Nauplius Eye Research Articles

Two new genera of cyclopinid copepods (Crustacea) from anchihaline caves on western Mediterranean and eastern Atlantic islands

Abstract Troglocyclopina balearicagen nov. sp. nov.andMuceddina multispinosagen nov. sp. nov.are described from the flooded coastal karst of the Balearic Islands, and from caves on Sardinia, the Balearics, and Lanzarote (Canaries), respectively. Both taxa seem to prefer anchihaline habitats with water salinities in excess of 18 ‰, althoughTroglocyclopinahas also been found in more reduced salinity cave lakes located some distance from the coast. These new taxa are the first cyclopinids to be reported from caves, all previous citations of cyclopinids from hypogean environments relate only to the marine interstitial. The small clutch-size exhibited byTroglocyclopina balearica(two eggs per sac) and the absence of the exopodal seta on the antenna ofMuceddina multispinosaare interpreted as troglomorphic features, in addition to the absence of the nauplius eye and the lack of body pigmentation in both taxa. The derivation of both taxa from shallow-water, hyperbenthic marine ancestors is proposed.

Embryogenesis, hatching and larval development of Artemia during orbital spaceflight

Developmental biology studies, using gastrula-arrested cysts of the brine shrimp Artemia franciscana, were conducted during two flights of the space shuttle Atlantis (missions STS-37 and STS-43) in 1991. Dehydrated cysts were activated, on orbit, by addition of salt water to the cysts, and then development was terminated by the addition of fixative. Development took place in 5 ml syringes, connected by tubing to activation syringes, containing salt water, and termination syringes, containing fixative. Comparison of space results with simultaneous ground control experiments showed that equivalent percentages of naupliar larvae hatched in the syringes (40%). Thus, reactivation of development, completion of embryogenesis, emergence and hatching took place, during spaceflight, without recognizable alteration in numbers of larvae produced. Post-hatching larval development was studied in experiments where development was terminated, by intrduction of fixative, 2 days, 4 days, and 8 days after reinitiation of development. During spaceflight, successive larval instars or stages, interrupted by molts, occurred, generating brine shrimp at appropriate larval instars. Naupliar larvae possessed the single naupliar eye, and development of the lateral pair of adult eyes also took place in space. Transmission electron microscopy revealed extensive differentiation, including skeletal muscle and gut endoderm, as well as the eye tissues. These studies demonstrate the potential value of Artemia for developmental biology studies during spaceflight, and show that extensive degress of development can take place in this microgravity environment.

Remodeling of the Nauplius Eye into the Adult Ocelli during Metamorphosis of the Barnacle, Balanus amphitrite hawaiiensis: (Crustacea/cypris larva/photoreceptor/rhabdom/Ultrastructure).

The planktonic barnacle larva has a single median ocellus (nauplius eye), while the adult possesses two distinct sets of photoreceptors; a pair of lateral ocelli and a single median ocellus. The nauplius eye of the cypris larva of Balanus amphitrite hawaiiensis is composed of 14 visual cells grouped into three components (a pair of lateral components and a single ventral component) surrounding two centrally located pigment cells; each lateral component consists of 5 visual cells and the ventral component, 4 visual cells. In each component, the rhabdom is made up of apposing microvilli arising directly from the neighboring visual cell bodies. During metamorphosis into the adult form, the three components of the median ocellus become separated. Each lateral component migrates laterally on the mantle and is remodeled into the adult lateral ocellus, losing two visual cells but gaining new pigment and tapetum cells in the process. The ventral component remains in the mid portion and becomes the adult median ocellus without fundamental modification in composition. The visual cells in both ocelli undergo a marked increase in volume and form many finger-like dendrites. Rhabdomes are made up of interdigitating microvilli arising from the the dendrite tips.

Comments on the morphology of the pre-oral spine in Argulus (Crustacea: Branchiura).

