The photophore morphology of Selenoteuthis scintillans Voss and other lycoteuthids (Cephalopoda: Lycoteuthidae)

Females and juveniles of Selenoteuthis scintillans have photophores of several structural types, distributed on the tentacles and eyeballs, and within the mantle cavity and tail. Three distinct photophore types can be recognized on the basis of their accessory structures, though their photocytes are identical. The tail and some tentacular photophores (Type 1) lack any accessory optical structures; other tentacular and abdominal photophores (Type 2) have collagenous diffusing fibres; the anal and ocular photophores (Type 3) have a variety of iridosomes but no collagen. The distal tentacular organ is a double structure composed of a unit each of Type 1 and Type 2. Ocular photophores 1 and 5 are also double structures, composed of two Type 3 units. The photophores closely resemble in structure those of Lycoteuthis diadema. The photocytes have a marked fluorescence and luminesce on treatment with dilute hydrogen peroxide. The bio-luminescence intensity of the tail organ may be modified by chromatophore movements and has a blue-green spectral emission.
The photophores of juvenile Lampadioteuthis megaleia are similar in structure to those of Selenoteuthis but somewhat less complex. A comparison between the morphology of the photophores of lycoteuthid and enoploteuthid squids emphasizes the close similarity between the two families. At the ultrastructural level, certain photophores of both families have very characteristic microvillous blood vessels associated with the photocytes.     

Structural and ultrastructural comparison of photophores of two species of deep‐sea fishes: Argyropelecus hemigymnus and Maurolicus muelleri

The structure of the photophores (luminous organs) of two species of deep‐sea fishes from the Strait of Messina, Argyropelecus hemigymnus and Maurolicus muelleri , was examined. Although significant structural differences were identified between species, especially in photophore organization and distribution, ultrastructural comparisons indicated a marked similarity between them. The photocytes exhibited numerous secretory granules, of different electron density, embedded in an extremely developed rough endoplasmic reticulum. Numerous mitochondria were observed among the secretory granules. The lens appeared to be composed of tightly contiguous polyhedral cells. The reflector was made up of cells rich in guanine crystals embedded in an amorphous matrix and appeared to be surrounded by a layer of connective tissue full of melanocytes. Ventrally, every photophore was delimited by a thick cellular layer called the 'gelatinous layer' with dioptric properties. The results confirm that even though A. hemigymnus and M. muelleri differ widely phylogenetically, they exhibit adaptive convergence, involving similar morphology and physiology in these luminous structures.     

The comparative morphology of the photophores of the squid Pyroteuthis margaritifera (Cephalopoda: Enoploteuthidae)

Pyroteuthis margaritifera has morphologically distinctive photophores on the tentacles, eyeball and in the mantle cavity. The photogenic tissue in each photophore is identical, has a blue-green fluorescence and luminesces on treatment with dilute hydrogen peroxide. The photocytes frequently contain organized fibrillar material akin to that in the photocytes of certain other cephalopods. Several different types of blood vessel are present among the photocytes, including some, apparently restricted to the photophores, with a microvillous endothelium. Haemocyanin is present not only within identifiable blood vessels but also in some intercellular spaces.
On the basis of their characteristic optical systems the photophores can be separated into three types: (1) tentacular; (2) ocular and anal; (3) branchial and median abdominal. The tentacular photophores have collagenous reflector and light guide systems and the median ones are double organs. The ocular and anal organs do not have collagenous optical structures but an elaborate variety of reflective iridosomes. Those in the aperture of the photophores appear to act as interference filters. The branchial and abdominal organs have iridosomes as the major reflective tissue but collagenous fibrils function as light guides in the aperture of these organs and their emission is diffuse rather than collimated.     

