Salinity effects on arm regeneration in Luidia clathrata (Echinodermata: Asteroidea)

The effect of salinity (20, 25, and 30?psu) on regeneration of two arms of adult starfish Luidia clathrata (n?=?8 per salinity treatment group collected from Pensacola Bay, Florida, USA 30° 20′ N, 87° 13′ W) was examined in a laboratory experiment (November 2009 to March 2010) to test the hypothesis that L. clathrata is adapted to euryhaline conditions found in bays with regards to arm regeneration. Regenerating arm condition (lengths and weights) relative to treatment was 20-psu treatment?<?25-psu treatment?<?30-psu treatment, and non-regenerating arm condition was 20-psu treatment?<?25-psu treatment?=?30-psu treatment. Luidia clathrata is not adapted to lower salinity conditions found in bays with regard to arm regeneration, despite the common occurrence of the species in bays. Lower salinity in bays should reduce the ability of L. clathrata to recover from damage sustained during, or just prior to, low-salinity periods.     

Ultrastructural evidence for Sertoli-like cells in the testis of the asteroid,Luidia clathrata (Say) (Echinodermata: Platyasterida)

Non-germinal cells arise adjacent to the basal lamina and extend between the numerous germinal celli. Nuclei of these non-germinal cells may be positioned near the basal lamina or more peripherally between the spermatocytes. Thin cytoplasmic processes extend between the spermatocytes to the spermatids. These cytoplasmic processes vary in electron density from the cytoplasm of the germinal cells. These non-germinal cells closely resemble the vertebrate Sertoli cell.     

Fine structure of the spermatozoon of Marthasterias glacialis (Linnaeus) (Echinodermata; Asteroidea), with special reference to acrosomal morphology

The sperm of Marthasterias glacialis (Linnaeus) was studied by light and electron microscopy. It is a long uniflagellated cell of the “primitive” type. The head has a spherical shape and contains a nucleus with a spheroid acrosome lying in a cup-shaped anterior fossa. The acrosome is formed by an acrosomal vesicle surrounded by the periacrosomal material. The basal specializations of the acrosomal vesicle show a clear differentiation of its constituents resembling the structure of membrane. The midpiece contains a very large annular mitochondrion which encircles two perpendicular centrioles. The distal centriole is in close association with a pericentriolar radial complex. The tail, containing a common microtubular axoneme, is projected to a variable position.     

Effects of salinity and feeding on arm regeneration in the starfish Luidia clathrata (Say, 1825) (Echinodermata: Asteroidea)

The aim of this study was to determine: (1) salinity that maximizes arm regeneration in the starfish Luidia clathrata; and (2) if low food consumption or low salinity is the cause of the reduced rate of arm regeneration seen at low salinities.. An estimated salinity of 33 g kg^?1 produced maximum regeneration of two arms in L. clathrata. This salinity is typically greater than that found in bays that are the usual habitat for the species. Equivalent food consumption by L. clathrata in salinities of 20 g kg^?1 and 30 g kg^?1 resulted in greater regeneration in salinity of 30 g kg^?1, suggesting lower food consumption at low salinities is not the primary reason for lower regeneration. Higher food consumption compared to lower food consumption, both tested in salinity of 30 g kg^?1, did not increase regeneration, but resulted in more storage of energy in the pyloric caeca.     

The effect of salinity on coelomic fluid osmolyte concentration and intracellular water content in Luidia clathrata (Say) (Echinodermata: Asteroidea)

