Revision of Chone Krøyer, 1856 (Polychaeta: Sabellidae) from the eastern central Atlantic and Mediterranean Sea with descriptions of two new species

Chone Krøyer, 1856, is a genus of sabellid polychaetes frequently found in soft-bottom marine sediments. Banse (1972) commented on the definitional problems with the genus, noting that Krøyer ́s (1856) original intent in erecting the genus was to indicate the distinct nature of the palmate membrane. Fitzhugh (1989) stated that some specimens, identified as Chone infundibuliformis, have dorsal lips with dorsal radiolar appendages (elongate and distally tapered), whereas other specimens lack them (low and broadly rounded); he named them as Chone1 and Chone2, respectively. In his cladistic SCIENTIA MARINA 71(2) June 2007, 315-338, Barcelona (Spain) ISSN: 0214-8358


INTRODUCTION
Chone Krøyer, 1856, is a genus of sabellid polychaetes frequently found in soft-bottom marine sediments.Banse (1972) commented on the definitional problems with the genus, noting that Krøyer´s (1856) original intent in erecting the genus was to indicate the distinct nature of the palmate membrane.Fitzhugh (1989) stated that some specimens, identified as Chone infundibuliformis, have dorsal lips with dorsal radiolar appendages (elongate and distally tapered), whereas other specimens lack them (low and broadly rounded); he named them as Chone1 and Chone2, respectively.In his cladistic d) long (L), if the mucro is as long (or twice as long) as the paleal width (Fig. 2B); and e) extra long (XL) if it is three or more times longer than the paleal width (Fig. 2C).
Unless otherwise stated, every description is based on the available type material and any variation found in additional types is included in parentheses.In all species of Chone, the biannulate condition in thoracic segments is given by the presence of distinct intra-notopodial and intra-neuropodial grooves, less differentiated than inter-segmental grooves; when treated with methyl green all these grooves, the faecal groove and the noto-and neuropodial lips or lobes are not coloured.This pattern is omitted in descriptions.
Abdomen: Abdominal segments: 43 (27-44).Anterior segments: two transverse rows of elongate, narrowly hooded chaetae, upper row chaetae half as long as lower row ones; uncini with the main fang surmounted by four rows of teeth equal in size, occupying less than half of the main fang length, main fang not extending beyond breast (Fig. 3N).Posterior segments: very elongate, narrowly hooded chaetae, 25% longer than those of anterior segments; modified uncini with the main fang surmounted by 6-7 regular vertical rows of teeth equal in size, occupying three quarters of the main fang length, main fang not extending beyond breast, breast rectangular (Fig. 3O).Pygidium with rounded posterior margin.
Methyl green staining: Epidermis completely glandular stains uniformly in thorax and abdomen, dorsal, ventral and laterally (Figs 3A-C).The longitudinal grooves on the collar segment have dark rounded glands along their axis.The dorsal lips stain dark blue; the methyl green remains about 48 hours after staining.Pigmentation in the posterior end of the body is lost quickly.
Remarks: In this study, the designation of the neotype of Chone acustica (Claparède, 1870) (2000), since Claparède's collection is missing, making the recognition of his described taxa controversial.Chone acustica was described (as Dialychone) as lacking a palmate membrane; however, the recognition of the palmate membrane may be difficult in some instances.Thus, in specimens belonging to this species there may be a very low membrane connecting the radioles, just as a short extension from the branchial lobes or up to for a quarter of the branchial crown length as in Fitzhugh (1989), Knight-Jones et al. (1991) and Giangrande (1992) recorded in topotype materials.
For some specimens examined in this study, the palmate membrane extends along one half of the branchial crown length.The membrane could be easily broken due to the manipulation since, particularly in C. acustica, the membrane is extremely fragile and the flanges are very narrow.Hence, the presence and extension of the structure could be difficult to discern.
In old preserved materials the radioles are creamcolored, while in recent material they have red and white alternating bands; the red bands are cuticular, the white granulations are located inside each cartilaginous cell.This pattern also occurs in C. veleronis and C. perkinsi.Claparède described two otoliths in the peristomium; however, they are visible only when the collar is relaxed.
