New Species of Scalibregmatidae (Annelida) from Slope and Abyssal Depths off Eastern Australia

. 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 m 2 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.


Introduction
The present study is based on annelids of the family Scalibregmatidae collected as part of the RV Investigator cruise (No.IN2017_V03) along the eastern continental margin of Australia in May/June 2017 (Gunton et al., 2021).Scalibregmatids occur globally and range from the intertidal to the deep sea, but most species occur deeper than 100 m; this study represents the first report of deep-sea annelids of this family from Australian waters.
A review of the Scalibregmatidae was recently prepared by Blake (2020).The family includes approximately 70 species distributed in 15 genera identified largely by a suite of overlapping characters.Because so many species (and genera) occur in deep water, or are otherwise in habitats that are difficult to sample, there have been few species for which molecular sequences have been obtained.To date there have been no phylogenetic analyses, morphological or molecular, that would serve to support a systematic revision of the family (Blake, 2020).
Scalibregmatids have an areolated appearance due to the presence of one to six annulated rows of elevated pads per segment.Their bodies are typically either elongate with an expanded anterior end and narrow abdominal region (arenicoliform) or short, thick, and without an expanded anterior end (maggot shaped); a few species have long, linear bodies (Blake, 2020).Scalibregmatids typically have a bifid or T-shaped prostomium with frontal or lateral horns.Parapodia are biramous with simple podial lobes; dorsal and ventral cirri occur in posterior parapodia of some genera.Branchiae, when present, are limited to a few anterior segments and have numerous branches.Setae are all simple and include capillaries, furcate setae, and sometimes large recurved acicular spines.
Apart from several early studies using standard histological techniques, there has been little effort to analyse the internal anatomy of scalibregmatids.There have been no studies of the ultrastructure of any organ system.Little is known about scalibregmatid biology except that they are considered subsurface, burrowing, deposit feeders (Jumars et al., 2015).Random observations of swimming scalibregmatids and the presence of long natatory-like setae (Clark, 1954) and the presence of sperm of the ectaquasperm type (Blake, 2015) suggest that spawning takes place in the water column.However, spawning and early embryonic development are not known.Recent observations on postlarvae and juveniles provide important data on the developmental timing of morphology (Blake, 2015).

Materials and methods
Materials examined as part of this study.Biological samples were collected from 13 sites at one-degree intervals of latitude along the east coast of Australia from Tasmania (42°S) to Southern Queensland (24°S) on the RV Investigator (Cruise No. IN2017_V03), from 15th May to 16th June 2017.Seven Marine Parks (MP) were included (Freycinet MP, Flinders MP, East Gippsland MP, Jervis MP, Hunter MP, Central Eastern MP and Coral Sea MP) in the sampling areas.Benthic sampling was conducted at lower bathyal (c.2500 m) and abyssal (c.4000 m) depths, with seven comparative samples taken at shallower mid-bathyal depths (c.1000 m).Three types of sampling gear were used: beam trawl, Brenke Sled, and box core.Selected specimens were photographed alive prior to preservation.The majority were preserved in 95% ethanol (ETOH), the remainder in 10% buffered formalin.Sled and trawl samples were generally sieved through a 1-mm-mesh screen; box core sediments were sieved on a 0.3-mm-mesh screen.Trawl and sled deployments were generally successful, but most of the box core deployments were not.Annelid specimens collected during the voyage were shipped to the Australian Museum, Sydney (AM), Museums Victoria, Melbourne (MV), and the Natural History Museum, London (NHMUK) where they were registered and sorted to the family level.At the respective institutions, annelids fixed in formalin were soaked in water, then preserved and later sorted in 80% ETOH, while ethanol-fixed annelids were sorted in 95% ETOH.The specimens studied here were provided by the AM; registration numbers are prefixed W.
Morphological observations.Specimens were examined using a Wild M-5 stereomicroscope and a Zeiss RA research microscope equipped with phase contrast optics.Photomicrographs were taken with a Nikon D7100 camera mounted on both the stereo-and compound microscopes.For observation, specimens were first stained with an aqueous solution of Shirlastain A to highlight difficult-to-see surficial morphology.Some specimens were stained with a saturated solution of Methyl Green (MG) in 70% ETOH in order to identify staining patterns of subdermal glands evident on some species.Line drawings were first sketched in pencil using a drawing tube or camera lucida on the Zeiss RA and later transferred to Dura-Lar® matte film and inked.Photographs were edited in Photoshop.
Molecular analysis.Tissue for each species treated in this study was provided for DNA acquisition.However, DNA acquisition was largely unsuccessful, likely due to handling during collection and preservation.The only successful results were for cytochrome c oxidase subunit 1 (COI) and mRNA S18 for Asclerocheilus abyssalis sp.nov.and COI for Oligobregma profunda sp.nov.The data has been submitted to GenBank.Comments are provided for these two species.
