worms). Feeding by a live individual of C. jaspidea was observed in an aquarium by Santos Gomes (2011). Photographs therein show the individual ingesting a polychaete worm that was perhaps not too much shorter in length than the cone shell itself; the process of feeding (from the initial strike with the radula to completion of ingestion) took about eighteen minutes from start to finish.

REFERENCES

Puillandre, N., T. F. Duda, C. Meyer, B.M. Olivera & P. Bouchet. 2014. One, four or 100 genera? A new classification of the cone snails. Journal of Molluscan Studies 81: 1–23.

Santos Gomes, R. dos. 2011. Conus jaspideus (Mollusca: Neogastropoda: Conoidea) on the Brazilian coast. Journal of the Marine Biological Association of the United Kingdom 91 (2): 531–538.

Cochlespira

Shell of Cochlespira radiata, photographed by Jan Delsing.

This beauty is a member of the genus Cochlespira, another one of the conoid shells previously classed as 'turrids' (it now belongs in the family Cochlespiridae since the disassembly of Turridae in the broad sense). Cochlespira species can be relatively large as conoids go, reaching lengths of up to five centimetres. They are found in deep waters in various parts of the world, with a fossil record going back to the Eocene (Powell 1966; Powell treated the western Atlantic species as a separate genus Ancistrosyrinx, but this and the Indo-Pacific Cochlespira have since been synonymised). One of the genus' more distinctive features is a little hard to miss: that eye-catching keel around the outside of the whorls, ornamented with serrations or spines.

As with other deep-water conoids, our knowledge of how Cochlespira species live their lives seems to be pretty limited. The radula has a broad-based central tooth with a single median cusp, and a pair of marginal teeth that are elongate but not as slender as those of many other conoids (Powell 1966). The rhynchodeal walls in the foregut are muscular and the proboscis is long. The venom glands are well-developed but join the oesophagus at about its midlength rather than in the buccal mass (Simone 1999). The arrangement looks to my admittedly inexpert eyes like it might be suited for sucking up invertebrate prey, perhaps something that might be expected to be relatively slow-moving or soft-bodied.

REFERENCES

Powell, A. W. B. 1966. The molluscan families Speightiidae and Turridae. An evaluation of the valid taxa, both recent and fossil, with lists of characteristic species. Bulletin of the Auckland Institute and Museum 5: 1-184.

Simone, L. R. L. 1999. The anatomy of Cochlespira Conrad (Gastropoda, Conoidea, Turridae) with a description of a new species from the southeastern coast of Brazil. Revista Brasileira de Zoologia 16 (1): 103–115.

Zemacies: A Toothless Wonder

The Recent species Zemacies queenslandica, photographed by Jan Delsing.

What makes an organism a 'living fossil'? The phrase is one that has been thrown about a bit over the years but whose actual definition can be ambiguous. Many people use it to refer to a species that is supposedly little changed from its distant ancestors. An alternative interpretation, however, and I suspect the phrase's original inspiration, would be something that was first discovered as a fossil, only to be found alive at a later date. The coelacanth, of course, would be the textbook example of such a case (without necessarily being a good example). But you might be surprised at some of the animals that could be called a 'living fossil' under this definition. The white-tailed deer would be one, as would the bush dog of South America. And so would the subject of today's post.

Zemacies is a genus of conoid gastropods known from the south-west Pacific. It is relatively large as conoids go, with some growing over three inches in length. Shells are a slender, fusiform shape, often with prominent nodules on the whorls. The first known species, Z. elatior, was described from the Miocene of New Zealand. Over time, additional species were described from New Zealand and Australia, extending the age range of the genus from the Palaeocene to the Pliocene (Powell 1969). It wasn't until 2001, however, that living species of Zemacies were recognised in the deep sea around New Caledonia and Queensland.

Figure from Fedosov & Kantor (2008) showing appearance of pyriform organ in foregut of Zemacies excelsa (left), with cross-section of organ to show internal structure (right). Abbreviations: bl, bulb-like structure; gt, glandular tissue; ms, muscles; sgp, semicircular glandular pad; tf, tall folds underlain by glandular tissue; tn, tentacles.

The discovery of living specimens (or, at least, living until the time of their collection) led to the revelation that Zemacies was a very intriguing genus, in a way that would have probably never been guessed from fossil material alone. As has been described previously, one of the great innovations of conoids was the modification of the radula into a system for the injection of paralysing toxins. When researchers investigated the soft anatomy of Zemacies excelsa, however, they discovered that it turned away from this trend. Zemacies has lost both the radula and its associated poison glands, as well as the associated proboscis. In their place, one side of the foregut has grown a pear-shaped outgrowth, referred to as the pyriform organ, that is covered with glandular tentacles (Fedosov & Kantor 2008). This structure is so unusual that its initial discovery lead to the proposal of a new subfamily to separate Zemacies from all other conoids (it has since been placed by Bouchet et al., 2011, as a distinctive member of the family Borsoniidae).

