Ceratonereis gracilis ( Webster, 1884 )

Conde-Vela, Víctor Manuel, 2021, Revision of Ceratonereis Kinberg, 1865 recorded from the Caribbean Sea, with description of two new Ceratonereis species and a new combination of Platynereis Kinberg, 1865, Zootaxa 5026 (3), pp. 301-343 : 309-315

Ceratonereis gracilis ( Webster, 1884) reinstated

Figures 5–8

Nereis gracilis Webster, 1884: 313–314 , Pl. 9, figs 29–35 (homonym, not N. gracilis Hansen, 1882 ).

Ceratonereis gracilis Hartman 1938: 13–14 .

Ceratonereis mirabilis Perkins 1980: 4 , fig. 3e (partim, non Kinberg, 1865).

Type material. Northwestern Atlantic Ocean, Bermuda. Syntypes of Nereis gracilis USNM 4787 (2), Bermuda, 1876, Coll. G.B. Goode.

Additional material. Northwestern Atlantic Ocean, Bermuda. USNM 1436352 (1), St. George’s Island , 6–9 m, 25 August 1960, Coll . T Tucker . USNM 1490819 (1), Bermuda, S side of Ferry Reach, about ½ way along Kindley Field Rd. , 23 November 1976, narrow-bladed grass in mud substrate, Coll . ML Jones . USNM 1490818 (2), Bermuda , SW of Whalebone Bay, 17 November 1979, Coll . ML Jones . USNM 1490820 (1), Harrington Sound, Trunk Island , 12 August 1975, in rocks, Coll . ML Jones . AMNH 2405 (1), Castle Harbor Reef, Bermuda , 15 August 1931, Coll. Bermuda Oceanographic Expedition. AMNH 2504 (1), Castle Harbor Reef, Bermuda , 15 August 1931, Coll. Bermuda Oceanographic Expedition. AMNH 2538 (5 males), Bermuda , 18 August 1931, Coll. Bermuda Oceanographic Expedition. AMNH 556 (1 female), Bermuda , no date, Coll. A.E. Verrill and party.

Description of atoke. Syntypes of Nereis gracilis (USNM 4787) consist of two anterior fragments in fair condition ( Fig. 5A ); one anterior end with deep cuts along some chaetigers caused by previous dissections, 55 mm long, 1.2 mm wide at chaetiger 10 excluding parapodia, 30 chaetigers; another anterior end 76 mm long, 1.4 mm wide at chaetiger 10, 33 chaetigers. Specimen from Bermuda (USNM 1490819) complete, 14 mm long, 0.7 mm wide at chaetiger 10, 61 chaetigers. Two additional specimens from Bermuda (USNM 1490818) complete, one specimen used for description, 35 mm long, 1.1 mm wide at chaetiger 10, 73 chaetigers ( Fig. 5G ). Non-type female (AMNH 556) incomplete, not transformed, 5.2 mm long, 1 mm wide at chaetiger 10, 21 chaetigers ( Fig. 8A ); body filled with oocytes, parapodia as in atokes.

Body pale or whitish, glandular masses not observed ( Fig. 5E–H ).

Prostomium 1.8–2.0x wider than long, sub pentagonal, anterior margin deeply incised, dorsal groove present ( Fig. 5B, E, H ).

Antennae subulate, 1.5x longer than prostomium, not extending beyond palps ( Fig. 5B, E, H ).

Palpophores subcylindrical, twice longer than prostomium; tips of palpostyles pyriform ( Fig. 5B, E, H ).

Eyes rounded, subequal, in trapezoidal arrangement, blackish, as wide as basal diameter of antennae, lenses not visible, posterior pair not covered by achaetous ring ( Fig. 5B, E, H ).

Achaetous ring as long as chaetiger 1, anterior margin convex ( Fig. 5B, E, H ).

Tentacular cirri smooth, posterodorsal cirri extending backwards to chaetigers 16–18 ( Fig. 5 E, G, H ).

