Regular Urchins Research Articles

The evolution of neurosensation provides opportunities and constraints for phenotypic plasticity

Phenotypic plasticity is widely regarded as important for enabling species resilience to environmental change and for species evolution. However, insight into the complex mechanisms by which phenotypic plasticity evolves in nature is limited by our ability to reconstruct evolutionary histories of plasticity. By using part of the molecular mechanism, we were able to trace the evolution of pre-feeding phenotypic plasticity across the class Echinoidea and identify the origin of plasticity at the base of the regular urchins. The neurosensory foundation for plasticity was ancestral within the echinoids. However, coincident development of the plastic trait and the neurosensory system was not achieved until the regular urchins, likely due to pleiotropic effects and linkages between the two colocalized systems. Plasticity continues to evolve within the urchins with numerous instances of losses associated with loss of sensory abilities and neurons, consistent with a cost of maintaining these capabilities. Thus, evidence was found for the neurosensory system providing opportunities and constraints to the evolution of phenotypic plasticity.

Comparative ultrastructure of spermatozoa from two regular and two irregular New Zealand echinoids

Spermatozoa from four species of echinoids found in New Zealand had morphological characteristics typical of other echinoids, including a conical sperm head with an acrosome-capped nucleus, a midpiece, and a single long flagellum. The spermatozoa of Fellaster zelandiae, Echinocardium cordatum, Evechinus chloroticus, and Centrostephanus rodgersii also showed statistically significant differences in species-specific morphological characteristics. Evechinus chloroticus showed the most variable sperm morphology. The irregular urchins (F. zelandiae and E. cordatum) had short, wide sperm heads (head length:width ratios 2.93:1 & 2.97:1, respectively) with a long acrosome complex, while the regular urchins (E. chloroticus and C. rodgersii) had longer, narrower heads with a short acrosome complex (ratios 5.29:1 & 3.37:1). Spermatozoa of E. cordatum from the New Zealand population shared more characteristics with those of conspecifics from the Sea of Japan than those of conspecifics from the Baltic, reflecting the membership of the former two populations in a distinct Pacific clade. Volumetric calculations showed no evidence of phylogenetic grouping. Mitochondria of E. chloroticus spermatozoa were less than half the volume of those of C. rodgersii and E. cordatum, and those of F. zelandiae were intermediate in volume. These volume measurements will be useful in physiological studies of sperm performance and quality.

Directed growth characteristics and optoelectronic properties of Eu-doped ZnO nanorods and urchins

Inexpensive fabrication of europium (Eu3+)-doped zinc oxide (ZnO) nanoparticles, nanorods, and urchin systems obtained by rapid thermal annealing is being reported. The polyvinyl alcohol films containing a reactant mixture [Zn(CH3COO)2, Eu(CH3COO)3, and NaOH] were casted on Al-foils followed by thermal annealing at 80, 300, and 650 °C. Gradual change-over from spherically symmetric nanoparticles to nanorods along with urchin like structures are obtained under different annealing environment. The nanorods and urchins are expected to have grown as a result of spontaneous decomposition of Zn(OH)2 followed by unidirectional growth. The nanorods are dislodged from the regular urchin structures at a high annealing temperature of 650 °C because of the loss of the crystalline substrate support. The as-received ZnO products possessed hexagonal wurtzite structure for all the annealing cases-as evident from the x-ray diffraction patterns. The photoluminescence study on the samples has revealed dominant defect related emissions compared to the near band edge emission. The band edge emission (∼382 nm) is recovered in the urchin systems whereas Eu3+ related transitions observed at ∼591 nm (D50→F71) and ∼613 nm (D50→F72) remained intact with structural modification.