Chone acustica is unique among Mediterranean species by having a rudimentary rounded ventral collar shield, not easily discernible; short mucro and glandular ridge on chaetiger 2 broad dorsally (Table 1).Among the species of Chone two shapes of dorsal lips can be recognised: broadly rounded (as long as wide), or triangular (longer than wide, erect and elongated).The type species, C. infundibuliformis, has dorsal lips broadly rounded, as long as wide, without mid-rib; basally vascularised by a plexus of few, small blood vessels, but without branchial skeleton extensions (Tovar-Hernández and Sosa-Rodríguez, 2006); such as is the case in C. aurantiaca, C. duneri, C. gracilis, C. letterstedti, C. magna, C. mollis and C. picta.In comparison, the dorsal lips of C. acustica are pear-shaped (Figs 3C-D), with a small and rounded basal bulb, and very long neck (ten times longer than the bulb), with a groove running along their length (not as mid-rib).Internally, dorsal lips are basally vascularised by a plexus of several large blood vessels, and then one vessel runs along the neck (Fig. 3G), but there is no extension of the branchial skeleton.Other species with this internal features and elongate dorsal lips are: C. albocincta, C. americana, C. arenicola, C. bimaculata, C. collaris, C. diazi, C. ecaudata, C. farringtonae, C. johnstonae, C. longiseta, C. perkinsi, C. uebelackerae, C. usticensis, C. veleronis, and an undescribed species from the Pacific coast of Panama.
In the type species, Chone infundibuliformis, the anterior and posterior abdominal uncini are similar in shape (Tovar-Hernández and Sosa-Rodríguez, 2006).However, C. acustica has modified, posterior abdominal uncini (as rasp-shaped plates or Amphicorina-  type).This kind of modified uncini has a main fang surmounted by several regular, vertical rows of small equal in size teeth that occupy at least three quarters of the main fang length, and a poorly developed rectangular or sub-rectangular breast, instead of a few rows of unequal in size teeth occupying less than half of the main fang length, and a well developed breast, as anterior segment uncini (Tovar-Hernández and Sosa-Rodríguez, 2006).
Distribution and habitat: Widely distributed in the Mediterranean Sea in shallow, sandy-bottoms.Langerhans, 1880 (Fig. 4)
Branchial lobes and branchial crown: Insertion of the branchial lobes exposed beyond collar dorsally.Branchial crown length: 4 mm (2.5-3).Radioles: 6 pairs (5-6).Radioles with pinnules of equal length, each radiole has 3-5 dark spots on the flanges surrounding the cartilaginous skeleton of the radiolar axis (Figs 4A, I).Radiolar tips long.Palmate membrane extends up to three quarters of the branchial crown length.Lateral flanges (fl) broad (Fig. 4I).Dorsal lips triangular, erect, three times longer than wide, without mid-rib.Dorsal pinnular appendages: one short pair, united by a palmate membrane.Ventral lips rounded, about three quarters of the dorsal lips length.Ventral radiolar appendages: two pairs (1-2), as long as one quarter of the branchial crown length.
Abdomen: Abdominal segments: 33 (28-43).Anterior segments: two transverse rows of elongate, narrowly hooded chaetae, upper row chaetae half as long as lower row ones; uncini with the main fang surmounted by 4-5 regular rows of equal in size teeth in frontal view, occupying one half of the main fang length, main fang not extending beyond breast, breast rectangular (Figs 4J-K).Posterior segments: 1-2 very elongate, narrowly hooded chaetae, 25% longer than in anterior segments (Fig. 4E); modified uncini with the main fang surmounted by 6-7 regular vertical rows of equal in size teeth, occupying three quarters of the main fang length, main fang not extending beyond breast, breast rectangular (Figs 4L-M).Pygidium with triangular posterior margin, small cirrus, not easily discernible (Fig. 4A).
Gametes: Not seen in syntype, non-type materials immature.
Methyl green staining: Anterior half of the collar not coloured (Figs 4B-C).Ventrally, the posterior half of collar stains uniformly (Fig. 4B); dorso-laterally less coloured with small dark spots (Fig. 4D).The anterior margin of the ventral collar shield not coloured (Fig. 4B).Thorax and anterior abdomen with epidermis completely glandular, stains uniformly, dorsal and ventrally.Posterior abdomen not coloured, only spread, dark spots are present.Pygidium darker, after being returned to ethanol for some days, it remains stained.