Diagnosis (after Blake, 2020): Body variably shaped: (1) elongate and narrow throughout, (2) fusiform, (3) thick, maggot-shaped, or (4) elongate arenicoliform with anterior segments greatly expanded; with no more than 30 to 60 setigerous segments.Body with one to five annular rings on each segment; each ring usually composed of elevated pads; distribution of these rings and pads differs among species; venter with mid-ventral groove or ridge formed of elevated pads along body, limited to one part of body or entirely absent.Prostomium either bilobed or T-shaped with two frontal or lateral horns, sometimes long, ciliated, and functioning as palps; eyes present or absent; nuchal slits present.Proboscis eversible, soft, unarmed.Peristomium with a dorsal ring typically single, encompassing prostomium; ventral part with one to three rings forming upper and lower lips of mouth.Branchiae present or absent, when present limited to four to six or fewer anterior setigers, always with multiple branches, usually dichotomous.Parapodia biramous, with weakly developed podial lobes; interramal sensory organs or papillae present; dorsal and/or ventral cirri present or absent in middle and posterior segments, when present often with internal tubular glands; postsetal lamellae rarely present.Setae all simple, including capillaries, furcate or lyrate setae present or absent, acicular spines on anterior segments present or absent; short spinous setae often present anterior to capillaries on setigers anterior to those where furcate setae begin.Pygidium with two or more lobes; anal cirri present or absent.
Remarks.Scalibregmatids are active burrowers and subsurface deposit feeders that never form tubes.They are readily recognized by their large, often maggot-shaped, bodies that have a rugose or lumpy looking surface and a prostomium typically with frontal horns.The family is composed of 15 genera and c. 72 species (Blake, 2015(Blake, , 2020;;Read & Fauchald, 2022).In Australia, six named species in five genera (Asclerocheilus, Axiokebuita, Hyboscolex, Oligobregma, and Pseudoscalibregma)
Synonym.Kebuita Chamberlin, 1919:390 Remarks.The genus Asclerocheilus is the second largest in the family with 15 species, including the one described here.One species, A. tasmanius Kirkegaard, 1996 is herein transferred to the genus Oligobregma because the holotype has well-developed podial lobes and parapodial cirri.By definition such parapodia are not found in the genus Asclerocheilus.
The genus Asclerocheilus was reviewed by Hartmann-Schröder (1994) and Blake (2000).Both authors reviewed existing species and described new species.Hartmann-Schroder (1994) described a new species, A. shanei from shelf depths of 122 m in Tasmania, Australia.She also reviewed and tabulated the distribution of acicular spines, capillaries, and furcate setae for the nine then-known species.Blake (2000) redescribed A. beringianus, Ushakov, 1955, A. californicus Hartman, 1963 and established a new species, A. kudenovi Blake, 2000, based on old and newly collected offshore material from California.Blake (2000) also synonymized the genus Kebuita Chamberlin, 1919 with Asclerocheilus.In so doing, he also noted that Oncoscolex (Eumenia) heterochaetus Augener, 1906 had earlier been synonymized with Kebuita glabra (Ehlers, 1887) by Hartman (1938) and that because the latter was being referred to Asclerocheilus, the specimens identified A. heterochaetus Kudenov & Blake, 1978 from southeastern Australia became a junior homonym of O. heterochaetus Augener, 1906.For this reason, the homonym was renamed by Blake (2000) as A. victoriensis.Blake (2000) prepared a tabular summary of the 12 known species, expanding on the earlier summary by Hartmann-Schröder (1994).Subsequent to Blake (2000), Eibye-Jacobsen (2002) described two new species of Asclerocheilus from the Thai sector of the Andaman Sea in shelf depths of 40-80 m.
One new species, Asclerocheilus abyssalis sp.nov.has been discovered from off New South Wales.Each of the 15 known species of Asclerocheilus is compared in Table 1, thus updating the data reviewed by Hartmann-Schröder (1994) and Blake (2000).With the transfer of A. tasmanius to Oligobregma, A. abyssalis sp.nov. is the only member of the genus known from abyssal depths of 3000 m or greater.Although both A. beringianus and A. intermedius (Saint Joseph, 1894) are reported from deep-sea habitats, these depths are from the lower continental slope of ~2000 m, not abyssal depths.The remaining 12 species are from shallower continental shelf or upper slope depths (Table 1).

Description.
A large species, all specimens complete, with a thick sausage-shaped body, narrowing only in far posterior segments (Fig. 1A).Parapodia reduced, only slightly enlarged on setigers 1-3; rest of body with no prominent podial lobes; parapodial cirri entirely absent.Holotype with 37 setigers, 4.6 cm long, about 1 cm wide (AM W.49504); largest paratype (AM W.52704) with 39 setigers, 4.9 cm long, and 0.8 cm wide.Body segments divided by a transverse groove, dividing each segment into two raised annuli extending across the body (Fig. 1A, B); these biannulate parts then subdivided by numerous crossing grooves consisting of rows of pads along body forming a basic biannulate pattern along body; some middle segments becoming triannulate.These pads best observed in far posterior segments; in anterior and middle body segments, annuli and pads becoming stretched and expanded by enlarged body, obscuring individual pads.Setigers 1-3 with grooves and pads not evident due to enlarged parapodia.Venter with shallow mid-ventral groove containing ridge along mid-line from posterior lip of mouth (Fig. 1B); ridge composed of raised rounded pads between segmental transverse grooves.Branchiae absent.Colour in alcohol light tan to grey; a few isolated areas of brown pigment associated parapodia of setigers 1-3 on holotype, otherwise without body pigment; paratypes without pigment.
