Beadle, S. C. (1995). Retrodisplacement of the oral and anal openings in dendrasterid sand dollars. Evolution 49, 1203-1214.
In regular echinoids, the mouth opening (or peristome) and the anal opening (or periproct) are located centrally. In irregular echinoids, the peristome tends to shift toward the anterior end of the test, whereas the periproct typically shifts toward the posterior end. This produces an anatomically polarized morphology, which is consistent with functional expectations. In the dendrasterid sand dollars, however, the peristome and periproct have been displaced in the ''wrong'' directions; the peristome has shifted posteriorly, whereas the periproct has shifted anteriorly. These movements, which run counter to functional expectations, may be termed ''retrodisplacements.'' This study presents a new model for the development of the oral surface in dendrasterids. The model assumes that the ''Dendraster pattern'' of development (which occurs in dendrasterids) was derived from the older ''Echinarachnius pattern'' (which occurs in other northern Pacific sand dollars). The Echinarachnius pattern includes two successive phases of asymmetric growth: the first phase favors anterior growth, whereas the second phase favors posterior growth. These two phases are normally balanced, and at maturity, the rest appears to be symmetrical. But if the second phase of unequal growth were suppressed through a heterochronic change in development, the effects on test development would be profound. On the aboral surface, the predicted effects include posterior displacement of the apical system. On the oral surface, the predicted effects include retrodisplacement of the peristome and periproct, as well as conspicuous changes in ambulacral and interambulacral development. In fact, all of the predicted effects are characteristic features of dendrasterids. The model assumes that the oral and aboral surfaces could be simultaneously affected by the same developmental processes. This assumption is supported by empirical evidence: in dendrasterids, there is a strong correlation between the displacement of the apical system (on the aboral surface) and the displacement of the peristome (on the oral surface). The displacement of the apical system (known as ''apical eccentricity'') is regarded as a valuable adaptation, because it facilitates suspension feeding. But if oral and aboral development are linked, then selective pressure for apical eccentricity would simultaneously produce new oral characters as well. Thus, the retrodisplacement of the peristome and periproct in dendrasterids may be related to developmental constraints. These unusual characters may have little or no functional significance.

Bryan, P. J., Qian, P. Y., Kreider, J. L., and Chia, F. S. (1997). Induction of larval settlement and metamorphosis by pharmacological and conspecific associated compounds in the serpulid polychaete Hydroides elegans. Marine Ecology-Progress Series 146, 81-90.
Field populations of the serpulid polychaete Hydroides elegans occur in dense aggregations. Preliminary laboratory assays showed that planktonic larvae H. elegans from Hong Kong waters did not settle and metamorphose without proper chemical cues and could remain planktonic up to 14 d in laboratory culture. Adult H. elegans capture conspecific larvae with feeding tentacles but cannot readily consume older, competent larvae. Contact between adult feeding tentacles and larvae may increase larval exposure to adult associated inductive compounds. In this study, we tested the effects of homogenates of adult worms and their tubes, as well as a variety of artificial inducers, on settlement and metamorphosis of H. elegans larvae. Conspecific adult homogenates induced 39 and 82% of larvae to settle and metamorphose within a period of 2 and 4 d, respectively. Homogenates of the adult tube alone did not induce settlement, indicating that the inducer originates from the worm, Extraction and assays on crushed adult homogenates revealed that the inductive compounds from adults are smaller than 10 000 daltons and can be bound to amberlite XAD-7. Further isolation and identification of the conspecific associated inducer will enable studies of chemoreceptors and signaling pathways involved in metamorphosis. Additionally, among 5 artificial inducers tested, isobutyl methylxanthine (IBMX) induced a high percentage of normal metamorphosis while gamma-aminobutyric acid (GABA), choline chloride, dihydroxyphenyl L-alanine (L-DOPA), and potassium chloride evoked a low percentage of settlement, but abnormal metamorphosis. Ammonia had no effect on the metamorphosis of H. elegans.

