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

. 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 m 2 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.


Introduction
The present study is based on annelids of the family Cirratulidae collected as part of the RV Investigator cruise (IN2017_V03) along the eastern continental margin of Australia in May/June 2017 (Gunton et al., 2021) and represents the first report of deep-sea annelids of this family from Australian waters.
Annelids included in the present study include new species in the cirratulid bitentaculate genera Aphelochaeta, Chaetocirratulus, Chaetozone and Kirkegaardia.
Morphological observations. Specimens intended for morphological study 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 data.
Owing to the reduced number of cirratulid specimens collected and their overall poor condition, there were insufficient non-type materials available to sacrifice for molecular analysis. Most species were represented by only one or two specimens that could be confidently referred to any one species, and due to their small size were not appropriate for dissection of body parts. Furthermore, after staining with either Shirlastain A or Methyl Green, type specimens of each species were not suitable for molecular analysis.

Remarks.
The Cirratulidae currently include about 300 known species (Blake & Magalhães, 2019;Blake, 2019Blake, , 2021Blake & Dean, 2019;Grosse et al., 2021) that are generally separated into genera and species having numerous tentacular filaments (multitentaculates, about 80 species) and species having two tentacular filaments or dorsal tentacles (bitentaculates, about 220 species). The multitentaculates are mostly found in nearshore habitats, rarely offshore, whereas the bitentaculates are found in all habitats including the deep sea. The discovery of new species in recent years has mostly involved bitentaculates due to emphasis on previously unexplored offshore and deep-water habitats. In the present study seven new species are described in four of the bitentaculate genera: Aphelochaeta (2), Chaetocirratulus (2), Chaetozone (2), and Kirkegaardia (1).
The following species are included in this article:  Blake, 1991 Type species: Tharyx monilaris Hartman, 1960. Original designation by Blake (1991).

Genus Aphelochaeta
Diagnosis (after Blake, 2018). Prostomium conical to rounded; peristomium elongate with pair of grooved dorsal tentacles arising either on peristomium or anterior to setiger 1. Anterior segments often expanded, crowded or uncrowded; abdominal segments sometimes beaded or moniliform in appearance; setae simple capillaries lacking distinct serrations using light microscopy, but distinct fibrils may be visible using SEM; posterior end frequently expanded, tapering to a simple pygidial lobe.