Remarks: Langerhans (1880: 115) noted the average measurements of C. arenicola indicating that he had originally examined more specimens than two; however, only one syntype was deposited in the Museum of Natural History in Vienna.The syntype is partially dried, broken, lacks a branchial crown and is mounted in a micro slide.However, the original description and drawings of C. arenicola permit the unequivocal identification of specimens well distributed in the Mediterranean Sea and eastern central Atlantic.
The radioles of C. arenicola have irregular lateral purple spots in the radiolar axis skeleton, on flanges (not in the rachis), and colour extends into the pinnules.In other species, such as C. perkinsi and C. veleronis, the radioles have coloured bands along the radiolar axis, but not in the flanges, and as in C. arenicola, the colour extends into the skeletal cells of the pinnules.However, in these species the radiolar colour pattern is observed only in fresh or recently preserved specimens.
Chone arenicola, C. gambiae n. sp. and C. dunerificta n. sp.have the insertion of the branchial lobes exposed beyond collar; however, the anterior peristomial ring lobe is triangular, not exposed beyond collar in C. arenicola (bilobed and exposed in C. gambiae n. sp., and in C. dunerificta n. sp.) (Table 1).The anterior peristomial ring is exposed in all specimens examined, but a small variation in the degree of the exposition of the peristomium due to the fixation process is observed.
Branchial lobes and branchial crown: Insertion of the branchial lobes not exposed beyond collar.Branchial crown length: 1.75 mm (0.8-1.5).Radioles: 5 pairs (4-5).Radioles with pinnules of similar length.Radiolar tips short (Fig. 5D).Palmate membrane extends up to one half of the branchial crown length.Lateral flanges broad (Fig. 5D).Dorsal lips triangular, erect, two times longer than wide, with a groove along dorsal margin.Dorsal pinnular appendages: one short pair.Ventral lips about one quarter the length of dorsal lips, broadly, distally rounded.Ventral radiolar appendages (vra): 4 pairs, longest appendages about as long as the branchial crown, the shortest about the collar length (Fig. 5C).
Gametes: One syntype male, spermatozoa with rectangular acromose and two rounded small mitochondria; one syntype female with small eggs in a little incision between thorax and abdomen; sex for other syntypes undeterminable.
Methyl green staining: Ventrally, the epidermis is completely glandular and stains uniformly in thorax and abdomen (Figs 5E-F).Dorsally and laterally, no colour is retained, except in the second chaetiger.
Remarks: Four original syntypes of Chone collaris (Langerhans NHMW 1966, 2287) were examined.All specimens have the anterior margin of the collar crenulated, which agrees with Langerhans's original collar illustration (Fig. 29b).
Chone collaris is unique among Chone species in having the anterior margin of the collar crenulated; however, this feature is homoplastic, being found in many species of Amphicorina (Rouse, 1994).Knight-Jones et al. (1991)  Distribution and habitat: eastern central Atlantic Ocean and Mediterranean Sea, typical of photophilic algae of shallow waters, and it can occasionally be found in sandy bottoms.Malmgren, 1867 (Fig. 6)  6A-C).Branchial crown length: 7-8 mm.Radioles: 10-12 pairs.Radioles with median pinnules three times longer than proximal ones.Radiolar tips extra long (Fig. 6L).The palmate membrane extends about three quarters of the branchial crown length.Lateral flanges broad.Dorsal lips broadly rounded in frontal view, as long as wide, without mid-rib, resemble the ventral lips, longer than wide in dorsolateral view.Dorsal pinnular appendages: one pair about one quarter of the branchial crown length, united by a palmate membrane.Ventral lips rounded, as long as wide, about one quarter of the dorsal lips length.Ventral radiolar appendages: 3 pairs about one half of the branchial crown length.
Thorax: Chaetiger 1: two groups of eight elongate, narrowly hooded chaetae.Chaetigers 2 to 8: Notopodia: two rows of elongate, narrowly hooded chaetae; one anterior row with bayonet chaetae, two posterior rows with symmetrical, paleate chaetae with medium mucro (Fig. 6J).Pre-and post-chaetal lobes well developed (Fig. 6B).Neuropodia: two irregular rows of acicular uncini, heads in the same direction, the oldest upper parts of the torus have only one row (one quarter of the tori length), main fang surmounted by four rows of teeth, occupying one half the main fang length (Fig. 6K); second tooth enlarged, located in the midline.Narrow glandular ridge on chaetiger 2. Thoracic segments biannulate.
