Kirkegaardia Blake, 2016 (Annelida: Cirratulidae) from Southeastern Brazil with description of nine new species

This is the first taxonomic study of cirratulid polychaetes of the genus Kirkegaardia Blake, 2016 from Brazil. Nine new species of the genus are described from the Southern Brazilian coast (50–3000 m deep). The genus Kirkegaardia is generally subdivided into three distinct groups of species (Kirkegaardia dorsobranchialis-heterochaeta, Kirkegaardia baptisteae-tesselata and Kirkegaardia luticastella) and several out-group species for which relationships remains to be defined. In this study, new species were included in the Kirkegaardia dorsobranchialis-heterochaeta and Kirkegaardia baptisteae-tesselata groups. Kirkegaardia dorsobranchialis-heterochaeta is characterized by thoracic parapodia elevated producing a channel between the notopodia, elongate pre-setigerous region that is either entirely smooth or modified with a dorsal ridge and/or rings, and noto- and neurosetae capillaries denticulated. As belonging to this group, K. blakei sp. nov., K. brisae sp. nov., K. goytaca sp. nov., K. jongo sp. nov. and K. papaveroi sp. nov. are described here. Kirkegaardia baptisteae-tesselata includes species that lack thoracic parapodia elevated and mid-dorsal thoracic groove, although a dorsal ridge is sometimes developed. In the pre-setigerous region dorsal ridges and rings are present or absent. Most species in this group have neurosetae denticulated, and notosetae capillaries of other types. This study adds K. helenae sp. nov., K. medusa sp. nov., K. nupem sp. nov. and K. zafirae sp. nov. to the latter species group. In addition, two new records are provided for K. hampsoni. A key to cirratulid polychaete species reported from Brazilian waters is provided.


Introduction
Cirratulidae Ryckholt, 1851 [1] is a family of sedentarian annelids that are recognized by the numerous tentacles and paired filamentous branchiae located on the anterior segments [2]. The family Cirratulidae comprises 21 genera and 291 species described [3]. Cirratulids are deposit feeding organisms, mostly small (measuring about 2.5 cm long) and inhabit all oceans from the intertidal to the deep sea in consolidated and unconsolidated sediments [4,5]. As deposit feeders, some cirratulids have been reported as bio-indicators of organic enrichment in studies of marine environmental assessment [6][7][8]. Cirratulids are also interesting organisms for studies on annelid reproduction because they show different modes of sexual and asexual reproduction, including parthenogenesis and viviparity [9][10][11]. Also, they exhibit a high capacity of regeneration [11][12][13][14][15]. The taxonomy of cirratulids is challenging because the specimens have few morphological characters that are often lost during collection and manipulation, which makes describing new species difficult [16][17][18]. Bitentaculate cirratulids are not well known in Brazil [19,20], as only 28 species have been registered up to date, according to the most recent species compilation [21]. The genus Kirkegaardia Blake, 2016 [22] has not been recorded from Brazil. Kirkegaardia is a recently described genus that includes many synonymized species of other genera; for example, Kirkegaardia dorsobranchialis (Kirkegaard, 1959) [23], Kirkegaardia heterochaeta   [24], and Kirkegaardia secunda (Banse & Hobson, 1968) [25], which were originally described in the genus Tharyx Webster & Benedict, 1887 [26].
Kirkegaardia is characterized by having a long and thin body with slightly expanded anterior and thoracic segments; a pair of dorsal tentacles inserted in the final portion of the peristomium or in the first thoracic setiger; usually with several pairs of branchiae, beginning from the peristomium; and denticulate or serrated capillaries. Species of Kirkegaardia (and earlier as Monticellina) were recorded in both the Northern [2,27] and Southern Atlantic Ocean [28]. In South America, the genus has only been recorded for Argentina, from which Kirkegaardia morae (Elias, Rivero & Orensanz, 2017) [28] was described.

Material and methods
The Campos Basin is bordered to the south by the top of Cabo Frio, which separates it from the Santos Basin; to the north by the top of Vitória, which separates it from the Espírito Santo Basin; and to the west by Precambrian rocks, which emerge near the city of Campos dos Goytacazes (RJ) (Fig 1) [29]. The region is characterized by the low river input and coastal and shelf upwelling of cold, nutrient-rich South Atlantic Central Water. These events are enhanced during austral spring and summer seasons under prevailing NE winds on the Cabo Frio coast (23S/42W), but also can occur intermittently all year round and reach hundreds of miles on the platform [30,31].