Parapodia reduced along entire body.Setigers 1-3 with noto-and neuropodia elongate rounded mounds separated by  Hartman, 1963Hartman, , 1966Hartman, , 1969  low ridge; large curved acicular spines arising from curved groove on posterior side of podia.Subsequent parapodia of middle segments reduced to minute, oval, barely visible mounds, dorsal and ventral cirri entirely absent.
Setae from setiger 4 through middle segments with 5-6 simple capillaries in both noto-and neuropodia.Furcate setae not observed in anterior and middle segments, but in prepared slide mounts, 3-4 minute capillaries, some sickleshaped, observed in a bundle at base of 1-2 of the larger noto-and neuropodial capillaries (Fig. 2E).Furcate setae of posterior setigers with unique morphology consisting of a short, narrow, sharply pointed tyne lacking denticles and a second tyne a long capillary-like blade with numerous denticles along inner margin (Fig. 2F-G).These unusual furcate setae numbering about 5-8 in posterior notopodia with 3-4 much larger simple capillaries; furcate setae also occur in posterior neuropodia but number no more than 2-4 with 2-3 capillaries.Typical short bifid furcate setae as found in other scalibregmatids not present.

Remarks.
Out of 15 known species of Asclerocheilus, only three including A. abyssalis sp.nov.are reported to have the three anteriormost setigers with acicular spines (Table 1).The other two are A. intermedius (Saint-Joseph, 1894) from the eastern North Atlantic in shelf depths, and A. shanei Hartmann-Schröder, 1994 from off Tasmania, Australia, also in shelf depths.Another Australian species, A. victoriensis Blake, 2000 from Victoria in shallow subtidal depths, has four anterior setigers with acicular spines.The other 11 known species have either only one or two anterior setigers with acicular spines.
Asclerocheilus abyssalis sp.nov. is the only abyssal species of the genus and differs from other species of Asclerocheilus and all known scalibregmatids in the nature of the unusual furcate setae where a simple short smooth tyne or spur extends from the base of a second branch consisting of a long capillary-like blade with numerous thin denticles along the inner side (Fig. 2F-G).These unusual furcate setae occur in fascicles with larger smooth capillaries in posterior setigers.
There is little DNA data for scalibregmatids of the genus Asclerocheilus.The DNA sequencing effort for A. abyssalis sp.nov.only produced results for COI and 18S rRNA.The successful COI sequence for A. abyssalis sp.nov.diverged as a long branch not clustering with any published sequences of Asclerocheilus or other genera.The 18S rRNA sequence has an uncorrected distance of 5-6% from various scalibregmatid genera.
Etymology.The epithet is from abyss, Latin for a bottomless pit or the deep sea, in reference to this species being collected from abyssal depths greater than 3000 m.

Genus Axiokebuita Pocklington & Fournier, 1987
Type species: Axiokebuita millsi Pocklington & Fournier, 1987, by monotypy.Blake, 2020): Body elongate, with segments similar throughout, but some species with a fusiform shape; segments with one to four annulated rings composed of small, inconspicuous elevated pads, best developed on middle and posterior segments; venter with weakly developed median ridge.Prostomium triangular to pentagonal, truncate on anterior margin with long, subterminal ciliated lateral horns; eyes absent, nuchal organs in narrow grooves on posterior part.Peristomium a single, complete ring, weakly incised dorsally, divided into upper and lower lips of mouth ventrally; formed from large expanded lobes; unique paired ciliated "neck organs" present posterior to lower lip of mouth.Parapodia narrow ventral postsetal cirrus.Branchiae absent.Setae all capillaries, furcate and spinous setae absent; long, natatory-like setae present or absent.Pygidium reduced, short anal cirri present or absent; or with two pad-like lobes covered with papillae or papillae absent.Numerous cilia and ciliary patterns, present on lateral horns, prostomium, and interramal papillae; unique paired ciliated patches on ventral side of body.

Diagnosis. (Emended after
Remarks.The genus Axiokebuita and type species, A. millsi were originally described from upper slope depths off Nova Scotia (Pocklington & Fournier, 1987).In the same paper, the authors referred Kebuita minuta Hartman (1967) from Antarctica to their new genus while at the same time referred some of the Antarctic specimens to A. millsi implying that the species was bipolar in distribution.Records of Axiokebuita are few; the literature was reviewed by Blake (2020).Parapar et al. (2011) examined specimens of A. minuta from Antarctica and among other things, referred the type-species, A. millsi to synonymy with A. minuta thus establishing the species as more or less cosmopolitan and bipolar in distribution.Unfortunately, these authors did not examine any specimens of A. millsi as part of their review.Martinez et al. (2013) recently described a new species, A. cavernicola from marine caves in the Canary Islands.