A histological study of the pre-oral spine and associated structures in Argulus japonicus reveals that two exceptionally long and slender muscles casuse retraction of the spine into the spinal sheath. Originating from the body wall mid-dorsally the two muscles proceed through the nerve ring and the blood-filled lumen of the spinal sheath before being inserted on a bolster of tissue constituting the base of the spine. Movement of the spinal sheath is affected by two muscles originating from a common apodeme in the dorsal body wall, just posterior to the nauplius eye, and inserted on the lateral walls of the base of the spinal sheath. Two ducts, each leading from a glandular complex in the lateral parts of the carapace, proceed rostrally through the haemocoelic spaces. After passing the tritocerebrum laterally they accompany the retractor muscles of the spine on their course to the base of the spine. Passing through the bolster of tissue at the base of the spine the two ducts run all the way up to the tip of the spine where they open separately. The glandula praeboscoidalis is not associated with the pre-oral spine since its duct runs posteriorly in the wall of the proboscis. The labial spines are associated with giant glandular cells located beneath the optic tracts. © 1992 Wiley-Liss, Inc.

Ultrastructural study of the naupliar eye of the ostracodeVargula graminicola (Crustacea, Ostracoda)

Ostracodes, like other crustaceans, have a simple naupliar eye that is built upon a theme of three eye cups surrounded by a layer of screening pigments. The single naupliar eye of the ostracodeVargula graminicola is situated medially on the dorsal-anterior side of the body and has three fused eye cups, two dorso-lateral and one ventral. Each eye cup has the following components: (1) pigment cells between the eye cups, (2) tapetal cells, (3) retinular cells with (4) microvillar rhabdomeres, and (5) axons extending into the protocerebrum. Typically two retinular cells contribute lateral microvilli to each rhabdom. The two dorso-lateral eye cups have about 40 retinular cells (20 rhabdoms) and the ventral eye cup has about 30 retinular cells (15 rhabdoms). Typical of myodocopid naupliar eyes (as reported from light microscopic studies), no lens cells or cuticular lenses were observed. The presence of tapetal cells identifies theVargula eye as a maxillopod-ostracode type crustacean naupliar eye. It is unlikely that the naupliar eye ofV. graminicola functions in image formation, rather it probably functions in the mediation of simple taxis towards and away from light.

Morphology of the Nervous System of Barnacles: the Median Ocellus ofBalanus Hameri (=Chirona Hameri)(Crustacea: Cirripedia)

The barnacle cypris larva possesses a pair of laterally placed compound eyes and a median nauplius eye which is tripartite in structure. Concomitant with the metamorphosis to the juvenile is the loss of compound eyes and the nauplius eye separates into its three constituent parts (Walley, 1969). The two dorsolateral components of the nauplius eye come to lie under the rostral shell plates, whereas the ventral component forms the median ocellus which underlies the mantle flaps of the scutal plates at the posterior margin of the adductor muscle (Figure 1).

The Functions of Eye and Body Movements in Labidocera and Other Copepods

ABSTRACT Male Labidocera have three eyes derived from the nauplius eye. The dorsal pair have large lenses and are fused to give a single mobile eyecup containing a transverse row of 10 rhabdoms. This rhabdom row scans across 35° of the dorsal visual field at rates of up to 3 Hz, and it is suggested that the scanning movements are concerned with the detection of conspecifics. In addition there are movements which enable the eyecups to track a source of light, and these are mediated by three other receptors in each eyecup. The tracking movements are closely linked to tail movements which tend to keep the animal’s back directed towards the light. The total effect is to stabilize both body and eye direction against involuntary disturbance. Other pontellid copepods show similar visually controlled tail movements, but without the eye movements.