The material analyzed for the present study came from two independent projects carried out in Southeastern Brazil, under the coordination of the research center CENPES/PETRO-BRAS (Petrobras Research Center): HABITATS-Environmental Heterogeneity in the Campos Basin (from 400 to 3000 m depth) and AMBES-Environmental Heterogeneity in the Espírito Santo Basin and northern region of the Campos Basin (from 50 to 3000 m depth). All permits required to conduct sampling are held by CENPES/PETROBRAS. The sediment was collected with a 0.25 m 2 box-corer (Ocean Instruments, USNEL Spade Corer MK I). Samples were separated into three strata (0-2 cm, 2-5 cm, and 5-10 cm) and sieved with 0.3-0.5 mm meshes. The collected specimens were immediately preserved in 10% formalin, and later rinsed in fresh water and finally stored in 70% ethanol. Identifications were based on morphological characters. Specimens were examined under a stereomicroscope, compound light microscope, and scanning electron microscope (SEM). Specimens used for SEM were first dehydrated in a series of progressively increasing concentrations of ethanol (70-100%), critical point dried, covered with~25 nm of gold, and then examined and photographed using the Electron Microscopy Laboratory (Protozoology, UFRJ). All specimens were measured using the ZEN 2012 blue version program from images taken with a camera attached to a Zeiss Primo Star optical microscope. Additionally, some specimens were stained with methyl green to investigate species-specific staining patterns. Type specimens and paratypes of the nine newly described species were deposited in the Polychaete Collection of the Rio de Janeiro National Museum-MNRJ / UFRJ, RJ, Brazil.

Nomenclatural acts
The electronic edition of this article conforms to the requirements of the amended International Code of Zoological Nomenclature. Hence, the new names contained herein are available under that Code from the electronic edition of this article. This published work and the nomenclatural acts are registered in ZooBank. The ZooBank LSIDs (Life Science Identifiers) can be resolved and the associated information viewed through any standard web browser by appending the LSID to the prefix @http://zoobank.org/@. The LSID for this publication is: urn: lsid:zoobank.org:pub: 7297C752-D78C-4A6D-B795-B870A099AFE5. The electronic edition of this work was published in a journal with an ISSN, and has been archived and is available from the following digital repositories: LOCKSS [author to insert any additional repositories].

Systematics
Family Cirratulidae Ryckholt, 1851. Diagnosis. Body elongated, cylindrical, region anterior and/or posterior segments sometimes expanded. Thoracic region often expanded, abdominal region narrow or moniliform, sometimes expanded in the pre-pygidial region. Prostomium narrow and conical or wide, without appendages, with or without eyes. Peristomium achaetous, with or without rings. One or more pairs of tentacles located on the segmental groove that separates the peristomium from the first setiger or on the thoracic setigers. Dorsal tentacles grooved arise as single pairs or as multiple groups of filaments and cylindrical branchiae. Branchiae long, inserted dorsally at the base of the notopodium, usually present up to the abdominal region. Pharynx ventral, unarmed. Parapodia reduced, bi-ramous, with rudimentary lobes. Many epidermal simple chaetae, such as capillaries, simple hooks, bidentate or multidentate. Pygidium with a simple lobe, sometimes with sub-anal disk, or terminal cirrus [2,32].
Genus Kirkegaardia Blake, 2016. Type species: Monticellina heterochaeta (Laubier 1961) [24] Type locality. Banyuls-sur-Mer (France). Diagnosis. Bitentaculate, with very distinct body regions. Prostomium short without annulations. Peristomium usually long and cylindrical, with annulations. Dorsal tentacles located in the final portion of the peristomium. Thoracic parapodia with inflated notopodia forming dorsal sulcus in the thoracic region or thoracic parapodia inflated, leaving the dorsal region as a crest. Parapodia of the non-inflated abdominal region laterally positioned. Posterior segments usually expanded or enlarged. Pre-pygidial abdominal segments wider than long and often expanded. Setae capillaries with distinct smooth (denticulate) edge, often basally expanded.