• 1.1. The concentrations (mM) of osmolytes in the coelomic fluid of Luidia clathrata kept at 25‰S seawater (control individuals) were: 345, Na⁺; 10, K⁺; 10, Ca²⁺; 44, Mg²⁺; 387, Cl⁻; 0.67, amino acids; 0.09, NH₄⁺.
• 2.2. When individuals were transferred from 25‰S to 15‰S or 35‰S, the concentrations of inorganic ions in the coelomic fluid usually equilibrated within 24hr and became the same as those in the medium.
• 3.3. The intracellular water content (g intracellular H₂O/g solute-free dry tissue) of the pyloric caeca and tube feet of control individuals throughout the experiment was 2.13 and 5.40, respectively.
• 4.4. In tissues of individuals transferred to 15‰S, the intracellular water content increased by an average 50% in 12 hr but returned to 19% above control levels during 1 week.
• 5.5. In tissues of individuals transferred to 35‰S, the intracellular water content decreased by an average 17% in 12 hr and did not change during 1 week.
• 6.6. Luidia clathrata is an osmoconformer and partial cell volume regulator within the seasonal salinity range it encounters.

     

Effect of nutrition on the excretion rate of soluble nitrogenous products of Luidia clathrata (say) (Echinodermata; Asteroidea)

• 1.1. Groups of Luidia clathrata were fed maintenance level diets of Donax variabilis (50% protein by dry weight) or Penaeus duorarum (80% protein) or were starved.
• 2.2. The NH₄⁺ excretion rates for all treatments increased from 6.06 ± 2.55 to 14.39 ± 4.31 μg NH₄⁺ − N/g dry wt per hr after 20 days.
• 3.3. The urea excretion rate for all treatments was 1.25 ± 3.39 μg urea-N/g dry wt per hr for 56 days.
• 4.4. The pyloric caecum index (percentage of wet body weight) decreased 16.5 and 73.4%, for Donax variabilis-fed and starved sea stars, respectively. The pyloric caecum index of Penaeus duorarum-fed sea stars increased 81.5%. The protein level of the pyloric caeca was 47.00 ± 4.14% of the dry weight for the fed animals and 37% for the starved animals.
• 5.5. Increased NH₄⁺ excretion rates with starvation or presumed maintenance diets appear to be due to tissue catabolism.

     

Regenerative capacity and biochemical composition of the sea star Luidia clathrata (Say) (Echinodermata: Asteroidea) under conditions of near-future ocean acidification

The present study examines sublethal effects of near-future (year 2100) ocean acidification (OA) on regenerative capacity, biochemical composition, and behavior of the sea star Luidia clathrata, a predominant predator in sub-tropical soft-bottom habitats. Two groups of sea stars, each with two arms excised, were maintained on a formulated diet in seawater bubbled with air alone (pH 8.2, approximating a pCO₂ of 380 μatm) or with a controlled mixture of air/C0₂ (pH 7.8, approximating a pCO₂ of 780 μatm). Arm length, total body wet weight, and righting responses were measured weekly. After 97 days, a period of time sufficient for 80% arm regeneration, pyloric caecal indices, and protein, carbohydrate, lipid, and ash levels were determined for body wall and pyloric caecal tissues of intact and regenerating arms of individuals held in both seawater pH treatments. The present study indicates that predicted near-term levels of ocean acidification (seawater pH 7.8) do not significantly impact whole animal growth, arm regeneration rates, biochemical composition, or righting behavior in this common soft bottom sea star.     

Rate of regeneration of two arms in the field and its effect on body components in Luidia clathrata (Echinodermata: Asteroidea)

The incidence of arm regeneration, effects of arm regeneration on non-regenerating body components and rate of arm regeneration were examined under field conditions. Approximately 60% of Luidia clathrata found in the upper portion of Tampa Bay, Florida were regenerating one or more arms. Individuals with two arms amputated at the disk edge took 380 days to regenerate completely. Both arms of an individual regenerated at the same rate. Length of regenerating arms initially increased faster than dry mass. No difference was found between non-regenerating and regenerating individuals for the dry mass of the body wall, pyloric caeca, and gonad of a non-regenerating arm. The absolute masses of the gonad and pyloric caeca were low through out the year possibly indicating a low food environment. Based on the rate of regeneration, arm loss just prior to the reproductive season may reduce the reproductive potential of this species.     