The morphology of photophores in the garrick,cyclothone braueri (Family: Gonostomatidae): an ultrastructure study

A contribution to the knowledge of the photophore structure of the mesopelagic fish Cyclothone braueri (Gonostomatidae) from the central Mediterranean Sea (Strait of Messina) is given by means of a structural and ultrastructural study, to better identify and classify the real anatomical structures costituing these luminous organs. The photocytes exhibit numerous secretory granules, of different electron density, embedded in an extremely developed rough endoplasmic reticulum. The lens appear to be composed of tightly contiguous polyhedral cells. The reflector is made up of cells rich in guanine crystals, embedded in an amorphous matrix and is surrounded by a layer of connective tissue containing melanocytes. Unlike the present knowledge, it is shown that the bioluminescence emitted from C. braueri light organs has glandular nature, with photophores similar to type α from Bassot classification. The phenomenon of adaptive convergence, documenting how the morphology and physiology of the light organs of teleosts is similar in different species despite their taxonomic distance, is confirmed also for C. braueri.     

The fine structure of the light organ of the glowworm Lampyris noctiluca

Summary The four main parts of the glowworm light organ are the cuticle, the hypodermis, the photocyte layer and the reflector cell layer. The hypodermis is one cell thick and it contains hypodermic glands. These glandular cells have a lumen that opens to the outside of the cuticle. Projecting into the lumen are numerous microvilli. Between the hypodermis and photocytes are typical insect tunicated nerve fibres. They pass down between the photocyte and reflector layer cells. They do not appear to innervate the photocytes and they are thought to innervate adjacent muscle fibres or to be sensory. Tracheoles are commonly present between the photocytes but no tracheolar end organs are found. The photocytes contain amorphous granules, mitochondria, photocyte granules and a vesiculated reticulum. All, except the mitochondria, are absent from the reflector layer and so probably have some connection with light production. The reflector layer contains glycogen granules, clear spaces thought to be the sites of urate crystals, and membranous granules. The latter granules are sometimes found in photocytes adjacent to the reflector layer whilst amorphous granules are sometimes absent from these adjacent cells. So a cell layer with some features of the photocyte and reflector layer cells is present. These morphological findings are discussed with regard to the unknown function of the reflector layer and the control of light emission. Acknowledgments. We would like to thank Professor J. Z. Young and Dr. E. G. Gray for their advice and encouragement, Mrs. Jane, Astafiev for drawing fig. 1, Mr. S. Waterman for photographic assistance, Miss Cheryl Martin for secretarial assistance, and many colleagues for help in collecting specimens of glowworms.     

Ultrastructural organization of lantern shark (Etmopterus spinax Linnaeus, 1758) photophores

Etmopterus spinax Linnaeus, 1758 is a deep-sea lantern shark that emits blue light thanks to thousands of tiny cup-shaped organs made of a pigmented sheath enclosing light-emitting cells topped by an iris-like structure and a lens. In this study, we investigate the ultrastructure of these photophores in order to improve our understanding of the light emission process. The presence of a novel layer, a putative reflector upholstering the pigmented sheath, is highlighted. The intracellular organization of the photocytes is addressed. They appear as regionalized cells: their basal area is occupied by an ovoid nucleus, their medial area is highly vesiculated and their apical area, oriented toward the photophore center, displays small granular inclusions. We hypothesize this granular area to be the intracellular site of photogenesis in E. spinax, as it is also the most fluorescent part of the photocyte.     

Ultrastructural features of the light organs of Histioteuthis macrohista (Mollusca: Cephalopoda)

The general morphology and ultrastructure of the epidermal and arm tip photophores of H. macrohista have been compared. Both types of photophore have similar structures
and the photocytes of each are characterized by dense aggregations of endoplasmic reticulum. The filter region of the epidermal photophores contains protoporphyrin.     