Several features of Axiokebuita species are reported as characteristic for the genus and differ from most Scalibregmatidae including (1) long thickened subterminal lateral prostomial horns (termed palps by Parapar et al., 2011 andMartinez et al., 2013) that are ciliated and likely assist in feeding and burrowing); (2) the presence of paired sensory "neck" organs on the peristomium ventral to the mouth and separate from the prostomial nuchal organs; (3) a unique pygidium present on some species, that bears a pair of lobes covered with minute papillae; (4) absence of furcate and acicular spines; (5) the presence of ciliary bands on the prostomial horns and elsewhere on the prostomium and body; (6) displacement of the interramal sense organ from a position between the parapodia to a location closer to the notosetae.
Among these characters, the long thickened lateral prostomial horns, neck organs, and absence of furcate setae and acicular spines appear to be more or less consistent among species.However, the pygidial morphology is not consistent and slender spinous setae are known from some specimens (Blake & Hilbig, 1990).
As part of a larger study of deep-water scalibregmatids, new collections of Axiokebuita millsi and other species are being re-evaluated and compared based on the new characters identified by Parapar et al. (2011).That study when published will serve to update the systematics of this genus and status of the closely related genera Scalibregmides Hartmann-Schröder, 1965 and Speleobregma Bertelsen, 1986 (Blake, in preparation).In the meantime, Axiokebuita australis sp.nov.has been discovered in the deep-water samples collected as part of the RV Investigator IN2017_V03 survey off Southeastern Australia.That species is here described and compared with other known species.

Axiokebuita australis sp. nov.
urn:lsid:zoobank.org:act:C93CC779-84C1-4FC0-8252-FEE01BBA2968 033 complete, but damaged and in two parts, with 19 setigers, about 6 mm long, about 1.2 mm wide (posterior section removed for DNA).Body thick, sausage-shaped; more or less rectangular in cross section (Fig. 3A, C), without dorsal or ventral grooves or ridges along body.Segments with one or two rows of elevated pads across dorsum; setigers 1-4 with a biannulate pattern (Fig. 4A); most of body with uniannulate segments; ventrally, each anterior and middle segment with one to four annulated rows, these narrow, with separate raised pads indistinct, appearing more or less as single elevated ridge; posteriorly ventral surfaces with a single row of raised pads more or less continuous with dorsal rows (Fig. 3C, D).Colour in alcohol light tan with no pigmentation.Parapodia reduced to blister-like swellings throughout, with noto-and neurosetae arising from notch on posterior sides.Notopodia with single short, oval to rounded postsetal lamella, this less conspicuous in posterior setigers; neuropodia with an elongate, fingerlike lamella; both lamellae from setiger 2 or 3 continuing to posterior end (Fig. 4B).Setae all thin capillaries in spreading fascicles throughout; furcate setae not observed.Notosetae long, with up to 35-45 per fascicle.
Remarks.Axiokebuita australis sp.nov. is most similar to A. millsi, the type-species, in lacking papillated pygidial lobes.Specimens of A. millsi from off New England in bathyal depths were observed as part of a separate study (Blake in preparation) to have a fusiform-shaped body, two large non-papillated lobes around the anal opening, and 2-3 rows of annulated pads along the body; these observations agree with the published observations of Pocklington and Fournier (1987) from off Nova Scotia.In contrast, A. australis sp.nov.has a sausage or grub-shaped body, 6-8 small lobes around the anus, and two annulated rows of pads on setigers 1-4 but only a single row along the rest of the body.
Etymology.The epithet is from the Latin australis, in reference to the Australian and Southern Hemisphere location of this species.
Distribution.Continental slope and abyssal plain off SE Australia, Tasmania and Victoria, 2793-4064 m.
Diagnosis.Body elongate and arenicoliform with rows of elevated pads on dorsal and ventral segmental surfaces.Prostomium T-shaped with two prominent frontal horns; eyes present or absent; nuchal organs present.Peristomium achaetous, surrounding prostomium dorsally and forming upper and lower lips of mouth ventrally.Branchiae absent.Parapodia with well-developed dorsal and ventral cirri; interramal papilla present or absent.Capillaries present in all parapodia; furcate setae present anterior to capillaries from an anterior setiger: 2, 3, 4 or later; some species with short, slender, blunt, or pointed spinous setae anterior to Description.Holotype mostly complete, missing pygidial segment, with 23 setigers, 13.6 mm long, 1.3 mm wide across first four anterior setigers, 2.32 mm wide across expanded middle setigers.Paratype smaller but incomplete, with middle segments removed for DNA analysis.Setigers 1-4 narrow (Fig. 5A, B), body expanded from setigers 5-10 then narrowing to posterior end.Body with transverse rows of raised pads best observed on setigers 1-4 (Fig. 5A, B) and 11-22; pads in 4-5 rows on expanded middle segments, but obscured by stretching, best seen ventrally.Dorsally, setiger 1 with a single enlarged medial dorsal pad; setiger 2 with a row of large pads; setigers 3-4 with three transverse rows of pads (Fig. 5A); setigers 11-22 with 3-4 narrow transverse rows of pads.Ventrally with a single transverse pad on setiger 1, setigers 2-3 with three rows of pads; setiger 4 with two rows of pads (Fig. 5B); prominent mid-ventral ridge extending from setiger 1 to end; ridge interrupts transverse rows of pads at each segmental boundary (Fig. 5B).Branchiae absent; posterior end not present on either specimen.Colour in alcohol, opaque white.
