The vas deferens of the spider crab,Libinia emarginata

Sperm enter the anterior vas deferens individually in the spider crab male. There they become surrounded by secretion products from the cells of the vas deferens, and are compartmentalized into spermatophores of varying size. The anterior vas deferens can be divided into three regions. The epithelium of the anterior vas deferens varies regionally from low to high columnar. The cytoplasm contains vast arrays of rough endoplasmic reticulum and Golgi complexes but few mitochondria. Intercellular spaces contain septate junctions, gap junctions and vesicles. Once the spermatophores have been formed in the anterior vas deferens, they are moved posteriorly to the middle vas deferens where they are stored and surrounded by seminal fluids. The epithelial cells of the middle vas deferens contain large amounts of rough endoplasmic reticulum and Golgi complexes. Numerous micropinocytotic vesicles appear, forming at the cell surface and within the apical cytoplasm. Their suggested function is the resorption of secretion products of the anterior vas deferens which initiated compartmentalization of the spermatozoa into spermatophores. The posterior vas deferens functions primarily as a storage center for spermatophores until they are released at the time of copulation. Seminal fluid surrounding the spermatophores is produced in this region as well as in the middle vas deferens. The cells of this region contain vast arrays of vesicular rough endoplasmic reticulum and Golgi complexes. The cells are multinucleate. Microtubules are numerous throughout the length of the cells and appear to insert on the plasma membrane.     

Methyl farnesoate induced ovarian maturation in the spider crab,Libinia emarginata

Summary

To overcome the problem of getting crustaceans to reproduce in captivity, eyestalk ablation or X-organ sinus gland removal is commonly utilized in commercially important species such as shrimp. We have investigated the effect of unilateral and bilateral eyestalk ablation on methyl farnesoate (MF) production by mandibular organs (MOs) and on ovarian maturation in female spider crabs Libinia emarginata, a useful model since these animals are in a terminal molt and are devoid of a functional Y-organ. Non-reproductive, over-wintering female L. emarginata were induced to be reproductive by feeding and increasing the holding temperature to stimulate the endocrine system. In addition, we removed X-organ sinus glands by eyestalk ablation either unilaterally (UEA) or bilaterally (BEA) to further stimulate MF synthesis by MOs. Endogenous MF in the hemolymph was extracted and quantified by means of HPLC and in some cases by GC/MS. Oocyte growth and egg quality were studied simultaneously to determine how they were related to MF levels found during vitellogenesis. The initial MF concentration in unablated controls was low, 0.31 ng/ml of hemolymph, and this increased (p<0.05) to about 1 ng/ml by 2 weeks, remaining at about that level for the remainder of the experiment. Eyestalk ablation significantly stimulated MF concentrations by week 1 to nearly 2 and 3.5ng/ml in the UEA (p <0.01) and BEA (p <0.001) animals, respectively. Oocytes appeared to respond to increased MF levels, as ovarian maturation was initiated from the point at which MF increased (p <0.05). Thereafter, the rate of oocyte growth was directly correlated with the extent of elevation of MF. The gonado-somatic index [(GSI) = gonad weight/body weight × 100] of controls at the start was about 1.5 and increased to 6.5 by week 4. Mature oocytes were reached at a GSI around 7. Oocyte maturation was accomplished at week 2 in BEA, week 3 in UEA, and later than week 4 in controls. After maturation, oocytes started to degrade in some ablated animals, particularly in the bilaterally ablated ones where the highest MF concentrations were observed. These data indicate that MF elevations are required for stimulating ovarian maturation in Crustacea. MF appears to accelerate gonad development during the vitellogenic process, but may be deleterious at high concentrations. These results have a significant and important application and implications for aquaculture.     