The spectral sensitivity of eye movements in response to light flashes inDaphnia magna

The crustaceanDaphnia magna responds to a flash of light with a ventral rotation of its compound eye; this behavior is termed eye flick. We determined the spectral sensitivity for the threshold of eye flick in response to light flashes having three different spatial characteristics: (1) full-field, extending 180° from dorsal to ventral in the animal's field of view; (2) dorsal, 30° wide and located in the dorsal region of the visual field; (3) ventral, same as dorsal but located ventrally. All three stimuli extended 30° to the right and to the left of the animal's midplane. We found that spectral sensitivity varies with the spatial characteristics of the stimulus. For full-field illumination, the relative sensitivity was maximal at 527 nm and between 365 nm and 400 nm, with a significant local minimum at 420 nm. For the dorsal stimulus, the relative sensitivity was greatest at 400 nm, but also showed local maxima at 440 nm and 517 nm. For the ventral stimulus, the relative sensitivity maxima occurred at the same wavelengths as those for the full-field stimulus. At wavelengths of 570 nm and longer, the responses to both dorsal and ventral stimuli showed lower relative sensitivity than the full-field stimulus. No circadian or other periodic changes in threshold spectral sensitivity were observed under our experimental conditions. Animals which had their nauplius eyes removed by means of laser microsurgery had the same spectral sensitivity to full-field illumination as normal animals. Our results are discussed in terms of our current knowledge of the spectral classes of photoreceptors found in theDaphnia compound eye.

Photosensitivity of the calanoid copepod Acartia tonsa

The light intensity and spectral sensitivities of the calanoid copepod Acartia tonsa Dana were determined by measuring phototactic responses. Adult females displayed only positive phototaxis. The dark-adapted copepod, which possesses a single naupliar eye, perceived light at intensities as low as 2.8x1011 photons m-2 s-1. The action spectrum for positive phototaxis had no clear maxima but rather showed a broad range of greatest sensitivity from 453 to 620 nm. This sensitivity encompassed those wavelengths that are maximally available at the depth where the copepod is found during the day. This spectral overlap, coupled with the finding that the copepod requires light cues for nocturnal vertical miration, suggests that broad spectral sensitivity is an adaptive mechanism to maximize light intensity sensitivity during migration.

THE LARVAL COMPOUND EYE OF BARNACLES

The compound eye of the cypris larva of Balanus crenatus comprises about 10 ommatidia. The ommatidia possess a crystalline cone formed by three cone cells, two distal pigment cells, and six retinular cells that together form the rhabdom. The compound eye of the cypris larva of Balanus exhibits similarities to that of branchiurans and ostracodes, but the latter two groups share more common characteristics. Adult barnacles have reduced nauplius eyes (Fahrenbach, 1965; Krebs and Schaten, 1976). Their sessile life requires little visually stimulated behaviour, the shadow reflex being the best known (Gwilliam, 1963). The planktonic larval forms, known as nauplii, have well-developed nauplius eyes (Kauri, 1962) capable of serving in light/dark perception. Between the planktonic nauplii and adult sessile forms, a short-lived cypris appears (Bookhout and Costlow, 1959), adapted for settlement. In contrast to all other stages, the cypris larva has a pair of small but morphologically well-differentiated compound eyes (Fales, 1928; Walley, 1969). The settlement behaviour has been analysed and the role of light guidance has been established (Barnes et al., 1951). Nothing is, however, known about the fine structure of the eyes of the cypris larva. Further, the kinship of the barnacles (Cirripedia) with related groups is poorly known as regards eye structure. The structure of the nauplius eye places the barnacles in the maxillopod-ostracode group (Elofsson, 1966). The present study was undertaken to elucidate the above problems.

Structure Du Rhabdome De L'Oeil Nauplien Adulte D'Artemia (Anostraca)

The rhabdom of the adult nauplius eye of Artemia is distributed as a spacial net near the pigment cups. Each retinula cell has proximal rhabdomeric surfaces, which constitute a ring around the cell or just one cellular side, and which intermingle with those of neighbouring cells to form a closed rhabdom of a structure not comparable to that of ommatidia. The whole is irregular and aleatory. By one of its poles the rhabdom is in contact with the space between the retinula cells and the pigment cup and progressively becomes more slender by the opposite pole and reaches different levels. It is sometimes possible to find a rhabdomic portion isolated from the rest.