Pharynx not everted in syntypes, dissection avoided to prevent further damage, everted in non-type specimen ( USNM 1490820 ) ( Fig. 5C–D ). Jaws brown to dark brown ( Figs 5C–D , 6A ), 6 teeth extended along cutting edge ( Fig. 6A ). Maxillary ring cylindrical, oral ring frustum-shaped, both ring with similar length and width ( Fig. 5C– D ) .

Maxillary ring: I= 0; IIa= 6 (6–12) and IIb= 14 (7–14) cones in ellipse; III= 6 (6–10) cones in round; IVa= 10 (10–13) and IVb= 14 (10–14) cones in round ( Fig. 5C–D ). Oral ring: V= 0; VIa-b=1 slightly lamelliform papilla; VII–VIII= 0 ( Fig. 5C–D ). Ridge pattern of areas VI–V–VI, λ-shaped.

Paired oesophageal caeca absent.

Dorsal cirri filiform, progressively relatively longer; 3x longer than neuroacicular ligule in chaetiger 2, 7x longer in chaetiger 7, 4.2x longer in chaetiger 13, 6x longer in chaetiger 23, 9x longer in chaetiger 42, 7.8x longer in chaetiger 60, 20x longer in chaetiger 71 ( Fig. 6B–H ).

Dorsal ligule subulate, progressively shorter and becoming digitiform toward posterior chaetigers, present throughout chaetigers; 2.3x longer than neuroacicular ligule in chaetiger 7, 0.7x length of neuroacicular ligule in chaetiger 13, 0.6x length in chaetiger 23, 0.7x length in chaetiger 42, 0.2x length in chaetiger 60, 0.6x length in chaetiger 71 ( Figs 6B–H , 7A–C ).

Notopodial prechaetal lobe absent throughout ( Figs 6B–H , 7A–C ).

Median ligule subconical or digitiform, progressively longer toward posterior chaetigers; 1.3x longer than neuroacicular ligule in chaetiger 7, as long as in chaetiger 13, as long as in chaetiger 23, 1.5x longer in chaetiger 42, 1.2x longer in chaetiger 60, 1.6x longer in chaetiger 71 ( Figs 6B–H , 7A–C ).

Neuroacicular ligule subconical throughout, progressively relatively shorter toward posterior chaetigers. Neuropodial superior and inferior lobes absent ( Figs 6B–H , 7A–C ).

Neuropodial postchaetal lobe digitiform in first two chaetigers, lamelliform and shorter than neuroacicular ligules thereafter, disappearing toward most posterior chaetigers ( Figs 6B–H , 7A–C ).

Ventral ligule digitiform throughout, progressively shorter toward posterior chaetigers; 1.3x longer than neuroacicular ligule in chaetiger 2, as long as in chaetiger 7, 0.7x length of neuroacicular ligule in chaetiger 13, 0.5x length in chaetiger 23, 0.5x length in chaetiger 42, 0.4x length in chaetiger 60, 0.7x length in chaetiger 71 ( Figs 6B–H , 7A–C ).

Ventral cirrus filiform, extending beyond tip of neuroacicular ligule in posteriormost chaetigers; twice longer than neuroacicular ligule in chaetiger 2, 1.6x longer in chaetiger 7, 1.5x longer in chaetiger 13, 1.5x longer in chaetiger 23, 1.5x longer in chaetiger 42, 1.7x longer in chaetiger 60, 3.2x longer in chaetiger 71 ( Figs 6B–H , 7A–C ).

Aciculae amber throughout. Notoaciculae present in first two chaetigers ( Figs 6B , 7A ). Notoaciculae narrower than neuroaciculae in anterior chaetigers, becoming as wide as in following chaetigers ( Figs 6B–H , 7A–C ).

Notochaetae both short-bossed heterogomph spinigers and falcigers; spinigers in all chaetigers, pectinate, teeth minute, decreasing in size toward tip; falcigers appearing from chaetigers 15–16, pectinate, teeth coarse, distal teeth barely extending beyond blade tip, blade tip with a distal tooth, giving a bifid appearance ( Fig. 7D–F ), shaft becoming slightly stouter and blades longer toward posterior chaetigers ( Fig. 7D–F ).