Prostomium broadly curved across anterior margin, weakly expanded laterally, dorsally narrowing posteriorly producing V-shape (Fig. 5A); merging with narrow peristomium; with two short, rounded lobes emerging subapically from anterior margin and extending forward forming a pair of short frontal horns (Fig. 5A, B), both horns with groove or notch producing weak bilobed appearance (Fig. 5A, B); eyes absent; nuchal organs visible as numerous fine cilia between posterior lateral margin of prostomium and narrow peristomial ring.Peristomium a single ring (Fig. 5A), dorsally merging with posterior margin of prostomium and ventrally forming lips of mouth with two anterior lobes, two lateral lobes, and about eight short narrow posterior lobes or papillae (Fig. 5B).
Heavy curved acicular spines present in both noto-and neuropodia of setigers 1-3 (Fig. 5A, B); notopodia of setigers 1-2 with 4-5 spines in first and second rows and 2-3 long capillaries in second row, setiger 3 with 3-4 spines in first row and all capillaries in second row.Neuropodia of setigers 1-2 with 3-4 spines in anterior and posterior rows, accompanied by a few capillaries; setiger 3 with 3-4 spines in first row and all capillaries in second row.Setiger 4 with all capillaries in two rows of both noto-and neuropodia.Individual spines curved, narrowing to pointed tip bearing distinct arista (Figs 5C, D, 6D).Short spinous setae anterior to heavy spines or capillaries absent.Furcate setae short, first present from setiger 5 anterior to long capillaries; furcate setae of posterior setigers longer, spine-like, more numerous, ten or more per noto-and neuropodium (Fig. 6A).Furcate setae with long unequal tynes bearing short bristles tween tynes (Figs 5A, 6E).
Remarks.Oligobregma aristata sp.nov.differs from other species off eastern Australia in having anterior acicular spines with an aristate-like tip.In addition, the short frontal horns of the holotype are distinctly notched or weakly bifid and the dorsal and ventral cirri of posterior parapodia are inflated and have nipple-like tips.Such frontal horns and dorsal and ventral cirri have not been observed previously in other scalibregmatids.The only other species of Oligobregma reported with aristate acicular spines is O. mucronata Blake, 2015 from the East Antarctic Peninsula in upper slope or bathyal depths less than 1000 m.However, O. mucronata has triangular-shaped dorsal and ventral cirri that taper to pointed tips instead of swollen asymmetrical cirri with nipple-like tips.
Etymology.The epithet is from arista, Latin for long pointed awn (of grasses) or ear; in reference to the pointed tip of the acicular spines of this species.Description.Three type specimens from Sta. 023 all complete: holotype (AM W.52686) with 28 setigers, 12.2 mm long, 2.8 mm wide across expanded anterior section; 0.6 mm wide across narrow posterior section, and 1.4 mm wide across far posterior pre-pygidial expanded section; paratype (AM W.52687) with 28 setigers, 12 mm long, 2.8 mm wide across expanded anterior section and 0.8 mm wide across narrow posterior section; paratype (AM W.52688) with 26 setigers, 12 mm long, 2.2 mm wide across expanded anterior section and 0.4 mm wide across narrow posterior section.
Prostomium broadly curved across anterior margin, expanded laterally, merging posteriorly with narrow peristomium; with two short, rounded frontal horns emerging subapically from anterior margin (Fig. 7A); eyes absent; nuchal organs as grooves between posterior lateral margin of prostomium and peristomium, cilia not observed.Peristomium a lobed ring surrounding prostomium dorsally and laterally (Fig. 7A), ventrally surrounding mouth as single anterior ridge and about eight elongate ventral and lateral lobes; proboscis a relatively smooth sac everted on both paratypes (Fig. 7A).
Parapodia with short conical lobes on setigers 1-13, from setiger 14 lobes becoming longer, developing prominent dorsal and ventral cirri (Fig. 8B); dorsal cirri directed dorsolateral, asymmetrical, triangular-shaped, terminating with short rounded tip (Fig. 8C); ventral cirri directed ventrolateral, asymmetrical with broad basal attachment and short nipple-like tip (Fig. 8D); both dorsal and ventral cirri with darkly pigmented tubular glands directed towards tips (Fig. 8C, D); ciliated rounded button-like interramal papilla present (Fig. 8E).Heavy curved acicular spines present in both noto-and neuropodia of setigers 1-3 and a few in notopodia of setiger 4; notopodia of setigers 1-2 with 8-9 spines in first and second rows and 2-3 long capillaries in second row, setiger 3 with 5-7 spines in first row and all capillaries in second row, setiger 4 with a few narrow spines with capillaries in first row and all capillaries in second row.Neuropodia of setigers 1-2 with 5-7 spines in anterior and posterior rows, accompanied by a few capillaries in second row; setiger 3 with 3-4 spines in first row and all capillaries in second row.Setiger 4 with all capillaries in two rows.Individual spines curved, narrowing to pointed tip or more elongated capillary tip; shaft of spines hirsute with numerous fibrils present along shaft (Fig. 7C,  D).Short spinous setae anterior to heavy spines present on notopodia of setigers 2-3.Furcate setae short, first present on setiger 4 or 5 anterior to long capillaries; furcate setae of posterior setigers longer, spine-like, more numerous with ten or more per noto-and neuropodia.Furcate setae with long unequal tynes bearing short bristles between tynes ( Figs 7E, 8F).