Remarks: Banse (1972: 466) synonymised C. bimaculata with C. duneri because the main reason for describing C. bimaculata was the presence of a glandular ridge on chaetiger 2, but this structure is a shared characteristic of Chone, Euchone and Jasmineira, group called "Chonea" after phylogenetic analyses by Cochrane (2003).Chone bimaculata is recognised as a valid species on the basis that it has unique features and differs from C. duneri.Both species have the insertion of the branchial lobes and the bilobed anterior peristomial ring lobe exposed beyond collar, and radiolar tips extra long (comprising approximately a third of the length of radioles).Chone bimaculata differs from C. duneri in that lateral flanges are narrow (broad in C. duneri); the antero-dorsal margin of posterior peristomial ring collar is incised (not incised in C. duneri); the entire length of mid-dorsal collar margins forms two prominent lobes, covering a narrow gap (broad gap in C. duneri); the anterior peristomial ring collar is partially exposed beyond collar dorsally (completely exposed in C. duneri); the ventral collar shield is trapezoid-shaped (horseshoe-shaped in C. duneri); modified posterior abdominal uncini (anterior and posterior abdominal uncini similar in C. duneri), and pygidium with rounded posterior margin (triangular in C. duneri).Distribution: Chone duneri was described from Spitzbergen (Norway) but has been regarded as having a very wide distribution: Madeira (Langerhans, 1880), North Sea (Hofsommer, 1913), Ireland (Southern, 1914), Alaska (Pettibone, 1954), Washington (Banse, 1972), Florida, Gulf of Mexico, and the Caribbean (Perkins andSavage, 1975), Colombia (Rodríguez-Gómez, 1988), Mexican Caribbean (Jiménez-Cueto and Salazar-Vallejo, 1991), Italian coasts (Giangrande, 1992), and Pechora Sea (Dahle et al. 1998, Cochrane, 2000); however, most of the records contain discrepancies in the diagnostic characters observed (Sabine Cochrane pers.com.).
According to Cochrane (2000), only the materials from the Pechora Sea (in the southeastern, and northern parts of the Barents Sea) agree with the original description, and with the redescription by Hofsommer (1913) (Jutland).The present study shows that the distribution of this species is restricted to the Arctic Ocean.Thus, the records from the Mediterranean Sea of Giangrande (1992) A., August 1995 (1).
Thorax: Chaetiger 1: two groups of elongate, narrowly hooded chaetae.Chaetigers 2 to 8: Notopodia: superior group with two irregular rows of elongate narrowly hooded chaetae; inferior group with one anterior row of bayonet chaetae; two posterior rows with paleate chaetae with medium-sized mucro (Fig. 7H).Neuropodia: acicular uncini distributed as a regular row, main fang surmounted by four rows of teeth equal in size, occupying less than half of the main fang length (Fig. 7I).Glandular ridge on chaetiger 2 very narrow (Fig. 7A).Thoracic segments biannulate.
Abdomen: Abdominal segments: 29 (23-28).Anterior segments: two transverse rows of elongate, narrowly hooded chaetae, upper row chaetae half as long as lower row ones; uncini with the main fang surmounted by four rows of teeth equal in size, occupying less than half of the main fang length, main fang not extending beyond breast (Figs 7J-K).Posterior segments: very long, narrowly hooded chaetae, 25% longer than those of anterior segments; modified uncini with the main fang surmounted by 6-7 regular vertical rows of equal in size teeth, occupying three quarters of the main fang length, main fang not extending beyond breast, breast rectangular (Figs 7L-M).Pygidium with a triangular posterior margin (Figs 7A, N).Methyl green staining pattern: Thorax and abdomen stains uniformly, dorsal and ventrally (Figs 7A-C, E).Collar segment darker laterally (Figs 7B-C, E), the ventral collar shield and the anterior end of collar unstained.Abdominal posterior region with dark glandular spots.
Etymology: The specific name refers to the similarity between this species and Chone duneri.Derived from the Latin ficta, meaning false.Southern, 1914 (Fig. 8)

Description
Colour, body shape and size: Body partially dehydrated, covered by sediment grains.Body length: 7 mm, width: 0.5 mm.