Remarks.
To date, only ten valid species of Aphelochaeta have been reported from abyssal depths of about 3000 m and greater (Blake, 2018(Blake, , 2019. In the present study, two new species have been identified in the samples from off the Australian east coast. Others are most certainly present, but the available specimens are either too fragmented or damaged to characterize. Description. All specimens incomplete: holotype (AM W.52706) with 61 setigers, 8.9 mm long, 0.61 mm wide across peristomium, 0.72 mm wide across setiger 8; paratype (AM W.52716) a mature female, with 39 setigers, 5.8 mm long, 0.3 mm wide across anterior setigers; with eggs measuring 120-200 µm in longest diameter. Ventral ridge present from setiger 1 (Fig. 1B), continuing along anterior and middle segments; in middle segments ridge becomes expanded medially at each segmental junction. Dorsal grooves and ridges absent. Colour in alcohol, light tan with no additional pigment.
Pre-setiger region elongate, thickened, about as long as first eight setigers ( Fig. 1A-B). Prostomium triangular, tapering to narrow rounded tip ( Fig. 1A-C); eyespots absent; nuchal organs narrow slits on posterior lateral margins (Fig. 1C). Peristomium elongate, with three annular rings interrupted dorsally by prominent dorsal crest (Fig. 1A); ventrally only first ring apparent, rest of venter relatively smooth, with a low ridge transitioning to a distinct ventral ridge from setiger 1 continuing along body ( Fig 1B). Mouth with several rounded lobes inside posterior lip (Fig.  1B). Dorsal tentacles arise from posterior margin of third peristomial ring; first pair of branchiae lateral to dorsal tentacles (Fig. 1A, C); second pair of branchiae on setiger 1 dorsal to notosetae; subsequent branchiae in a similar position. Most branchiae missing or broken, represented by scars or stubs.
Nature of posterior end and pygidium unknown.
Methyl Green staining. Stain concentrates in the ventral intersegmental grooves on anterior and middle setigers producing a distinct band that extends from the base of each parapodium down and around each segment being interrupted mid-ventrally by the longitudinal groove. There are no other areas of the body that retain stain. The stain is very evident on the specimens from Sta. 016 (including holotype), but weaker on the specimens from Sta. 31.
Remarks. Among species of Aphelochaeta described from abyssal depths, A. jubata sp. nov. is most similar to Aphelochaeta clarionensis Blake, 2019 from the abyssal depths of the Clarion-Clipperton Fracture Zone in the Pacific Ocean, in having the peristomial rings interrupted by a dorsal crest. However, A. clarionensis has only two peristomial rings instead of three in A. jubata sp. nov. In addition, the MG staining patterns of the two species differ in that A. clarionensis has a distinct pattern on the pre-setiger region and no pattern on the body segments. In contrast, A. jubata sp. nov. has no pre-setiger staining pattern, but stain is retained as intersegmental bands on anterior and middle segments.
Another abyssal species of Aphelochaeta with a distinct dorsal peristomial crest is Aphelochaeta brandtae Blake, 2018 from the Southern Ocean and Weddell Sea, Antarctica. However, in contrast to A. jubata sp. nov., A. brandtae has two peristomial rings instead of three, and a prominent MG pattern on the pre-setiger region and broad bands across the venter of anterior segments instead of no pre-setiger pattern and the stain retained on anterior and middle segments is concentrated in the narrow intersegmental grooves.
Etymology. The epithet is from the Latin, juba for mane or crest, in reference to the distinctive dorsal crest found on the peristomium of this species. Description. A small species, holotype only specimen, complete with 28 setigers, 3.2 mm long and 0.47 mm wide across anterior setigers. Body expanded over first nine setigers, then narrowing to consistent width along rest of body (Figs 2A, 3A). First 8-9 individual setigers short, each 11-12 times wider than long, following segments longer, about three times wider than long ( Fig. 2A); far posterior segments becoming rounded, weakly moniliform (Fig. 2C).
Each segment separated from following by relatively deep intersegmental grooves. Dorsal surface of all segments smooth without dorsal longitudinal grooves or ridges. Ventral surface of body with prominent mid-ventral ridge line composed of transverse raised ridges that together Pre-setiger region relatively short, thickened, about as long as first six setigers ( Fig. 2A). Prostomium short, pear-shaped, tapering to narrow tip (Figs 2A-B, 3A-B); eyespots absent; nuchal organs not observed. Peristomium with three annular rings and one narrow achaetous segment, all complete dorsally ( Fig. 2A); these all merged ventrally providing smooth ventral surface from anterior margin of peristomium to setiger 1 (Fig. 2B). Mouth of opening anteriorly, visible only in frontal view, a only visible ventrally as narrow slit between first peristomial ring and prostomium. Dorsal tentacles arise from middle of third peristomial ring ( Fig. 2A); first pair of branchiae arises on achaetous segment anterior to setiger 1; subsequent branchiae arise on posterior margin of individual segments dorsal to notosetae ( Fig. 2A). All branchiae missing or broken, represented only by scars or short stubs.

Methyl Green staining.
Weak stain on prostomium and in intersegmental areas of anterior segments where subdermal glands occur; otherwise no pattern.

