Sand Dollar Species Research Articles

Young colonization history of a widespread sand dollar (Echinodermata; Clypeasteroida) in western Taiwan

Arachnoides placenta is the most common sand dollar species in western Taiwan. Due to its lack of fossil record, the arrival of this species in Taiwan could not be estimated until now. Fragments of A. placenta was recovered sorting through a 1981- museum collection of sand dollars collected off Mailiao county, western Taiwan. Additional echinoderm specimens were recovered from Holocene sediments nearby, but no fragments of A. placenta were found, indicating a decline in the living population. A total of 11 echinoderm samples, including five specimens that were assigned to A. placenta with certainty, were sent for radiocarbon dating. Results showed that studied echinoderm fragments range from modern (after 1950) to as old as 2680 ± 55 a BP and the oldest date is from A. placenta. It is evident that Taiwan is an active migration front for A. placenta due to the relatively young arrival age for this pandemic species which is widespread in the Indo-West Pacific region. Additionally, the DNA sequence, including the cytochrome c oxidase subunit I (cox1) gene, of the species was obtained to conduct the first molecular phylogenetic study of sand dollars in Taiwan.

The Historical and Biographical Context of Gregory's Diverticulum, an Unusual Organ in Sand Dollars

Gregory's diverticulum is a conspicuous digestive tract element found in selected sand dollar (Echinoidea: Clypeasteroida) species. This organ, a transitory structure of the juvenile organism, was named after the American zoologist Emily R. Gregory (1863–1946). Although it had been observed before by the renowned echinoid researcher and former director of the Museum of Comparative Zoology Alexander E. Agassiz, Gregory was the first to describe the organ as a distinct entity on the basis of the ubiquitous sand dollar species Echinarachnius parma. However, despite presenting her discovery at several national and international conferences, as well as in short papers, Gregory's find remained largely unmentioned by contemporary echinoderm researchers. With the erroneous assessment of one of the most eminent authorities on echinoid taxonomy and systematics Theodor J. Mortensen that the organ she discovered does not exist, Gregory's work seemed destined to fall into oblivion. However, in the second half of the 20th century, several unpublished master's theses provided unequivocal evidence for the existence of the organ, thus reviving interest in research on Gregory's diverticulum. The present article gives a historical overview of studies related to Gregory's diverticulum, provides the first comprehensive biography of Emily R. Gregory, describes the circumstances of the organ's discovery, and explores why the research of a female zoologist was seemingly not met with much enthusiasm during her lifetime.

Hidden genetic history of the Japanese sand dollar Peronella (Echinoidea: Laganidae) revealed by nuclear intron sequences

The marine environment around Japan experienced significant changes during the Cenozoic Era. In this study, we report findings suggesting that this dynamic history left behind traces in the genome of the Japanese sand dollar species Peronella japonica and P. rubra. Although mitochondrial Cytochrome C Oxidase I sequences did not indicate fragmentation of the current local populations of P. japonica around Japan, two different types of intron sequence were found in the Alx1 locus. We inferred that past fragmentation of the populations account for the presence of two types of nuclear sequences as alleles in the Alx1 intron of P. japonica. It is likely that the split populations have intermixed in recent times; hence, we did not detect polymorphisms in the sequences reflecting the current localization of the species. In addition, we found two allelic sequences of theAlx1 intron in the sister species P. rubra. The divergence times of the two types of Alx1 intron sequences were estimated at approximately 14.9 and 4.0 million years ago for P. japonica and P. rubra, respectively. Our study indicates that information from the intron sequences of nuclear genes can enhance our understanding of past genetic events in organisms.