Supracicular neurochaetae short-bossed heterogomph spinigers and long-bossed heterogomph falcigers; spinigers with blades as in notopodial ones; falcigers pectinate, teeth minute, distal teeth barely extending beyond blade tip, blade tip rounded along first 15–17 chaetigers, with a distal tooth and bifid appearance thereafter, blades becoming wider toward posterior chaetigers ( Fig. 7G ).

Infracicular neurochaetae both long-bossed heterogomph spinigers and falcigers; spinigers with blades as in notopodial ones; falcigers pectinate, teeth minute, distal teeth barely extending beyond blade tip, blade tip rounded along first 15–17 chaetigers, with a distal tooth and bifid appearance thereafter ( Fig. 7H–J ), blades longer than supracicular falcigers in anterior chaetigers and becoming shorter toward posterior ones, blades becoming narrower toward posterior chaetigers, uppermost falcigers with longer blades than lowermost ones ( Fig. 7H–J ).

Pygidium funnel-shaped ( Fig. 5F ); anal cirri filiform, as long as last 9–10 chaetigers ( Fig. 5F–G ).

Description of male epitoke. Non-type male (AMNH 2538) complete ( Fig. 8B ), 12.7 mm long, 1 mm wide at chaetiger 10, 69 chaetigers, used for description.

Body pale or yellowish, pigmentation absent ( Fig. 8A–B ).

Prostomium 1.2x wider than long, subpentagonal, anterior margin deeply incised, dorsal groove present ( Fig. 8B–C ).

Antennae lanceolate, as long as prostomium, not extending beyond palps ( Fig. 8B–C ).

Eyes rounded, subequal, in trapezoidal arrangement, blackish, 1.5x wider than basal diameter of antennae, lenses visible, posterior pair not covered by achaetous ring ( Fig. 8B–C ).

Achaetous ring as long as chaetiger 1, anterior margin convex ( Fig. 8A–C ).

Tentacular cirri smooth ( Fig. 8A ), posterodorsal cirri extending backwards to chaetiger 15.

Pharynx dissected. Shape and size of both maxillary and oral rings difficult to interpret since the pharynx was not everted.

Maxillary ring: I=0; IIa= 8 (7–10) and IIb= 12 (10–12) cones in ellipse; III= 7 (7–8) cones in round, IVa= 11 (10–11) and IVb= 13 (13–15) cones in ellipse. Oral ring: V=0; VIa-b= 1 slightly lamelliform papilla, VII-VIII=0. Ridge pattern of areas VI–V–VI, λ-shaped.

Paired oesophageal caeca absent.

Body divided into three regions: 1) pre-natatory region includes chaetigers 1–16 (15–16), 2) natatory region includes chaetigers 17–37 (36–37), 3) caudal region from chaetiger 38 (37–38) to end of body ( Fig. 8B ).

Pre-natatory region with parapodia resembling atokous ones ( Fig. 8E–F ). Most dorsal cirri detached ( Fig. 8E– F ). Dorsal ligule subconical, as long as neuroacicular ligule. Notopodial prechaetal lobe absent ( Fig. 8E–F ). Median ligule subconical, as long as neuroacicular ligule ( Fig. 8E–F ). Neuroacicular ligule subconical, progressively relatively longer toward middle chaetigers ( Fig. 8E–F ). Neuropodial superior and inferior lobes absent ( Fig. 8E–F ). Neuropodial postchaetal lobe digitiform in anterior chaetigers, lamelliform and shorter than neuroacicular ligule thereafter. Ventral ligule subconical, 1.2x longer than neuroacicular ligule in first two chaetigers, as long as thereafter ( Fig. 8E–F ). Ventral cirrus basally swollen and 1.8x longer than neuroacicular ligule in first two chaetigers, filiform and 1.6x longer thereafter ( Fig. 8E–F ).