Tooth Advancement Muscles in the Sand Dollar Echinarachnius parma

As the teeth of sand dollars are chipped and abraded during use, they are continuously renewed by growth in the plumule. During biting, the plumule. During biting, the teeth are secured in place and held immobile by mutable collagenous dental ligaments, which react the axial forces upon the teeth. During advancement, they are propelled along the dental slides by a pair of dental promoter muscles flanking each tooth, close to the plumule. At the abaxial (or plumular) end of the tooth slides are small, paired styloid processes. The dental promoter muscles originate in the superficial stromal spaces of these processes and insert on the dental membrane. Upon contraction of the promoter muscles, force is transferred to the tooth by tension in its surrounding membrane, which is well endowed with collagen fibrils and bundles. Although some of the bundles wrap around trabecular pillars of the tooth surface, there does not appear to be any direct connection of the muscles to the teeth. However, the muscle fibers do penetrate into the stromal spaces of the jaw and seem to be tethered to trabeculae by bundles of collagen. Smaller muscular regions of the dental membrane, between the plumule and promoter muscles, are possibly antagonists responsible for elongation of the promoter muscles. Additional key words: mutable collagenous tissue, echinoid, growth, Aristotle's lantern Aristotle's lantern in sea urchins is a structure containing five convergent teeth, each supported in a dental slide formed from the grooved surface of an ossicle called a pyramid. In Regular, globose urchins (Cidaroida, Diadematacea, Echinacea, etc.) the lantern can be protruded, and the teeth are used for scraping and grasping food (Hyman 1955; Smith 1984). In sand dollars (Clypeasteroida) the lantern (Fig. 1) is not protrusible, and the teeth converge almost horizontally to crush ingested material (Ellers & Telford 1991). The teeth are seated in deeply grooved pyramids or jaws (Fig. 2). The occlusal (Fig. 3) end can readily be observed to chip and flake when feeding on hard materials (Ellers & Telford 1991). New material is added to the tooth at the abaxial end, in the plumule (Figs. 3, 4) (e.g., Hyman 1955; Markel 1970). Throughout life, wear at the occlusal tips is replaced by the gradual advancement of the tooth along the dental slide. As they bite, the teeth of sand dollars are loaded axially, in a direction opposite that of tooth advancement (Lelievre et al. 1995). The axial forces sustained in biting are reacted by the dental ligaments (Figs. 5, 6) composed of mutable collagenous tissue (MCT) a Author for correspondence. E-mail: telford@ zoo.utoronto.ca (Ellers & Telford 1996). Mutable collagenous tissues, found in all classes of echinoderms, have the remarkable ability to undergo profound changes in stiffness under neural control (Motokawa 1984; Wilkie 1984, 1996). In a series of papers (Trotter & Koob 1995; Thurmond & Trotter 1996; Trotter et al. 1996) it has been shown that live cells are actively involved in the softening and stiffening processes of sea cucumber body walls, from which specific plasticizers and stiffeners have been isolated (Koob-Edmunds et al. 1996). The dental ligaments in a sand dollar (Dendraster excentricus) are known to be mutable (Ellers & Telford 1996, 1997) as are those in a regular sea urchin (Diadema setosum) (Birenheide 1990; Birenheide & Motokawa 1996). The mechanism of tooth advancement has never been explained. Birenheide (1990) noted the presence of MCT in the dental slides of a regular urchin, Paracentrotus lividus, but he did not investigate the forces responsible for movement of the teeth along the slides. We reported the presence of small dental promoter muscles in Dendraster excentricus (Ellers & Telford 1996). At that time we suspected that they operated in conjunction with MCT More recent experiments (Ellers & Telford 1997) have demonstrated that the teeth of Dendraster excentricus can be moved forward reThis content downloaded from 157.55.39.153 on Mon, 19 Sep 2016 04:44:50 UTC All use subject to http://about.jstor.org/terms

Induction of metamorphosis of larval echinoids (Strongylocentrotus droebachiensisandEchinarachnius parma) by potassium chloride (KCI)

Summary Potassium chloride (KCI) added to filtered seawater induced larval metamorphosis of the regular urchin Strongylocentrotus droebachiensis and the irregular urchin Echinarachnius parma in the absence of any other stimulatory substance, although the sensitivities of these two species differed. Larvae of S. droebachiensis were not affected by concentrations below 80 mM (above normal seawater levels), whereas 10 mM was enough to induce significantly more larvae of E. parma to metamorphose than a filtered seawater control (used to assess spontaneous metamorphosis in the absence of any inductive cue). Relatively high concentrations of KCl (i.e., above 60 mM), which did not appear to adversely affect larvae of S. droebachiensis, were toxic to larvae of E. parma. Presently, some 15 species of marine invertebrates (representing five different phyla) have larvae which are known to react (i.e., settle, attach, or metamorphose) in response to elevated K+ (KCl) levels. K+ (KCl), which is thought to induce larval metamorphosis via depolarization of externally accessible cells (Baloun and Morse, 1984), appears to be fairly non species-specific as a metamorphic inducer.