New echinoderm remains in the buried offerings of the Templo Mayor of Tenochtitlan, Mexico City

Between 1978 and 1982 the ruins of the Templo Mayor of Tenochtitlan were exhumed a few meters northward from the central plaza (Zócalo) of Mexico City. The temple was the center of the Mexica’s ritual life and one of the most famous ceremonial buildings of its time (15th and 16th centuries). More than 200 offerings have been recovered in the temple and surrounding buildings. We identified vestiges of 14 species of echinoderms (mostly as disarticulated plates). These include six species of sea stars (Luidia superba, Astropecten regalis, Astropecten duplicatus, Phataria unifascialis, Nidorellia armata, Pentaceraster cumingi), one ophiuroid species (Ophiothrix rudis), two species of sea urchins (Eucidaris thouarsii, Echinometra vanbrunti), four species of sand dollars (Mellita quinquiesperforata, Mellita notabilis, Encope laevis, Clypeaster speciosus) and one species of sea biscuit (Meoma ventricosa grandis). They date back to the reigns of kings Axayacatl (AD 1469-1481), Tizoc (AD 1481-1486), Ahuitzotl (AD 1486-1502), and Motecuhzoma II (AD 1502-1520). Apparently the presence of echinoderms in the offerings is related to the realm of Tlaloc (god of rain and earth). It is believed this organisms, like other marine animals, were used by the priests, like other marine animals, to represent the aquatic underworld of Mesoamerican world-view. Rev. Biol. Trop. 65(Suppl. 1): S168-S179. Epub 2017 November 01.

Expression patterns of wnt8 orthologs in two sand dollar species with different developmental modes

Two wnt8 orthologs, Smwnt8 and Pjwnt8, were isolated from an indirect developing sand dollar, Scaphechinus mirabilis, and a direct developing sand dollar, Peronella japonica, respectively. The expression patterns of two genes during early development were examined by whole mount in situ hybridization. The expression of Smwnt8 was initiated in the micromeres at the late 16-cell stage and expanded at the 64-cell stage to the whole vegetal hemisphere, including the presumptive endomesodermal regions. The timing of the initiation of Pjwnt8 transcription in the presumptive endomesoderm region was delayed by 2–3 cell cycles compared to that of Smwnt8. The delay, or molecular heterochrony, of Pjwnt8 transcription strongly suggests the existence of a substantial evolutionary change in the early endomesodermal specification of P. japonica. In addition to the endomesodermal expression during early embryogenesis, bilateral expressions were observed commonly in the ectoderm of two sand dollar species during larval stages.

Micromere‐derived signal regulates larval left‐right polarity during sea urchin development

The micromeres (Mics) lineage functions as a morphogenetic signaling center in early embryos of sea urchins. The Mics lineage releases signals that regulate the specification of cell fates along the animal-vegetal and oral-aboral axes. We tested whether the Mics lineage might also be responsible for differentiation of the left-right (LR) axis by observing of the placement of the adult rudiment, which normally forms only on the left side of the larvae, after removal of the Mics lineage. When all of the Mics lineage were removed from embryos of the regular sea urchin Hemicentrotus pulcherrimus between the 16- and 64-cell stages, the LR placement of the rudiment became randomized. However, the immediate retransplantation of the Mics rescued the normal LR placement of the rudiment, indicating that the Mics lineage releases a signal that specifies LR polarity. Additionally, we investigated whether the specification of LR polarity of whole embryos in the indirect-developing sea urchin H. pulcherrimus is affected by LiCl exposure, which disturbs the establishment of LR asymmetry in a direct-developing sea urchin. Larvae derived from normal animal caps combined with LiCl-exposed Mics descendants were defective in normal LR placement of the rudiment, suggesting that LiCl interferes with the Mics-derived signal. In contrast, embryos of two sand dollar species (Scaphechinus mirabilis and Astriclypeus manni) were resistant to alteration of LR placement of the rudiment by either removal of the Mics lineage or LiCl exposure. These results indicate that the Mics lineage is involved in specification of LR polarity in the regular sea urchin H. pulcherrimus, and suggest that LiCl impairs the normal LR patterning by affecting Mics-derived signaling.