Remarks. The specimens from the Campos Basin are similar to the type specimens of Kirkegaardia hampsoni Blake, 2016 [22], described for Massachusetts (USA), by having an elongated, smooth peristomium, a dorsal peristomial crest that extends from the final portion prostomium to the first thoracic setiger, and a mid-dorsal channel or thoracic groove; the region closer to the prostomium that has one or two rings. Specimens from the Campos Basin are similar to K. hampsoni in having the dorsal tentacles inserted in the posterior portion of the peristomium and by having the first pair of branchiae inserted lateral to the dorsal tentacles on the peristomium, and with the second pair of branchiae arising from the first setiger. K. hampsoni from the Campos Basin also has a narrow ridge in the middle of the dorsal thoracic groove, and the medial abdominal segments are increasingly shorter and wider as in K. hampsoni. K. hampsoni specimens from the Campos Basin differ in having between 9-12 thoracic setigers, instead of 10-15 thoracic setigers as described by Blake [27]. The presence of a peristomial ridge K. hampsoni places the species in the Kirkegaardia dorsobranchialis-heterochaeta group as defined by Blake [22], which includes: K. annulosa, K. cristata, K. kladara and K.
hampsoni. The present work represents the record of K. hampsoni for the South Atlantic Ocean. K. hampsoni, was found between 19 to 121 m in the Campos Basin whereas Blake [27] records K. hampsoni from between 30 to 150 m. According to Blake [22] K. hampsoni was registered locally as Tharyx and/or Monticellina dorsobranchialis at various locations on the continental shelf of the US Atlantic, from the Gulf of Maine to the mid-Atlantic, the Campos Basin record points out that K. hampsoni is a species with extensive distribution, but more in-depth studies on the distribution of Kirkegaardia species including K. hampsoni are needed. The samples from the Campos Basin are not complete, and it is not possible to observe the prepygidial region and the pygidium. Diagnosis. Abdominal region with simple capillaries, gradually replaced by denticulated capillaries. Pre-pygidial abdominal region slightly expanded with 8-10 setigers, with long setae with curved tips and simple denticulated setae.
Remarks. Kirkegaardia blakei sp. nov. has the peristomial rings with 3-4 very well-marked and concentrated rings at the end of the peristomium. According to Blake [22], these rings are usually smooth, and often difficult to see in optical microscopy, sometimes requiring SEM for verification. Kirkegaardia blakei sp. nov. has noto and neurosetae denticulated capillaries in the abdominal region, and unusual long setae modified with a gently curved tip, without denticles or fibrils in the pre-pygidial one. The abdominal region of K. blakei sp. nov. is similar to K. hampsoni, however K. hampsoni has only denticulated setae. For all these characteristics, the species was considered new for science.
Etymology. This species is named in honor of Dr. James Blake for his important works that contributed to the knowledge of polychaetes, including the family Cirratulidae.

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Diagnosis. Thoracic parapodia elevated above dorsal surface producing a groove between notopodia. Two or three rings on anterior region of peristomium. Pre-pygidial region slightly expanded with pygidium formed by an enlarged ventral lobe.
Remarks. Kirkegaardia brisae sp. nov. is similar to K. cryptica (Blake, 1996) [2]. These species have a conical and wide prostomium, tentacles in the posterior portion of the peristomium, the first pair of branchiae postero-lateral to the tentacles and noto-and neurosetae denticulate. K. brisae sp. nov. differs from K. cryptica in that it has three rings with the first two short and narrow and the third longer than the two short ones instead of being smooth and without annulations as in K. cryptica. Kirkegaardia brisae sp. nov. is similar to K. annulosa (Hartman, 1965) [37] due to the location of peristomial rings right after the prostomium, but K. annulosa has a peristomial and thoracic crest, while K. brisae sp. nov. has no crest. K. brisae sp. nov. is also similar to K. baptisteae (Blake, 1991) [27] in that they both have an expanded pre-pygidial region, but the latter differs in having a pygidium formed by a narrow terminal lobe. In contrast, K. brisae sp. nov. has a terminal lobe expanded distally. For these characteristics, the species was considered as new to science.