Microspectrophotometry of the visual pigment of the spider crab Libinia emarginata

Summary Isolated dark-adapted rhabdoms from the spider crab Libinia emarginata were examined by microspectrophotometry to determine the visual pigments present and their light-sensitive characteristics. The rhabdoms contain a single pigment with _max=493 nm. Upon one minute irradiation with bright orange light this pigment forms a light-stable photoproduct with nearly the same _max as the parent pigment but with slightly greater absorption to the long wavelength side of the absorption peak. On exposure to orange or yellow light in the presence of 5% glutaraldehyde, however, the pigment of Libinia rhabdoms bleaches slowly.The photosensitive pigment of properly oriented, transversely illuminated rhabdoms shows isotropic and dichroic regions, corresponding to layers of the rhabdom in which the microvilli are respectively parallel and perpendicular to the direction of propagation of the measuring beam. The maximum dichroic ratio is about 2, with most absorption when the plane of polarization is parallel to the microvillar axes.

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Zusammenfassung Die isolierten, dunkeladaptierten Rhabdome von Libinia emarginata wurden mikrospektrophotometrisch untersucht, um die Sehfarbstoffe und ihre lichtempfindlichen Eigenschaften zu entdecken. Die Rhabdome enthalten ein einziges Pigment (_max 493 nm). Nach einer Bestrahlungszeit von 1 min mit hellem orangem Licht entsteht ein lichtfestes Photoprodukt mit beinahe dem gleichen _max wie das ursprüngliche Pigment, aber mit etwas größerer Absorption gegen die langwellige Seite des Absorptionsmaximums hin. Das Pigment von Libinia-Rhabdomen bleicht langsam aus, wenn man es orangem oder gelbem Licht in Gegenwart von 5% Glutaraldehyd aussetzt.Werden richtig orientierte Rhabdome von der Seite belichtet, so zeigt das lichtempfindliche Pigment teils Isotropismus teils Dichroismus. Im ersten Fall sind die Mikrovilli parallel zur Richtung des Meßstrahles orientiert, im zweiten Fall stehen sie senkrecht dazu. Das größte Dichroismus-Verhältnis liegt bei 2. Man erhält die größte Absorption, wenn die Polarisationsrichtung parallel zur Achse der Mikrovilli steht.

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This work was supported by U.S.P.H.S. grant NB-03333. Some of the experiments were done at The Marine Biological Laboratory, Woods Hole, Mass.     

Seasonal differences in methyl farnesoate esterase activity in tissues of the spider crab Libinia emarginata

Summary

Methyl farnesoate (MF), an unepoxidated form of insect JH III, is present in Crustacea. MF is synthesized by the mandibular organs and is degraded to fomesoic acid (FA) by peripheral tissues. In this study we investigated MF degradation by esterases in hepatopancreas, ovary, testes and hemolymph of the spider crab Libinia emarginata collected at different times of the year to determine seasonal differences. The conversion of MF to FA varied among the tissues. In the summer, the hepatopancreas showed the greatest esterase activity (52.8% conversion in females and 59.16% in males), and it was twice as high (28.86%) in ovaries than in the testes (12.16%), but was low in the hemolymph of both sexes (10.84% in males, and 6.97% in females). In the fall, the conversion of MF to FA was significantly reduced in all tissues (ovary 8.55%, testes 6.21%, hepatopancreas 10.22%, hemolymph 3.96%). Eyestalk ablation of animals in the fall restored MF esterase activity to summer levels. When tissues from these animals were incubated with OTFP, a specific inhibitor of JH esterase, MF metabolism was significantly reduced. These results suggest that MF esterase activity depends on direct induction by MF, and its degradation is by a specific esterase(s).     

The mandibular organ of the female spider crab,Libinia emarginata,in immature,mature, and ovigerous crabs

The cells of mandibular organs of female Libinia emarginata exhibit changes in substructure during molting and vitellogenesis. The cytoplasm is that of a steroid-hormone producing cell. The cells do not appear to produce ecdysones.     

Relationship of claw form and exoskeleton condition to reproductive system size and methyl farnesoate in the male spider crab,Libinia emarginata

Summary

Methyl farnesoate (MF) expression and reproductive system size were compared in five representative groups of male L. emarginata selected from a sample collected in November. The groups differed from each other with respect to carapace size (small, intermediate and large), relative propodus size (small and large claw forms), and condition of the exoskeleton (abraded and unabraded). Large males with large claws and abraded exoskeletons had reproductive system indices which were significantly larger than any other group. The mandibular organs of these crabs also had significantly higher rates of methyl farnesoate synthesis in vitro. Hemolymph titers of methyl farnesoate were also highest in this group, but were not significantly different from the group with small carapaces, small claws and unabraded exoskeletons. Methyl farnesoate titers were significantly lower in all other groups of unabraded animals with small or large claws. These results suggest that methyl farnesoate may play a role in morphogenesis and reproduction in male L. emarginata.     