The relationship between egg size and the duration of the facultative feeding period in marine invertebrate larvae

Feeding larvae of marine invertebrates fuel development from both endogenous egg energy and exogenous energy obtained from the planktonic environment. Although both sources of energy likely influence certain larval stages, only the effects of exogenous food have been well studied. Despite the lack of research on the effects of egg size on larval stages, investigators have hypothesized that egg size influences the duration of the facultative feeding stage—the stage in which larvae can feed but do not have to because development is still being fueled by egg energy. To test this hypothesis, we investigated six species of sand dollars with different sized eggs and quantified the duration of the larval facultative feeding period of each species by comparing when fed and starved larvae diverged in size. Regardless of whether phylogeny was taken into account, the duration of the facultative feeding period was positively correlated with egg size. We further determined that our conclusions were not sensitive to either our estimation of the duration of the facultative feeding period, or the branch lengths of the phylogeny we used. This relationship is likely a result of larger eggs being provisioned with more energy, and may affect how well larvae can cope with natural variability in food concentrations. Furthermore, our results support an assumption of a theoretical model developed to understand the evolution of different life-history strategies in marine invertebrate larvae, which suggests that this relationship has important evolutionary consequences.

The contribution of the facultative feeding period to echinoid larval development and size at metamorphosis: a comparative approach

Planktotrophic invertebrate larvae have two dissociable stages during development, a facultative feeding period, whose length is determined by the amount of maternal provisioning in the egg, and an obligate feeding period, whose length is determined by the quantity of exogenous energy needed to reach metamorphic competence. Here we set out to experimentally test the impact of feeding during the facultative feeding period at two food concentrations (limiting and nonlimiting) on larval development time and juvenile quality. We used two closely related subtropical sand dollar species that differ in the quantity of maternal investment for these comparisons: Leodia sexiesperforata (large egg, long facultative feeding period) and Mellita tenuis (small egg, short facultative feeding period). We found that feeding during the facultative period accelerates development to metamorphosis only in M. tenuis and only at the high food ration. Feeding during the facultative feeding period had no effect on development time for M. tenuis at a food limiting concentration and for L. sexiesperforata at either food concentration. Furthermore, we found feeding during the facultative period to significantly increase quantity of carbohydrates and lipids at metamorphosis only for M. tenuis in nonlimiting food concentration. Thus, our data reveal a two-fold benefit of the facultative feeding period for a poorly provisioned species under high food conditions but little effect on a well-provisioned species. We discuss our results in reference to McEdward's [McEdward, L.R., 1997. Reproductive strategies of marine benthic invertebrates revisited: facultative feeding by planktotrophic larvae. Am. Nat. 150, 48–72] facultative feeding model.

Molecular heterotopy in the expression of Brachyury orthologs in order Clypeasteroida (irregular sea urchins) and order Echinoida (regular sea urchins).

The expression patterns of Brachyury (Bra) orthologs in the development of four species of sand dollars (order: Clypeasteroida), including a direct-developing species, and of a sea urchin species (order: Echinoida) were investigated during the period from blastula to the pluteus stage, with special attention paid to the relationship between the expression pattern and the mode of gastrulation. The sand dollar species shared two expression domains of the Bra orthologs with the Echinoida species, in the vegetal ring (the first domain) and the oral ectoderm (the second domain). The following heterotopic changes in the expression of the Bra genes were found among the sand dollar species and between the sand dollars and the Echinoida species. (1) The vegetal ring expressing Bra in the sand dollars was much wider and was located at a higher position along the AV axis, compared with that in the Echinoida species. The characteristic Bra expression in the vegetal ring of the sand dollar embryos was thought to be involved in the mode of gastrulation, in which involution continues from the beginning of invagination until the end of gastrulation. (2) Two of the three indirect-developing sand dollar species that were examined exhibited a third domain, in which Bra was expressed on the oral side of the archenteron. (3) In the direct-developing sand dollar embryos, Bra was expressed with an oral-aboral asymmetry in the vegetal ring and with a left-right asymmetry in the oral ectoderm. In the Echinoida species, Bra was expressed in the vestibule at the six-armed pluteus stage.