Natatory region with most dorsal cirri detached ( Fig. 8G–H ), crenulations absent. Dorsal ligule subconical, 0.3x length of neuroacicular ligule throughout ( Fig. 8G–H ). Notopodial prechaetal lobe rounded, lamelliform, 0.6x length of neuroacicular ligule throughout ( Fig. 8G–H ). Median ligule subconical, 1.3x longer than neuroacicular ligule in anterior chaetigers, 1.2x longer than thereafter ( Fig. 8G–H ). Neuroacicular ligule subconical, mucronate, progressively relatively shorter toward posterior chaetigers, distally flattened ( Fig. 8G–H ). Neuropodial inferior lobe digitiform, present in anterior chaetigers only ( Fig. 8G–H ). Neuropodial postchaetal lobe transformed into flabelliform ventral lamella, half as long as neuroacicular ligule in anterior chaetigers, as long as toward posterior chaetigers ( Fig. 8G–H ), reaching and fusing with ventral ligule ( Fig. 8H ). Ventral ligule subconical and 0.3x length of neuroacicular ligule in anterior chaetigers ( Fig. 8G ), rounded and 0.2x length toward posterior chaetigers ( Fig. 8H ). Ventral cirrus filiform and 1.6x longer than neuroacicular ligule in anterior chaetigers and 1.3x longer toward posterior ones; upper and lower lamella appearing toward posterior chaetigers, upper one obovate and twice longer than rounded lower one.

Caudal region with parapodia resembling atokous ones ( Fig. 8I–J ). Most dorsal cirri detached ( Fig. 8I–J ). Dorsal ligule subconical, blunt tip, progressively relatively longer toward posterior chaetigers; 0.3x length of neuroacicular ligule in anterior chaetigers ( Fig. 8I ), half as long as toward posterior chaetigers ( Fig. 8J ). Medial ligule subconical, progressively relatively longer toward posterior chaetigers, as long as neuroacicular ligule in anterior chaetigers ( Fig. 8I ), 1.7x longer toward posterior chaetigers ( Fig. 8J ). Neuroacicular ligule subconical, mucronate, progressively relatively shorter toward posterior chaetigers ( Fig. 8I–J ). Ventral ligule digitiform in very first chaetigers, absent thereafter ( Fig. 8I–J ). Ventral cirrus filiform, 1.2x longer than neuroacicular ligule in anterior chaetigers ( Fig. 8I ), 1.3x longer toward posterior chaetigers ( Fig. 8J ).

Aciculae amber throughout. Notoaciculae present in first two chaetigers ( Fig. 8E ). Notoaciculae narrower than neuroaciculae in anterior chaetigers, becoming as wide as in following chaetigers ( Fig. 8E–J ).

Both noto- and neurochaetae resembling atokous ones in pre-natatory region, replaced with paddle-like, shortbossed heterogomph chaetae in natatory region. Caudal region lacks chaetae excepting aciculae.

Pygidium with four rounded lobes, each one with a small lamella; anal cirri absent ( Fig. 8D ).

Remarks. The syntypes of C. gracilis are in poor condition, most dorsal cirri are missing and the remaining ones are broken. Ceratonereis gracilis and C. mirabilis are very similar, especially in the short-bossed notopodial falcigers (usually used to separate species), so it is not surprising they were synonymized. Perkins (1980) redescribed C. mirabilis based on the Brazilian syntypes and the Bermudan syntypes of Nereis gracilis all in poor condition, and additional material from the Gulf of Mexico and the Caribbean Sea. Perkins (1980) noted differences between syntypes of C. mirabilis and N. gracilis , but they were considered “of less importance”. The differences in the number of paragnaths and the relative size of the chaetae were attributed to differences in size between the syntypes of both species, but how he reached that conclusion is unclear. The few specimens available for this study prevent this hypothesis from being tested, but in the specimens examined, the ranges largely overlap between both species, so here I focused on the differences in the parapodial characteristics.

Regarding parapodia, Perkins (1980) stated that they are similar in both species and highlighted that N. gracilis also have ventral cirri reaching tips of ventral ligules in anterior chaetigers and are longer than all ligules in posterior chaetigers as it appeared in the original description by Webster (1884). The first feature is shared with the other two species studied by Perkins (1980), Ceratonereis tentaculata and C. singularis , whereas the second one is unique for C. mirabilis (doubtful in C. tentaculata ); however, the author described and figured ventral cirri shorter than neuroacicular ligules for specimens from Gulf of Mexico and Florida ( Perkins 1980, fig. 3c, d). Based on the specimens examined here, C. gracilis and C. mirabilis share both features mentioned above, and only C. maya n. sp. has ventral cirri surpassing neuroacicular ligules in posterior chaetigers.