Remarks.
To date, only 12 valid species of Aphelochaeta have been described from abyssal depths of about 3000 m or greater (Blake, 2018(Blake, , 2019. Aphelochaeta readi sp. nov. is the twelfth species in this group and the only one having multiple peristomial rings that cross the dorsal surface, yet do not cross the ventral surface leaving it smooth. In addition, the distinct widening of the first 8-9 setigers followed by a narrow middle and posterior body with a few far posterior moniliform segments terminating in a simple pygidial lobe is distinctive. Unlike other cirratulids encountered in this study and at other deep-water locations, A. readi sp. nov. is the only one to have the mouth opening directed frontally, not visible in ventral view. Etymology. This species is named in honour of Dr Geoffrey Read, Marine Biologist with the National Institute of Water & Atmospheric Research Ltd (NIWA), Wellington, New Zealand in recognition of his long-time role as Chief Editor of annelids for the World Register of Marine Species (WoRMS). In addition, Dr Read has long maintained a website site dedicated to polychaetes and provides a wide range of assistance in addressing problems with zoological nomenclature and locating references, many of which are long out of print.
Diagnosis. (after Blake, 2018) Prostomium broadly rounded anteriorly or wedge-shaped; eyespots absent; with a pair of small nuchal slits or depressions at posterior edge. Peristomium with a single pair of grooved dorsal tentacles arising from posterior margin or interface with setiger 1. First pair of branchiae arising from posterior margin of peristomium, an achaetous segment, or setiger 1. Body typically thick and fusiform over many segments, rarely with middle or posterior body segments beaded or moniliform; individual segments short, numerous. Setae include capillaries on most setigers and thick, pointed acicular spines in neuropodia and a few in notopodia or spines in neuropodia only; spines few, often small and inconspicuous, not forming cinctures. Individual spines straight to weakly sigmoid. Pygidium with a simple ventral lobe.

Remarks. Species of
Chaetocirratulus include a small group of bitentaculate cirratulids that share characteristics of both the multitentaculate genus Cirratulus Lamarck, 1818 and the bitentaculate genus Chaetozone. The genus was established by Blake (2018) to accommodate a group of large bodied Chaetozone species that had a short wedge-shaped prostomium and only a few acicular spines, not arranged in spreading fascicles or in the more typical cinctures. Blake (2018) reported on six species of this genus, three new to science, all from the southern hemisphere: four from Antarctica; two from off western South America. Blake (2022) reported on four additional species from the western North Atlantic Ocean, three of which were new to science. In the present study, two new species agreeing with the diagnosis of Chaetocirratulus have been encountered, bringing the total number of known Chaetocirratulus species to twelve. Description. A small species, holotype complete, with about 65 setigers, 13.1 mm long, 1.1 mm wide across anterior setigers and about 1.2 mm wide across middle setigers, narrowing posteriorly. Body elongate, thick, grub-like, but not fusiform; segments short, wide, anterior segments about 4.5 times wider than long (Fig. 4A); posterior segments about six times wider than long (Fig. 4C). In cross section, body segments dorsoventrally flattened, but with dorsum and venter rounded; with ventral ridge extending from peristomium continuing along entire body; dorsal ridge or groove absent. Individual segments all uniannulate, but middle and posterior segments crossed with numerous thin wrinkles. Colour in alcohol: light tan.

Chaetocirratulus bathyalis
Pre-setiger region about as wide as long, as long first five setigers (Fig. 4A). Prostomium wedge-shaped in dorsal and ventral view, narrowing to rounded tip ( Fig. 4A-B); with rounded, bulbous shape in lateral view; eyespots absent; nuchal organs large, crescent-shaped grooves on posterior lateral margin. Peristomium with lateral and ventral grooves producing three rings (Fig. 4A), a narrow anterior ring followed by two more-or-less equal larger rings; surmounted by irregular shaped dorsal crest not crossed by peristomial grooves (Fig. 4A). Ventrally, peristomial rings only weakly apparent; mouth opening encompassed by first ring, with upper lip formed by about six lobes (Fig. 4B). Dorsal tentacles arise from a narrow groove between third peristomial ring and setiger 1, possibly an achaetous segment (Fig. 4A). First pair of branchiae lateral to dorsal tentacles in same groove. Subsequent branchiae arise dorsal to notosetae from setiger 1, continuing on subsequent setigers (Fig. 4B). Most branchiae missing or reduced to stubs or scars.
Posterior end narrowing to short pygidium with cap-like rounded lobe (Fig. 4C).
Methyl green staining. Individual gland cells staining all along body, producing bands of speckles over individual segments; dense concentrations of speckles on peristomium especially last ring and dorsal crest.