Variation of cleavage pattern permitting normal development in a sand dollar, Peronella japonica : comparison with other sand dollars

Peronella japonica, a sand dollar, forms an abbreviated pluteus larva and metamorphoses within 3 days without feeding. In the present study, the cleavage pattern of Peronella embryos was found to be quite irregular in the vegetal blastomeres at the fourth cleavage. Less than half of the embryos examined formed four typical micromeres. The majority formed zero, one, two or three typical micromeres of regular size, and the blastomere(s) remaining in the vegetal-most region was atypical in size and/or its direction of division. Most embryos were able to form pluteus larvae and a considerable proportion of these metamorphosed into juvenile sea urchins, regardless of whether or not they had formed four typical micromeres of regular size, although embryos which formed no typical micromeres developed into pluteus larvae less frequently. The micromere progeny in Peronella embryos form skeletogenic mesenchyme cells. The average numbers of skeletogenic mesenchyme cells in the three sand dollar species, Clypeaster japonicus, Astriclypeus manni and P. japonica were 62, 122 and 219, respectively. In these species, the skeletogenic mesenchyme cell-specific glycoprotein (msp130) was first detected immediately after ingression of the primary mesenchyme cells, spicules appeared at the early gastrula stage and triradiate spicules were found in late gastrulae. Appearance of these characteristics was markedly accelerated in the embryos of A. manni and P. japonica in comparison with those of C. japonicus. Each step in the formation of larval spicules was equally accelerated in A. manni and P. japonica, although the appearance of the adult skeleton was further accelerated in P. japonica in comparison with A. manni, possibly because of omission of the four- to eight-armed pluteus stages.

Computer simulation of deposit-feeding by sand dollars and sea biscuits (Echinoidea: Clypeasteroida)

A computer simulation of deposit feeding by several species of sand dollars and sea biscuits is presented. The simulation uses the size distribution of food-gathering podia, areal contribution of sediment size classes to total sediment surface area and empirically determined collection coefficients for each podial size collecting each sediment particle size. The simulation generates frequency data for the particles encountered and those successfully harvested. G tests show that the simulation results accurately mimic the distribution of particle sizes found in the food grooves of feeding animals. The simulation can be used to predict what the species would be expected to collect from other real or hypothetical sediment mixtures. This allows a theoretical comparison of feeding behavior between species which do not normally co-occur: for example, Echinarachnius parma (Lamarck), Melitta isometra Harold & Telford and Leodia sexiesperforata (Leske) would all draw over 90% of their diet from the 100–400 ftm particle size classes. The simulation also permits calculation of the numbers of particles contacted but not collected, which indicates the relative effort of feeding on different sediment mixes.

Derivatives of sperm-activating peptide III (SAP-III) associated with eggs of sand dollars, Clypeasterjaponicus and Astriclypeusmanni

1. 1. NIne sperm-activating peptides were isolated from the egg jelly of sand dollars Clypeaster japonicus and Astriclypeus manni, and their amino acid sequences were determined. 2. 2. The peptides elevated cyclic GMP and cyclic AMP concentrations in spermatozoa of respective species and caused a shift in the apparent molecular weight of a major sperm protein of the respective species of sand dollars. 3. 3. The peptides stimulated their own sperm respiration rate one half-maximally at about 0.1–1.9 nM under slightly acidic pH. 4. 4. Egg jelly extract from Peronella japonica contained a substance(s) which stimulates C. japonicus sperm respiration.

Sterol compositions of echinoids (sea urchin, sand dollar and heart urchin)

1. 1. The sterol compositions of five species of echinoids (sea urchin, sand dollar and heart urchin) were determined by GLC, Cholesterol was the major sterol in all animals. 2. 2. Two species of sea urchins contained high levels of C 27-sterols (98 per cent). 3. 3. Two species of sand dollars and a species of heart urchin contained considerable amounts of C 28-sterols (16–43 per cent).