Etymology. This species is named in honor of Mrs. Suzanne Marie Thérèse Bris in recognition of her encouragement to young scientists in the study of polychaetes.
Description. Holotype with 76 setigers, body 4.6 mm long, 0.12 mm wide in thoracic region, and 0.13 mm wide in abdominal region. All specimens incomplete. Prostomium short conical ( Fig 5A); Eyes absent. Peristomium elongate, with a single short posterior ring; with a prominent dorsal crest along most of length, merging with thoracic crest (Fig 5A). Dorsal tentacles on short peristomial ring (Fig 5A). First pair of postero-lateral branchiae to the tentacles; second pair of branchiae in setiger 1 dorsal to notosetae (Fig 5A), continuing segmentally to middle of abdominal region. Thoracic region narrowing after about 14-16 setigers, with a thoracic crest ending. After end of thoracic crest, thoracic region with a narrow groove, visible in light microscope (Fig 5A). Abdominal segments wider than long. Parapodia with poorly developed lobes. Thoracic parapodia with 5-6 capillary noto-and neurosetae per segment. Posterior abdominal parapodia with 4-5 denticulated notosetae ( Fig 5B) and six or seven denticulated neurosetae per segment (Fig 5C). Denticulated neurosetae appear from abdominal setigers 30 to 38. Abdominal neurosetae smaller than notosetae in first abdominal segments, noto-and neurosetae of same size in middle segments of abdominal region. Pre-pygidial segments and pygidium absent.

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Remarks. Kirkegaardia goytaca sp. nov. is similar to K. carinata Blake, 2016 [22] in that both have a narrow body, abdominal segments wider than long, thoracic crest, tentacles in the posterior portion of the peristomium, and first pair of postero-lateral branchiae to the tentacles between the peristomium and the first setiger. However, K. carinata presents the first pair of branchiae inserted in the groove that separates the peristomium from the first setiger, while K. goytaca sp. nov. has the first pair of branchiae inserted in the peristomial ring. In addition, K. goytaca sp. nov. has a peristomial crest, while K. carinata only thoracic crest. The presence of a peristomial crest throughout the peristomium brings K. goytaca sp. nov., K. jongo sp. nov. and K. papaveroi sp. nov. to a group of four species, Kirkegaardia dorsobranchialis-heterochaeta. Kirkegaardia goytaca sp. nov. differs from K. cristata in having only a single ring at the end of the peristomium, while K. cristata has three well-marked peristomial rings. Kirkegaardia goytaca sp. nov. differs from K. annulosa in having the thoracic region very narrow, while K. annulosa has a thoracic region expanded. Kirkegaardia goytaca sp. nov. also differs from K. kladara in having the first pair of branchiae inserted in the final portion of the peristomium, while in K. kladara the first pair of branchiae occurs from the first thoracic setiger. For all these characteristics, the species was considered as new to science.
Etymology. This name is in honor of the extinct local ethnic group uetaká, also known as Goytacá. These native people lived along lowlands from the northern Macaé River to Espírito Diagnosis. Peristomium large, with 3-4 rings, first pair of branchiae postero-lateral to the tentacles in setiger 1. Noto and neurosetae denticulate in abdominal region. Pre-pygidial abdominal region prominently expanded.
Remarks. Kirkegaardia helenae sp. nov. belongs to the Kirkegaardia baptisteae-tesselata group, due to their similar morphology, species in this group have elevated thoracic parapodia, and a mid-dorsal channel is not produced, although a dorsal crest sometimes develops. Kirkegaardia helenae sp. nov. is similar to K. zafirae sp. nov. and K. baptisteae in that it presents denticulated noto and neurosetae, although it differs from both species in that its first pair of branchiae appear in the first setigerous and not in the posterior region of the peristomium. Kirkegaardia helenae sp. nov. also differs from K. zafirae sp. nov. in that it does not have a ventral sulcus in the pre-pygidial region. The shape of the pre-pygidial region of K. helenae sp. nov. is similar to that of K. lueldredgei, but it has abdominal segments that are wider than long, unlike K. lueldredgei, which has abdominal segments that are longer than wide. These species also differ in the number of neurosetae in the posterior abdominal region, two or three setae in K. lueldredgei, and 7-10 in K. helenae sp. nov. The disposition of the tentacles and first pair of branchiae of K. helenae sp. nov. is similar to K. setosa (Dean & Blake, 2009) [38] but this species has only denticulate neurosetae and K. helenae sp. nov. has noto and neurosetae denticulate in its abdominal region. For these characteristics, the species was considered as new to science.
