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The fossil tapeworm from mid-Cretaceous Kachin amber (~99 Ma; million years in the past) and the comparability with the tentacle of an extant trypanorhynch tapeworm. A. Microscopic picture of fossil tapeworm; B. Micro-CT picture of fossil tapeworm; C. Scanning electron microscopy picture of an extant trypanorhynch tapeworm. Credit score: NIGPAS
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The fossil tapeworm from mid-Cretaceous Kachin amber (~99 Ma; million years in the past) and the comparability with the tentacle of an extant trypanorhynch tapeworm. A. Microscopic picture of fossil tapeworm; B. Micro-CT picture of fossil tapeworm; C. Scanning electron microscopy picture of an extant trypanorhynch tapeworm. Credit score: NIGPAS
Cestoda, generally often called tapeworms, is a big class throughout the platyhelminth phylum with about 5,000 species described thus far. Lately, researchers from the Nanjing Institute of Geology and Paleontology of the Chinese language Academy of Sciences (NIGPAS), in collaboration with scientists from Yunnan College, Germany, the U.Ok., and Myanmar, have reported an enigmatic fossil from mid-Cretaceous Kachin amber, relationship to about 100 million years in the past.
This research, revealed in Geology on March 22, supplies proof not solely of the primary partial physique fossil of a tapeworm but in addition, arguably, probably the most convincing physique fossil of a flatworm, thus offering new info on the early evolution of tapeworms.
Cestoda infect all main teams of vertebrates, together with people and livestock, and are present in practically all marine, freshwater, and terrestrial ecosystems. Their dimension is variable, starting from lower than one millimeter to greater than 30 meters in size.
Tapeworms are often characterised by adults with a scolex (greedy head), a brief neck, and a segmented physique consisting of a number of units of genitalia (proglottids). Their scolex sometimes has hooks, suckers, or hooked tentacles that assist them cling to the alimentary tract of their hosts. Most tapeworms have an obligate parasitic life cycle involving two or three hosts. They haven’t any mouth or digestive tract, and take up vitamins immediately from the intestines of their hosts.
The order Trypanorhyncha is probably the most various tapeworm group within the marine realm and contains one of the crucial ubiquitous and readily acknowledged parasites of marine fish. Trypanorhynch tapeworms are characterised by a scolex with two or 4 bothria and a novel tentacular equipment with 4 evaginable tentacles adorned with hooks as extensions of the tentacle sheaths throughout the scolex. Their larvae infect a variety of marine invertebrates (e.g., crustaceans) and teleosts, and their adults are discovered within the stomachs and intestines of sharks and rays.
Molecular clock analyses calibrated in opposition to host fossil knowledge estimate that trypanorhynch tapeworms most likely originated across the Triassic/Jurassic boundary about 200 million years in the past, however their very own fossils have by no means been discovered.
“The fossil document of tapeworms is extraordinarily sparse on account of their mushy tissues and endoparasitic habitats, which significantly hampers our understanding of their early evolution,” mentioned Wang Bo, the research’s lead researcher. Nonetheless, he added that his workforce had “reported the primary physique fossil of a tapeworm.”
In line with the researchers, this fossil shows distinctive exterior and inside options which might be most according to the tentacles, together with the hook morphology, of extant trypanorhynch tapeworms that parasitize marine elasmobranchs (primarily sharks and rays). Remarkably, virtually all extant trypanorhynchs are endoparasites of marine elasmobranchs.
Presumed tapeworm eggs have been reported from a Carboniferous shark coprolite. Nonetheless, the one broadly accepted fossil document previous to the Quaternary is proscribed to eggs found in a Permian shark coprolite, suggesting that the connection between tapeworms and elasmobranch vertebrates had already been established by then. Though a tapeworm embryo inside an egg has been reported, it’s questionable on account of a scarcity of confirmed traits.
A hypothetical ecological reconstruction of the fossil trypanorhynch tapeworm. Credit score: Yang Dinghua
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A hypothetical ecological reconstruction of the fossil trypanorhynch tapeworm. Credit score: Yang Dinghua
As for precise tapeworm fossils, the oldest supposed document comes from the Devonian of Latvia, when circlets of hooks with sucking disks had been discovered on placoderm and acanthodian fishes. Though the association of the hooks is according to extant monogeneans, no different physique construction was discovered. As well as, two cysts resembling trematode metacercariae had been reported from mid-Cretaceous Kachin amber, however no legitimate morphological particulars had been supplied to help this declare.
Equally, a supposed physique fossil of Rhabdocoela found in Eocene Baltic amber was plausibly reinterpreted as air bubbles. “This makes the present discover probably the most convincing physique fossil of a platyhelminth ever discovered,” mentioned Luo Cihang, first writer of the research and a Ph.D. candidate from NIGPAS.
This research, which supplies an distinctive instance of a marine endoparasite trapped in amber, has additionally shed new gentle on the taphonomy of amber.
Particularly, the researchers confirmed that amber can protect the interior construction of helminths. Utilizing high-resolution micro-CT, they found that the inside of the present fossil has a folded longitudinal construction that seems to run in a spiral across the longitudinal axis and extends to the anteriormost half.
That is according to the invaginated tentacle of a trypanorhynch. In the meantime, the rootless hooks are additionally the identical as these of trypanorhynchs. Earlier research had proven that inside constructions may very well be preserved intact as in extant varieties, however such research all centered on arthropods.
“Our outcomes present that amber can protect the interior construction of helminths equivalent to tapeworms on geologic time scales,” mentioned Wang.
Together with the exceptional instance of a marine endoparasite trapped in amber, some gleicheniacean trichomes and a scale insect nymph had been additionally preserved with the partial worm fossil in the identical amber specimen. This clearly signifies a terrestrial or onshore surroundings on the time of entrapment in resin. As well as, many sand grains had been evenly distributed all through the amber, suggesting that the fossil was entombed in a sandy surroundings. Moreover, earlier proof reveals that the Kachin amber was deposited in a near-shore surroundings.
One potential state of affairs for the deposition of the tapeworm within the amber is that its elasmobranch host was stranded by a tide or storm. Beneath such a state of affairs, the host was then bitten by a higher-level terrestrial predator or scavenger. When the host was ingested by the predator, the tentacle was pulled away, dislodged from the gut, and caught to close by resin.
“Our research additional helps the speculation that the Kachin amber was most likely deposited in a paralic paleoenvironment, and in addition highlights the significance of amber analysis in paleoparasitology,” mentioned Wang.
Extra info:
Cihang Luo et al, Distinctive preservation of a marine tapeworm tentacle in Cretaceous amber, Geology (2024). DOI: 10.1130/G52071.1
Journal info:
Geology