Fibre Couplings in the Placenta of Sperm Whales, Grows to A
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news and views Most (but not all) nematodes are small Daedalus and nondescript. For example, Placento- T STUDIOS nema gigantissima, which lives as a parasite Fibre couplings in the placenta of sperm whales, grows to a CS./HOL length of 8 m, with a diameter of 2.5 cm. The The nail, says Daedalus, is a brilliant and free-living, marine Draconema has elongate versatile fastener, but with a fundamental O ASSO T adhesive organs on the head and along the contradiction. While being hammered in, HO tail, and moves like a caterpillar. But the gen- it is a strut, loaded in compression. It must BIOP eral uniformity of most nematode species be thick enough to resist buckling. Yet has hampered the establishment of a classifi- once in place it is a tie, loaded in tension, 8 cation that includes both free-living and par- and should be thin and flexible to bear its asitic species. Two classes have been recog- load efficiently. He is now resolving this nized (the Secernentea and Adenophorea), contradiction. based on the presence or absence of a caudal An ideal nail, he says, should be driven sense organ, respectively. But Blaxter et al.1 Figure 2 The bad — eelworm (root knot in by a force applied, not to its head, but to have concluded from the DNA sequences nematode), which forms characteristic nodules its point. Its shaft would then be drawn in that the Secernentea is a natural group within on the roots of sugar beet and rice. under tension; it could not buckle, and the Adenophorea. Based on studies of free- would form a perfect tie. But how to apply living species, a paraphyletic nature for the and Rhabditoidea (which are probably sister a force to the point of a nail? Well, suppose Adenophorea — that is, a group comprising groups), Strongyloididae, Apelenchida and the blow on its head lasted only a an ancestor but not all of its descendants — Tylenchida. The Strongylida comprises ver- microsecond. In this time, the shock would has previously been suggested (for example, tebrate parasites without an intermediate travel only a millimetre or so down the by Lorenzen2), but the position of the various host (an example is the hook worm). The nail. The compressed region would be far parasitic groups has always caused trouble. Rhabditoidea, by contrast, comprises free- too short to buckle. The pulse would travel One of the most interesting results of the living species, such as the favourite experi- down the nail, and would force the point new phylogeny is the discovery that there mental model Caenorhabditis elegans, and into the material being fastened. Any have been many parallel shifts of feeding insect parasites. And the Strongyloididae reflected energy would travel safely back strategy within the phylum. The ancestral comprises mammalian parasites, many of up the nail as a tension. form was obviously free-living, but the which infest horses, pigs and cattle. Now only the most rigid materials results of Blaxter et al. support the idea that Blaxter et al. also identified a large para- could have an impact time of a parasitism has evolved independently many sitic group within the Secernentea, compris- microsecond. A diamond hammer driving times. Of the plant parasites, for example, the ing three groups of vertebrate parasites (the a diamond nail would be wonderful order Triplonchida comprises only plant Ascaridida, Spirurida and Oxyurida) and engineering but disastrous economics. But parasites, whereas Dorylaimida comprises one group of invertebrate parasites (the in electronics, microseconds are positively both omnivores and plant parasites. And the Rhigonematida). Of the Ascaridida, some leisurely. A piezoelectric transducer could sister orders Aphelenchida and Tylenchida species (for example, Ascaris spp.) live in ver- hit a nail thousands of times a second. both comprise fungivores, plant parasites tebrate intestines. But others, such as species Quartz is piezoelectric, and quartz fibres — among which the eelworms (Fig. 2) para- of Anisakis, have more complex life cycles, have amazing tensile strength. So Daedalus sitize many important crops, such as potato with a crustacean as the first host, a fish as the is now inventing the quartz-fibre and sugar beet — and animal parasites. second host and a fish-eating bird or mam- piezoelectric nail. The animal parasites also belong to sever- mal as the final host. The Spirurida live in His ‘piezonail’ will be a fine, flexible al groups that probably evolved indepen- vertebrate tissues, and they are transferred fibre with plated electrodes, and embedded dently. Outside the Secernentea, the Trico- by biting or sucking insects. Well-known in a plastic reinforcing jacket. You will fit it cephalida comprises mammalian parasites species include the filaria worm and the whip into a recess in its pulse-generator (such as the trichina worm) which do not worm. Of the Oxyurida, the pinworm is a ‘hammer’, hold it firmly against the object have an intermediate host. But the Mermithi- common but harmless human parasite. to be nailed, and switch on. The burst of da mainly comprises species that have a Finally, the Rhigonematida comprises para- pulses will force it silently and instantly juvenile stage in which they infest insects. sites of terrestrial arthropods. into the material, giving a strong, Within the Secernentea are the Strongylida The establishment of a natural — that is, tensioned, firmly bound tie. In thick or phylogenetic — classification for the nema- hard materials, the piezonail will not even todes is an absolute necessity for all aspects need a head; friction will hold it firmly T STUDIOS of nematode studies, practical as well as enough. Many thin ties are superior to one theoretical. Moreover, the classification thick one, so the hammer will also accept a described by Blaxter et al. will be an invalu- ‘polynail’ containing many parallel TLIN/HOL T able tool for parasitologists, who search for piezonails in one jacket. relationships between parasitic species. They Construction will be transformed. The NIGEL CA can use this information to look for free- global toll of bent nails, bruised thumbs living relatives of important parasites that and ringing ears will plummet as the may be difficult to culture, or for ways in piezonail spreads through engineering, which to combat pests. carpentry and DIY bodging. A piezonailed Claus Nielsen is at the Zoological Museum, structure will be strong, stable, secure — University of Copenhagen, Universitetsparken 15, and somewhat enigmatic. Its myriads of DK-2100 Copenhagen, Denmark. fine fixing fibres will be almost invisible, e-mail: [email protected] giving no clue as to what holds it together, Figure 1 The good — Steinernema bibionis, a 1. Blaxter, M. L. et al. Nature 392, 71–75 (1998). or how to get it apart again. 2. Lorenzen, S. in Concepts in Nematode Systematics (eds Stone, free-swimming parasitic nematode used for A. R., Platt, H. M. & Khalil, L. F.) 11–23 (Academic, New York, David Jones biological control of vine weevils. 1983). 26 NATURE | VOL 392 | 5 MARCH 1998 Nature © Macmillan Publishers Ltd 1998.