Etymology. This species is named in honor of Dr. Helena Passeri Lavrado, for her important contribution to Brazilian marine biology.

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Presence of a small segment, demarcating the separation of the pre-pygidial region from the other abdominal segments.
Description. Complete holotype with 58 setigers, 2.4 mm long, 0.2 mm wide in thoracic region, and 0.07 mm wide in abdominal region. Prostomium narrow, triangular (Fig 7A). Eyes absent. Peristomium with 2-3 rings and dorsal crest (Fig 7A). Dorsal tentacles on posterior margin of peristomium (Fig 7A). First pair of branchiae postero-lateral to the tentacles on the
Remarks. The presence of a peristomial crest brings K. jongo sp. nov. as well as K. papaveroi sp. nov. and K. goytaca sp. nov. to the group of four species considered to be from deep sea: K. annulosa, K. cristata, K. kladara and K. hampsoni. Among these species, K. hampsoni and K. jongo sp. nov. do not have a visible crest in the thoracic region. K. annulosa differs from K. jongo sp. nov. by having hooks in addition to modified setae, and pre-pygidial segments ventrally flattened culminating in a conical pygidial lobe. Kirkegaardia jongo sp. nov. has no hooks, and the pre-pygidial segments are fully expanded, culminating in a small rounded pygidial lobe. Kirkegaardia kladara differs from K. jongo sp. nov. by the presence of a thoracic crest and with the first pair of branchiae on setiger 1, whereas in K. jongo sp. nov. the first pair of branchiae are on the posterior margin of the peristomium. Kirkegaardia cristata, differs from K. jongo sp. nov. in having an extremely long prostomium and moniliform segments in the abdominal region while K. jongo sp. nov. has a triangular prostomium, and abdominal segments wider than long. K. cristata also has a thoracic ridge, and K. jongo sp. nov. does not have a thoracic crest. Kirkegaardia hampsoni differs from K. jongo sp. nov. in having a peristomium without rings, while K. jongo sp. nov. has two or three annulations in the peristomium, and by the number of abdominal setae per fascicle, 8-12 in K. hampsoni, and 4-6 in K. jongo sp. nov. For all these differences, the species was considered as new to science.
Etymology. This species is named after the quilombolan dance known as "jongo", as a tribute to the African legacy left in the southeastern Rio de Janeiro State, region that comprises a large part of the sampling points where Kirkegaardia jongo has been collected.
Description. All specimens incomplete, holotype with 43 setigers, 9.0 mm long, 0.12 mm wide in the thoracic region, and 0.10 mm wide in abdominal region. Prostomium long, conical (Fig 8A). Eyes absent. Peristomium with one ring, without dorsal crest (Fig 8A). Dorsal tentacles on posterior margin of peristomium (Fig 8A). First pair of branchiae postero-lateral to the tentacles in setiger 1, second pair of branchiae in setiger 2; branchiae present only in thoracic region. Thoracic region narrow, with 7-10 setigers, without dorsal groove (Fig 8A). Abdominal segments longer than wide (Fig 8B and 8C); first abdominal segments shorter than median abdominal segments (Fig 8B). Parapodia with poorly developed lobes. Thoracic parapodia with four or five capillary noto-and neurosetae per segment. Posterior abdominal parapodia with four or five capillary notosetae simple with numerous thin fibrils (Fig 8D), and 4-8 denticulate neurosetae per fascicle (Fig 8E). Denticulate neurosetae from abdominal setigers 1968) [25] in only having denticulate neurosetae. Kirkegaardia baptisteae has a nuchal organ lateral to the prostomium and first pair of branchiae anterior to the tentacles. In contrast, the first pair of branchiae from K. medusa sp. nov. is postero-lateral to the tentacles. They also differ in that, K. baptisteae has abdominal segments that are wider than long, while K. medusa sp. nov. has abdominal segments that are longer than wide, up to the median abdominal region. Kirkegaardia dutchae differs from K. medusa sp. nov. by the presence of a peristomial crest and the lateral position of the 1st pair of branchiae to the tentacles. Kirkegaardia neotesselata differs has an elevated peristomial crest that merges with the thoracic crest, while K. medusa sp. nov. has no crest. K. serratisseta has a thoracic region with about 40 segments, while K. medusa sp. nov. only has 7 to 10 abdominal segments. For all these characteristics, the species was considered as new to science.
