This brief review discusses the different ways in which the study of gelatinous plankton has contributed to an understanding of the physiology and evolutionary relationships of other animals.

In the pelagic habitat, the bodies of resident animals provide much of the ecological substrate available for other organisms to attach, find shelter, and seek food. In Monterey Bay, California, the doliolid Doliolula equus provides substrate for multiple symbionts. These include a mutualist hydroid, commensal ciliates, and a parasitic amphipod. This new doliolid is described based on in situ observations from a remotely operated vehicle, and from the laboratory examinations of 43 colonies comprising hundreds of living, individual blastozooids. Doliolula equus differs from other members of the suborder Doliopsidina in the shape of its body, the length and configuration of its third muscle band, the size of its buccal siphon, and the position of the spiral gland. The new doliolid was found principally at depths between 300 and 400 m. This species is bioluminescent, hermaphroditic, and about one zooid in ten is peppered with orange pigment spots. A variety of other, obviously related, yet undescribed forms has been observed in the eastern Pacific.

Three new species of Fritillaria are described from specimens collected by a remotely operated vehicle (ROV) between 180 and 735 m depth in Monterey Bay, California. Fritillaria rex becomes the largest species now described for this genus (trunk length up to 10 mm, tail length up to 18 mm). This species is characterized by five or six narrow muscle bundles on each side of the tail, slit-shaped spiracles, a spherical ovary and a cylindrical testis. Fritillaria amphigonadis (trunk length up to 5.2 mm, tail length up to 7.5 mm) is characterized by two narrow muscle bundles on each side of the tail, slit-shaped spiracles, paired spherical ovaries, and a unique pi-shaped testis. Fritillaria lucifer (trunk length up to 4.1 mm, tail length up to 7.0 mm) has 12 extremely thin muscle bundles distributed broadly across the tail, rounded spiracles, a spherical ovary and a U-shaped testis. An additional mesopelagic Fritillaria appears to be consistent with the description of the Mediterranean F. fage, but specific differences in pharyngeal cells, cellular patterns on the tail, and gonadal morphology suggest that the specimens from Monterey Bay are a new variety, F. fagei mbarii. Based on the relatively limited number of collections (i.e. only 20 specimens yielding four unique taxa), it would appear that the possible diversity of larvaceans that live below the surface mixed layer is significantly underestimated.

Published behavioural, DNA sequence, and morphologic data on six populations of Mastigias, five from marine lakes and one from the lagoon, in Palau are summarized. Each marine lake population is distinguished from the lagoon population and from other lake populations by an unique suite of characteristics. Morphological differences among Mastigias populations in Palau are greater than those recorded between any previously described species of Mastigias, whereas molecular differences are far less (≤2.2% in COI and ITS1) than those found between medusae identified in the field as Mastigias papua (>6% in COI and ITS1). Thus, each marine lake population in Palau is described as a new subspecies of Mastigias cf. papua: remengesaui (in Uet era Ongael), nakamurai (in Goby Lake), etpisoni (in Ongeim'l Tketau), saliii (in Clear Lake), and remeliiki (in Uet era Ngermeuangel).

Siphonophores (Cnidaria: Hydrozoa) are dominant members of the carnivorous plankton, and they are known for their ability to produce bioluminescence. Here we describe two new calycophoran species (sub-family Prayinae) that are unique in their morphological and optical traits. One species, Gymnopraia lapislazula gen. nov., sp. nov., displays a dramatic form of blue structural coloration, and the other, Lilyopsis fluoracantha, sp. nov., bears an exceptional amount of fluorescence–enough to give a greenish cast during white-light illumination. We also introduce a consistent terminology for siphonophore axes and zooids, discuss characters important for distinguishing the known prayine genera, and suggest that the presence or absence of a disjunct pedicular canal could be of diagnostic value for the group.

This updated re-description of the prayine siphonophore Rosacea cymbiformis includes figures of all zooids (except larval nectophores) and is based on material held in the collections of the Natural History Museum (NHM), London. Rosacea cymbiformis was originally described in 1830 under the name Physalia cymbiformis, and subsequently reported many times during the 19th Century. However, during the 20th Century it was confused with the closely related species R. plicata, and the two species are still not clearly differentiated. Previous descriptions are reviewed herein, including conflicting interpretations of nectophore designation in R. plicata, and bract orientation in R. cymbiformis and R. plicata. To identify these siphonophores to species level and separate them from other closely related prayines, it is essential to distinguish the first definitive nectophore from the second, and the right paired bracteal canals from the left canals. This becomes critical when only detached siphonophore zooids are available, as for example, in plankton samples collected with nets. A summary of the differences between R. cymbiformi and the five other currently recognized Rosacea species, R. plicata, R. repanda, R. limbata, R. flaccida and R. arabiana, is presented. The full synonymy of R. cymbiformis is too long for inclusion here and is deferred to a later paper.

Two reciprocally monophyletic mitochondrial clades of the commercially valuable jellyfish Catostylus mosaicus are endemic to south-eastern Australia. Here, medusae in the two clades are shown to differ also in colour and in the dimensions of their papillae, oral disk, and bell depth. They are referred to two varieties recognized in 1884 by von Lendenfeld. The clade occupying localities adjacent to Bass Strait is redescribed as subspecies C. mosaicus conservativus; the clade from New South Wales and southern Queensland spans the type locality (Port Jackson) of C. mosaicus and is designated C. mosaicus mosaicus. Their ecology and colour, in the context of von Lendenfeld's original descriptions, and the implications for fisheries are discussed.

New tools and techniques invigorate taxonomy through discovery and description of new organisms. New editions of the International Code on Zoological Nomenclature explicitly attempt to accommodate scientific advances, the problems they bring, and individual expertise in documenting the diversity of animal life. Yet, in practice, one of the most important biological and technical advances of the last quarter century—the democratization of large scale sequencing of DNA—remains at the fringe of metazoan taxonomy, where it keeps remarkable company with evolution. I discuss a more inclusive approach to taxonomy, primarily in the context of differentiating and describing species and subspecies of Scyphozoa. Global concern regarding biodiversity has rejuvenated efforts to discover and describe species; it may yet stimulate a renaissance if biological classification adopts a total evidence approach.