Structure and function of the eversible glands of the aquatic firefly <Emphasis Type="Italic">Luciola leii</Emphasis> (Coleoptera: Lampyridae)

Summary. When attacked or otherwise disturbed, larvae of the aquatic firefly Luciola leii display fork-shaped glands laterally from the meso- and metathorax as well as each abdominal segment. Glandular eversion is accompanied by a strong pine oil-like odour, thanatosis and glowing from paired larval light organs. Observations by SEM and TEM revealed that there are numerous, almost spherical protuberances, measuring 9 μm in diameter on the surface of each gland. Each protuberance is connected to a well developed secretory cell via a 0.1 μm thick and 0.2 μm long stalk and bears three to six 7 μm long spines on its apex. The convoluted glandular walls measure 0.2 μm. The cytoplasm of the secretory cells is characterized by the presence of numerous mitochondria and an extensive system of cisternae and tubular endoplasmic reticulum. Preliminary GC-MS analysis of the glandular secretion revealed two volatile terpenoids: terpinolene and γ-terpinene. Choice and no-choice bioassays involving fish and ants as well as other predators demonstrate that the secretions serve as an effective deterrent against a range of ecologically relevant enemies. The larval postural adjustments, light emission, everted glands, and glandular release of distasteful or repellent compounds, appear to function as a multi-modal, aposematic larval defence. The tandem evolution of glandular secretions and conspicuousness in larval fireflies could partially explain their successful radiation into both aquatic and terrestrial habitats.     

Some observations on spawning and fecundity in the luminescent fish Photoblepharon palpebratus

Spawning pairs of the fish Photoblepharon palpebratus (Boddaert), a bioluminescent shallow-water species from the Banda Islands, were observed in captivity for the first time. Both female individuals of the two pairs studied were slightly larger than the males, and possessed rounder tail-fin edges, criteria which can be used for sexing. Laboratory and field observations indicate that during several dark nights in April and May one female could produce a total of up to 1,000 sticky, transparent, 1.2-mm diameter, spherical, buoyant eggs, which after a brief planktonic phase of 5 to 10 h continue their development while adhering to a substrate. This short planktonic phase might explain why P. palpebratus only occurs around the Banda Islands, although similar habitats can be found elsewhere in the South Moluccan Sea. In addition to large ripe eggs, two size-classes of immature eggs were found in the ovaries. In the aquarium pairs of P. palpebratus tended to occupy a limited area but did not show aggressive territorial behaviour.     

Skin papillae as possible electroreceptors in the deep-sea eel Cyema atrum (Cyemidae: Anguilloidei)

Surface structure and internal organization of prominent skin papillae in the mesopelagic eel Cyema atrum have been investigated by scanning and transmission electron microscopy. Each papilla is club-shaped and possesses a pore at its distal end. A central rod, filled with cellular strands and surrounded by a 30 to 40 m wide matrix of clear material, runs from the tip to the base of the papilla. A cluster of cells, located 60 m below the surface of the skin, appears to be connected with the lateral line nerve. The lack of stereo- and kinocilia on the one hand, and the presence of a central rod and a terminal pore on the other, demonstrate that the cutaneous papillae in C. atrum cannot be regarded as typical lateral-line neuromasts. They share several features with electroreceptors, known from other fishes. It is postulated that C. atrum and other deep-sea species with similar skin papillae have been able to partially substitute vision and other senses useful for orientation by electroreception.     

Structure and function of the eversible organs of several genera of larval firefly (Coleoptera: Lampyridae)

Larval defensive behaviour and eversible organ morphology were compared in the firefly species Luciola cruciata Motschulsky 1854, L. lateralis Motschulsky 1860, L. leii Fu et Ballantyne 2006, Lampyris noctiluca Linnaeus 1767, Pyrocoelia analis Fabricius 1801, P. pectoralis Oliver 1883, P. sp. and two Diaphanes species. In all cases the eversible organs are located on the pleural cuticle, dorsal to the spiracle, but there is considerable variation between species in their number, size and shape. In La. noctiluca they are confined to the abdomen, whereas in the other species they also occur on the meta- and mesothorax. In La. noctiluca and the Pyrocoelia species the organs are columnar in shape, contrasting with the forked organs of the Luciola and Diaphanes species. The eversible organs of the Luciola species, which are all aquatic, are remarkably larger (relative to body length) than those of the other, terrestrial species. On organ eversion the Luciola species emit an odour resembling pine oil, the Diaphanes species smell weakly of mint and L. noctiluca and the Pyrocoelia species produce no discernible scent, though ants are nonetheless repelled by contact with everted L. noctiluca organs. The organs of all the species studied support protuberances on their external surface, though these too vary in shape, size and ornamentation between species. In all species except L. noctiluca each protuberance is connected to a well-developed globular body via a long, thick stalk. Circular foveae are located in the centres of these globular bodies. The globular bodies consist of secretory cells characterized by the presence of numerous mitochondria and an extensive system of cisternae and tubular endoplasmic reticulum. Behavioural tests revealed that small larvae run away instead of becoming immobile and glowing, whereas large larvae start to glow when disturbed. The study shows that the eversible larval organs form an important part of a defensive arsenal in the Lampyridae.     

The lateral-line organs of the larvae of the deep-sea fish Cataetyx memorabilis (Ophidiidae): A scanning-electron and light-microscope study

A prominent lateral-line system found in 10 mm long larvae of the deep-sea fish Cataetyx memorabilis Meyer-Rochow (1970) is not present in the adults. Size and height of larval lateral-line papillae measured in stereo pairs of electron micrographs are compared with light microscopy of sectioned material. Lateral-line papillae are separated from each other by 3 to 7 myomeres (0.5 to 1 mm). A papilla is 50 m wide and approximately 15 m high. The 7 or 8 sensory hairs, which are about 30 to 40 m long, are not embedded in a jellylike transparent substance. Behavioural and taxonomical consequences of the findings are discussed.     

Clockwork blue: on the evolution of non-image-forming retinal photoreceptors in marine and terrestrial vertebrates

This paper presents a hypothesis that could explain why blue light appears to dominate non-image-forming (NIF) ocular photoreception in marine as well as terrestrial vertebrates. Indeed, there is more and more evidence suggesting that 'novel' retinal photoreceptors, which are sensitive to blue light and were only discovered in the 1990s, could be a feature shared by all vertebrates. In our view, blue light photoreception evolved and persisted as NIF photoreception because it has been useful in the colonisation of extensive photo-dependent oceanic habitats and facilitated the move of vertebrates from an aquatic to a terrestrial environment. Because the available scattered evidence is compatible with the validity of our hypothesis, we hope that our rationale will be followed up. Indeed, it (1) involves testable predictions, (2) provides plausible explanations for previous observations, (3) unites phenomena not previously considered related to one another and (4) suggests tests that have not been carried out before. Overall, our approach not only embraces cross-disciplinary links; it, moreover, serves as a reminder of an all-embracing evolutionary history, especially with regard to a ubiquitous photoreceptive 'clockwork-blue' in marine and terrestrial vertebrates.