Echinoderms, Babel and the Confusion of Nomenclature

Among the many cryptic annotations, we find that By this great plague of the confusion of tongues, appeareth God's horrible judgements against man's pride and vaine glory. Whether systematists are more prideful and vainglorious than others, we would hesitate to say, but nowhere has this judgment been felt more severely than in the realm of taxonomic nomenclature. This is a field plagued by a veritable Babel of tongues. We have recently been confronted by a nomenclatural problem for the solution of which there appears to be no modus operandi. The phylum Echinodermata includes five extant classes universally known as Echinoidea (sea urchins), Holothuroidea (sea cucumbers), Crinoidea (feather stars and sea lilies), Asteroidea (sea stars or starfish) and Ophiuroidea (brittle or serpent stars). In The Zoological Record (Edwards, 1982), the latter two have been combined in the class Stelleroidea (starlike echinoderms) and that is how they appear in possibly the best modern general textbook (Barnes, 1980). Wise men have urged that the suffix -oidea should designate a superfamily (Recommendation 29A, International Code, 1985). What, then, are these time-honored classes to be called? Our personal interest lies in the class now inappropriately named Echinoidea. The distinguished Editor of Zoomorphology, Otto Kraus, who drew the problem to our attention, proposed that the class be named Echinoida, as it was by Siewing (1985). But this creates a new problem: all of the orders of sea urchins are designated by the suffix -oida and, if that were not enough, the name Echinoida itself is already in use for that order which includes Echinus and Echinometra, as well as several other regular urchins. Within all other classes of living echinoderms, the ordinal suffix is -ida, as in Paxillosida, Ophiurida, Dendrochirotida, etc. Perhaps the solution would be to change the classes to the suffix -oida and then change all of the orders of urchins to -ida, thus bringing some uniformity to the phylum. However, we think that this has some serious disadvantages because we would lose the linguistic convenience of referring to the clypeasteroids, for example, including but not limited to the family Clypeasteridae. Terms such as spatangoids, cassiduloids and so on are far too useful to be given up without a struggle. And besides, we refuse to live in a world without the disasteroids! It is beyond contemplation. In search of inspiration we consulted Barnes (1980) to see what is done with other groups of animals. The awful extent of the Babylonian judgment immediately became apparent. The class Hydrozoa has two orders suffixed -ina (one of which includes two suborders with the same ending), one -ida, one -phora and one -oida. The Turbellaria seem to fare slightly better with four -ida's, two -coela's, two -ata's and one -phora; but note, in this class, -oida is occasionally used for suborders. The two orders of digonont rotifers are curious: one enjoys an -idea suffix; the other -oidea. On the other hand, the monogonont orders include two -acea's and an -ima. Hope

Observations on the clypeasteroid Echinocyamus pusillus (O. F. Müller)

The tiny echinoid Echinocyamus pusillus (O. F. Müller) is equipped with specialized external structures that suit it for a wide variety of environments. Special features include the ability to burrow in sediments of fine sand to shell gravel and to climb vertically. Specimens dredged off the west coast of Scotland were observed in aquaria and with the SEM. E. pusillus is characterized by three kinds of spines, and by two of pedicellariae. In contrast to sand dollars, the spines play a passive rôle in the feeding and burrowing operation, probably retaining a defensive nature as in the regular urchins. It is the podia that are chiefly involved in climbing, burrowing, righting, and probably feeding. Surface ciliary currents transport particles, but not to the mouth; they may have a respiratory or cleansing function. Experimental animals did not burrow in either very fine or very coarse sand, probably because a certain relationship exists between particle weight and podia size. E. pusillus shares behavioural and structural characteristics with regular and irregular urchins. It is not a true sand dollar, but may illustrate an evolutionary stage towards such a form.