Bushman, F. D., and Crain, W. R., Jr. (1983). Conserved pattern of embryonic actin gene expression in several sea urchins and a sand dollar. Dev Biol 98, 429-36.
An examination of the size and relative abundance of actin-coding RNA in embryos of four sea urchins (Strongylocentrotus purpuratus, Strongylocentrotus droebachiensis, Arbacia punctulata, Lytechinus variegatus) and one sand dollar (Echinarachnius parma) reveals a generally conserved program of expression. In each species the relative abundance of these sequences is low in early embryos and begins to rise during late cleavage or blastula stages. In the four sea urchins, actin- coding RNAs increase between approximately 9- and 35-fold by pluteus or an earlier stage, and in the sand dollar about 5.5-fold by blastula. A major actin-coding RNA class of 2.0-2.2 kilobases (kb) is found in each species. A smaller actin-coding RNA class, which accumulates during embryogenesis, is also present in S. purpuratus (1.8 kb), S. droebachiensis (1.9 kb), and A. punctulata (1.6 kb), but apparently absent in L. variegatus and E. parma. In S. droebachiensis, actin- coding RNA is relatively abundant in unfertilized eggs and drops sharply by the 16-cell stage. This is in contrast to the other sea urchins where the actin message content is relatively low in eggs and does not change substantially in the embryos throughout early cleavage. The observations in this study suggest that the pattern of embryonic expression of at least some members of this gene family is ancient and conserved.

Cabanac, A., Hamel, J. F., and Himmelman, J. H. (1993). Morphological Adaptations of the Sand Dollar Echinarachnius- Parma to Righting Itself. Canadian Journal of Zoology-Revue Canadienne De Zoologie 71, 1274-1276.
Though the radial symmetry of the sand dollar Echinarachnius parma is striking, we show that the mass and thickness of the anterior portion is greater than that of the posterior portion. By adding weights to either portion and quantifying the righting response, we demonstrate that the asymmetry in body mass is required to allow the sand dollar to right itself.

Cabanac, A., and Himmelman, J. H. (1996). Population structure of the sand dollar Echinarachnius parma in the subtidal zone of the northern Gulf of StLawrence, eastern Canada. Canadian Journal of Zoology-Revue Canadienne De Zoologie 74, 698-709.
We examined changes in populations of Echinarachnius parma with depth on subtidal sediment slopes in the Mingan Islands. Size distributions showed the presence of two major groups measuring 1-21 and 37-62 mm in length, respectively. Intermediate-sized sand dollars were rare. Juveniles (<28 mm in length) were extremely abundant at 16 and 20 m depth (460-660/m(2)) and decreased in number with decreasing depth, whereas the density of adults was relatively stable at different depths. Juveniles were more frequently buried (95%) than adults (30%). Analysis of growth lines and of shifts in juvenile cohorts indicated that growth rate increased with size up to a maximum between 20 and 40 mm and then decreased sharply. The bimodal size structure is possibly due to the accelerated growth rate at intermediate sizes. We hypothesize that sand dollars move to shallower water with increasing size to take advantage of food resources, possibly benthic diatoms, which are more abundant there. Large individuals are probably better adapted than juveniles to exploiting shallower water because they are less likely to be transported by water turbulence.

Cabanac, A., and Himmelman, J. H. (1998). Directional movement of the sand dollar Echinarachnius parma. Ophelia 48, 93-102.
Responses of the sand dollar Echinarachnius parma to various stimuli were quantified. Sand dollars in the laboratory showed a strong preference for upslope movement. Further, observations in a flume showed a preference for upstream movement for large but not small individuals. Observations of lagged large (45-55 mm in length) sand dollars in the field confirmed the preference for upslope movement, but also indicated an effect of other factors. The tendency to move upslope supports the hypothesis that the predominance of large sand dollars in shallow water is due to a migration from greater depths. The similarity in the positions of tagged living and dead sand dollars after 8 days of stormy conditions demonstrated that changes in position during strong turbulence was determined by the interaction of hydrodynamic forces and body form rather than by behaviour. Most tagged small sand dollars (20-30 mm) which were released disappeared and we expect this is because they are readily transported by even weak wave and current conditions.

