Sea urchins have been a well-used model of fertilization and of the molecular biology of embryonic development. Our understanding of the molecular identity of adult tissues, on the other hand, has lagged significantly, a deficiency all too apparent with recent successes in mutational analyses in transgenerational studies. Here we focus on the developmental timing of gonadogenesis with particular reference to developmental features of when a juvenile reaches adulthood and begins to make eggs and sperm. We find a large variation in timing of reaching fertility in Lytechinus variegatus such that in 4.5 months, animals that have reached a mass/body ratio and making eggs or sperm. This is correlated with the external metric of opening of the gonadopore, indicative of gametogenesis. We identify a sac-like structure in juveniles that by both morphological and transcriptomic analysis appears to be an indeterminant gonad that transitions into an ovary or testis. We follow this development into adulthood and compare the transcriptomes of gonads and gametes to all 16 major tissues of the adult, revealing a broad definition of the tissue types, and displaying genes that are differentially enriched, and/or specifically expressed by each tissue. These datasets serve as a guide for gene selection in traditional CRISPR/Cas9 mutagenesis, for design of integrated transposase reporters, and for parsing out unique functions in tissues that in combination give this animal its unique attributes. Overall design: Major tissues from adult sea urchins (Lytechinus variegatus) were isolated and stored in Trizol. Total RNA was extracted for each sample and sent to Novogene for next-generation bulk RNA sequencing following the manufacturer's instructions. Libraries were sequenced by Novogene in a paired-end fashion. Gonads and presumptive gonads were isolated from Lv at 4.5 month post fertilization (4.5 mpf). These tissues were isolated and stored in Trizol. Total RNA was extracted and sent to Admera Health for next-generation bulk RNA sequencing following the manufacturer's instructions, in a paired end fashion.