Development of pedicellariae in the pluteus larva of Lytechinus pictus (Echinodermata: Echinoidea)

Three tridentate pedicellariae develop in the pluteus larva of Lytechinus pictus. Two are located on the right side of the larval body and the third is on the posterior end of the larva. The pedicellariae form from mesenchyme associated with the larval skeleton which becomes enclosed in an invagination of larval epidermis. The mesenchyme within the pedicellaria primordium aggregates into groups of cells that become skeletogenic tissues which secrete the pedicellaria jaws, and smooth and striated muscles. Nerves and sensory cells develop within the epidermis covering the pedicellariae. Pedicellaria formation takes 3 days and occurs about midway through the development of the adult rudiment. During metamorphosis the pedicellariae are shifted to the aboral surface of the juvenile.Pedicellariae that develop in the larvae are fully operable prior to metamorphosis and do not appear to be released from any rudimentary state of development by metamorphosis. At least 16 echinoid species are reported to form pedicellariae in the larva. The precocious development of these adult structures appears to be dispersed throughout the orders of regular urchins.

Lebensspuren of Dysaerobic, Bathyal Basin, California Borderland: ABSTRACT

The low oxygen waters and bathyal depths of Santa Cruz basin provide harsh conditions for marine life, yet the basin supports a surprisingly high density and diversity of macrofauna. In contrast, biogenic sedimentary structures are low in density. Bottom photographs from 117 stations show a biogenically produced micro-hummocky topography with few resolvable biogenic traces. Recognizable lebensspuren are of three main classes: tracks and trails, depressions, and fecal matter. Echinoderms, the most abundant epifauna on the slope and adjacent basin floor, produce most of the large tracks and trails. Significantly, many tracks and trails are less distinct than similar markings of the abyss owing to the soupy, thixotropic nature of the basinal sediment. Depressions made by ast roids, regular urchins, and bottom-dwelling fish are most common at relatively shallow depths. A characteristic, circular depression made by a feeding, tubicolous polychaete is restricted to the lowermost slope and adjacent basin floor. Holothurian fecal strands dominate the photographically resolvable feces of this bathyal environment. These holothurian feces take the clothes-line form common to the abyss. X-ray radiography and photography of box-core sediment slabs reveal an indistinct burrow mottling resulting from the thixotropic response of the sediment to biogenic disturbance and lack of density contrast for radiography. Although open burrows are common in bottom photographs, few are recognizable in box-core slabs. Similarly, surface lebensspuren have poor preservation potential. When lithified, this bathyal sediment will probably be bioturbate-textured. End_of_Article - Last_Page 703------------

THE EFFECT OF SIZE, TEMPERATURE, OXYGEN LEVEL AND NUTRITIONAL CONDITION ON OXYGEN UPTAKE IN THE SAND DOLLAR,MELLITA QUINQUIESPERFORATA(LESKE)

1. Rates of respiration in a closed vessel conformed to oxygen concentrations in surrounding water until a low level (1 ml O2/liter) of oxygen was attained.2. Respiratory rates of small animals were proportionally higher on both a dry weight and nitrogen weight basis than rates of large animals (slope for ml O2 respired/hr per animal was 0.5485 for dry weight and 0.5670 for nitrogen) in a closed vessel.3. Respiratory rates of field acclimatized animals were slightly higher at summer temperatures (30-33° C) than at winter water temperatures (15-20° C) with evidence for partial acclimatization presented.4. Respiratory rates of starved animals were lower than rates of non-starved animals with starvation depressing the rates of smaller animals more than rates of larger animals.5. Respiratory rates in an open system were approximately twice as high as rates in a closed system due to greater activity of animals in the open system.6. Comparison of day versus night respiration showed no obvious trends.7. Respiratory rates of M. quinquiesperforata are slightly higher than rates of a similar weight, tropical, regular urchin as reported in the literature.