Remarks.By having a few anterior acicular spines on setiger 4, and all spines of setigers 1-4 hirsute, Oligobregma bathyala sp.nov.has some similarity to O. brasierae Wiklund et al., 2019 from the Clarion Clipperton Zone (CCZ), which also has acicular spines on setigers 1-4.The two species while both occurring in deep-water Pacific habitats, differ in the following respects.Oligobregma bathyala sp.nov.has short, rounded frontal horns that are subterminal and directed anteriorly, the posterior noto-and neuropodial cirri are broad basally, asymmetrical, and bear internal tubular glands, and the peristomium consists of a single ring with several dorsal and lateral lobes.In contrast, O. brasierae has large rounded frontal horns that are located anterolateral on the prostomium, the posterior noto-and neuropodial cirri are more erect and not asymmetrical and bear internal glands that are not tubular, and the peristomium is a single smooth ring without lobes.
The only previously described species of Oligobregma reported with tubular-shaped glands in the noto-and neuropodial cirri is O. mucronata Blake, 2015 from the east Antarctic Peninsula.However, O. mucronata has acicular spines limited to setigers 1-3 instead of 1-4; the posterior cirri are more erect, not as asymmetrical, and have more of the tubular glands than O. bathyala sp.nov.In addition, the acicular spines of O. mucronata are distinctly aristate instead of a mix of spines having pointed to long, capillary tips.

Biology.
A few isolated eggs measuring 95-100 µm in diameter are present in the holotype and one paratype (AM W.52699).
Etymology.The epithet is from the Greek, bathys for deep.Description.Holotype complete with 27 setigerous segments, 10.5 mm long, 0.35 mm wide across prostomium, 0.6 mm wide across setiger 1, and 1.45 mm wide across expanded setigers; complete paratype with 29 setigers (AM W.53992), 11.9 mm long, 1.0 mm wide across anterior setigers and 2 mm wide across expanded middle setigers.Body narrow over first four setigers (Figs 9A, 10A), then expanded through next 6-8 setigers, thereafter abruptly narrowing to posterior end (Fig. 10A), but sometimes with a few far posterior setigers again becoming expanded.Colour in alcohol opaque white, without body pigment.

Distribution
Body segments with transverse annular rows of weakly raised pads; all setigers from 2-5 with 3-4 annular rings, best observed in middle and posterior segments (Fig. 10B); setigers 1-3 and swollen segments with annular rings and raised pads not readily apparent.Venter with prominent ventral raised midline from setiger 1 continuing along entire body; this ridge appearing lumpy where it crosses over annular rings.Branchiae absent.Pygidium of holotype elongate with four short anal cirri and six short lobes surrounding anal opening (Fig. 9C).
Prostomium broadly curved across anterior margin, weakly expanded laterally, V-shaped dorsally, narrowing posteriorly, interrupting peristomial rings and extending onto dorsal surface of setiger 1 (Fig. 9A); with two short, rounded lobes emerging subapically from anterior margin and extending forward forming short frontal horns (Figs 9A, 10B); horns sometimes merged with lateral anterior prostomial margins; eyes absent; nuchal organs narrow slits along posterior margins anterior to peristomium.Peristomium a double-lobed ring surrounding prostomium dorsally and laterally, ventrally surrounding mouth with circle of raised lobes (Fig. 9B).Short proboscis everted on some specimens, each with numerous papillae on anterior end.
Heavy curved acicular spines present in both noto-and neuropodia of setigers 1-3 (Fig. 9A); notopodia of setigers 1-2 with 6-8 spines in first row and long capillaries in second row, setiger 3 with 3-4 spines in first row and capillaries in second row; largest specimens sometimes with 1-2 spines also in second row of setiger 1. Neuropodia with 3-5 spines in anterior row in setigers 1-2, accompanied by posterior row of capillaries; setiger 3 with 0-3 spines in first row and capillaries in second row.Individual spines curved, narrowing to pointed tip (Figs 9D-E, 10D).Notopodial spines more robust than those of neuropodia.Short spinous setae anterior to heavy spines or capillaries present or absent, if present only on neuropodia of setigers 3-4.Furcate setae short, first present from setiger 5 or 6 anterior to long capillaries in both noto-and neuropodia; furcate setae of posterior setigers longer, spine-like.Both short and long furcate setae with long unequal tynes bearing short bristles between tynes (Figs 9F , 10E); these numbering 3-4 per notoand neuropodium in anterior segments and 8-10 or more in posterior most segments.
