Seven new species of Scalibregmatidae are described from deep waters off the east coast of Australia. Samples were collected as part of the RV Investigator voyage IN2017_V03 in May/June 2017 using a Brenke sledge and 0.25 m2 box core. Sample depths reported in the present study were from the lower continental slope of about 2450 m to abyssal depths up to 4280 m. These collections provide the first scalibregmatid polychaetes to be described from deep water off Australia. The new species of Scalibregmatidae are in the genera Asclerocheilus (1), Axiokebuita (1), Oligobregma (4), and Pseudoscalibregma (1). Each of the new species is compared and contrasted with their known congeners. Asclerocheilus and Oligobregma are the largest genera of the family in terms of numbers of species; the known species of each of these genera are tabulated and compared. The Scalibregmatidae known from abyssal depths of about 3000 m and greater are reviewed and discussed.

In the deep ocean, whale falls (deceased whales that sink to the seafloor) act as a boost of productivity in this otherwise generally food-limited setting, nourishing organisms from sharks to microbes during the various stages of their decomposition. Annelid worms are habitual colonizers of whale falls, with new species regularly reported from these settings and their systematics helping to resolve biogeographic patterns among deep-sea organic fall environments. During a 2017 expedition of the Australian research vessel RV Investigator to sample bathyal to abyssal communities off Australia’s east coast, a natural whale fall was opportunistically trawled at ~1000 m depth. In this study, we provide detailed taxonomic descriptions of the annelids associated with this whale-fall community, using both morphological and molecular techniques. From this material we describe nine new species from five families (Dorvilleidae: Ophryotrocha dahlgreni sp. nov. Ophryotrocha hanneloreae sp. nov., Ophryotrocha ravarae sp. nov.; Hesionidae: Vrijenhoekia timoharai sp. nov.; Nereididae: Neanthes adriangloveri sp. nov., Neanthes visicete sp. nov.; Orbiniidae: Orbiniella jamesi sp. nov.), including two belonging to the bone-eating genus Osedax (Siboglinidae: Osedax waadjum sp. nov., Osedax byronbayensis sp. nov.) that are the first to be described from Australian waters. We further provide systematic accounts for 10 taxa within the Ampharetidae, Amphinomidae, Microphthalmidae, Nereididae, Orbiniidae, Phyllodocidae, Protodrilidae, Sphaerodoridae and Phascolosomatidae. Our investigations uncover unique occurrences and for the first time enable the evaluation of biogeographic links between Australian whale falls and others in the western Pacific as well as worldwide.

In May–June 2017 an expedition on board RV Investigator sampled benthic communities along the lower slope and abyss of Australia’s eastern margin from off mid-Tasmania to the Coral Sea. Over 200 annelids of the family Serpulidae collected during the voyage were collected and deposited in the Australian Museum in Sydney. Among them there was a new species of the poorly known abyssal (3754–4378 m) genus Spirodiscus. Serpulids typically build cylindrical calcareous tubes attached to hard substrates. Until now, only three serpulid species inhabiting free-lying polygonal tubes were reported from the deep sea: Spirodiscus grimaldii Fauvel, 1909 with quadrangular spirally coiled tubes, Bathyditrupa hovei Kupriyanova, 1993 with quadrangular tusk-shaped tubes, and Spirodiscus groenlandicus (McIntosh, 1877) with octagonal tusk-shaped tubes. The new species, S. ottofinamusi sp. nov. has very characteristic thin tusk-shaped unattached fluted tubes similar to those found in S. groenlandicus, but it differs by the details of collar, thoracic tori and abdominal chaetae. Morphologically, it has a pinnulated opercular peduncle and flat geniculate abdominal chaetae like filogranin serpulids but lacks thoracic Apomatus chaetae like serpulins. The first DNA sequences of this mysterious taxon places the new species within the filogranins in sister group relationship with Chitinopoma serrula.