Chang, S. W., Steimle, F. W., Reid, R. N., Fromm, S. A., Zdanowicz, V. S., and Pikanowski, R. A. (1992). Association of Benthic Macrofauna With Habitat Types and Quality in the New-York Bight. Marine Ecology-Progress Series 89, 237-251.
Previous qualitative and limited quantitative analyses of benthic data from the New York Bight, USA, have suggested associations among macrofauna and sediment characteristics, including levels of chemical contamination. Benthic data from 3 summers (1980 to 1982) of sampling were used to examine more thoroughly these relationships. Factor and canonical analyses confirmed that a limited group of macrofaunal taxa (Ceriantheopsis american us, Nephtys incisa, Capitella spp., Nucula proxima and Ampelisca agassizi), historically considered indicators of habitat quality, were indeed valid indicators. Ordination analyses provided greater detail about the association of, and between, sediment variables and the 80 most frequently occurring species. The results allowed a characterization of the New York Bight benthic habitat, encompassing the range from an undisturbed habitat to the lowest quality habitat. One species group was consistently associated with minimally contaminated sediments and appears to represent a basic natural benthic macrofaunal assemblage for the Bight. This group included taxa such as the sand dollar Echinarachnius parma and several species of amphipods (e.g. Byblis serrata, Corophium crassicorne and Ampelisca agassizi) as well as some polychaetes (e.g. Goniadella gracilis and Exogone hebes). Species that were the most common in the contaminated areas of the Bight were mainly polychaetes (e.g. Tharyx acutus, Nephtys incisa, Pherusa affinis and Capitella spp.) as well as the Nemertinea (Cerebratulus lacteus), an anemone (Ceriantheopsis americanus), a phoronid (Phoronis architecta) and the nut clam Nucula proxima.

Crowther, R. J., Wu, S. C., and Whittaker, J. R. (1988). Cell differentiation features in embryos resulting from interphylum nuclear transplantation: echinoderm nucleus to ascidian zygote cytoplasm. Dev Biol 130, 443-53.
When an echinoderm nucleus was transplanted into an ascidian zygote cytoplast there was developmental cooperation at the cellular level between nucleus and cytoplasm of these normally nonhybridizable species. A blastula stage nucleus from the sand dollar Echinarachnius parma was injected into an activated but nonnucleate egg fragment of the ascidian Ciona intestinalis. During culture, some of the "hybrid" embryos displayed ultrastructural evidence of cellular differentiation. Two recognizable features were (1) extracellular matrix components, and (2) neural cell characteristics, including elaboration of associated cilia. Nonnucleate zygote fragments alone, and such fragments injected with seawater or punctured by glass needle, did not develop organized subcellular structures. Morphologic expressions resulting from nuclear transplantations between these two phyla (Echinodermata and Chordata) seemingly indicate functional interactions at a gene regulatory level. Creation of such nuclear-cytoplasmic hybrids suggests thereby a means of exploring the nature of the egg cytoplasmic agents in ascidian embryos that appear to determine gene expression related to histospecific differentiation products.

Jewett, S. C., Feder, H. M., and Blanchard, A. (1999). Assessment of the benthic environment following offshore placer gold mining in the northeastern Bering Sea. Marine Environmental Research 48, 91-122.
The effects of offshore placer gold mining on benthic invertebrates were assessed on 'sand' and 'cobble' substrates in Norton Sound, northeastern Bering Sea. Mining with a bucket- line dredge occurred nearshore in 9-20 m during June to November 1986-90. Sampling nearly a year subsequent to mining demonstrated minor alteration of substrate granulometry with no clear trends. However, benthic macrofaunal community parameters (total abundance, biomass, diversity) and abundance of dominant families were significantly reduced ar mined stations. Many of the dominant taxa are known prey of the locally important red king crab (Paralithodes camtschaticus). Dominance of opportunistic species and small sizes at unmined and mined sites represents faunal responses to the natural dynamics of the region where establishment of populations of large, sexually-mature individuals is typically precluded. Multi-year bathymetric surveys of an area only mined in 1986 showed a continued smoothing of ocean bottom relief, decreasing size of tailing footprint, and shoaling of depressions left by mining. An ordination (multidimensional scaling) of taxon abundance data from mined (1 year after mining), recolonizing(2-7 years after mining) and unmined stations shows configurations that reflect disturbance. Recovery of the biota was underway in both substrates after 4 years, but this process was interrupted in the fall of the fourth year (1990) by several severe storms. Mining effects are contrasted with local natural disturbances. (C) 1999 Elsevier Science Ltd. All rights reserved.