Remarks.Oligobregma profunda sp.nov., with anterior acicular spines in both rami of setigers 1-3, is most similar to O. aristata sp.nov., O. mucronata, and O. tasmania n. comb.All are from the southern hemisphere and most from deep water.Of these, O. aristata sp.nov.and O. mucronata have acicular spines with aristate tips, whereas O. profunda sp.nov.and O. tasmania n. comb.have spines with blunt or pointed, not aristate, tips.Oligobregma tasmania n. comb. is an abyssal species known only from its original account (Kirkegaard, 1996) and several important characters were not mentioned or well-illustrated.However, Kirkegaard (1996: fig. 6a) suggests that the posterior dorsal cirri are low, not erect or prominent and the prostomium as figured suggests that two short lateral horns arise from a narrow prostomial lobe (Kirkegaard, 1996: fig. 6b).In contrast, the dorsal and ventral cirri of O. profunda sp.nov.are prominent triangular-shaped cirri that taper to a pointed tip and the prostomium has two short, rounded frontal horns arising from a broadly curved anterior margin.
Little molecular data is available for species of Oligobregma.However, COI sequences were successful for O. profunda sp.nov.and diverged about 9% from O. brasierae and O. tanai, two abyssal species from the CCZ.As presented in Table 2, species of Oligobregma may be divided into three groups based on the number of anterior setigers having acicular spines.The two CCZ species have acicular spines on setigers 1-4, whereas O. profunda sp.nov.has acicular spines on setigers 1-3.Description.A small species, holotype complete with 29 setigers, 8.8 mm long, 0.87 mm wide across setiger 4, expanded middle segments 1.4 mm wide; most paratypes smaller, mostly juveniles, largest complete with 23 setigers, 3.45 mm long and 0.45 mm wide across setigers 1-4.Holotype with setigers 1-4 short, 4-5 times wider than long, following segments becoming thicker, about three times wider than long (Fig. 11A), producing sausage-shaped middle section, then narrowing again in posterior half of body.Smaller paratypes and juveniles enlarged and sausageshaped from about setiger 5-6 (Fig. 12A), then narrowing again in far posterior setigers.
Prostomium V-shaped or triangular, with anterior margin broadly curved, dorsally tapering to narrow posterior margin, extending over peristomium and merging with setiger 1 (Fig. 11A); ventrally merging with anterior lip of mouth (Fig. 11B); two short frontal lobes or horns arising subterminal from anterior margin of holotype (Fig. 11A); these not developed or present as developing anlage on juveniles or smaller specimens (Fig. 11B); eyes absent; nuchal organs as grooves between posterior lateral margin of prostomium and peristomium, cilia not observed.Peristomium with two narrow rings dorsally and laterally, interrupted mid-dorsally by posterior end of prostomium (Fig. 11A); ventrally dominated by expanded oral area consisting of anterior lip with about five large lobes and posteriorly by numerous narrow lobes forming large posterior lip of mouth (Fig. 11B).Many specimens with short proboscis emergent.
Pygidium of holotype with terminal anus surrounded by about 4-5 large lobes; four short anal cirri present (Fig. 11C).Smaller specimens lacking anal cirri or those present as short emergent anlage of cirri.
Remarks.Oligobregma renuncula sp.nov. is unusual among known species of Scalibregmatidae in the presence of prominent darkly pigmented pairs of nephridia clearly visible ventrally of all specimens examined.Details of nephridial morphology are known for Scalibregma inflatum through the studies of Danielssen (1859) and Ashworth (1901) and for Sclerocheilus minutus Grube, 1863 through work by DeHorne and DeHorne (1913), all summarized by Goodrich (1945).Although pairs of nephridia have been well-studied in these scalibregmatids and are visible in prepared optical sections or by histology, they have not been recorded as being pigmented and conspicuous in general observations.Ashworth (1901) characterized the nephridia of Scalibregma inflatum and presumably all scalibregmatids as consisting of four parts: (1) a small funnel that opens segmentally on the anterior septa and leads to (2) a short tube that connects to (3) a larger and elongated U-shaped tube consisting of two linked parallel ciliated tubes that lead to (4)  the nephridiopore.According to Ashworth (1901) the ciliated U-shaped tube is the only part of the nephridial morphology that is visible without dissection.In O. renuncula sp.nov. the visible portion includes the two adhering parts of the U-shaped tube, one part of which is pigmented and the other clear and unpigmented (Fig. 12F).The pigment is contained in numerous minute spherical bodies (Fig. 12G) the nature of which requires histology or electron microscopy (but see below).
In addition to the pigmented nephridia, O. renuncula sp.nov. is easily distinguished from the three other deep sea species of Oligobregma from off eastern Australia identified in this study by the numerous elongated and internally striated glands present in the dorsal and ventral cirri of posterior parapodia.