Setal morphology of grooming appendages in the spider crab,Libinia dubia

In crustaceans, grooming behaviors decrease fouling by removing debris from the exoskeleton and body structures; these grooming behaviors improve respiration, sensory reception, movement, and reproduction. Setal morphologies of the following grooming appendages in the decapod crustacean spider crab Libinia dubia are examined including the first pereiopod (cheliped), first, second, and third maxillipeds (mouthparts), and first, second, and third epipods (internal extensions of the maxillipeds). The objective of this study was to describe setal morphologies of these grooming appendages and to elucidate possible functions and efficiencies of setal structures. Spider crabs are hypothesized to have elaborate setal morphologies, mainly for cleaning specialized decorating setae as well as for cleaning inside the gill chamber, which has a higher likelihood of becoming fouled compared to other decapods such as shrimps. Fourteen setal types are documented and included several varieties of serrate and pappose setae as well as simple setae, cuspidate setae, papposerrate setae, and canoe setae. Maxillipodal epipods in the gill chamber are free of fouling, suggesting the setation on the third maxilliped protopod has an efficient functional morphology in removing debris before water enters the gill chamber. Serrate setae may function for detangling and separating structures whereas pappose setae may function for fine detailed grooming. The cheliped is the only grooming appendage that can reach decorating setae and it contains only pappose setae; thus decorating setae is not likely groomed in a manner that would greatly decrease fouling. J. Morphol. 277:1045–1061, 2016. © 2016 Wiley Periodicals, Inc.     

Vitellogenesis stimulated by thoracic ganglion implants into destalked immature spider crabs, Libinia emarginata.

Since destalked immature female Libinia emarginata fail to molt to maturity (Hinsch, 1972) and implants of thoracic ganglion of adult females into young females of Potamon dehaani caused a doubling of ovarian weight and differentiation of yolk granules (Otsu, 1963), the effects of the thoracic ganglion implantation on sexual maturation in Libinia was investigated. Destalked immature Libinia with a maximum carapace length of 4-5 cm received two implants of adult female thoracic ganglion at 10-day intervals. All of the surviving experimental animals and destalked controls molted to immaturity. Most of the experimental animals failed to complete a successful molt and few survived longer than 3-4 days. The experimental animals that survived for over a week showed signs of yolk deposition not observed in the destalked controls. Eggs in several stages of vitellogenesis were scattered throughout the gonad in the animal showing the most pronounced effect. This was not observed in any of the destalked controls.     

Cellular basis for polarized light perception in the spider crab,Libinia

Summary Differential increases in the numbers of pinocytotic vesicles, multivesicular bodies and total complex bodies occurred in the cytoplasm of specific photoreceptor cells in the compound eye of the crab Libinia exposed for six hours to polarized light with various e-vector orientations. These data coupled with previous results on the same species proved that the seven retinular cells in each ommatidium formed two functional groups selectively light adaptable by e-vectors oriented 90° apart. One group (Channel I, comprising Cells 1, 4 and 5) was more affected by horizontal polarization; the other (Channel II, comprising Cells 2, 3, 6 and 7) was more affected by vertical polarization.This confirmed by a quite independent technique the conclusion reached from electrophysiological experiments on the crab Cardisoma that decapod compound eyes have two orthogonal polarization analyzer channels. In addition the present data showed that both channels occur in each ommatidium as hypothesized on previous electron microscopic evidence and that the axes of maximum absoprtion in the two retinal channels were parallel to the long axes of their cells' rhabdom microvilli, horizontal in Channel I and vertical in Channel II. The latter relations in turn supported the hypothesis that the dichroism of rhodopsin was fundamental to the analyzer mechanism.This research has been supported by U. S. Air Force Grant AFOSR 1064 and NASA Grant NGR 07-004-055. The authors wish to thank Professor Joseph G. Gall for generously sharing his electron microscope facilities.     