Reflector of the body photophore in lanternfish is mechanistically tuned to project the biochemical emission in photocytes for counterillumination

Lanternfish, a family Myctophidae, use ventro-lateral body photophores for camouflage of the ventral silhouette, a strategy called counterillumination. While other deep-sea fishes possess pigmented filters and silver reflectors to match sunlight filtering down through the depths, myctophids developed a blue-green reflector for this purpose. In this study, we showed in a lanternfish Diaphus watasei that the reflector comprised monolayered iridophores containing multilayered guanine crystals which enable high reflection with light interference colouration. Platelets shape in body photophores is an unique near-regular hexagonal, probably to allow the homogeneity of reflection angle of the luminescence from photocytes. Focus point of the parabola-like reflector is positioned on the photocytes that ensures the light produced from the photocytes is redirected to the ventral direction. In vitro luminescence reaction using purified luciferase and the substrate coelenterazine showed the light emission at λ_max 454 nm, while reflection spectra of the iridophores exhibit peaks at longer wavelength, which accomplish to alter the luminescence emitted from photocytes to longer wavelength to fit the mesopelagic light environment. Taken together, we revealed multiple mechanistic elaborations in myctophid body photophores to achieve effective control of biochemical luminescence for counterillumination.     

Reevaluation of coleoid cephalopod relationships based on modified arms in the Jurassic coleoid Mastigophora

Mastigophora brevipinnis Owen, 1856, is a 'fossil teuthid' presently considered to be a member of the coleoid cephalopod Suborder Loligosepiina Jeletzky, which in turn has been placed by various authors in or near the Vampyromorpha Grimpe. Recent morphological and biochemical analyses indicate that vampyromorphs are more closely related to the Octopoda than to the Decapodiformes. Fossils of Mastigophora from the Oxford Clay (Jurassic: Callovian) show soft-tissue preservation and evidence of arm crown specialization. Some of these fossils have up to eight short, thick arms with circular sucker-like structures and filiform distal extensions, plus what appear to be the bases of two thinner ventrolateral arms. The latter lack proximal suckers and curve medially to insert into the arm crown, similar to the tentacles that are the modified ventrolateral arms of living squids and cuttlefishes. This suggests that the thinner structures were decapod-like tentacles. If Mastigophora had tentacles homologous with those of modern decapods, then it was a decapod, because this synapomorphy defines the Decapodiformes. This indication of decapod affinities for Mastigophora brings into question the relationships of the other 'fossil teuthids'. The inferred relationship of the Loligosepiina, including Mastigophora , with the Vampyromorpha, based largely on similarities of gladius morphology with that of living Vampyroteuthis , may reflect shared plesiomorphic characters.     

Different types of photophore in the oceanic squids Octopoteuthis and Taningia (Cephalopoda: Octopoteuthidae)

The oceanic squid Octopoteuthis danue Joubin has one type of photophore on the head, body and arms, but another type on the eight arm tips. The first type has acomplexcapillary network, with elastic walls and a thick reflector. The arm tip organs have no such capillary core but a dense matrix containing paracrystalline assemblies.
Taningia danae Joubin (the only other genus in the family Octopoteuthidae) has only two large arm tip photophores. These are similar in their general organization to the arm tip photophores of Octopoteuthis , but their detailed structure is quite different.
There has evidently been independent evolution of photophores in this family of squids.     

Pharmacomorphological study of denervation induced by 6-hydroxydopamine in Porichthys photophores

The effects of 6-hydroxydopamine (6-OHDA) on the bioluminescent response of Porichthys photophores were investigated as part of a pharmacological study of the neural control of luminescence in this fish. Subcutaneous injections of 6-OHDA induce a luminescent response similar to that of norepinephrine (NE), suggesting a sympathomimetic action. The luminescent response to electrical stimulation is almost completely and irreversibly abolished within 24 hours following low-dose treatment of the photophores with 6-OHDA, while the sensitivity of these organs to exogenous NE is increased significantly over the few days post-treatment. During this period the photophores continuously emitted a steady low-level glow. Electronmicroscopic studies of such photophores revealed progressive destruction of the nerve endings. Photophore luminescent sensitivity to NE subsequently became sub-normal, and at this stage electron microscopy revealed an increasingly larger number of damaged photocytes, supportive cells and, in one case, lens cells. From these results it is suggested that 6-OHDA initially impairs neuro-photocyte transmission by destroying catecholaminergic nerve endings. In turn, the transmitter reuptake mechanism is also impaired, thus accounting for development of supersensitive responses to exogenous NE. Subnormal luminescent responses to NE appear as a result of loss of photocyte competence due to structural deterioration. The latter are interpreted as the consequence of removal of trophic factors supplied by the photophore adrenergic innervation.Suppression of luminescent response to both electrical stimulation and exogenous NE in photophores treated with higher doses of 6-OHDA, may be due to a direct effect of this drug on the receptor sites of the photocytes.     