A new species of Melinna (family Melinnidae) is described from the abyssal depths off the east coast of Australia. All material was collected during the RV Investigator voyage “Sampling the abyss” (IN2017_V03) in May–June 2017 from Bass Strait, Tasmania/Victoria using a beam trawl at 4197–4133 m depth. The new species Melinna hamulus sp. nov. differs from all other species of Melinna by having around 45 abdominal segments, dorsal membrane with 13–17 projections, four pairs of branchiae completely free and occurring in depths of over 4000 m. Phylogenetic relationships between our new species and other species within the family Melinnidae were assessed using the nuclear 18S and the mitochondrial 16S and cytochrome oxidase subunit I (COI) gene fragments. The results revealed that Melinna hamulus sp. nov. was genetically distinct from all other species of Melinnidae. This is the first species of Melinna to be described from Australian waters. We provide a new standard for description of species of Melinna and provide further detail on three existing species: Melinna albicincta Mackie & Pleijel, 1995, Melinna elisabethae McIntosh, 1914 and the type species of the genus Melinna cristata (Sars, 1851) using morphological characters illustrated with light and scanning electron microscopy photographs. We provide a table with the main diagnostic characters of all described species of Melinna together with type localities and depths.

Seven new species of Cirratulidae are described from deep waters off the east coast of Australia. Samples were collected as part of the RV Investigator voyage IN2017_V03 in May/June 2017 using a Brenke sledge and 0.25 m2 box core. Sample depths reported in the present study were from the lower continental slope of about 2100 m to abyssal depths up to 4170 m. These collections provide the first cirratulid polychaetes to be described from deep water off Australia. The new species of Cirratulidae are in the genera Aphelochaeta (2), Chaetocirratulus (2), Chaetozone (2), and Kirkegaardia (1). Each of the new species is compared and contrasted with their known congeners. The bitentaculate Cirratulidae known from abyssal depths of 3000 m and greater are reviewed and discussed.

The epibenthic onuphid genus Nothria Malmgren, 1867 presently comprises 21 accepted species. We are reporting here on specimens collected during six deep-sea expeditions of the RV Investigator from 2015–2018 to the Great Australian Bight (GAB) and off eastern Australia from Tasmania to Queensland, describing eight new species of Nothria. This is the first integrated study of the genus, sequencing the markers COI, 16S rDNA and 28S rDNA from 37 specimens and employing conventional and exploratory morphological characters as well as tube consistency and structure for identification. Molecular data provided strong support for recognition of the eight new species and the Nothria otsuchiensis Imajima, 1986 species complex. Since the analysis of morphology between the specimens of this complex has not revealed any obvious differences, it may represent a complex of cryptic species. Nothria digitata sp. nov. was collected at a depth of 400 m whilst the remaining seven new species are from depths of 980–2751 m. Nothria deltasigma sp. nov., N. digitata sp. nov. and N. minima sp. nov. were collected at a single station each, while N. josae sp. nov. and N. simplex sp. nov. were found at two stations. However, N. delta sp. nov. displayed the widest distribution, occurring at GAB, Tasmania and Jervis Bay Marine Park, NSW. Most stations yielded only one species, Jervis Bay Marine Park and south of Brians, Tasmania, harboured two, but an astounding example of sympatry was discovered at Huon Marine Park, Tasmania, where three species, N. delta sp. nov., N. lizae sp. nov. and N. orensanzi sp. nov. were collected together in one station.

The deep-water mysid crustaceans of Australia have been barely known. Recent explorations of RV Investigator (CSIRO) in the southeast Australian waters discovered a unique fauna. In this special study of the marine subfamily Boreomysinae (family Mysidae) in Australia, five species from both genera Boreomysis and Neobirsteiniamysis are reported, including two new species for science: B. inopinata sp. nov., B. sibogae, B. sphaerops, B. urospina sp. nov. and N. inermis. Among the members of the subfamily, only B. sibogae has been previously known from Australia. The genus Neobirsteiniamysis and its bipolar-amphitropical species N. inermis are firstly recorded in Australia. Boreomysis inopinata sp. nov. has additional spinules on the outer spine of the antennal scale, which are not found in other species of the subfamily. Boreomysis urospina sp. nov. has the longest first segment of the uropodal exopod, laterally terminated by three spiniform setae; and its uropodal endopod is armed with up to five medial spiniform setae, the largest number in the subfamily. This species is included in a newly established subgenus Petryashovia subgen. nov., which unites epi-mesopelagic boreomysines, lacking the rostral projection, having rather small ventrolateral lobes of the carapace, and the 1-segmented propodus of the pereopods. The subfamily and generic diagnoses are updated. Additionally, a fragment of the mtDNA COI gene was sequenced for most of the studied species.