Remarks. Chaetocirratulus bathyalis sp. nov. is similar to
Chaetocirratulus pinguis (Hartman, 1978) from Antarctica in having noto-and neuropodial spines from setiger 1. The two species differ in that C. pinguis has a distinctly fusiform body, three weakly developed peristomial rings with no dorsal crest, a shallow mid-dorsal groove along the body but no ventral ridge, and individual segments that are distinctly biannulate (Blake, 2018). In contrast, C. bathyalis sp. nov. has a thickened but not fusiform body, at least two well-developed peristomial rings and a prominent dorsal crest, no mid-dorsal groove but a distinct ventral ridge, and uniannulate segments with numerous transverse wrinkles. In addition, the MG staining pattern differs between the two species: in C. pinguis the retained stain is largely limited to the pre-setiger region where the prostomium stains lightly and the peristomium stains heavily, especially laterally. In contrast, C. bathyalis sp. nov. has stain concentrated in individual glands, producing bands of speckles all along the body and dense concentrations of speckles on the last peristomial ring and dorsal crest.
Etymology. The epithet is from the Greek, bathys, for deep, in reference to the deep-water habitat of this species.
Distribution. Australia, lower continental slope off New South Wales, 2324-2634 m.   Description. All specimens incomplete, including four anterior fragments and one posterior fragment. Holotype largest specimen, with 60 setigers, 10.6 mm long, 0.9 mm wide across anterior setigers; largest paratype with 25 setigers, 3.0 mm long, 1.0 wide. Body with thick, crowded segments along entire body (Figs 5A-B, 6C-E); individual segments up to ten times wider than long. Anterior segments with transverse lumpy dorsal ridge (Fig. 5A), but without longitudinal grooves or ridges; venter with prominent midventral ridge along entire body composed of broad medial bulge on each segment (Figs 5B, 6B), connected midventrally at intersegmental groove. One paratype a mature female with large eggs in two swollen posteriormost setigers of fragment ( Fig. 6C-D). Eggs 160-200 µm in longest diameter. Colour in alcohol tan without any obvious pigment.
Posterior fragment narrowing to short conical pygidial lobe.

Methyl Green staining.
No general pattern, however intersegmental grooves retain stain to varying degrees ( Fig.   6D-E, arrows), with dorsal surface of some middle and posterior segments staining lightly.
Remarks. Chaetocirratulus glebalis sp. nov. is an entirely unique cirratulid in the nature of the numerous lobes and lumps on the pre-setiger region and on the body segments. The species is referred to Chaetocirratulus because of the relatively thickened body, short anteriorly rounded presetiger region and hidden nature of the prostomium. I know of no other cirratulids from deep water or shallower depths with a similar appearance. The morphology and arrangement of the acicular spines is, however, similar to some species of Chaetozone, except that posterior segments do not have cinctures and the spines are not large nor sigmoid in shape.
Biology. The large protruding eggs (160-200 µm) on the paratype suggest direct or lecithotrophic development, which would be expected for an abyssal species. However, long natatory-like capillaries might suggest a mechanism for movement at the sediment-water interface at the time of spawning. The short, blunted pre-setiger region suggests that the species burrows by pushing particles out the way and opening cracks in the sediment rather than moving between particles.
Etymology. The epithet is from the Latin, gleba for lump, in reference to the lumpy segmental appearance of the body of this species.
Distribution. Abyssal plain between Victoria and Tasmania, eastern Australia, 4170 m.