On the anatomy of the misophrioid copepods, with special reference toBenthomisophria palliataSars

The misophrioids are a small but phylogenetically important order of copepods, comprising only three species, which exhibit a mosaic of characters drawn from both gymnoplean and podoplean lineages. The skeletomuscular system ofBenthomisophria palliatais described in detail and comparative observations are made onB. cornutaandMisophria pallida. All were found to possess a carapace-like posterior extension of the cephalosome which completely encloses, both dorsally and laterally, the first pedigerous somite beneath. This structure is a posterior outgrowth of the maxilliped-bearing somite and is not derived from the tergite of the pedigerous somite that it encloses. It may represent a modification of the somitic hyaline frill common to many copepods. Its presence is apparently associated with the ability ofBenthomisophriato gorge itself until virtually all the free space within the prosome is occupied by the gut. The gut contents ofB. palliatareveal that it feeds on relatively large food particles. The probable feeding mechanism is inferred from the ranges of movement possible at each of the joints of the feeding appendages and from their musculature. The probable swimming mechanism is also inferred from similar data for the thoracic limbs. The skeletomusculature of other copepod groups is compared with that ofBenthomisophria. The extrinsic muscles of the cephalic appendages and both the extrinsic and intrinsic muscles of the swimming legs were found to be relatively uniform throughout the Copepoda. The longitudinal trunk muscles and intrinsic muscles of the cephalic appendages were found to be more subject to modification during adaptive radiation in habit and feeding strategy respectively. Both species ofBenthomisophriaexhibit ornamentation of the integument. This is described and a strengthening role is attributed to the intricate system of lamellae and ridges present. Laterally on the cephalosome ofBenthomisophriaspecies are areas of funnel-shaped cone organs standing erect from the body surface and bearing a spherical globule of secretion distally. They are positioned so that the long setae of the reflexed antenna and mandibular palp sweep over them. It is concluded that the secretion is spread over the surface of the carapace-like structure by the setae. Its function may be protective. The gross anatomy of the other organ systems is described. The highly distensible gut has large lateral caecae which can expand to accommodate large amounts of food. The musculature of the hindgut is described, as is the postulated sequence of events during defaecation. AdultB. palliatapossess paired antennary glands as the functional excretory organs. The maxillary gland is absent. In other copepod groups the maxillary gland is the functional excretory organ of the adult. The central nervous system is described. The complete absence of the nauplius eye throughout the life cycle of misophrioids is noted. The heart is absent fromB. palliata. InMisophria pallidait is a barrel-shaped structure about 40 µm long, with weakly muscular walls. It has anterior and posterior ostia only and is suspended from the dorsal body wall by short muscle fibres. The reproductive system is described in both sexes. Male and female have paired gonads, ducts and genital openings. The oviducts open into cavities (genital antra) within the genital somite, which are closed off externally by the plate formed from the fused sixth legs. The male possesses relatively simple vasa deferentia which are poorly differentiated into functional zones. The phylogenetic position of the misophrioids is discussed. They exhibit an unusual combination of ancestral, unique and convergent characters which makes assessment of their affinities difficult. It is tentatively suggested that the Misophrioida, which merits ordinal rank, is more closely related to the Harpacticoida than to any other order.