Branchial lobes and branchial crown: Insertion of the branchial lobes not exposed beyond collar.Branchial crown length: 3.5 mm.Radioles: 8 pairs.Radioles with all pinnules long.Radiolar tips medium to long.Palmate membrane extends about three quarters of the branchial crown length.Lateral flanges broad.Dorsal lips broad at the base elongate towards the tip.Ventral lips rounded, small, one quarter of the dorsal lips length.Ventral radiolar appendages: 6 pairs.
Peristomium: Anterior peristomial ring lobe exposed beyond collar, distally bilobed.Posterior peristomial ring collar: antero-dorsal, ventral and lateral margins entire, ventral margin slightly higher than dorsal; entire length of mid-dorsal collar margins forms a narrow gap.Ventral collar shield swollen, trapezoidal-shaped, two times wider than long.Ratio of posterior peristomial ring collar length vs. chaetiger 2 length, in lateral view: 1:1.
Thorax: Chaetiger 1: two groups of elongate, narrowly hooded chaetae.Chaetigers 2 to 8: Notopodia: superior group with two irregular rows of elongate narrowly hooded chaetae; inferior group SCI.MAR., 71( 2 with one anterior row of bayonet chaetae; two posterior rows with paleate chaetae with short mucro (Fig. 8B).Neuropodia: acicular uncini distributed as a regular row, main fang surmounted by four rows of teeth, second tooth enlarged, located offset midline, dentition occupying less than three quarters of the main fang length.Glandular ridge on chaetiger 2 narrow.Thoracic segments biannulate.Pre-and post-chaetal lobes well developed.
Abdomen: Abdominal segments: 18. Anterior segments: two transverse rows of elongate, narrowly hooded chaetae, upper row chaetae half as long as lower row ones; uncini with the main fang surmounted by four rows of teeth, second tooth enlarged, dentition occupying less than half of the main fang length, main fang not extending beyond breast.Posterior segments: very long, narrowly hooded chaetae; modified uncini with the main fang surmounted by 6-7 regular vertical rows of teeth equal in size, occupying three quarters of the main fang length, main fang not extending beyond breast, breast rectangular.Pygidium with triangular posterior margin, pygidial cirrus broken.
Methyl green staining pattern: The epidermis is completely glandular, stains uniformly in thorax and abdomen, dorsal, ventral and laterally (Figs 8A, C).
Remarks: Until recently, Chone filicaudata has been the only widely-known Chone member possessing a pygidial cirrus, such that findings of any Chone specimen with pygidial cirrus were inevitably recorded as C. filicaudata (Cochrane, 2000).However, there are more species sharing this feature.Thus, Chone filicaudata has been highly recorded from the Mediterranean Sea (Bellan, 1964;Harmelin, 1969;Amoureux, 1976;Drago et al. 1978;Farina et al. 1985;Giangrande, 1992).However, none of the authors illustrated their specimens, or described them in detail, except for the last one, and her records for the Mediterranean Sea do not correspond with the type material of C. filicaudata: her specimens have the anterior peristomial ring lobe entire, triangular (bilobed in C. filicaudata); radiolar tips medium-length (short in C. filicaudata); radiolar flanges broad (narrow in C. filicaudata); the dorsal methyl green staining pattern is less coloured than ventral (stained uniformly dorsal and ventrally in C. filicaudata).Southern (1914) illustrated the paleate chaetae in two different views (Fig. 32F), the first one is a narrower, bilaterally swollen form, the second one shows a well developed palea, but this relative shape depends on the angle in which chaetae are seen.The examination of type material confirms that C. filicaudata has well-developed, paleate chaeta.
Distribution: North Atlantic Ocean.
Abdomen: Abdominal segments: 42.Narrow, glandular ridge on segment 9 (gr9) (Figs 9A, D).Anterior segments: two transverse rows of elongate, narrowly hooded chaetae, upper row chaetae half as long as lower row ones; uncini with the main fang surmounted by four rows of teeth equal in size, occupying less than half of the main fang length, main fang not extending beyond breast (Fig. 9F).Posterior segments: very long, narrowly hooded chaetae, 25% longer than those of anterior segments; modified uncini with the main fang surmounted by 6-7 regular vertical rows of equal in size teeth, occupying three quarters of the main fang length, main fang not extending beyond breast, breast rectangular (Fig. 9G).Pygidium with triangular posterior margin and short cirrus (Fig. 9B).