Genus Chaetozone Malmgren, 1867
Type species: Chaetozone setosa Malmgren, 1867, by monotypy. Blake, 2018). Prostomium blunt to conical, elongate to short, usually lacking eyespots, with a pair of small nuchal slits or depressions at posterior edge. Peristomium with a single pair of grooved dorsal tentacles arising from posterior edge of peristomium, or sometimes more posterior on an asetigerous anterior segment, or rarely on an anterior setiger. First pair of branchiae arising from peristomium, an achaetous segment or first setiger; sometimes with first two pairs of branchiae on a single anterior segment. Body usually expanded anteriorly and narrowed posteriorly, rarely with middle or posterior body segments beaded or moniliform; posterior end often expanded. Setae include capillaries on most setigers and sigmoid acicular spines in neuropodia and notopodia, with spines typically concentrated in posterior segments forming distinct cinctures with spines carried on elevated membranes; cinctures with few to many spines sometimes encircling entire posterior end, accompanied with none to many alternating capillaries; bidentate spines sometimes present in juveniles or occasionally in ventral-most position of far posterior setigers of adults, accompanying unidentate spines in cinctures; some species with long, natatory-like capillary notosetae, sometimes limited to gravid individuals. Pygidium a simple lobe, disk-like, with long, terminal cirrus, or few short lobes.

Remarks.
Chaetozone is the largest of the cirratulid genera with about 75 species (Blake, 2022). Species of Chaetozone  are typically recognized by having acicular spines in both noto-and neuropodia and with those of posterior segments frequently numerous and arranged in conspicuous spreading fascicles that often entirely encircle the body providing a characteristic armature. However, several species have a reduced number of acicular spines that are not superficially conspicuous and as such are peripheral to the above definition (Blake, 2022). In the present study, two species of Chaetozone were identified, but none of the specimens were complete precluding an exact determination of the number of acicular spines and their arrangement in posterior segments. However, the morphology of the pre-setiger region agrees well with other related species of Chaetozone and makes a comparison of soft morphology feasible.  anterior 5-10 setigers narrow, c. 4.5 times wider than long (Fig. 7A), followed by swollen "stomach" area of about six setigers containing numerous eggs and an enlarged loop of the intestine filled with fine sediment (Fig. 8A-B); abdominal segments becoming moniliform, with partial cinctures developing on posterior segments of fragment. Paratype without enlarged "stomach" area but with some thickening of posterior thoracic segments filled with fine sediment particles. Dorsal and ventral crests and ridges absent. Eggs of holotype numerous, tightly packed, from about setiger 10 to 22, each egg 100-120 µm in longest diameter with conspicuous germinal vesicle. Colour in alcohol: opaque white, with no body pigment.
Parapodia reduced to low ridges or mounds from which setae arise; posterior parapodia becoming moniliform with cinctured segments developing on posteriormost segments of both specimens. Anterior setae all long capillaries numbering about 10-12 per fascicle, including long natatory-like setae in most notopodia of anterior and middle segments (Fig. 8A-C). Neuropodial acicular spines from setiger 22 and notopodial spines from setiger 24 on holotype. Spines numbering six in neuropodia and two in notopodia in setiger 24, or last setiger of incomplete holotype. Spines accompanied by 1-2 capillaries in neuropodia and 2-3 in notopodia. Individual spines with basal manubrium at emergence from podial lobes; spines only weakly curved, tapering to narrow pointed tip (Fig. 7C).
Methyl Green staining. Stain retained on lateral sides of peristomium, otherwise no pattern.
Remarks. Chaetozone abyssalis sp. nov. belongs to a group of deep-sea species that includes Chaetozone australosetosa Blake, 2018 and Chaetozone biannulata Blake, 2018, both from Antarctic seas, and Chaetozone profunda Blake, 2022 from deep water in the western North Atlantic. Each of these species has two peristomial rings with the large second ring bearing dorsal tentacles well anterior to the first pair of branchiae and setiger 1, suggesting that an achaetous segment is incorporated into the peristomium. Chaetozone abyssalis sp. nov. is most similar to C. australosetosa in having a relatively thick pre-setiger region instead of one that is long, narrow, and tapering anteriorly to a pointed prostomium. Chaetozone abyssalis sp. nov. differs from C. australo setosa in having the first peristomial ring expanded and separated from the prostomium instead of narrow and conical tapering to a prostomium that is mostly merged with it. The number of posterior spines between the two species cannot be compared due to the absence of complete specimens of C. abyssalis sp. nov.
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.