Unfortunately, the bathyal habitat of living Zemacies means that we as yet have no idea of its preferred prey and consequently little idea of how the pyriform organ is used when feeding. The internal cavity of the pyriform organ contains an array of longitudinal muscles, suggesting that it can be extended out the front of the animal in place of the usual proboscis. The tentacles may function to grasp or adhere to the prey, and/or the glandular tissue underlying them may secrete toxins or digestive enzymes, while the action of the pyriform organ against the foregut wall during withdrawal of the prey may serve to crush it (I wonder what the efficacy of this arrangement may be against something with a strong but not calcified cuticle, such as a deep-water crustacean). A similar foregut structure (also associated with loss of the radula and proboscis) has been identified in another conoid genus, Horaiclavus, though phylogenetic analysis of the Conoidea indicates that the two genera almost certainly evolved these structures independently. Horaiclavus also differs from Zemacies in that the muscular foregut outgrowth lacks any associated glandular tissue and is presumably entirely mechanical in its action (Fedosov & Kantor 2008). Perhaps one day someone will finally observe one of these deep-sea genera in their native habitat and provide us with a solution to the mystery of their life styles.

REFERENCES

Bouchet, P., Y. I. Kantor, A. Sysoev & N. Puillandre. 2011. A new operational classification of the Conoidea (Gastropoda). Journal of Molluscan Studies 77: 273–308.

Fedosov, A., &. Y. Kantor. 2008. Toxoglossan gastropods of the subfamily Crassispirinae (Turridae) lacking a radula, and discussion of the status of the subfamily Zemaciinae. Journal of Molluscan Studies 74: 27–35.

Powell, A. W. B. 1969. The family Turridae in the Indo-Pacific. Part 2. The subfamily Turriculinae. Indo-Pacific Mollusca 2 (10): 215–415.

Deep Pleurotomella

The type species of Pleurotomella, P. packardi, copyright Forum Natura Mediterraneo.

'Turrid' time again! Though the disassembly of the enormous mass that was the old gastropod family Turridae (now several families of the superfamily Conoidea) has left the subject of today's post, the genus Pleurotomella, as a member of the Raphitomidae rather than the Turridae. Pleurotomella is a widespread genus, with species found in deeper parts of ocean basins around the world. As with many deep-water animals, we know relatively little about their lifestyles, though they are undoubtedly predators like other conoids. Like other conoids, Pleurotomella species have a radula with the teeth modified into hypodermic syringes for the injection of toxins. At least some species (including the type) are blind (Bouchet & Warén 1980) and I can imagine that they attack relatively sedentary prey such as worms.

Taxonomically speaking, Pleurotomella has one of those histories that can make a grown taxonomist just want to sit down and cry. I've already mentioned this horrible genus in my earlier post on Asperdaphne as a player in one of those scenarios where a misunderstood type species leads a genus to jettison almost all of the species previously associated with it and pick up a whole bunch of new ones that it never held before. An inordinate number of deep-water 'turrid' species seem to have been dumped into Pleurotomella at some time or other, many of which are probably only remotely related to the true Pleurotomella. However, since Bouchet & Warén (1980) redescribed the type species Pleurotomella packardi as part of a revision of north-east Atlantic 'turrids', we have much better grounds for the genus' recognition (Beu 2011). Species of Pleurotomella have strongly inflated whorls that are evenly rounded except for a concave 'ramp' below the suture between whorls. The shell contracts rapidly to a narrow base, and has prominent, sharp and often curved axial ridges.

Multispiral (left) and paucispiral (right) protoconches of Mangelia species, from Bouchet (1990). Scale bars = 200 µm.

Again as was the case in the Asperdaphne post, a notable factor in the taxonomic complications of Pleurotomella has been matters relating to the protoconch, the larval shell that remains perched throughout development at the tip of the post-larval shell, the teleoconch. Because the features of the protoconch such as ornamentation may often differ from those of the teleoconch, it can often be of significance in gastropod taxonomy. A lead proponent of the importance of the protoconch in 'turrid' taxonomy was the New Zealand malacologist A. W. B. Powell who produced an influentiall classification of turrids between the 1940s and 1960s. Nevertheless, Powell did note an interesting phenomenon: the common existence of 'genus pairs' that were all but indistinguishable in teleoconch morphology but very distinct in their protoconches. Because Powell regarded the teleoconch as phylogenetically less significant than the protoconch (in accord with Ernst Haeckel's old dictum that ontogeny should recapitulate phylogeny), he concluded that these 'genus pairs' must represent separate lineages converging on a single adult morphology.