Overgrazing of Seagrasses by a Regular Urchin, "Lytechinus variegatus"

Overgrazing of Seagrasses by a Regular Urchin, "Lytechinus variegatus"

Feeding and the control of volume within the tests of regular sea‐urchins

The rigid, fluid filled, echinoid test presents problems of internal volume control when the vital functions of the animal involve the introduction of material, from outside the test, into the internal fluid systems. The volume of food in the guts of echinoids can be shown to vary considerably in the short term, to an extent which demands considerable capabilities for internal volume compensation. This is achieved by adjusting the quantity of fluid held within the gut so that, although the volume of food may vary widely, the total volume of the gut remains constant within narrow limits. The volume of gut fluid varies inversely with the quantity of food, and ingestion of food through the mouth is compensated by ejection of an equal volume of fluid from the anus. Defaecation is compensated by intake of fluid into the gut. On starvation, the gut becomes completely fluid filled and free from food.The food of regular urchins is habitually compacted into regularly sized subpherical pellets covered with a tough mucus coating. The formation of coated pellets takes place in the buccal cavity and pharynx. The pellets remain discrete throughout their passage along the gut. The mucus coating resists digestion and remains intact even after defaecation. The functional morphology of the buccal cavity and pharynx is described in detail.It is suggested that the functional significance of the pellets is associated with the gut fluid, volume compensation mechanism, which requires free flow of fluid throughout the length of the gut. It is also suggested that the siphon may be implicated in volume control, where fine adjustment of gut volume can be achieved by balancing ejection of fluid from the anus with intake of water through the mouth, but that the water intake is by the siphonal route, thus avoiding the necessity of flushing and diluting the enzyme rich digestive stomach region.

Comparative respiration of tropical echinoids

1. 1. The rates of oxygen consumption of six species of tropical sea urchins were determined. 2. 2. The oxygen consumption rates of three species of epifaunal, regular urchins were significantly higher than the rate of two infaunal, irregular species. 3. 3. Oxygen consumption rates of a cidarid species which lacks peristomeal gills were intermediates between the oher two groups.

‘Skin Digestion’ and Epidermal Absorption in Irregular and Regular Urchins and their Probable Relation to the Outflow of Spherule-Coelomocytes

‘Skin Digestion’ and Epidermal Absorption in Irregular and Regular Urchins and their Probable Relation to the Outflow of Spherule-Coelomocytes

The Histology and Activities of the Tube-feet of Echinocyamus pusillus

ABSTRACT The histology of the suckered, buccal sensory, and respiratory tube-feet and their ampullae, where they occur, of the clypeasteroid sea-urchin Echinocyamus pusillus is described. Each suckered tube-foot possesses two sets of special muscles for attachment and detachment, a ring of mucous glands to assist in attachment, and a ring of sensory cilia. The stem retractors are in four columns, whose differential contraction provides the means of postural movement relative to the test. The ampullae of these tube-feet are exceedingly thin-walled, apparently musculo-epithelial, with anastomosing contractile elements. The canal between tube-foot and ampulla contains a swollen coelomic epithelium which may help to maintain the nerve relationships of the system. The activity of the suckered tube-feet is compared with that of the tubefeet of the starfish, Asterias rubens. The buccal tube-feet, larger than the suckered tube-feet, have large disks underlain by a thick nerve plexus supported by transverse fibres ; a ring of sensory cilia surrounds the disk. They have no mucous glands and no suckers, and are presumably entirely sensory, probably both tactile (the cilia) and chemoreceptive (the disk). The respiratory tube-feet are thin-walled sacs, the walls consisting of an outer ciliated and an inner non-ciliated (coelomic) epithelium with cross-connexions for support; where the coelomic epithelium lines the pair of canals through the test it is heavily ciliated. In the specializations of its tube-feet this urchin is shown to share some features with the regular urchins and others with the spatan-goids.