Johnson, L. G. (1998). Stage-dependent thyroxine effects on sea urchin development. New Zealand Journal of Marine and Freshwater Research 32, 531-536.
Thyroxine, one of the iodinated hormones produced by vertebrate thyroids, has been reported to accelerate late larval development in several sea urchins (Chino et al. 1994) and in the crown-of-thorns starfish (Johnson & Cartwright 1996), but thyroxine effects on earlier portions of echinoderm development have not been reported. I investigated thyroxine effects on developmental rates during several periods spanning development from early cleavage to metamorphosis in the New Zealand sea urchin Evechinus chloroticus (Valenciennes). Thyroxine treatment slowed development between the eight-cell stage and assembly of the four-armed pluteus and mid-larval development between the four-armed and six-armed stages. Thyroxine treatment accelerated progress of eight-armed plutei toward settling, but did not alter the final percentages of larvae that settled and metamorphosed to juvenile urchins. Acceleration of late larval echinoderm development by thyroxine may indicate a relatively ancient evolutionary origin of thyroxine's effects on developmental processes (Johnson 1997).

Pearce, C. M., and Scheibling, R. E. (1994). Induction of Metamorphosis of Larval Echinoids (Strongylocentrotus-Droebachiensis and Echinarachnius-Parma) By Potassium-Chloride (Kcl). Invertebrate Reproduction & Development 26, 213-220.
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.

Prena, J., Schwinghamer, P., Rowell, T. W., Gordon, D. C., Gilkinson, K. D., Vass, W. P., and McKeown, D. L. (1999). Experimental otter trawling on a sandy bottom ecosystem of the Grand Banks of Newfoundland: analysis of trawl bycatch and effects on epifauna. Marine Ecology-Progress Series 181, 107-124.
An experimental study of the effects of otter trawling was conducted in a deep (120 to 146 m) sandy bottom ecosystem of the Grand Banks of Newfoundland from 1993 to 1995. Each year, three 13 km long corridors were trawled 12 times within 31 to 34 h with an Engel 145 otter trawl equipped with rockhopper foot gear. The width of the disturbance zones created was on the order of 120 to 250 m. The total biomass of invertebrate bycatch in the trawl decreased significantly over the 12 sets, even though only a very small proportion of the biomass present was removed and each set did not pass over exactly the same area of seabed. An influx of scavenging snow crabs Chionoecetes opilio into the trawled corridors was observed after the first 6 sets (approximately 10 to 12 h). Benthic organ isms in trawled and nearby reference corridors were sampled with an epibenthic sled. Their biomass was on average 24% lower in trawled corridors than in reference corridors. At the species level, this biomass difference was significant for snow crabs C, opilio, sand dollars Echinarachnius parma, brittle stars Ophiura sarsi, sea urchins Strongylocentrotus pallidus and soft corals Gersemia sp. The reduced biomass of epibenthic organisms in trawled corridors is thought to be due to several interacting factors including direct removal by the trawl, mortality, damage, predation and migration. The homogeneity of the macro-invertebrate community collected by epibenthic sled was lower in trawled corridors. Sand dollars, brittle stars and sea urchins demonstrated significant levels of damage from trawling. The mean individual biomass of epibenthic organisms was lower in trawled corridors suggesting size specific impacts of trawling, especially for sand dollars. No significant effect of trawling was observed in the 4 dominant mollusc species captured by the sled (Astarte borealis, Margarites sordidus, Clinocardium ciliatum and Cyclocardia novangliae). This experiment indicates that otter trawling on a sandy bottom ecosystem can produce detectable changes on both benthic habitat and communities, in particular a significant reduction in the biomass of large epibenthic fauna.

Rappaport, R. (1976). Furrowing in altered cell surfaces. J Exp Zool 195, 271-8.
Understanding the process which established the cell division mechanism requires analysis of the role of the responding surface as well as that of stimulatory subsurface structures. Cell surface was altered by the expansion which occurs during exovate formation. Exovates appear on the surface of fertilized Arbacia lixula, Paracentrotus lividus and Echinarachnius parma eggs in response to extreme flattening. They result from cytoplasmic outflow initiated in a very restricted portion of the egg surface. Observations of the formation process in pigmented A. lixula eggs revealed that the original surface may be expanded about 100 fold as the exovate swells. When exovates formed 15-30 minutes after fertilization contain the mitotic apparatus, they divide synchronously with flattened controls. If nucleated exovates are established after the beginning of first cleavage, furrows appear in ten minutes. Exovates established after the beginning of second cleavage develop furrows four minutes after the entrance of the the mitsotic apparatus. Cytoplasm beneath damaged exovate surfaces sometimes develops partial constrictions independently of the surface in the plane the furrow would have occupied. These results suggest that normal surface structure is unnecessary for furrow establishment and function.