Description.
A moderately-sized species, holotype only specimen, incomplete, broken in two pieces, with 39 setigers, 8.4 mm long, 0.38 mm wide across setiger 1 and 0.80 mm across widest thoracic segments. Body with narrow presetiger region and about first eight setigers then expanding (Fig. 10A) and becoming widest over setigers 14-20, then narrowing posteriorly (Fig. 10A). All anterior and middle setigers short; anterior setigers about 4.5 times as wide as long; widest middle setigers about ten times wider than long; posterior setigers narrowing (Fig. 10A), becoming moniliform, about as wide as long (Fig. 10D). Simple ventral groove present from anterior border of setiger 1 (Fig. 9B); in middle setigers, groove joined by a conspicuous mid-ventral swelling at junction of each segment on venter. Colour in alcohol light tan; body with areas of dark pigment along most of body, mostly concentrated in intersegmental areas and as parapodial bands (Fig. 10A-C arrows); some branchiae pigmented.
Pre-setiger region about as long as first five setigers, consisting of a long, narrow prostomium, followed by a bulbous first peristomial ring and smooth second ring (Fig.  9A). Prostomium tapering anteriorly to a narrow tip (Figs  9A-B, 10A-B); eyespots absent; nuchal organs visible in a pit on dorsolateral margin (Fig. 10A). Peristomium with first bulbous ring merging with prostomium dorsally (Figs 9A, 10A-B) and forming anterior lip of mouth ventrally (Fig.  9B); second peristomial ring rectangular, merging seamlessly with setiger 1 dorsally (Fig. 9A), forming posterior lip of mouth ventrally, then merging with setiger 1 posteriorly (Fig. 9B). Three ciliated oral lobes observed within mouth opening (Fig. 9B). Dorsal tentacles arising from middle of second peristomial ring with first pair of branchiae arising posterior to tentacles on posterior margin (Fig. 9A). Second pair of branchiae on posterior border of setiger 1 dorsal to notosetae; subsequent branchiae in similar position; most branchiae missing with location observed as scars or stubs along most of body.
Parapodia of anterior setigers reduced to low mounds from which setae arise; middle expanded setigers with parapodia more prominent, narrow, forming lateral lobes; posterior segments again with parapodia reduced. Anterior setae all long capillaries numbering about 7-9 per fascicle, including long natatory-like setae in most notopodia of anterior and middle segments. Acicular spines from setiger 24 in neuropodia and setiger 31 in notopodia. Spines numbering five in neuropodia and three in notopodia in setiger 38 or with eight spines on a side, but not as cinctures; however, nature of far posterior segments and spines unknown. Spines accompanied by 1-2 capillaries in neuropodia and 3-4 in notopodia. Individual neuropodial spines with basal manubrium near emergence from podial lobes, thick, weakly curved, tapering to narrow pointed tip (Fig. 9D); notopodial spines longer and straighter than neuropodial spines (Fig. 9C).

Methyl Green staining. No pattern.
Remarks. Chaetozone adusta sp. nov. is easily recognized by the nature of the two peristomial rings of which the first is enlarged and bulbous and the second is smooth and merges with setiger 1 as well as the narrow anterior segments that transition to a distinctly enlarged middle section that then narrow to moniliform posterior segments. In addition, the body is distinctly pigmented with brown areas along most of its length, including distinct bands on the anterior borders of individual anterior and middle body segments. Chaetozone adusta sp. nov. is most similar morphologically to two other deep-water species: Chaetozone grasslei Blake, 2019 from the abyssal Pacific Ocean and Chaetozone lophia Blake, 2022 from the U.S. Atlantic slope in bathyal depths. Both of these species also have two peristomial rings of which first is bulbous and the second is smooth. Chaetozone grasslei differs from C. adusta sp. nov. in having a long, narrow, threadlike body consisting of segments that are mostly rounded or moniliform instead of moniliform segments being limited to posterior setigers. Chaetozone lophia species differs from C. adusta sp. nov. by having instead of lacking a distinct dorsal crest on the bulbous first peristomial ring. In addition, while the new Atlantic species has an enlarged middle body region, this is the result of the intestine having intestinal loops that form a "stomach" packed with sediment.
The only other deep-water species with extensive body pigment is Chaetozone brunnea Blake, 2006 from the U.S. Pacific coast off northern California. The California species however is an entirely different kind of Chaetozone, in having two peristomial rings, but with the first tightly merged with the prostomium and the second likely being an achaetous segment where the dorsal tentacles arise anteriorly on that segment instead of at the posterior margin where the branchiae occur. In addition, C. brunnea has full cinctures with an armature of up to 16 acicular spines on a side. Another unusual characteristic of C. brunnea is the presence of a prominently enlarged "stomach" at the juncture of the anterior and abdominal segments, which in some specimens results in a distinct twist to the body.
Etymology. The epithet is from the Latin, adustus, for brown or swarthy, in reference to the brown pigment that characterizes this species.
Distribution. Abyssal plain off southeastern Victoria, eastern Australia, 4107 m.