Fine structure and optical properties of an ostracode (Crustacea) nauplius eye

InNotodromas monachus, the three cups of the nauplius eye are formed by four pigment cells. The insides of the cups are lined with tapetal cells, which produce several layers of reflecting crystals. The reflecting crystals form a concave mirror in each cup upon which the retinular cells rest. The two-celled rhabdoms are few and perpendicular to the tapetal layer. The axons from the tripartite eye leave the retinular cells distally in three separate groups. The eye is thus of the inverse type. Large lens cells, with a low refractive index, are present in the open part of each cup. Distal to the lens cells, highly refractive lenses are formed in the cuticle. These lenses serve to decrease the effective curvature of the mirrors, thus enabling the reflectors to produce a focused image on the retina. The ventral cup differs by the lack of a cuticular lens and has degenerated-appearing cellular elements. The investigated nauplius eye is the only one known with both a mirror and a highly refractive lens in the dioptric apparatus.

The Organ of Bellonci in Ostracodes: An Ultrastructural Study of the Rod‐shaped, or Frontal, Organ

AbstractUltrastructural observations of the rod‐shaped organ in Cypridina norvegica and Paraconchoecia elegans indicate homology with the organ of Bellonci of other crustaceans. In C. norvegica the organ is situated close to the ventral cup of the nauplius eye. Distally in the organ, several ciliary ramifications of the sensory neurons protrude into internal cavities formed by bordering cells. Six dendrites, with cell bodies within and in front of the brain, form the proximally bifurcated nerve, which enters the protocerebrum in the region of the medullae terminales. In this species the organ represents the deep receptor of the organ of Bellonci complex. In P. elegans the external part of the organ is situated between the proximal parts of the antennulae. Four dendrites in two groups emerge from the protocerebrum. Distally, they form branching cilia that are in close contact which the cuticle of the organ, thus forming a receptor similar to the superficial receptor of the organ of Bellonci complex of other crustaceans. It is suggested that the terms frontal organ and rod‐shaped organ be abandoned in favour of the term organ of Bellonci.

Rhabdom Adaptation and Its Phylogenetic Significance

AbstractElofsson, R. (Zoological Institute, University of Lund, S‐223 62 Lund, Sweden.) Rhabdom adaptation and its phylogenetic significance. Zool. Scr. 5 (3–4): 97–101, 1976. — The rhabdoms of arthropod compound eyes are structurally differentiated into open, fused layered, and fused continuous. All are capable of perceiving polarized light. The fused layered, and under certain conditions the fused continuous, perform particularly well. — The fused layered rhabdoms occur in malacostracan crustaceans and in various insect groups. This, together with, among other things, the presence of open rhabdoms in insects and crustaceans, indicates convergent development of organs and parts of organs. — Elaborate visual organs of more than one kind occur in crustaceans, as is exemplified by the compound and nauplius eyes. This shows that more than one construction on the organ level is possible in a restricted taxo‐nomical unit for the. perception of light. The different rhabdom types performing well in receiving polarized light also show parallel evolution on a level below the organ. — The result of adaptation analyses indicates the need for a restricted use of the concept of homology basic to morphological investigations and a base for phylogenetic speculations. It also envisages a fruitful approach to a peep into the workshop of evolution. — It is concluded that a fully formed compound eye in arthropod ancestors is hardly conceivable. A realistic alternative is an inherent capacity of forming a compound eye. Thus the ancestral compound eye could have ranged from nothing to a partly‐developed stage. The recent eyes need not originate from one source.

Distribution of monoaminergic neurons in the nervous system of non-malacostracan crustaceans.

A comparative investigation of the distribution of monoaminergic neurons in non-malacostracan crustaceans was performed with the histochemical fluorescence method of Falck-Hillarp. Two fluorophores were found: the more widespread of the two emits a green fluorescence; and the more sparsely distributed emits a yellow to brown-yellow fluorescence. Specific green fluorescent areas were shown to exist in the protocerebrum. The central body and the optic ganglia of the compound eye (where present) are always fluorescent. Moreover, the centre of the nauplius eye may have a green fluorophore, as in ostracods, and a neuropile area, here called the frontal area. These neuropile centres are known from ordinary histological studies of the nervous system. In addition, there are specific monoaminergic centres, such as the so-called dorsal area of phyllopods and anostracans as well as the copepod specific areas. Specific monoaminergic areas appear in the deutocerebrum and the suboesophageal ganglion where they are particularly well developed. Presumed sensory neurons in the cavity receptor organ of Artemia saliva are shown to be monoaminergic. Monoaminergic sensory neurons have not been described previously in Arthropods. Presumed motor innervation of hind-gut and trunk muscles is also found, and it is concluded that in crustaceans neurons of every type (sensory, internuncial, motor) may be monoaminergic.