Fine structure of the spermatozoon in the mite Parasitus niveus (Mesostigmata,Acari)

The spermatozoa of the mite, Parasitus niveus, are rod-shaped cells possessing a very elongated and zig-zag shaped nucleus. The cytoplasm is filled by so-called “striated bodies” and mitochondria. The plasmalemma forms five complicated structures, called stiff bands. In the peripheral cytoplasm lie flattened canaliculi and flattened cisternae. The morphology of the spermatozoa is compared with that of other mite spermatozoa described in the literature.     

Fine structure of the mature spermatozoon of rhynchocinetes typus,crustacea decapoda

Rhynchocinetes typus spermatozoa obtained from the vas deferens have the shape of a round-headed nail. The head measures 30 μm in diameter and 14 μm of height. At the center of the flat face of the head emerges a single rigid spike of 53 μm in length. Cross sections of this spike show that it has a wall of 0.4 μm in thickness and a core of 0.6 to 0.8 μm. The outer surface of the spike has a longitudinal striation. When the spermatozoa are placed in sea water it is possible to observe the unfolding of rays. The number of rays in different spermatozoa of the same individual varies from 9 to 13. Each ray is formed by a channel-like sheath that contains a rigid rod that occupies about 1/3 the length of the ray. This rod has a transverse striation with a periodicity of 185A. The rays are bound among them by a thin membranous sheet that is highly folded in vas deferens spermatozoa. At the distal end of each ray there is a rigid spine of 50 μm in length. The nucleus is coplanar to the radial plane and it extends through the rays. The structure and ultrastructure of R typus spermatozoa depart from that reported for spermatozoa of other Caridea species.     

The ultrastructure of the spermatozoon of Lernaeocera branchialis (Copepoda : Pennellidae)

Spermatozoa are produced by males of the fish-parasitic copepod, Lernaeocera branchialis, on the flounder (Platichthys flesus) host and packaged into spermatophores. Mature spermatozoa from spermatophores have been investigated with light microscopy and t.e.m. and s.e.m. techniques. Each is a filiform cell up to 30 µm long and 1 µm in diameter, being symmetrically tapered at each end to produce a javelin-shaped configuration. Surface s.e.m. appearances suggest that the cell is helically twisted. The spermatozoon possesses no flagellum, no nuclear envelope, no mitochondria and no orthodox acrosome. For most of its length the cell has a four-lobed appearance in transverse section and contains little more than a cylindrical sleeve of pseudomembranous material with which is associated finely filamentous or granular material which is assumed to be nuclear chromatin. The spermatozoon is immobile in seawater.The ultrastructure of L. branchialis spermatozoa has been compared with that of eight other copepod species.     

Ultrastructure of spermiogenesis and mature spermatozoon of Anonchotaenia globata (von Linstow, 1879) (Cestoda,Cyclophyllidea, Paruterinidae)

Yoneva, A., Georgieva, K., Mizinska, Y., Nikolov, P. N., Georgiev, B. B. and Stoitsova, S. R. 2010. Ultrastructure of spermiogenesis and mature spermatozoon of Anonchotaenia globata (von Linstow, 1879) (Cestoda, Cyclophyllidea, Paruterinidae). — Acta Zoologica (Stockholm) 91 : 184–192 The ultrastructure of spermiogenesis and of the spermatozoon of a species of the family Paruterinidae is described for the first time. The spermiogenesis of Anonchotaenia globata starts with the formation of a differentiation zone with two centrioles associated with thin striated roots. One of the centrioles gives rise to a free flagellum followed by a slight flagellar rotation and a proximodistal fusion of the flagellum with the cytoplasmic protrusion. This pattern corresponds to Type III spermiogenesis in cestodes. The spermatozoon consists of five distinct regions. The anterior extremity possesses an apical cone and a single helically coiled crested body. The cortical microtubules are spirally arranged. The axoneme is surrounded by a periaxonemal sheath and a thin layer of cytoplasm filled with electron‐dense granules in Regions I–V. The periaxonemal sheath is connected with the peripheral microtubules by transverse intracytoplasmic walls in Regions III and IV. The nucleus is spirally coiled around the axoneme. Anonchotaenia globata differs from Dilepididae (where paruterinids have previously been classified) in the type of spermiogenesis, the lack of glycogen inclusions and the presence of intracytoplasmic walls. The pattern of spermiogenesis is similar to that in Metadilepididae and Taeniidae, which are considered phylogenetically close to Paruterinidae.     