Genus Kirkegaardia Blake, 2016
Type species: Monticellina heterochaeta Laubier, 1961. Designated by Blake (2016. Homonym: Monticellina Laubier, 1961. Preoccupied by Monticellina Westblad, 1953 Diagnosis (after Blake, 2016): Bitentaculate cirratulids with distinct body regions and all setae distally pointed. Pre-setigerous region typically elongate, cylindrical, with short, blunt prostomium and long peristomium with none to many weakly developed annulations or peristomium short and thick; dorsal tentacles arising on posterior margin of peristomium, anterior to setiger 1. Thoracic notopodia often shifted dorsally, elevated, producing distinct dorsal groove along thoracic region; other species with thoracic parapodia more lateral, leaving broad elevated dorsum; parapodia of middle and posterior region lateral. Middle body segments longer than wide, frequently beadlike; posterior segments wider than long, somewhat crowded, with posterior most segments usually expanded or enlarged. Setae including simple capillaries with fibrils observed under SEM and denticulated capillaries with distinct denticles present along one edge of setae; denticles visible at 400-1,000×; blades usually basally expanded. Pygidium with simple ventral lobe.
Remarks. Species of Kirkegaardia are characterized by having capillary setae that have denticulated or serrated edges. Although the denticles are often difficult to see in light microscopy, they are highly diagnostic. In the present study, a single species, Kirkegaardia glabra sp. nov. has close relatives, also from deep water. Pre-setiger region about three times as long as wide (Figs 11A, 12A); prostomium and peristomium merging dorsally, separated by mouth ventrally (Fig. 11A). Prostomium conical, tapering to narrow rounded tip; eyes absent; oval-shaped nuchal organs present on posterior lateral margins (Fig. 11A). Peristomium elongate, smooth without annulations, dorsal surface with paired longitudinal grooves producing low mid-dorsal crest from prostomium to anterior margin of setiger 1 (Fig. 11A). Dorsal tentacles arising on posterior margin of peristomium, with first pair of branchiae posterolateral to tentacles (Fig. 11A); second pair of branchiae on posterior margin of setiger one dorsal to notosetae and on edge of mid-dorsal channel; subsequent thoracic branchiae in similar location. Branchiae mostly absent, reduced to scars or stubs.
Parapodia reduced, with podial lobes of short anterior setigers rounded, inconspicuous; segments of longer segments; with no obvious podial lobes. Intersegmental grooves with glandular tissue retaining MG when applied (see below). Setae all denticulated capillaries with about 6-9 capillaries in anterior noto-and neuropodia and 5-6 in more posterior setigers. Capillaries with minute denticles along one edge (Fig. 11B), with details best observed at 1000× in light microscope, but visible at 400×; notosetae long, thin; neurosetae shorter, becoming more spinous than notosetae. Notosetae with denticles directed ventrally and denticles of neurosetae directed dorsally, and visàvis.
Nature of posterior end and pygidium unknown.
Methyl Green staining. Methyl Green imparts a diagnostic staining pattern to this species (Fig. 12A). The prostomium and peristomium are relatively unstained; the anterior setigers retain a light stain on the anterior half of individual segments, this becoming intense on setigers 9-12, then entirely absent on following segments. All segments retain stain in the intersegmental grooves which produces bands surrounding the body in posterior segments (Fig. 12A).  setiger region and weak or absent on anterior setigers, with only setigers 9-12 having an intense stain. In addition, while the intersegmental grooves retain stain along most of the body in K. glabra sp. nov., it is the parapodia themselves that retain the stain in K. carinata.

