This video is called Ocean Life – Arthropods.
From Duke University in the USA:
Study finds surprising new branches on arthropod family tree
February 10, 2010
Any way you look at it — by sheer weight, species diversity or population — the hard-shelled, joint-legged creepy crawlies called arthropods dominate planet Earth. Because of their success and importance, scientists have been trying for decades to figure out the family relationships that link lobsters to millipedes and cockroaches to tarantulas [see also here] and find which might have come first.
In a scientific and technological tour de force that was nearly a decade in the making, a team of scientists from Duke University, the University of Maryland and the Natural History Museum of Los Angeles County have compared genetic sequences from 75 different species to draw a new family tree that includes every major arthropod lineage. Some of the relationships are so surprising that new names had to be coined for five newly-discovered groupings.
A big surprise to tumble out of the new tree is that the closest living relatives of insects include a small and obscure group of creatures called remipedes that were only discovered in the late 1970s living in a watery cave in the Bahamas. With linear bodies like centipedes, simple legs and no eyes, it was thought that this small group — now placed with cephalocarids in the newly-named Xenocarida or “strange shrimp” — would be found at the base of the crustacean family tree.
Now, after analyzing 62 shared genetic sequences across all the arthropods, the researchers are putting the strange shrimp together with the six-legged insects, Hexapoda, to form a new group they dubbed Miracrustacea, or “surprising crustaceans.” As a “sister clade” to hexapods, the Xenocarida likely represent the sort of creature that came onto land to start the spectacular flowering of the insect lineage, said Cliff Cunningham, a professor of biology at Duke who led the study.
Triops, a 2-inch crustacean that looks like a cross between a horseshoe crab and a mayfly, had also been thought of as an early crustacean, but it too was shown to have a relatively modern origin in the new analysis, Cunningham said.
“Taxonomists have been arguing about these things for decades, and people kept coming at this with one data set after another,” Cunningham said. This latest study has created a fuller picture of the arthropod family tree by using more species and more genes, he said.
Beginning in 2001, Jeffrey Shultz, an associate professor of entomology at Maryland, led the efforts to figure out which species needed to be sequenced for a robust comparison, and then to round up suitable specimens of each. The study included nematodes, scorpions, dragonflies, barnacles, copepods and centipedes.
Remipedes, one of the two species of Xenocarida in the study, had to be fetched from partially submerged limestone caves in the Yucatan Peninsula and preserved just so. Bitty creatures called mystacocarids that live between grains of sand were captured by the Natural History Museum’s Regina Wetzer, using a microscope on a Massachusetts beach. …
The spiders, ticks and scorpions of the subgroup Chelicerata are shown to have split from the line leading to insects and crustaceans even before the millipedes and centipedes of the subphylum Myriapoda. Most recent molecular studies had grouped these arachnids in Chelicerata together with millipedes and centipedes of the Myriapoda. But the new analysis puts millipedes and centipedes together with crustaceans and insects in a group taxonomists had long ago named Mandibulata.
“The only thing people thought they knew before molecular data was available was that the Myriapods were with the insects,” Shultz said. But that turned out to be wrong. Even the grouping Crustacea is no longer correct, since it includes the six-legged insects.
Within the insect group Hexapoda, the good news for taxonomists who have grouped insects according to body shape and features is that they were pretty much on the mark, Shultz added.
New fossils from the Middle Jurassic period show what at least one species of spider, Eoplectreurys gertschi, looked like when dinosaurs dominated the planet: here.
Nicknamed ‘Crabzilla’ after the fictional giant monster, the Japanese Spider Crab has a body the size of a basketball and its legs can straddle a car. They will eventually measure a massive 15ft: here.
Shrimp in Drinking Water Are Microscopic and Harmless: here.
Discovering Tiny Juvenile Horseshoe Crab on First Day of Spring: here.
Horseshoe Crab Mating in Full Swing on Outer Cape Cod: here.
Photo of the Day: Horseshoe Crabs: here.
Climate Change Implicated in Decline of Horseshoe Crabs: here.
How to Tell the Difference Between a Dragonfly and a Damselfly: here.
Scientists have greatly revised their estimate of the number of spiders, insects and other arthropod species, according to a new study: here.
Two new Gammarus species (Crustacea, Amphipoda) from Iran: here.
Female mating failures in insects: here.
Kergueleniidae fam. nov. (Crustacea: Amphipoda: Lysianassoidea) in Australian waters: here.
From COSMOS magazine:
Walking cactus gives arthropod evolution a leg-up
Thursday, 24 February 2011
by Taylor Burns
CAMBRIDGE: An international team of paleontologists may have found the evolutionary key to the most diverse species on earth – in the form of a walking, sea-dwelling, armoured ‘cactus’.
The study, published in Nature, documents the discovery of an unusual worm-like creature from Cambrian-era China. The fossil suggests the species to have developed robust, hardened legs before the acquisition of an armoured torso, raising questions about the evolution of arthropods in general, from scorpions to wasps to butterflies.
“Arthropods are the richest species on earth – there are over one million described species. Thus, the origins of arthropods is always a hotly contested issue,” said lead author Jianni Liu, an earth scientist at Northwest University in Xi’an, China. “But until now we didn’t have a single fossil with appendaged joints indicating an early arthropod. Our fossil shows a link – that’s the important point.”
Absence of suggestive fossils
The evolutionary stems of most modern species were born 500 million years ago in the Cambrian explosion – a period of rapid, complex evolution that diversified what was otherwise relatively small and simple life. Mineralised organisms became common for the first time, allowing for fossilisation.
Despite the richness of the era, however, there has been a notable absence of suggestive fossils that connect arthropods to a common ancestor.
Liu and her colleagues suggest that they may have found this link, situating lobopodians – a group of small, sea-faring animals originating in the Early Cambrian, resembling modern velvet worms or water bears – as potential ancestors of arthropods in general.
Arthropod or lobopodian?
Although the ‘walking cactus’ (Diania cactiformis) is, in many ways, a typical lobopodian, it is remarkable for also sharing features with arthropods. Most notably, its limbs are armoured, implying that it is close the point of arthropodisation.
“When I got the fossils, I was so surprised,” said Liu. “I couldn’t understand a creature with a soft body but hardened limbs. It’s really on the way to arthropods.”
The ‘walking cactus’ lived mostly in the sea, no more than 200 metres away from the shore at any given time, Liu said. Although data is not readily available, the researchers speculate that it was a kind of sediment feeder, extracting nutrients from the soil like certain worms today.
Did hard legs precede armour?
Another possibility is that it used its spindly legs to catch creatures and eat them, similar to numerous modern arthropods.
These two potential feeding habits highlight the dilemma of the finding: how far along is the arthropodisation process in this lobopodian? And can we confidently claim it to be a common ancestor for arthropods in general?
Evolution of blindness in scolopendromorph centipedes: insight from an expanded sampling of molecular data: here.
Millipede Taxonomy after 250 Years: Classification and Taxonomic Practices in a Mega-Diverse yet Understudied Arthropod Group: here.
Long-bodied Water Scorpion: here.