The Christmas tree hydroid Pennaria disticha is listed as one of the most common introduced species in Hawaii. Firstly reported in Kaneohe Bay (Oahu) in 1928, it is now established throughout the entire archipelago, including the Northwestern Hawaiian Islands, a U.S. National Monument and World Heritage site. The Hawaiian population of P. disticha has also been reported as being the source of further introductions to Palmyra Atoll in the U.S. Line Islands. Using a phylogenetic hypothesis based on a 611 base pair fragment of the mitochondrial 16S barcoding gene, we demonstrate that P. disticha is a complex of cryptic species, rather than one species with cosmopolitan distribution. We also show that in Hawaii there are three species of Pennaria, rather than one introduced species. Two of these species share haplotypes with specimens from distant locations such as Florida and Panama and may have been introduced, possibly from the Atlantic Ocean. A third species could either represent a lineage with nearly cosmopolitan distribution, or another introduced species. Our dataset refutes the widely accepted idea that only one lineage of P. disticha is present in Hawaii. On the contrary, P. disticha in Hawaii may be the outcome of multiple independent introductions of several morphologically undistinguishable cryptic lineages. Our results uncover an unsuspected complexity within the very common hydroid P. disticha, and highlight the need for routine use of molecular tools, such as DNA barcoding, to improve the identification and recognition of non-indigenous species.

Medusae of Turritopsis dohrnii undergo reverse development in response to physical damage, adverse environmental conditions, or aging. Senescent, weakened or damaged medusae transform into a cluster of poorly differentiated cells (known as the cyst stage), which metamorphose back into a preceding life cycle stage, the polyp. During the metamorphosis, cell transdifferentiation occurs. The cyst represents the intermediate stage between a reverting medusa and a healthy polyp, during which cell transdifferentiation and tissue reorganization take place. Here we characterize and compare the transcriptomes of the typical polyp and newborn medusa stages of T. dohrnii with that of the cyst, to identify biological networks potentially involved in the reverse development and transdifferentiation processes. The polyp, medusa and cyst of T. dohrnii were sequenced through Illumina RNA-sequencing and assembled using a de novo approach, resulting in 92,569, 74,639 and 86,373 contigs, respectively. The transcriptomes were annotated and comparative analyses among the stages identified biological networks that were significantly over-and under-expressed in the cyst as compared to the polyp and medusa stages. Biological processes that occur at the cyst stage such as telomerase activity, regulation of transposable elements and DNA repair systems, and suppression of cell signaling pathways, mitotic cell division and cellular differentiation and development may be involved in T. dohrnii9s reverse development and transdifferentiation. Our results are the first attempt to understand T. dohrnii9s life-cycle reversal at the genetic level, and indicate possible avenues of future research on developmental strategies, cell transdifferentiation, and aging using T. dohrnii as a non-traditional in vivo system.

The phylogeny of the Upside-Down Jellyfish (Cassiopea spp.) has been revised multiple times in its history. This is especially true in the Florida Keys, where much of the Cassiopea stock for research and aquarium trade in the United States are collected. In August 2021, we collected 55 Cassiopea medusae at eight shallow water sites throughout the Florida Keys and sequenced COI, 16S, and 28S genes. Mitochondrial genes demonstrate that the shallow waters in Florida are inhabited by both Cassiopea xamachana and a non-native Cassiopea andromeda lineage, identified in multispecies assemblages at least thrice. While C. xamachana were present at all sites, the C. andromeda-mitotype individuals were present at only a minority of sites. While we cannot confirm hybridization or lack thereof between the C. xamanchana and C. andromeda lineages, these previously unknown multispecies assemblages are a likely root cause for the confusing and disputed COI-based species identities of Cassiopea in the Florida Keys. This also serves as a cautionary note to all Cassiopea researchers to barcode their individuals regardless of the location in which they were collected.

Podocoryna loyola, a new hydractiniid species, has been found on artificial substrates in Baía de Paranaguá, southern coast of Brazil, since April 2007. Its main morphological characteristics are: (1) polymorphic colonies with reticular stolons or encrusting hydrorhiza not covered by periderm and smooth chitinous spines; (2) newly-released medusae with eight tentacles and small interradial gonads; (3) mature medusae with eight tentacles and unbranched oral lips; gastric peduncle absent. Molecular data show that P. loyola is distinct from all other examined species of Podocoryna, and from P. hayamaensis Hirohito (1988), its sister species from Japan. As the polyps having been noted only quite recently, and in having been found only on man-made objects in port areas and estuaries, the species is most likely exotic to the region.