Philiris diana Waterhouse & Lyell, 1914 from the Wet Tropics of northeastern Queensland was previously thought to be monotypic, being most closely related to Philiris papuanus Wind & Clench, 1947 from Cape York Peninsula, Australia, and mainland New Guinea. However, a new subspecies was recently discovered on the Atherton Tableland, which we illustrate, diagnose and describe as Philiris diana fortuna ssp. nov. It appears to be a narrow-range endemic, restricted to montane forest (750–1,090 m asl) and allopatric or parapatric from the nominotypical subspecies Philiris diana diana Waterhouse & Lyell, 1914, which is largely restricted to low to mid-altitude forests in the coastal escarpment in the Cairns-Kuranda district. Despite being separated by a minimum distance of only 20–25 km, the two taxa show substantial phenotypic differences in wing pattern elements, but negligeable differences according to the mitochondrial COI barcode region (mean p-distance = 0.28%). The habitat and biology of the new taxon are summarized, and likely historical processes driving divergence between upland and lowland populations of this species hypothesized.

In 1885 the Geographical Society of Australasia sent the steam launch Bonito to chart the Fly and Strickland Rivers (now in Western Province, Papua New Guinea). The Expedition spent five months in New Guinea with the primary objectives of survey and biological exploration. The type locality of the murid rodent Melomys muscalis froggatti Troughton, 1937, described from a single specimen obtained during the Expedition, is localized to the region of the base camp at Observation Bend, Strickland River, based on the original Expedition maps and the unpublished diary reminiscence of the collector W. W. Froggatt. A review of the mammal collection obtained during that Expedition has not been reported previously, perhaps due to the poor surviving documentation. Several months after the Expedition returned to Sydney, Australian Museum curator E. P. Ramsay prepared a list of 22 mammal specimens received by the Museum. Twenty specimens attributed to the Expedition were not entered into the collection registers until 1913, half of which are likely to be incorrectly associated with the Expedition. Most specimens were registered with very limited data about collection date and locality. Of the 22 specimens originally received by Ramsay, eight rodents and two flying foxes (Pteropus spp.) have not been located in the Collection, but might remain unrecognized as specimens with no data. It is possible that additional mammal specimens were sent by the Geographical Society of Australasia to other institutions at the conclusion of the Expedition.

The systematic and somewhat controversial history of Risa Becker is presented, and its relationship with Diasemocera Bezzi (tribe Psilopini, Ephydridae) is documented by morphological evidence and an association with host plants in the family Amaranthaceae. The tribe Risini Papp (as Risidae) is synonymized with Psilopini Cresson. Notorisa gen. nov., from Australia, is described (type species: Notorisa mcalpinei sp. nov.; Australia. Victoria: Big Desert National Park, near Lake Hindmarsh; 36°03.7'S 141°54.8'E). Achaetorisa Papp is retained as a subgenus within Risa and includes five species, including two new combinations: Risa brevicornis (Papp) comb. nov., Risa salsolae (Mathis & Zatwarnicki) comb. nov., and two new species: R. brevirostris sp. nov. (Israel. Ẕomet Zohar; 31°08.5'N 35°21.6'E) and R. nettae sp. nov. (Israel. Ẕomet Zohar; 31°08.5'N 35°21.6'E). A fourth new species is described in the subgenus Risa: R. (Risa) kotrbae sp. nov. (Israel. Ẕomet Zohar; 31°08.5'N 35°21.6'E).