Our new find is exciting because it shows that mandibulates (to which crustaceans belong) and chelicerates were already present as two distinct evolutionary trajectories 520 million years ago, which means their common ancestor must have existed much deeper in time.
They compared this to the nervous systems of horseshoe crabs and scorpions and found without doubt that the creature belonged to the chelicerate family.
Arachnids, and other chelicerates, lack a mineralized exoskeleton, thus their fossil record is sporadic and relies heavily on "windows" of exceptional preservation (Table 2).
Our total dataset for amber and non-amber spiders yields 979 fossil species; thus spiders show the highest levels of paleodiversity approaching three times as many species as the next largest chelicerate groups (Table 1).
Phylogeny and systematic position of Opiliones: a combined analysis of chelicerate
relationships using morphological and molecular data.
It is unknown why chelicerates
produce the D optical isomer of lactate whilst other arthropods, such as crustaceans, produce the L optical isomer and others (most insects) appear to have lost the expression of the LDH gene (Long & Kaplan 1968; Sacktor & Wormser-Shavit 1966).
The relatively large size of scorpions, compared with most other chelicerates
, implies that low depth of field issues are not likely to be experienced unless imaging the smallest of scorpions, or very small structures such as chelicerae and tarsi.