Etymology. This species name refers to the Greek myth of Medusa. Medusa is often seen as evil but was convicted of a crime committed by the God Poseidon, who is more powerful and less vulnerable. This species name represents the fight against misogyny, which is suitable for a study performed by female researchers.
Remarks. Kirkegaardia nupem sp. nov. is similar to K. carrikeri (Dean & Blake, 2009) [38] by the conical shape of the prostomium, presence of the peristomial crest, positioning of the dorsal tentacles in the posterior portion of the peristomium, by the first pair of branchiae from setiger 1, and by the presence of a shallow ventral groove in the pre-pygidial region. Kirkegaardia nupem sp. nov. differs from K. carrikeri in that it does not have annulations in the peristomium. The number of noto-and neurosetae in the abdominal region differs between species; K. carrikeri has from 2 to 4 neurosetae in the posterior abdominal region, whereas K. nupem sp. nov. has from 14 to 16 neurosetae in the posterior abdominal segments. Kirkegaardia carrikeri has only denticulated neurosetae throughout the abdominal region, while K. nupem sp. nov. has denticulated noto-and neurosetae in the abdominal region. Pre-pygidial segments of K. nupem sp. nov. resembles K. cryptica (Blake, 1996) [2] due to the presence of ventral

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groove, but K. cryptica has the first pair of branchiae present postero-lateral to the tentacles on the peristomium, while K. nupem sp. nov. has the first pair of branchiae on setiger 1. For all these characteristics, the species was considered as new to science.
Etymology. The epithet is a reference to the Institute of Biodiversity and Sustainability (NUPEM / UFRJ) acronym, where the beginning of this taxonomic work was developed. Institution recognized for its quality in undergraduate and graduate education, and in the production of scientific knowledge.
Description. Holotype with 63 setigers, 2.4 mm long, thoracic region 0.09 mm wide, 0.1 mm high, abdominal region 0.06 mm wide. Prostomium short, triangular, bluntly rounded on anterior margin (Fig 10A). Eyes absent. Peristomium elongated, with one lateral groove producing two rings, peristomial dorsal crest present (Fig 10A). Dorsal tentacles on posterior margin of peristomium. First pair of branchiae posterolateral to dorsal tentacles at boundary with setiger 1 (Fig 10A), branchiae rarely present in abdominal segments. Thoracic setigers about as wide as long for first nine or ten setigers, with parapodia shifted dorsally and elevated above mid-dorsal surface, forming distinct mid-dorsal groove on thoracic segments (Fig 11A), thoracic crest present (Figs 10A and 11A). Abdominal segments becoming longer and narrower and with parapodia located laterally (Fig 11B). Thoracic parapodia with smooth capillaries numbering about 4-6 in notopodia and neuropodia. Anterior abdominal segments with smooth capillaries in noto-and neuropodia gradually replaced by denticulate capillaries, fascicles reduced to 3-5 setae in abdominal setigers. Noto-and neurosetae heavily serrated or denticulated (Fig 10B and 10C). Neurosetae with denticles and serrated edge of fibrils along shaft from about 20 abdominal setigers (Fig 10C). Pre-pygidial region expanded with dorsal groove (Fig 10D). Pygidium formed by a simple ventral lobe (Fig 10D).
