The pigmented and reproductive structures of Mespilia globulus.

(A) Red and Blue distinct color morphs. (B) Phylogenetic position of M. globulus among echinoid sea urchins (Mongiardino Koch et al., 2026). (C) Banded spines and blue ensheathed pedicellaria visible in the aboral region using light microscopy (C and D) and SEM (E) (scale bar 500µm). (D) The ovaries are arranged in tubular structures with closely opposed oocytes. (F and G) The developing oocytes are of very similar sizes, here misshapen from the ovary dissection. (H) Sperm have the characteristic triangular shaped head and long flagellar tail.

Development, HCR staining and CRISPR/Cas9 in M. globulus

(A) Confocal images of the development of M. globulus from early gastrulation through to an early juvenile. Nuclei in cyan and Muscle fibers in Magenta. (B) HCR stainings in early gastrula of the nodal and notch transcripts. (C) HCR stainings of nodal in pluteus larva. In (B,C), left and right panels correspond to lateral and apical views and nuclei are counterstained with DAPI. (D) control of CRISPR/Cas9 knockout showing the pigment cells in an early pluteus (arrowhead) in three different imaging modalities. (E) Cas9 inactivation of the pigmentation gene polyketide synthase (PKS) resulting in albinism, a phenotype with a lack of pigmentation as seen in the same imaging modalities.

Developmental rate of different urchin species.

hpf: hour post fertilization, dpf: day fertilization, dpf: week fertilization, mpm: month post metamorphosis. Sexual maturity corresponds to the ability to make gametes.

The genome of Mespilia globulus and the evolution of sea urchin genomes.

(A) HiC contact map highlighting the 21 assembled chromosomal scale scaffolds. (B) Gene density in the chromosomes of M. globulus indicated several gene duplication hotspots associated with gene families involved in organismal novelties of sea urchins (see Figure 5). (C) Evolution of sea urchin genome architecture using single copy orthologues annotated for ancestral echinoderm linkage groups.

Genome-wide distribution of sex-biased coverage across chromosomes.

(A) Average normalised sex coverage ratio (M/F) for each chromosome of the male and female assemblies. The difference in coverage was assessed using a Wilcoxon rank test with a FDR correction (*: p-value=0, ** P-value < 1e-5, * p-value <0.05) (B) Distribution of M/F sex ratio in the 21 chromosomes across genomic windows. Red indicates relative female enrichment, blue indicates relative male enrichment, and white indicates balanced coverage. (C) Region on a putative arm of chromosome 4 showing a female bias.

Gene family evolution and tissue expression of selected multifunctional gene families.

(A) Ultrametric tree used for the CAFE analysis, with pie charts summarising expanded, contracted, and unchanged gene families at terminal and internal nodes. (B) Proteome composition, showing the proportions of singleton, duplicate, and multi-copy genes in each species. (C) Left, normalised heat map showing significant expansions and contractions (*) for each gene family from the cafe output; right, tissue expression of the same gene families across Mespilia globulus tissue transcriptomes.