Biology.One specimen (AM W.53994) had eggs 130-135 µm in diameter.A detailed examination of the pigmented nephridia from one paratype (AM W.53994) using Phase Contrast optics magnified to 3000× revealed that the pigmented spherical bodies might be sperm nuclei; each sphere is approximately 2.5 µm in diameter; some appear to have an acrosome on one side, but no tail was observed.These observations suggest that the pigmented nephridia might serve as sperm storage organs or possibly spermatophores.Any further study of these unusual structures will require electron microscopy.
Etymology.The epithet is from the Latin, renis, for kidney, in reference to the conspicuous pigmented nephridia that characterize this species.
Distribution.Abyssal depths off eastern Australia from New South Wales to Queensland, Coral Sea, 4005-4280 m.
Setigers 1-3 with capillaries arranged in 3-4 rows in both noto-and neuropodia of holotype, 2-3 rows on smaller paratypes, each successive row with longer setae; spinous  setae not present on any specimens.Furcate setae from setiger 2 continuing on noto-and neuropodia on all setigers, these numbering 2-4 on anterior setigers, increasing to 9-10 per podium on posterior setigers of holotype; only 3-4 on smaller paratypes.Furcate setae present in first row followed by longer capillaries in subsequent row; each furcate seta with a pair of long tapering unequal tynes (Figs 13F, 14C) with minute denticles along inner borders of tynes (Fig. 14C).
Pygidium a simple lobe surrounding anus; holotype with one anal cirrus, subsequently lost; one paratype with anal two cirri; based on other species of this genus, this species likely with at least four anal cirri.
Remarks.Pseudoscalibregma glandipodium sp.nov. is most similar to P. bransfieldium (Hartman, 1967) from continental slope depths of Antarctic seas in having dorsal and ventral cirri appearing as bulbous glandular extensions of the podial lobes.The two species differ in that P. glandipodium sp.nov.has no interramal cirrus between the noto-and neuropodia and no short acicular spines in the first few setigers, whereas P. bransfieldium has both of these characters.In addition, P. bransfieldium is reported to have a ventral groove along the body (Blake, 2015), whereas P. glandipodium sp.nov.has a relatively smooth ventral surface.Ecologically, P. glandipodium sp.nov. is a lower slope and abyssal species reaching depths of 4000 m.In contrast, P. bransfieldium is an Antarctic shelf and upper slope species reaching depths of only about 900 m (Blake, 2015).
Etymology.The epithet is from the Latin glandis, for glandular, and podium, for a foot-like structure in reference to the glandular nature of the parapodia of this species.
Distribution.Eastern Australia, off Tasmania and New South Wales; lower continental slope and abyssal depths, 2480-4026 m.

Discussion
Abyssal Scalibregmatidae.To date, and including new species described in the present study, about 77 species of Scalibregmatidae in 15 genera are known and recognized (Blake, 2020;Read & Fauchald, 2022).Of these, 19 valid species from five genera are known from lower continental slope and rise and abyssal depths of 2700-3000 m and greater, with 14 of these exceeding depths of 4000 m (Table 3).These 19 species represent 25% of the known species of Scalibregmatidae, most of which have been described in the last 25 years, reflecting the increasing interest in deep-water  Hartman & Fauchald, 1971;Blake, 2020 exploration.The dominant deep-sea scalibregmatid genus is Oligobregma with 13 of 17 species occurring in abyssal depths.
Of the 19 abyssal scalibregmatid species listed here, 16 occur either in the North Atlantic Ocean, central Pacific Ocean, eastern Australia or seas around Antarctic.There are no published records from abyssal depths in the Indian Ocean, South Atlantic Ocean, or from most areas of the North Pacific Ocean.However, as part of long-term monitoring of a deep-ocean dredged material disposal off San Francisco, California, at least eight undescribed species of Scalibregmatidae are known from depths of 2800-3200 m in the Pacific (Blake et al., 2009;Blake unpublished).
In addition to the species listed in Table 3, Hartman (1965) and Hartman & Fauchald (1971) recorded Asclerocheilus beringianus Ushakov, 1955, a bathyal species from the Bering Sea in abyssal depths down to 5018 m from the western North Atlantic.However, no specimens that could be referred this species were collected after extensive surveys of the U.S. Atlantic slope from the US/Canadian boundary to off South Carolina in depths 2000-3500 m.Instead, several undescribed scalibregmatid species were encountered (Blake, unpublished).Hartman & Fauchald (1971) also described Neolipobranchius glabrus from 4436 m from the same surveys.Blake (2015) reexamined the holotype of this species and determined that it was a juvenile and lacked all typical scalibregmatid characteristics and suggested it was a juvenile of Travisia.

Table 2 .
(continued from previous page).Remarks.With the addition of O. tasmania, transferred from Asclerocheilus, and four new species described here, there are now a total of 17 known species of Oligobregma, which now surpasses Asclerocheilus (with 15 species) as the largest genus in the family.Most species of Oligobregma are from the deep sea, with 13 of the 17 species reported from lower continental slope or abyssal depths.The morphology and distributions of all 17 species are compared in Table2.
Number.COI: OP572114.Etymology.The epithet is from profundus, Latin for deep in reference to the deep-sea habitat of this species.