Based on the both type and non-type material examined, C. gracilis differs from C. mirabilis in the following features: 1) in C. gracilis , dorsal cirri are 4.2x longer than neuroacicular ligule in chaetiger 13, 6x longer in chaetiger 23, whereas in C. mirabilis they are 8x longer and 10.3 longer, respectively; 2) in C. gracilis , dorsal ligules of anterior chaetigers are as wide as median ligules, whereas in C. mirabilis they are narrower; 3) in C. gracilis , dorsal ligules of chaetigers 10–13 surpass the half of median ligules, whereas in C. mirabilis they are shorter; 4) in C. gracilis , ventral ligules of chaetigers 10–13 are 1.3x longer than neuroacicular ligules, whereas in C. mirabilis they are 0.7x the length of the neuroacicular ligules; 5) in C. gracilis , ventral cirri in chaetigers 20–23 does not surpass ventral ligules whereas in C. mirabilis they greatly surpass them; 6) in C. gracilis , the distal teeth of notopodial and neuropodial falcigers of middle and posterior chaetigers are longer and sharper than in C. mirabilis . Therefore, C. gracilis is regarded as a valid species and reinstated, with a distribution restricted to Bermuda.

Figures

FIGURE 5. Ceratonereis gracilis (Webster, 1884) reinst. Syntypes of Nereis gracilis Webster, 1884 A, B (USNM 4787); non-type C, D (USNM 1490820), E–G (USNM 1490818), H (USNM 1490819). A, whole fragments, dorsal view. B, anterior end, dorsal view. C, pharynx, dorsal view (arrow tips point slightly lamelliform papillae in areas VI). D, pharynx, ventral view. E, anterior end, dorsal view. F, posterior end, dorsal view. G, whole specimen, dorsal view. H, anterior end, dorsal view. Scale bars: A, E, 1 mm; G, 2 mm; B–D, F, H, 0.5 mm.

FIGURE 6. Ceratonereis gracilis (Webster, 1884) reinst. Non-types A (USNM 1490819), B–H (USNM 1490818). A, left jaws, dorsal view. B, chaetiger 2, left parapodium. C, chaetiger 7, left parapodium. D, chaetiger 13, left parapodium. E, chaetiger 23, left parapodium. F, chaetiger 42, left parapodium. G, chaetiger 60, left parapodium. H, chaetiger 71, left parapodium. Scale bars: A, 0.1 mm; B–H, 0.2 mm.

FIGURE 7. Ceratonereis gracilis (Webster, 1884) reinst. Syntypes of Nereis gracilis Webster, 1884 A–C (USNM 4787); nontype D–J(USNM 1490819). A, chaetiger 3, right parapodium.B, chaetiger 8, right parapodium. C, chaetiger 16, right parapodium. D, notopodial short-bossed heterogomph falciger, chaetiger 23. E, notopodial short-bossed heterogomph falciger, chaetiger 30. F, notopodial sshort-bossed heterogomph falciger, chaetiger 40. G, supra-acicular long-bossed heterogomph falciger, chaetiger 23. H, sub-acicular long-bossed heterogomph falcigers, chaetiger 23. I, sub-acicular long-bossed heterogomph falcigers, chaetiger 40. J, sub-acicular long-bossed heterogomph falcigers, chaetiger 57. Scale bars: A–C, 0.2 mm; D–J, 10 µm.

FIGURE 8. Ceratonereis gracilis (Webster, 1884) reinst. Non-type female A (AMNH 556); non-type male B–J (AMNH 2538). A, whole specimen, dorsal view. B, whole specimen, dorsal view. C, anterior end, dorsal view. D, posterior end, dorsal view. E, chaetiger 2, right parapodium. F, chaetiger 7, right parapodium. G, chaetiger 17, right parapodium. H, chaetiger 32, right parapodium. I, chaetiger 41, right parapodium. J, chaetiger 66, right parapodium. Scale bars: A, B, 2 mm; C, D, 0.5 mm; E–H, 0.2 mm; I, J, 0.1 mm.