Methyl green staining pattern: After staining the dorsal epidermis have large, rounded, white spots on thoracic segments (acidophil glands, ag).The collar segment has lateral dark spots dorsally; ventrally it stains only in the basal half.The thoracic and abdominal segments stains as rectangles, only the margins are coloured, and white bands are visible (Figs 9A,D).
Etymology: This species is named in honour of Dr. Maria Cristina Gambi (Zoological Station of Naples, Italy), who collected the materials and kindly sent them to us for their study.
Remarks: Chone gambiae n. sp. is unique in having large acidophil glands on the epidermis, its glandular ridge on chaetiger 2 is broad laterally, and a glandular ridge is present on chaetiger 9.The presence of the glandular ridge on chaetiger 2 is one of the diagnostic characters for "Chonea" (Chone, Euchone and Jasmineira) according to Cochrane (2003); the presence of glandular ridges on abdominal segments has only been recorded in C. veleronis, and this property are also shared with some small species of Euchone (Banse, 1970) Giangrande, 1992 (Fig. 10) Additions to the description Colour, body shape and size: Trunk cylindrical, posterior abdomen depressed dorso-ventrally.Body length: 6-8 mm, width: 0.4 mm.Tubes unknown.
Methyl green staining pattern: The basal half of the collar ventral stains uniformly, the distal half is not coloured (Figs 10A, C).Ventrally, body stains uniformly (Fig. 10C).Dorsally segments are slightly coloured (Fig. 10D).The posterior abdomen is less coulored than the body anterior end (Fig. 10A).Laterally, there is no colour (Fig. 10A).
Distribution and habitat: Mediterranean Sea, on muddy sand bottoms with algal detritus.Giangrande, Licciano and Castriota, 2006 (Fig. 11) Chone usticensis Giangrande et al. 2006: 53-57  Methyl green staining pattern: The basal half of the collar and the basal half of the ventral collar shield stain uniformly; the distal half is not coloured (Fig. 11A).Dorsally, the collar segment has two dark spots in both corners, with dark glandular spots (Fig. 11B).Thoracic and abdominal segments stain uniformly (Fig. 11B).The pigment along the posterior end of the body is quickly lost.

Chone usticensis
Remarks: Chone usticensis, C. acustica and C. longiseta have extra long radiolar tips (Table 1).Chone acustica and C. usticensis have narrow radiolar flanges and the anterior peristomial ring lobe is triangular, not exposed beyond collar.For contrast, C. longiseta have broad flanges and anterior periostomial ring lobe bilobed, exposed beyond collar.The dorsal lips in C. acustica are extra long, 10 times longer than wide (three times longer than wide in C. longiseta).
Distribution and habitat: Mediterranean Sea, on mixed soft bottom with rhodoliths presents (Giangrande et al. 2006).

DISCUSSION
The present redescription of C. acustica allows us to consider the species as having the palmate membrane.This species was originally described as Dialychone due to the absence of palmate membrane by Claparède (1870), confirmed by Iroso (1921).Later, Knight-Jones et al. (1991) and Giangrande (1992) placed the taxon within Chone by observing a very low palmate membrane extending for about a quarter of the branchial crown length.Chone acustica was the first species in which the modified, posterior abdominal uncini (as rasp-shaped plates or Amphicorina-type) were found; however, although Claparède (1870), Iroso (1921) and LoBianco (1893) referred to the presence of Amphicorina type uncini in the abdomen, none of them mentioned the presence of inter-segmental variation of uncinal type.Considering also the structure of dorsal lips contrasting with the rounded one found in the type species C. the uncini are similar along the abdomen, and the dorsal lips are broadly rounded, vascularised by a plexus of few and small blood vessels, unlike those in C. acustica, C. arenicola, C. collaris, C. longiseta and C. usticensis (among others).These features could be enough to split the genus, but they must be thoroughly reviewed in all these species and taken in consideration in further studies to evaluate the phylogeny of Chone.However, based on the assessment of morphological characters, we recognise a subgroup of Chone which all are recorded from the Mediterranean Sea and the eastern central Atlantic.