Remarks. The presence of a peristomial crest brings Kirkegaardia papaveroi sp. nov. as well as Kirkegaardia jongo sp. nov., and Kirkegaardia goytaca sp. nov. into the group of species termed Kirkegaardia dorsobranchialis-heterochaeta by Blake [27] which includes the species: K. annulosa, K. cristata K. kladara and K. hampsoni. K. annulosa differs from K. papaveroi sp. nov. by having unusual spike like serrated neurosetae in addition to denticulated capillaries. Among these species, K. hampsoni and K. jongo sp. nov. differs from K. papaveroi sp. nov. by lacking the thoracic dorsal crest. Kirkegaardia papaveroi sp. nov. it differs from K. cristata in that it does not have a prominent ventral sulcus in the first abdominal setigers, in that it has 0-2 distinct rings in the peristomium instead of three. Kirkegaardia papaveroi sp. nov. differs from K. kladara by the branchiae arising lateral to the dorsal tentacles on the peristomium instead of setiger 1. K. goytaca sp. nov. differs from K. papaveroi sp. nov. by having the thoracic region extremely narrow. For all these differences, K. papaveroi was considered as new to science.
Etymology. This species is named in honor of Dr. Nelson Papavero for his important contribution to zoology in Brazil.

Discussion
According to Blake [22], the genus Kirkegaardia consists of at least three distinct groups of species and several outlier species for which relationships have yet to be defined. The three main groups are Kirkegaardia dorsobranchialis-heterochaeta (16 species); Kirkegaardia baptisteaetesselata (23 species); and Kirkegaardia luticastella group (4 species), in addition to outlier species, with characters of other genera or species not fully characterized (5 species). The species described here belong to the groups of Kirkegaardia dorsobranchialis-heterochaeta and Kirkegaardia baptisteae-tesselata.
The species of the group Kirkegaardia dorsobranchialis-heterochaeta have thoracic parapodia elevated producing a channel between the notopodia, elongate pre-setigerous area that is either entirely smooth or modified with a dorsal ridge and/or rings and denticulated capillaries in both the noto-and neuropodia [22]. This group may be further divided into four subgroups based on peristomial morphology: (1) Peristomium smooth, without dorsal ridge; (2) Peristomium elongate, smooth with a peristomial ridge limited to the anterior half; (3) Peristomium with a dorsal ridge along its entire length; this study adds to this subgroup the species K. papaveroi sp. nov., K. goytaca sp. nov. and K. jongo sp. nov; (4) Peristomium unusually long, lacking a dorsal ridge and with 5-6 rings. Although K. blakei sp. nov. and K. brisae sp. nov. exhibit 3-4 rings only, we suggest that these species are more comparable to the ones of the latter subgroup 4, but the number of peristomial rings is expanded to 3-6.
The group of Kirkegaardia baptisteae-tesselata includes species that do not have thoracic parapodia elevated, and a mid-dorsal channel is not produced, although a dorsal ridge is sometimes developed. In the pre-setigerous area, dorsal ridges and rings are present or absent. Most species in this group have denticulations on the neurosetae but not on the notosetae. Those characters are seen in K. nupem sp. nov., K. helenae sp. nov., K. medusa sp. nov., and K. zafirae sp. nov.. Despite that we categorize the species described herein in these groups, it is important to emphasize the need for in-depth studies on the phylogeny of Cirratulidae and Kirkegaardia, so that these groups and their synapomorphies can be well defined.
In this study, the use of the methyl green stain has not shown to be a decisive tool for the identification of morphological characters, as none of the described species showed a wellmarked colour pattern among the specimens (S1 Fig). Several studies have pointed to methyl green staining as a very useful tool for taxonomic identification of different families of polychaetes, such as Capitellidae, Cirratulidae, Paraonidae, Sabellidae and Spionidae [39][40][41]. However, the use of this technique for taxonomy requires standard methodological procedures, for example, the time of exposure to MG, the concentration of the MG solution, and washing times to remove excess MG, so we can be sure that the patterns found in each species or group do not differ due to differences in the methodologies applied for staining.
The present study firstly described ten species of Kirkegaardia from Brazil, expanding the number of records for the genus in the coast and deep sea of South America. With the nine new species described in this article, the number of Kirkegaardia species has increased from 41 to 50, becoming now one of the most speciose genera of Cirratulidae. In South America, Kirkegaardia morae (Elias, Rivero & Orensanz, 2017) [28] was the only registered species before the new species and new records presented here. Additionally, we report a new occurrence for the South Atlantic Ocean (Kirkegaardia hampsoni).