Rappaport, R. (1977). Tensiometric studies of cytokinesis in cleaving sand dollar eggs. J Exp Zool 201, 375-8.
Tensions exerted by cleavage furrows of Echinarachnius parma were measured by means of calibrated, flexible glass needles. The tensions exerted by the first and second furrows in isometric contraction were, respectively, 1.58 X 10(-3) dyne (S.D. 0.41 X 10(-3) dyne) and 1.43 X 10(-3) dyne (S.D. 0.44 X 10(-3) dyne). The difference between the two means is not significant. The tensions exerted by the same cleavage furrow at two different lengths, of which the shorter was about 66% the length of the longer, were not significantly different. When the progress of a second cleavage furrow was mechanically blocked, it continued to exert maximum tension up to 9 minutes after its companion blastomere, which served as a time control, completed cleavage.

Rappaport, R. (1985). Repeated furrow formation from a single mitotic apparatus in cylindrical sand dollar eggs. J Exp Zool 234, 167-71.
The methods used previously to demonstrate the ability of a single mitotic apparatus to elicit multiple furrows involved considerable cell distortion and did not permit the investigator to control the positioning of the parts or to observe satisfactorily the early stages of furrow development. In this investigation, Echinarachnius parma eggs were confined in 82 microns i.d. transparent, silicone rubber-walled capillaries, and the mitotic apparatus was moved by pushing the poles inward with 55-microns-diameter glass balls. When the mitotic apparatus was shifted immediately after the furrow first appeared, a new furrow appeared in the normal relation to the new position in 1-2 minutes. The same mitotic apparatus could elicit up to 13 furrows as it was shifted back and forth by alternately pushing in the poles. The previous furrow regressed as the new furrow developed. The operations protracted the furrow establishment period to as long as 24.5 minutes after establishment of the first furrow. The characteristics of furrow regression were related to the distance the mitotic apparatus was moved. It is unlikely that regression was caused either by stress imposed on the surface or the removal of the mitotic apparatus from the vicinity of the furrow.

Rappaport, R. (1999). Absence of furrowing activity following regional cortical tension reduction in sand dollar blastomere and fertilized egg fragment surfaces. Dev Growth Differ 41, 441-7.
The purpose of the present investigation was to test experimentally the possibility that division mechanism establishment at the equator of sand dollar eggs may be a consequence of cortical tension gradients between the equator and the poles. Cytochalasin has been shown to decrease tension at the sea urchin egg surface. The concave ends of cytochalasin D-containing agarose cylinders were held against regions of the surface of Echinarachnius parma blastomeres and enucleated fertilized egg fragments. The ability to interfere with normal furrowing activity was used as a biological indicator of the effectiveness of cytochalasin. When agarose containing 2 microg/mL cytochalasin contacted the equatorial region of the blastomeres resulting from the first cleavage, or the equatorial surfaces of nucleated fertilized egg halves, furrowing was blocked, stalled or delayed, indicating that the concentration of cytochalasin was effective. When the same concentration of cytochalasin was applied to the poles, the cells and nucleated fertilized egg fragments divided in the same way as the controls, indicating that the effectiveness of the cytochalasin did not spread from the poles to the equator and that bisection did not interfere with the division of nucleated fertilized egg fragments. When the same concentration of cytochalasin was applied to diametrically opposed surfaces of enucleated, spherical egg fragments, there was no evidence of furrowing activity between the areas that contacted the cytochalasin or in any other part of the surface. Because of the tension-reducing effect of cytochalasin, a tension gradient existed between the regions affected and unaffected by cytochalasin. The results strongly suggest that establishment of the division mechanism by simple gradients of tension at the surface is unlikely.

