Gordon Hendler

Designing efficient microlens arrays: lessons from Nature

Nature provides a whole host of superior multifunctional structures that can be used as inspirational systems for the design and synthesis of new, technologically important materials and devices. We review here the exceptional optical performance of microlens arrays formed by light-sensitive brittlestars, their structural and compositional features, and advantageous properties. We show that brittlestars form a nearly perfect optical device with micron-scale, lightweight, mechanically strong, aberration-free, birefringence-free, individually-addressed lenses, which offer a unique focusing effect, signal enhancement, intensity adjustment, angular selectivity, and photochromic activity. We discuss first materials fabrication strategies that were inspired by the principles involved in the formation of echinoderm calcitic structures. The biomimetic synthetic microlens arrays could be potentially used as highly tunable optical elements for a wide variety of applications.

Fine structure of the dorsal arm plate of Ophiocoma wendti: Evidence for a photoreceptor system (Echinodermata, Ophiuroidea)

SummaryThree structures in the dermis of the dorsal arm plate (DAP) of the brittlestar, Ophiocoma wendti, appear to comprise a photoreceptor system. The upper surface of the DAP bears transparent, knob-like, microscopic structures which are expanded peripheral trabeculae (EPT) of the calcite stereom. The EPT are part of the photoreceptor system and can facilitate light transmission through the DAP by decreasing light refraction, reflection and absorption that occur at stereom/stroma interfaces. Bundles of nerve fibres located below the EPT are a second component of the system, and may function as primary photoreceptors. The intensity of light impinging on the putative sensory tissue is regulated by the diurnal activity cycle of chromatophores, the third element of the system. During the day the chromatophores cover the EPT and thereby shade the nerve fibres. At night they retract into inter-trabecular channels, uncovering the EPT and thereby exposing the nerve fibres to transmitted light. Thus, the transparent stereom may play a role in photoreception, in addition to its generally recognized skeletal function. Although ciliated cells that may be sensory are present in the epidermis of Ophiocoma wendti, they do not appear to be photoreceptors. Functional analogues of the brittlestar photoreceptor system in other echinoderms are discussed, emphasizing the relationship between photosensitivity and the transparency of the stereom in several classes of Echinodermata.

A NEW SPECIES OF COPEPODA (THAUMATOPSYLLIDAE) SYMBIOTIC WITH A BRITTLE STAR FROM CALIFORNIA, U.S.A., AND DESIGNATION OF A NEW ORDER THAUMATOPSYLLOIDA

Abstract A new species of thaumatopsyllid copepod, Caribeopsyllus amphiodiae, is described based on adult specimens reared from nauplii inhabiting the stomach of a burrowing, amphiurid brittle star, Amphiodia urtica (Lütken), collected in California, U.S.A. It is the first member of the family to be reported from the eastern Pacific Ocean. Caribeopsyllus chawayi, its only known congener, inhabits the Caribbean Sea. All other thaumatopsyllid species occur in the eastern hemisphere. Caribeopsyllus amphiodiae is only the second thaumatopsyllid of which both sexes and sexual dimorphism have been described and for which a host species has been identified. Caribeopsyllus differs from confamilial genera by the presence of a 1-segmented leg 4 exopod. The new species is distinguished from C. chawayi by its general habitus, and by the absence of spiniform processes at the base of each exopodal spine of leg 1 and the first three exopodal spines of leg 2. Analysis of the phylogenetic relationships of Thaumatopsyllidae shows that it is not a member of any of the other previously established orders of Copepoda. Accordingly, a new order, Thaumatopsylloida, is proposed to accommodate the five species of thaumatopsyllids thus far reported and is shown to be a member of a Thaumatopsylloida-Monstrilloida-Siphonostomatoida clade.

