The stiffness (flexural rigidity) of live sperm flagella, Triton-demembranated flagella (axonemes), trypsin-digested axonemes, and doublet microtubules of the axonemes in echinoderms was determined from the relationship between their deformation when a stream of medium was applied and the viscous resistance of the medium acting on the flagellum. The stiffness of the flagellum beating in seawate...

A well-supported phylogeny of echinoderm classes has eluded morphological, embryological, molecular, and combined analyses. From this body of work it is apparent that (i) echinoids (sea urchins) and holothuroids (sea cucumbers) are related, and (ii) crinoids (sea lilies) are the sister taxon to extant eleutherozoan classes (asteroids, ophiuroids, echinoids, and holothuroids). However, the relat...

While some aspects of the phylogeny of the five living echinoderm classes are clear, the position of the ophiuroids (brittlestars) relative to asteroids (starfish), echinoids (sea urchins) and holothurians (sea cucumbers) is controversial. Ophiuroids have a pluteus-type larva in common with echinoids giving some support to an ophiuroid/echinoid/holothurian clade named Cryptosyringida. Most mole...

When echinoderms are conceptualized as hydraulic entities, the early evolution of this group can be presented in a scenario which describes how a bilateral ancestor (an enteropneust-like organism) gradually evolved into a pentaradial echinoderm. According to this scenario, the arms are outgrowths from the anterior/ posterior body axis of the bilateral pterobranchia-like intermediate. These outg...

Understanding of the echinoderm nervous system is limited due to its distinct organization in comparison to other animal phyla and by the difficulty in accessing it. The transparent and accessible, apodid sea cucumber Leptosynapta clarki provides novel opportunities for detailed characterization of echinoderm neural systems. The present study used immunohistochemistry against FMRFamide and hist...

Mesophotic ecosystems (50–400 m depth) of the southeastern Pacific have rarely been studied because logistical challenges in sampling across this remote zone. This study assessed how oxygen concentrations and other environmental predictors explain variation echinoderm assemblages at these mesophotic systems, where group is among predominant fauna. We compiled data on taxa 91 stations, from hist...