Ultrastructure of the spermatozoon of the American Alligator,Alligator mississippiensis (Reptilia: Alligatoridae)

This study details the ultrastructure of the spermatozoa of the American Alligator, Alligator mississippiensis. American Alligator spermatozoa are filiform and slightly curved. The acrosome is tapered at its anterior end and surrounded by the acrosome vesicle and an underlying subacrosomal cone, which rests just cephalic to the nuclear rostrum. One endonuclear canal extends from the subacrosomal cone through the rostral nucleus and deep into the nuclear body. The neck region separates the nucleus and midpiece and houses the proximal centriole and pericentriolar material. The distal centriole extends through the midpiece and has 9 × 3 sets of peripheral microtubules with a central doublet pair within the axoneme that is surrounded by a dense sheath. The midpiece is composed of seven to nine rings of mitochondria, which have combinations of concentrically and septate cristae. The principal piece has a dense fibrous sheath that surrounds an axoneme with a 9 + 2 microtubule arrangement. The sheath becomes significantly reduced in size caudally within the principal piece and is completely missing from the endpiece. Dense peripheral fibers, especially those associated with microtubule doublets 3 and 8, penetrate into the anterior portion of the principal piece axoneme. The data reported here hypothesize that sperm morphology is highly conserved in Crocodylia; however, specific morphological differences can exist between species. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Ultrastructure of spermiogenesis and the mature spermatozoon of Tetrabothrius erostris loennberg, 1896 (Cestoda, Tetrabothriidae)

The spermiogenesis of Tetrabothrius erostris is characterized by the following events: formation of a differentiation zone containing 2 basal bodies and a pair of rootlets; one of the basal bodies gives rise to a free flagellum, the other induces formation of a flagellar bud; rotation at 90° of the flagellum prior to its fusion with the middle cytoplasmic process of the differentiation zone and partial rotation of the flagellar bud; penetration of the nucleus between the rootlets and appearance of a spur-like protrusion in the differentiation zone; elongation and twisting of the differentiation zone, resulting in twisting of the peripheral microtubules and migration of the nucleus; formation of a crested body; proximal densification of the spermatozoon prior to its detachment from the spermatid rosette. The mature spermatozoon has a single axoneme of 9+“1” type and twisted peripheral microtubules. It consists of 3 portions: a proximal part with a crested body, a middle region rich in β-glycogen, and a distal part containing the nucleus. The pattern of spermiogenesis resembles most closely that in phyllobothriid tetraphyllideans, and probably reflects a relationship of the family Tetrabothriidae with this group.     

Ultrastructure of the biflagellate spermatozoon of tomopteris helgolandica greef, 1879 (annelida,polychaeta)