Coherently aligned nanoparticles within a biogenic single crystal: A biological prestressing strategy

Many roads to being tough A number of routes exist to increase toughness in both natural and human-made materials—for example, using secondary phases and precipitates or exploiting tailored architectures and shaped crystals. Polishchuk et al. detail the nanoscale internal structure of calcitic microlenses formed by a brittlestar (see the Perspective by Duffy). The segregation of magnesium-rich particles forms a secondary phase that places compressive stresses on the host matrix. This toughening mechanism resembles Guinier-Preston zones known in classical metallurgy. Science, this issue p. 1294 see also p. 1254 Coherent precipitation, known in metal alloys to provide substantial hardening and strengthening, is observed in a biomineral. In contrast to synthetic materials, materials produced by organisms are formed in ambient conditions and with a limited selection of elements. Nevertheless, living organisms reveal elegant strategies for achieving specific functions, ranging from skeletal support to mastication, from sensors and defensive tools to optical function. Using state-of-the-art characterization techniques, we present a biostrategy for strengthening and toughening the otherwise brittle calcite optical lenses found in the brittlestar Ophiocoma wendtii. This intriguing process uses coherent nanoprecipitates to induce compressive stresses on the host matrix, functionally resembling the Guinier–Preston zones known in classical metallurgy. We believe that these calcitic nanoparticles, being rich in magnesium, segregate during or just after transformation from amorphous to crystalline phase, similarly to segregation behavior from a supersaturated quenched alloy.

Neurophysiological characterization of the photoreceptor system in a brittlestar, Ophiocoma wendtii (Echinodermata: Ophuroidea)

Abstract 1. 1. The photosensitivity of Ophiocoma wendtii can be detected neurophysiologically by recording from single units within the nerve cord of isolated arms. 2. 2. Individuals show a strong light “ON” response and a relatively weak light “OFF” response, consistent with whole organism behaviour. 3. 3. The presence of an intraskeletal primary photoreceptor is corroborated by monitoring nervous response to light after the chemical disruption of successive layers of the integument. 4. 4. Results support the hypothesis that microscoplc, transparent structures of the skeletal plates (EPT), and their associated chromatophores and nerve bundles comprise a photoreceptor system. 5. 5. Analogous specializations in other echinoderms are suggested to account for “extraocular photo-sensitivity” that characterizes the phylum.

Echinodermata Collected at Rocas Alijos

Over 600 species of echinoderms are known from central eastern Pacific waters, but considerably fewer shallow-water taxa are reported from the region’s oceanic islands (Maluf, 1988, 1991). The relative impoverishment of the island fauna stems from biogeographic factors. However, the limited list of island species is, to some extent, an artifact of incomplete biological surveys. Therefore, additional information on eastern Pacific island biota is of systematic and zoogeographic importance. Data for certain remote localities are of special value. One such site, Rocas Alijos, lies in a transitional region between the temperate Californian and the tropical Panamic provinces.

Larval biology of thaumatopsyllid copepods endoparasitic in Caribbean ophiuroids.

Abstract The parasitic metanauplius larva of an undescribed species of Caribeopsyllus, the second thaumatopsyllid species to be reported from the Caribbean, was discovered in Ophiothrix angulata in Belize. In addition, metanauplii of Caribeopsyllus chawayi, whose free-living stages were previously known, were found to parasitize Ophiactis savignyi. Their ophiuroid hosts usually contained a single larva that caused them no discernable physical damage. Caribeopsyllus chawayi, which was initially described from Mexico, is here reported from Belize and is suggested to occur in Brazil. It might occur in the Pacific Ocean, as its host is circumtropical. Larvae of the Belizean thaumatopsyllids are exceptional among copepod nauplii for their large size, four pairs of appendages, true chelate mandibles, elaborate tripartite eyes, accessory photoreceptive structures (Gicklhorns organ), sexual dimorphism, and endozoic parasitism. Thaumatopsyllus paradoxus and Caribeopsyllus amphiodiae, the only other thaumatopsyllids with known metanauplii, have the same suite of specializations. However, metanauplii of the latter two species crawl, whereas the Belizean metanauplii swim. Both Belizean species have an antennal arthrite used for feeding and well-developed mandibular setae used for locomotion, which are lacking in C. amphiodiae. They leave the host as non-feeding positively phototactic copepodids. Morphological features distinguishing the metanauplii of Belizean species from that of C. amphiodiae indicate that the latter should be referred to a new genus if the systematic significance of its unique morphology is corroborated. Similarities between thaumatopsyllids and siphonostomatoids in the ontogenesis of their caudal rami suggest that Thaumatopsyllidae may belong to the Siphonostomatoida, or be closely allied.