NOTES ON THE BIOLOGY OF THE FIVE-LUNULED SAND DOLLAR

The five-lunuled sand dollar, Mellita quinquiesperforata (Leske, 1778), is abundant on the sand flats at Beaufort, North Carolina, where the following ob servations were made during a short stay in August, 1957, at the Duke Uni versity Marine Laboratory. Burrowing. The animal lives in shallow water in a horizontal position, usually completely covered by a thin layer of sand although sometimes the posterior lunule remains visible. Specimens observed were motionless although the animal can progress under the sand. On being removed and placed on top of the sand under water it promptly burrows under again. The statements about its method of burrowing in Pearse, Humm and Wharton (1942) are totally at variance with my observations and appear wholly erroneous. They say that in burrowing the animal moves directly downward, waving its spines and tube feet so as to move sand from beneath the test to the upper surface, and does not progress anteriorly as it descends. My observations on animals in their natural habitat agree with those of Kenk (1944) on the closely related Mellita lata at Puerto Rico. Unlike regular urchins, sand dollars and other irregular urchins are polarized with definite anterior and posterior ends and can move only in the anterior direction, that opposite the posterior lunule in the present species. When placed on the sand under water in its natural habitat Mellita promptly begins to bury itself. It does this by simply advancing into the sand in a horizontal or slightly oblique orientation, using its ordinary method of locomotion by waves of movement along the spines of the oral surface. Kenk gives a suc cession of photographs showing Mellita advancing into the sand, which rapidly covers it. I did not time the reaction but only a couple of minutes is required for the five-lunuled species to cover itself with a thin layer of sand whereupon it comes to a halt. It positively does not move downward, does not remove sand from beneath it, and does progress forward. It is improbable that the tube feet play any role in locomotion as they are small and feeble and of limited distribution. Lunules. Contrary to the statement of the Berrills (1957), in Mellita sand positively does not pass through the lunules from the oral to the aboral surface during the burrowing process. To the contrary as the animal advances into the sand, sand falls through the lunules to the oral surface, thus if anything retarding the burying process. It is known for a Japanese species (Ikeda, 1941) that the lunules are important in burrowing and righting but this is definitely not the case in Mellita. The further suggestion of the Berrills that the lunules strengthen the test by fusing the oral and aboral surface is extremely im probable because the two surfaces of the test are so much connected by interior

Studies in Heredity. II. Further Experiments in Crossing British Species of Sea-urchins

Two years ago I read a paper before the Society in which I gave the results which I had obtained by crossing the two species of sea-urchin Echinus esculentus and Echinocardium cordatum . The first of these is a regular urchin, the second an enocyclic urchin belonging to the order Spatangoidea. The results recorded in that paper were briefly these:—The egg of Echinocardium fertilised by the sperm of Echinus gives rise to a hybrid which exhibits a mixture of maternal and paternal characters, but only a small proportion of the hybridised eggs develop. The egg of Echinus fertilised by the sperm of Echinocardium develops a fertilisation membrane, but then breaks up into a heap of globules by the process known as cytolysis, and dies. Since writing that paper my experiments were repeated at Plymouth by Fuchs, now my colleague at the Imperial College, and he obtained different results. According to him the eggs of Echinus fertilised by the sperm of Echinocardium gave rise to hybrid larvae which were maternal in character, whilst the eggs of Echinocardium fertilised by the sperm of Echinus gave rise to hybrids of two kinds, some purely maternal in type and some resembling those which I had obtained.

Studies in heredity. II.—Further experiments in crossing British species of sea-urchins

Two years ago I read a paper before the Society in which I gave the results which I had obtained by crossing the two species of sea-urchin Echinus esculentus and Echinocardium cordatum . The first of these is a regular urchin, the second an enocyclic urchin belonging to the order Spatangoidea. The results recorded in that paper were briefly these:—The egg of Echinocardium fertilised by the sperm of Echinus gives rise to a hybrid which exhibits a mixture of maternal and paternal characters, but only a small proportion of the hybridised eggs develop. The egg of Echinus fertilised by the sperm of Echinocardium develops a fertilisation membrane, but then breaks up into a heap of globules by the process known as cytolysis, and dies. Since writing that paper my experiments were repeated at Plymouth by Fuchs, now my colleague at the Imperial College, and he obtained different results. According to him the eggs of Echinus fertilised by the sperm of Echinocardium gave rise to hybrid larvæ which were maternal in character, whilst the eggs of Echinocardium fertilised by the sperm of Echinus gave rise to hybrids of two kinds, some purely maternal in type and some resembling those which I had obtained.