Ontogenetic niche specialization of the spider crab Libinia ferreirae associated with the medusa Lychnorhiza lucerna

Symbiotic relationships in marine environments are not fixed and can change throughout the animal’s life. This study investigated the ontogeny of symbiosis of the spider crab Libinia ferreirae with the host medusa Lychnorhiza lucerna. We described the type of relationship, the temporal correlation among species, and food habits. More than 50% of the sampled crabs were symbionts, most in early life stages. The highest number of crabs found in a single medusa was 11. Symbiosis was observed throughout most of the year but was more evident in warm periods. The crab has many benefits in this relationship with a medusa. One is the use of food resources captured by the medusa, primarily copepods. Because the crab steals the medusa’s food, it is a kleptoparasitic relationship. There is a niche partition between symbiont and the free-living crabs as they occupy different habitats and use nonoverlapping food resources. Previous research reported that symbiosis first developed during the crab’s last larval phase (megalopa) when crab and medusa are in the same habitat. Observation of the crab’s behavior shows that symbiosis occurs when the crab can grab to the medusa when the host touches the sea bottom. The crab also took advantage of water currents, releasing itself from the substrate and then drifting toward the medusa. The symbiotic relationship that crabs have with the medusa provides then with a nursery, food resources, shelter, dispersion, and decreased competition with free-living adult crabs, all essential for the crab’s survival.     

Vitellogenocytes in the Hepatopancreas of Carcinus maenas and Libinia emarginata (Decapoda brachyura)

Summary

In addition to the ovary, the hepatopanocreas of female decapod crustaceans, Carcinus maenas, and Libinia emarginata is a source of yolk protein. The specific cells in the hepatopancreas that localize vitellogenins on tissue sections are revealed with lipovitellin-specific antiserum. These cells, designated vitellogenocytes, are believed to be responsible for vitellogenin synthesis in the hepatopanocreas. This conclusion is based upon immunolocalization which demonstrates a temporal relationship with vitellogenin synthesis in the hepatopanocreas. Specifically, when the oocytes are most active in vitellogenin uptake, the hepatopanocreas is producing vitellogenins most abundantly. Vitellogenocytes are relatively large and polymorphic, similar to the reserve-inclusion cells that were described by others. Yolk protein was not detected in other cells of the hepatopancreas, male reserve-inclusion cells, or pre-vitellogenic oocytes by the same method of staining. Vitellogenocytes resemble cyanocytes, the source of hemocyanin. Whether the vitellogenocytes and their precursors are related to other populations of hepatocytes, such as cyanocytes, is not known and has not yet been studied.     

Morphology and function of the reproductive tract of the spider crab Libinia spinosa (Crustacea, Brachyura, Majoidea): pattern of sperm storage

Morphology and function of the male reproductive tract, female spermatheca and patterns of sperm storage were assessed in the crab Libinia spinosa using histological methods. Testes are characterized by the presence of peripheral spermatogonia and different sequences of sperm maturity. Spermatophores begin to be packed in the last portion. The vas deferens consists of three sections: anterior, with undeveloped spermatophores and free sperm; median, with well-developed spermatophores; and posterior with granular secretions. Female spermathecae are of the ventral type, with a velum separating dorsal and ventral chambers. Live individuals were kept in the laboratory and arranged in pairs. An experiment was conducted toward the end of the reproductive season, in which males with the right gonopod excised were placed with receptive females. After mating, females were killed and the spermathecae dissected for histological study and observation of the pattern of sperm storage. Spermatozoa were found forming discrete sperm packages. New ejaculates can fill the entire spermatheca or be restricted to the ventral chamber; sperm are rounded, with a distinguishable acrosomal core. Old ejaculates are restricted to the dorsal chamber and are of irregular shape and larger size; an acrosomal core was not distinguishable. The secretions produced by the glandular epithelium of the dorsal chamber of the spermathecae are likely to have a role in the removal of dead sperm.