Rosenkranz, H. S. (1967). A non-nucleotide polymer found in the DNA of the sand dollar, Echinarachnius parma. II. Preliminary characterization. Can J Biochem 45, 281-7.
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Rosenkranz, H. S., and Carden, G. A. d. (1967). A non-nucleotide polymer found in the DNA of the sand dollar, Echinarachnius parma. I. Isolaion. Can J Biochem 45, 267-79.
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Salmon, E. D., and Wolniak, S. M. (1984). Taxol stabilization of mitotic spindle microtubules: analysis using calcium-induced depolymerization. Cell Motil 4, 155-67.
Taxol stabilizes or promotes the assembly of microtubules. In this report we characterize the rate, extent, and reversibility of taxol stabilization of calcium-labile microtubules in isolated mitotic spindles, principally from embryos of the sand dollar Echinarachnius parma. The intense depolymerizing action of 100 microM Ca2+ was used to assess the extent of stabilization by taxol. Changes in spindle microtubule assembly were evaluated and recorded by measuring changes in spindle birefringent retardation (BR). Membrane-free mitotic spindles, isolated with a calcium-chelating, nonionic detergent buffer, were stored in an EGTA-glycerol storage buffer to prevent microtubule depolymerization. When perfused with an EGTA-buffer without glycerol, microtubules in these isolated spindles depolymerized gradually over 60- 120 min; but in isolated spindles perfused with buffer that contained 100 microM Ca2+, BR decreased by 90% within 2-5 sec. In contrast, spindles that were pretreated for 3 min with 1 microM taxol, or for about 30 sec with 10 microM taxol, lost less than 10% of their initial BR when perfused with buffer containing 100 microM Ca2+. The rate and extent of microtubule stabilization by taxol depended on both the concentration and the duration of exposure to taxol. Taxol stabilization was reversible. After a 15 min preincubation with 1 microM or 10 microM taxol then washout, stability of spindle BR to 100 microM Ca2+ decreased exponentially with a time constant of 30-60 min. Thus taxol dissociates from spindle microtubules at significant rates; taxol-stabilized microtubules are not "fixed.".

Skalko, R. G., Thibodeau, L. F., and Niles, A. M. (1975). The distribution of annulate lamellae in eggs and zygotes of the sand dollar, Echinarachnius parma. Acta Embryol Exp 2, 87-99.
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Summers, R. G., and Hylander, B. L. (1974). An ultrastructural analysis of early fertilization in the sand dollar, Echinarachnius parma. Cell Tissue Res 150, 343-68.
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Suprenant, K. A., Dean, K., McKee, J., and Hake, S. (1993). Emap, an Echinoderm Microtubule-Associated Protein Found in Microtubule-Ribosome Complexes. Journal of Cell Science 104, 445-456.
The major non-tubulin polypeptide found associated with microtubules purified from unfertilized sea urchin eggs by cycles of pH-dependent assembly has a M(r) of 77,000. The 77,000 M(r) polypeptide is heat- and acid-labile, and is antigenically distinct from the mammalian brain MAPs, MAP-2 and tau. Affinity-purified antiserum against the 77,000 M(r) polypeptide was used to survey a variety of cells and tissues for the presence of antigenically related polypeptides. A cross-reacting polypeptide, ranging in M(r) from 72,000 to 80,000, was found in microtubule preparations from a wide variety of echinoderms, including sea urchins, starfish and sand dollars. Indirect immunofluorescence showed that the polypeptide was found in interphase as well as mitotic microtubule arrays. No cross-reacting material was detected in microtubules isolated from marine molluscs, mammalia brain or mouse B16 cultured cells. Because the 77,000 M(r) MAP is abundant in echinoderms, we have called it EMAP for echinoderm microtubule-associated protein. Although the precise function of the EMAP is not known, our data suggest that the EMAP is involved in the attachment of ribosomes to microtubules. Large numbers of ribosomes are attached to the walls of EMAP- containing microtubules, but not EMAP-deficient microtubules. Removal of the EMAP from the microtubule by salt-extraction results in the release of ribosomes from the microtubule, indicating that the EMAP may form part or all of the long tapered stalk that connects these two organelles.

Telford, M., and Ellers, O. (1997). Tooth advancement muscles in the sand dollar Echinarachnius parma. Invertebrate Biology 116, 255-261.
As the teeth of sand dollars are chipped and abraded during use, they are continuously renewed by growth in 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.

Tilney, L. G., and Gibbins, J. R. (1969). Microtubules and filaments in the filopodia of the secondary mesenchyme cells of Arbacia punctulata and Echinarachnius parma. J Cell Sci 5, 195-210.
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