Evidence for a widespread involvement of NO in control of photogenesis in bioluminescent fish

Krönström, J. and Mallefet, J. 2009. Evidence for a widespread involvement of NO in control of photogenesis in bioluminescent fish. —Acta Zoologica (Stockholm) 91 : 474–483. The presence of nitric oxide synthase (NOS) and nerve fibres in the photophores of seven bioluminescent fish species (Hygophum benoiti, Myctophum punctatum, Electrona risso, Cyclothone braueri, Vinciguerria attenuata, Maurolicus muelleri and Porichthys notatus) with endogenous photocytes, were investigated. Antibodies directed against neuronal and inducible NOS (n and iNOS respectively) and NADPH‐diaphorase activity were used to reveal the locations of NOS, while antibodies directed against acetylated tubulin were used to visualize nerve fibres. The nNOS antibody labelled structures in all investigated photophores except in the organs from P. notatus. The photocytes of P. notatus showed NADPH‐diaphorase activity. In the myctophid species, NOS‐like immunoreactivity was found in small intracellular structures of the photocytes and in nerve fibres reaching the photocytes. nNOS‐positive fibres were also found among lens/filter cells in V. attenuata, and in M. muelleri the cytoplasm of lens/filter cells contained NOS‐like material. In C. braueri, a cell type located at a collecting chamber for luminous products in the photophore contained NOS‐like material. All photophores received an innervation reaching the photocytes, as well as other components including lens/filter areas. The results of this study comply with an involvement of nitric oxide in the control of bioluminescence in several fish species.     

A biochemical characterization of the photophore lenses of the midshipman fish,Porichthys notatus Girard

The present study is a biochemical characterization of the photophore lenses of the midshipman fish, Porichthys notatus, a species that bears 800 photophores distributed over the body surface. The biochemical properties of the photophore lenses were compared with those of the eye lens with which they share a similar developmental origin and analogous function. To achieve a high refractive index, the vertebrate eye lens has a relatively high concentration of structural proteins (20–50%, depending on species) and a simple protein composition, that is, relatively few proteins are synthesized in comparison to other tissues. Similarly, the photophore lenses of P. notatus had a relatively high protein concentration (average = 29%, n = 5) and approximately 60% of the total soluble protein was represented by two subunit species of 33 kD and 35 kD on denaturing polyacrylamide gels. The structural proteins of the eye lens are of two principle types: 1) and polypeptides which belong to vertebrate lens-specific crystallin families, and, 2) enzymes recruited into the lens which take on the function of structural proteins. Here, we report that the two major photophore lens subunits of 33 kD and 35 kD are biochemically similar to each other, but are clearly distinct from any of the previously characterized crystallins. Therefore, we propose that photophore lenses appear to recruit a novel protein.     

Differentiation of the Opercular Integument in Rana pipiens

The opercular skin develops in its own specific fashion differing from other areas of the integument previously studied. It remains typically larval until it is sloughed off.
The opercular integument first deviates from the common skin development pathway at stage XV [1] when the rough endoplasmic reticulum. proliferates to form a large part of the cytoplasm and is accompanied by numerous large mitochondria. The Golgi apparatus becomes very large and many vesicles are found in the cytoplasm.
The mitochondria become large and swollen with atypical structure. The cytoplasm becomes highly vesiculated. Degeneration begins at the dermal edge of the basement lamella and proceeds toward the epidermis, being marked by the disorientation of collagen fibrils.
Epidermal cells become progressively more necrotic having cytoplasm consisting mainly of residual bodies and vesicles: the nucleus is the last cellular structure to undergo autolysis.
The dermal cells are the first to be lost (stages XVIII–XIX). The opercular integument is shed as a sheet of cells at stage XX when the forelimbs emerge. The necrotic zone of the opercular integument appears to stop at the junction of the body skin and the skin of the forelimb.     