The redescription of Mediterranean taxa in the present paper indicated that C. arenicola is characterised by: 1) large, lateral, irregular purple spots on the radiolar axis skeleton, on flanges (not in the rachis), 2) branchial lobes exposed beyond collar, 3) anterior peristomial ring lobe exposed beyond collar, and 4) posterior abdominal uncini modified.Chone collaris is unique among Chone species in having the margin of the collar crenulated.Chone longiseta, contrasting the original description, has the presence of paleate chaetae with short mucro; anterior peristomial ring lobe exposed beyond collar, bilobed; and modified, posterior abdominal uncini.The unique distinguishing features for the new species here reported, Chone gambiae n. sp., described from the Gulf of Naples, is the glandular ridge on chaetiger 2 broad laterally, and a narrow glandular ridge on chaetiger 9; lastly, Chone dunerificta n. sp., described from the Gulf of Salerno, is unique in having: long radiolar tips; anterior peristomial ring lobe exposed beyond collar, bilobed; branchial lobes exposed beyond collar and modified, posterior abdominal uncini.This last taxon is probably the most widely distributed within the Mediterranean Sea but is wrongly identified as C. duneri.Chone duneri is restricted to the Arctic Ocean and the records of C. filicaudata from the Mediterranean Sea are erroneous, as the species is distributed in the North Sea.

TABLE 1 .
-Selected features of some Chone species distributed in the Eastern Central Atlantic and Mediterranean Sea. e.
recorded C. collaris from Turkey's Aegean coast; they compared it with material from the North Sea, in which the collar is crenulated too, but the radioles have reduced flanges and very long filamentous tips.The ratio of posterior peristomial ring collar length vs. chaetiger 2 length, in lateral view is 1:1 in C. collaris in comparison with C. acustica, C. arenicola, C. longiseta, C. usticensis, C. gambiae n. sp., and C. dunerificta n. sp., in which this ratio is 1.5:1 (Table 1).Chone longiseta (described from Taranto), and C. duneri (described from Norway) resemble C. collaris in that the anterior peristomial ring lobe is bilobed and exposed beyond collar; however, C. collaris has peristomial eyes (absent in C. longiseta and C. duneri), and short radiolar tips (extra long in C. longiseta and C. duneri).
correspond to a new species herein described as Chone dunerificta n. sp.; the record for the Mexican Caribbean (Jiménez-Cueto and Salazar-Vallejo, 1991) corresponds to C. uebelackerae; the specimens from Colombia ofRodríguez-Gómez (1988)were not available, but the drawings and descriptions do not correspond with C. duneri.
: Chone dunerificta n. sp. was identified in previous studies from the Mediterranean coasts as C. duneri based on the methyl green staining pattern and the very long radiolar tips.However, they differ because in Chone dunerificta n. sp. the dorsal lips are triangular, erect (broadly rounded, as long as wide in C. duneri); radiolar tips long (extra long in C. duneri), and posterior abdominal uncini modified (not modified in C. duneri).Chone dunerificta n. sp., C. collaris, C. longiseta, C. bimaculata and C. gambiae n. sp.have the anterior peristomial ring lobe bilobed and exposed beyond collar (Table 1).Chone dunerificta n. sp., C. collaris, C. longiseta and C. bimaculata lacks a glandular ridge on chaetiger 9 (present in Chone gambiae n. sp.); C. collaris has the margin of collar crenulated (smooth in all others species); C. longiseta has ventral collar shield rectangular (horseshoe-shaped in C. dunerificta n. sp., C. collaris, C. longiseta and C. gambiae n. sp.while it is trapezoidal in C. bimaculata).Distribution and habitat: eastern central Atlantic Ocean and Mediterranean Sea, on shallow sandybottoms.

.
Chone americana, C. filicaudata and C. gambiae n. sp., have pygidial cirrus.Chone filicaudata and C. gambiae n. sp., have the anterior peristomial ring lobe incised, whereas it is intact in C. americana.The glandular ridge on chaetiger 2 is narrow in C. filicaudata, but laterally broad in C. gambiae n. sp.In Chone gambiae n. sp., C. dunerificta n. sp., C. collaris and C. longiseta, the anterior peristomial ring lobe is bilobed and exposed beyond collar (Table 1); however, the margin of the collar is crenulated in C. collaris (smooth in others).In Chone gambiae n. sp., the glandular ridge on chaetiger 2 is broad laterally (narrow in C. dunerificta n. sp., and C. longiseta), and an additional glandular ridge is present on chaetiger 9 (absent in C. dunerificta n. sp., and C. longiseta).