Remarks
Etymology. The epithet is derived from the Latin, glaber, for smooth in reference to the smooth, uninterrupted pre-setiger region of this species.

Species of Cirratulidae from abyssal depths
In the present study "abyssal" depths are regarded as beginning at about 3000 m and continuing to the deepest parts of the abyssal plain. Historically, the deep-sea fauna was considered to be impoverished. This idea was largely based on the difficulty of obtaining samples and the paucity of most of the more typical benthic fauna known from studies of shallow-water habitats. Although the Challenger Expedition (1872-1876) and later Galathea Expedition (1950-1952) demonstrated that life was found in the deepest parts of the ocean, it was generally considered to be species-poor. The use of coarse mesh trawls and dredges used in those early expeditions were unable to adequately collect the more numerous smaller benthos known to occur in shallow waters. Based largely on deep-water surveys during the 1960s, in which more quantitative samplers such as epibenthic sleds and fine-mesh sieves to separate the fauna from the sediments, benthic invertebrates from bathyal, slope, and abyssal depths in the North Atlantic Ocean were found to be far more diverse than previously believed (Sanders et al., 1965;Sanders & Hessler, 1969). Hartman (1965) and Hartman & Fauchald (1971) documented polychaetes from Sanders' North Atlantic surveys and collectively described more than 100 new species and several new genera. The introduction of quantitative box cores, multicores, and mega cores in subsequent years has yielded many more benthic invertebrate species and resulted in further estimates of high species richness in deep-sea sediments (e.g., Grassle & Maciolek, 1992).
The first compendium of abyssal polychaetes was by Hartman (1971) who listed 12 species of Cirratulidae in three genera. The majority of the cirratulid records she cited, however, were either not well documented or carried names that were derived from taxa, such as Chaetozone setosa Malmgren, 1867 that at the time were considered to be cosmopolitan in distribution. As a result, only two of the species listed by Hartman (1971) from 3000 m or greater are currently listed as valid in WoRMS. Recent studies of deep-water cirratulids by Blake (2006Blake ( , 2016Blake ( , 2018Blake ( , 2019Blake ( , 2022this study;Doner & Blake, 2006) allow for a more comprehensive summary of cirratulids from 3000 m and greater.
Out of approximately 300 known species of Cirratulidae, about 220 belong to the bitentaculate genera and include an increasing number of deep-water taxa as materials from various expeditions and monitoring surveys are analyzed. Table 1 includes a list of 37 species of Cirratulidae recently described, or documented from depths of 3000 m or greater.
These 37 abyssal cirratulids are all from relatively few geographic areas: eastern Pacific off California (7), Peru-Chile Trench (3), Equatorial Pacific Ocean (12), eastern Australia (6), Antarctic seas (5), Western North Atlantic Ocean (3), and the Mozambique Channel, Indian Ocean (1). There are large areas in the Northern Pacific Ocean, northeast Atlantic Ocean, South Atlantic Oceans, and Indian Oceans where no abyssal cirratulids have been reported. In addition, despite the fact that 12 new cirratulid species were described from the abyssal plain of the Clarion-Clipperton zone in the Equatorial Pacific Ocean by Blake (2016Blake ( , 2019; this area represents only a small fraction of the immense Pacific Basin. In keeping with the number of known species globally, the genera Aphelochaeta (12 species) and Chaetozone (15 species) are the best represented among the abyssal cirratulids that have been described to date. It is noteworthy that of the 37 species listed in Table 1, 34 have been described in the past 15 years, emphasizing the increasing interest in deep-sea exploration.