A probable homologue of the clavicle in the holostean fish Amia calva

The two pairs of appendages associated with the throat region in Amia are described.
The posterior serrated appcndage of Amia calva is considered a homologue of the clavicle. This theory is based on topographical similarity (a bony element situated in front of the ventral part of the cleithrum and overlapping the anterior margin of the adjoining part of the cleithrum), structural similarity (cellular bone with ridges bearing denticles arranged in distinct patterns), ontogenetic similarity (early ontogenctic ossification with other dements of the dermal shoulder girdle prior to the appearance of scales), and phylogenetic cvidcnce (presence of similar elements in the caturid Furo ).
Although the anterior serrated appendage of A. calva exhibits structural and topographical similarities to both scales and clavicles, the ontogenetic evidence favours an homology with scales.
The ossicles located dorsolateral and lateral to the anteroventral part of the cleithrum in Lepisosteus oculatus share structural and topographical similarities to both scales and clavicles. However, ontogenetic evidence indicates that these ossicles are scales rather than fragmented clavicles.     

Cytological changes during bioluminescence production in dissociated photocytes from the ophiuroid Amphipholis squamata (Echinodermata)

Bioluminescence in the ophiuroid Amphipholis squamata is produced by photocytes located within the spinal ganglia of arm spines. Ganglionic cells were dissociated (pronase digestion) and photocytes separated from other cell types by using a continuous density Percoll gradient. Aliquots from a stock suspension of photocytes in artificial sea water were stimulated to produce light by using KCl or acetylcholine and fixed for ultrastructural observation at different times of the luminous process. Preluminescent, luminescent, and postluminescent photocytes contained various intracytoplasmic structures, such as Golgi, flat and distended rough endoplasmic reticulum cisternae, bundles of fibrils, and up to six types of membrane-bounded vesicles. These structures either co-occurred or succeeded one another during the process of light production, indicating that they were most probably participating in the luminescence reaction. Two types of vesicles, sharing some ultrastructural features, probably represented the microsources of the photocytes. One type occurred almost exclusively in luminescent photocytes, and the other almost exclusively in postluminescent photocytes, suggesting that one may be transformed into the other. The latter type of vesicle contained densely packed fibro-tubular units, giving a characteristic paracrystalline appearance to postluminescent photocytes.     

Ultrastructural data on the scales of the dipnoan Protoptems annectens (Sarcopterygii, Osteichthyes)

The structure and the mineralization of the scales of the living dipnoan (lungfish) Protoptems annectens have been investigated by transmission electron microscopy (TEM). The thin and imbricated scales are composed of two layers: the squamulae and the basal plate. At the outer surface, the squamulae form isolated plates superficially ornamented with spines and concretions and made up of acellular bone. After demineralization, the squamulae show a heterogeneous organic matrix composed of thin randomly oriented collagen fibrils forming a loose network within which the concretions appear as electronlucent circular areas. Abundant and aggregated concretions are located within the spines. The crystallites are oriented by the collagen fibrils except in the concretions. Anchoring bundles composed of parallel collagen fibrils arise from the squamulae and connect the scales to the overlying dermis.
The basal plate, the most developed part of the scale, is made up of isopedine. Its main component consists of thick, closely packed collagen fibrils organized in a 'double twisted plywood-like structure'. Fibroblasts are present in the basal plate. Mineralization occurs only in few plies located beneath the squamulae. Mandl's corpuscles are found in front of the mineralization front. The mineral deposit is oriented by the collagen fibrils.
The scales of Protoptems annectens differ from the typical elasmoid scales of the teleosts by the peculiar structure of the squamulae, nevertheless they show enough structural characteristics to support the hypothesis that they can be considered as scales of the elasmoid grade, which have retained some plesiomorphic characteristics.