Some observations on the internal morphology of Hansen's nauplius y (Crustacea)

Abstract The internal morphology of the crustacean larval form that Hansen (1899) called nauplius y has revealed a remarkably advanced early nauplius. The nervous system is well developed and differentiated. It is connected with the anlagen of the compound eyes. A presumed filamentous base of the SPX-organ connects with these. The nauplius eye is present in a three-partite form with two retinula cells in each cup. The alimentary canal consists of the ectodermal oesophagus with an inner layer of longitudinal muscles and an outer circular layer, and of the endodermal midgut with cells having microvillous borders against the lumen. There is no proctodeum or anus present. There is a well-developed muscular system. The head contains a large gland with a paired ventral outlet. A new dorsocaudal organ of doubtful function is described. The morphological facts presented in this investigation indicate that the nauplius y, as knowledge stands today, is close to the Cirripedia.

A presumed new photoreceptor in Copepod crustaceans.

A new photoreceptor in the Copepoda is described. The organ, previously called Gicklhorn's organ (Elofsson, 1966a), is paired and is usually situated beneath the cuticle of the front. Each member of the pair consists of two cells. From the anterolateral position, two nerves lead to the lateral part of the brain. No connexion with the nauplius eye is found. Each cell of the organ has microvilli, two nuclei, dictyosomes, and large cisternae of the endoplasmic reticulum. Except for the binucleated condition, the cells closely resemble the retinula cells of the copepod nauplius eye. It is concluded that, because of its independent position, the new photoreceptor is not a detached part of the nauplius eye. As there are no accessory structures present and no missing links so far known, it is doubtful whether it can be regarded as a vestigial compound eye. The most plausible hypothesis is that the new presumed photoreceptor is an independent structure without connexions either with crustacean compound or nauplius eyes. If the function of the nauplius eye is considered by itself the improvement contributed by the new organ is probably modest because of its low level of organization. Some experimental evidence on light reception in Copepods points to a possible function in response to directed light.

On the nauplius ofCentropages yamadai Mori, copepoda

The nauplius ofC. yamadai shows the shape of typicalCentropages nauplius, as inC. hamatus andC. abdominalis. The nauplii of genusCentropages are oval in shape; somewhat rounded anteriorly and slightly pointed posteriorly. The rostrum is comparatively large. A nauplius eye is large at the proximal portion of the rostrum. There is a labrum with the minute spines on its posterior border. The antennule of 3 segments is oar-liked in outline as inCalanus, but on the ventral margin of terminal segment there is no seta. The abdominal portion is not divided from the carapace like that ofTemora orCalanus. There is no dorso-ventral flexure. The furcal setae are thick and long, and asymmetrical. An end seta which presents just dorsally against to a median seta, elongates backwards. The nauplius ofC. yamadai can be distinguished from nauplii of other species by the structure of appendages in the respective stages, but this nauplius is easily identified by the coloured body.

Photoreception in the nauplius eye of Pandalus borealis Kröyer: Decapoda, Crustacea

On the basis of past morphological studies the nauplius eye of Pandalus borealis has been regarded as a simple photoreceptor. This is the first physiological study on its light-sensing capabilities. Small extracellular metal electrodes were used to measure the eye's response (electroretinogram, ERG) to intensity and wavelength controlled light stimuli. Responses demonstrated characteristics similar to responses of other invertebrate photoreceptors. This leads to the conclusion that the nauplius eye of P. borealis is a functional photoreceptor.