More recent authors agree that, in this, Powell was wrong (Bouchet 1990). As noteworthy a source of taxonomic characters it may be, protoconch development is subject to selective and evolutionary pressures just as much as teleoconch development. The most regular difference between Powell's 'genus pairs' is that one would have a conical protoconch with a number of whorls (say three or four, referred to as multispiral) whereas the other would have a stubby round protoconch with at most about one-and-a-half whorls (paucispiral). This difference in protoconch morphology reflects a difference in how the larval shell is fed. In the original development path for gastropods, eggs hatch out to planktic larvae that feed themselves on other plankton (planktotrophy) before eventually settling and developing to maturity. However, many conoids (and other gastropods) have evolved eggs that have a large yolk; the developing embryos obtain their energy from the reserves in the yolk (lecithotrophy) and bypass the planktic stage, hatching directly as benthic crawlers. Because planktotrophs need their larval shell for longer than lecithotrophs, it becomes more developed; planktotrophs are multispiral, lecithotrophs are paucispiral. Powell's 'genus pairs' did not represent separate lineages evolving similar adult lifestyles, but members of the same lineage tackling early development different ways. As such, and because of the possibility that the change between planktotrophic and lecithotrophic development may have occured multiple times within a single group, most recent authors would not automatically recognise multispiral and paucispiral species as separate genera. Pleurotomella species mostly have multispiral protoconches, but some (including P. packardi and a number of Pacific species) have paucispiral ones.

Which is not to say that protoconch morphology has become irrelevant. Bouchet & Warén (1980) did maintain the genus Neopleurotomoides as separate from Pleurotomella on the basis of protoconch morphology, despite these two genera having very similar teleoconches. In this case, the difference is not just the number of spirals in the protoconch, but its ornamentation. Pleurotomella species with a multispiral protoconch have a cancellate (cross-hatch) pattern of ridges covering it, but Neopleurotomoides has a sparser ornament of one or two spiral keels crossed by axial ribs. The distinction between the two genera remains problemematic: species with a paucispiral protoconch (which is usually more or less unornamented) cannot be readily assigned to either genus, and there are many 'Pleurotomella' species for which the protoconch remains undescribed. But the take-away lesson, as so often in taxonomy, is this: no source of characters should be ignored, but nor should it be fetishised.

REFERENCES

Beu, A. G. 2011. Marine Mollusca of isotope stages of the last 2 million years in New Zealand. Part 4. Gastropoda (Ptenoglossa, Neogastropoda, Heterobranchia). Journal of the Royal Society of New Zealand 41 (1): 1–153.

Bouchet, P. 1990. Turrid genera and mode of development: the use and abuse of protoconch morphology. Malacologia 32 (1): 69–77.

Bouchet, P., & A. Warén. 1980. Revision of the north-east Atlantic bathyal and abyssal Turridae (Mollusca, Gastropoda). Journal of Molluscan Studies, Supplement 8: 1–119.

Syntomodrillia

Syntomodrillia cybele, copyright Korina Sangiouloglou.

Time, I think, for another visit to the often overlooked hotbed of gastropod diversity that is the 'turrids'. As alluded to here and here, these are the less differentiated members of the cone shell superfamily Conoidea, treated in the past as a single family Turridae but now classified into several different families.

Syntomodrillia is a genus in the conoid family Drilliidae. These are small shells, with recent species no more than a centimetre in length (Woodring 1970). Recent species of Syntomodrillia are found only in the American tropics, mostly in the Caribbean and the Gulf of Mexico, with a single species S. cybele (the one shown above) at the Galapagos Islands. The fossil record, however, may indicate a broader range for Syntomodrillia in the past, as Powell (1966) assigned species to this genus from the Oligocene to the Pliocene of Australasia and Okinawa. Syntomodrillia is similar in appearance to another drilliid genus, the somewhat magnificently named Splendrillia, and has been treated by some authors as a subgenus of the latter. Among the features distinguishing the two is the appearance of the longitudinal ribs running down the shell: in Syntomodrillia, the ribs completely cross each whorl, but in Splendrillia they are interrupted on the shoulder. The protoconch (larval shell) also differs between the two, with that of Syntomodrillia being slender with two whorls, whereas that of Splendrillia is broadly rounded and paucispiral (Powell 1966). This may indicate that the larval stage of Syntomodrillia is slightly longer and/or more active than that of Splendrillia.

Radula of Splendrillia, from Kantor & Puillandre (2012); mt = marginal teeth.

As described in an earlier post, the Conoidea have alternatively been known as the 'Toxoglossa' because many conoids have the radula modified for the injection of toxins (taken to the utmost in the cone shells, which may be capable of killing humans). The median and lateral teeth of the radula are reduced or lost, and the marginal teeth turn into disposable syringes. The Drilliidae, however, have not gone down this path: they retain a radula with well-developed saw-like lateral teeth. Though records of drilliid diet are decidedly sparse, they probably hunt soft-bodied prey by actively grabbing and tearing it, in contrast to the more refined eating habits of other conoids.

REFERENCES
Kantor, Y. I., & N. Puillandre. 2012. Evolution of the radular apparatus in Conoidea (Gastropoda: Neogastropoda) as inferred from a molecular phylogeny. Malacologia 55 (1): 55–90.

Powell, A. W. B. 1966. The molluscan families Speightiidae and Turridae: an evalution of the valid taxa, both Recent and fossil, with lists of characteristic species. Bulletin of the Auckland Institute and Museum 5: 1–184, 23 pls.

Woodring, W. P. 1970. Geology and paleontology of Canal Zone and adjoining parts of Panama: description of Tertiary mollusks (gastropods: Eulimidae, Marginellidae to Helminthoglyptidae). Geological Survey Professional Paper 306-D: 299–452, pls 48–66.