The spermatozoon of the polychaete Tomopteris helgolandica is of an aberrant type with two flagella, each measuring about 40μm. The nucleus is roughly conical and weakly bent. At the anterior end it is rounded and covered only by the nuclear and plasma membranes. Membraneous, electron-dense structures are applied laterally to the nucleus. These structures may have a helical arrangement. The middle piece contains about ten mitochondria, two centrioles, and two centriolar satellite complexes. The centriolar regions are connected with the posterior part of the nucleus. The axonemes of the two tail flagella lack the usual central complex with central tubules, radial spokes, or related structures. No arms seem to be present on the A tubules of the doublets. In the middle piece the tail flagella are surrounded by invaginations of the plasma membrane forming flagellar canals. The sperm has a bilateral symmetry whereas the primitive sperm has a radial symmetry. The occurrence of two tail flagella in this spermatozoon has no phylogenetical connection with biflagellate spermatozoa in other animal groups. A series of mutations has resulted in the development of two flagella emerging from the two centrioles, the lack of a central complex in the axoneme, and the lack of a typical acrosome. In the Polychaeta, sperm structure is generally more related to function that to phylogenetics. During swimming the spermatozoon of Tomopteris rotates around its longitudinal axis.     

The ultrastructural characters of the mature spermatozoon of Opechona bacillaris (Molin, 1859) (Digenea,Lepocreadiidae) a parasite of Scomber colias Gmelin, 1789 (Scombridae) off the coast of Dakar (Senegal)

This study presents the ultrastructure of the mature spermatozoon of Opechona bacillaris, a digenean belonging to the family Lepocreadiidae. The sperm cell of O. bacillaris exhibits the general pattern described in most of the Lepocreadioidea: two axonemes of the 9 + ‘1’ pattern of the Trepaxonemata, mitochondria, a cortical mitochondrion, a nucleus, electron‐dense material in the anterior extremity of the spermatozoon, external ornamentation of the plasma membrane with associated spinelike bodies, and granules of glycogen. However, particularities of O. bacillaris are the simultaneous presence in the anterior extremity of the spermatozoon of the electron‐dense material, a mitochondrion, and the absence of cortical microtubules. In the Lepocreadiidae, we describe for the first time in O. bacillaris spinelike bodies associated with the external ornamentation of the plasma membrane and two mitochondria. The first mitochondrion is moniliform and composed of a mitochondrial cord with joined mitochondrial bulges. The second mitochondrion shows a regular form. The posterior tip of the spermatozoon has only singlets to owing to the disorganization of the second axoneme and granules of glycogen as occurs in Hypocreadium caputvadum, the other studied species of the family Lepocreadiidae.     

Ultrastructure of spermiogenesis and the spermatozoon in Castrada cristatispina Papi, 1951 (Platyhelminthes, Rhabdocoela, Typhloplanida)

Spermiogenesis in Castrada cristatispina begins with the formation of a zone of differentiation containing two centrioles with associated striated rootlets and an intercentriolar body between them. The centrioles give rise to two parallel, free flagella of the Trepaxonemata 9 + '1' pattern, growing out in opposite directions. Spermatids undergo a latero-ventral rotation of the flagella and a subsequent disto-proximal rotation of centrioles, and a distal cytoplasmic projection appears. The former rotation involves the compression of a row of microtubules and allows the recognition of a ventral side and a dorsal side. At the end of the differentiation, the centrioles and cortical microtubules lie parallel to the sperm axis. The modifications of the intercentriolar body and the migration of the nucleus and the centrioles toward the distal projection are described. The mature spermatozoon of C. cristatispina is filiform, tapered at both ends and shares several features with the other Rhabdocoela gametes. Nevertheless, the posterior extremity is capped by an electron-dense material. A gradient between mitochondria and dense bodies exists along the sperm axis. This study has enable us a phylogenetic approach of the Rhabdocoela through a comparison of the ultrastructural features of C. cristatispina with the other Rhabdocoela taxa. We propose the disto-proximal rotation of centrioles as a synapomorphy of the Rhabdocoela.     

Ultrastructure of the head of ctenomys maulinus spermatozoon with special reference to the nucleus

The spermatozoa of the neotropical hystricomorph rodent Ctenomys maulinus have been examined cytochemically and under the transmission electron microscope. The head is flattened dorsoventrally. At the caudal end of the head there is a process oriented parallel to the tail. This process corresponds to a cylindrical extension of the nucleus, which constitutes a unique feature among mammals.