Ceratonereis singularis Treadwell 1929

Ceratonereis singularis Treadwell, 1929

Figures 2A, C; 17–19

Ceratonereis singularis Treadwell 1929: 1–3, figs 1–8. Perkins 1980: 17–26, figs 7a–c, 8a–e (partim).

Type material. Tropical Eastern Pacific, Mexico. Holotype male AMNH 1986, San Jose Island, Baja California Sur, Gulf of California, 25 March 1911, Coll. CH Townsend.

Additional type material. Holotype of Nereis singularis Treadwell, 1943 USNM 20092, 42.45, -47.1083, collected from surface, 8 August 1928, Coll. Carnegie Institution of Washington. Paratype (fide AMNN records) AMNH 2129, 42º10’N 47º19’W, Coll. Cruise of the non-magnetic ship, Carnegie Plankton Collection.

Additional material. Tropical Eastern Pacific, Mexico. LACM-AHF 7408 (2), R / V Velero III, Sta. 1093-40 (25°49’25”N 111°18’35”W), Puerto Escondido, Baja California Sur, 15–27 m depth, 10 February 1940, Coll. Allan Hancock Foundation (AHF). LACM-AHF 7410 (2), R / V Velero III, Sta. 1903-40 (25°49’25”N 111°18’35”W), Puerto Escondido, Baja California Sur, 15-27 m depth, 10 February 1940, Coll. AHF. LACM-AHF 7411 (5), R / V Velero III, Sta. 662-37 (25°31’35”N 111°01’45”W), off San Marcial Reef, Agua Verde Bay, Baja California Sur, 15 m depth, 11 March 1937, Coll. AHF. LACM-AHF 7412 (1), R / V Velero III, Sta. 683-37 (26°53’50”N 111°52’25”W), off Bahia Concepcion, Baja California, 22 m depth, 15 March 1937, Coll. AHF. LACM-AHF 7413 (1), R / V Velero IV, Sta. 2024-51(27°48’33”N 114°42’30”W to 27°49’00”N 114°42’09”W), Scammon’s Lagoon, Baja California Sur, 13-16 m depth, 18 Apil 1951, Coll. AHF. LACM-AHF 7415 (1), R / V Velero III, Sta. 277-34 (21°51’35”N, 105°54’30”W), Isabel Island, Nayarit, 18-46 m depth, 5 March 1934, Coll. AHF. LACM-AHF 7416 (3), R / V Velero IV, Sta. 1101-40 (25°31’00”N, 111°01’45”W), Agua Verde Bay, Baja California Sur, 18 m depth, 12 February 1940, Coll. AHF. LACM-AHF 7417 (2), R / V Velero III, Sta. 1103-40 (25°31’05”N, 111°02’30”W), Agua Verde Bay, Baja California Sur, shore, 12 February 1940, Coll. AHF. AMNH 1913 (75 males), San Jose Island, Baja California Sur, Gulf of California, electric light, April 1911, Coll. U.S.S. Albatross. AMNH 1950 (30 males), SE side Carmen Island, Baja California Sur, Gulf of California, electric light, 1911, Coll. U.S.S. Albatross.

Description of male epitoke. Holotype male (AMNH 1986) complete, 15 mm long, 1.5 mm wide at chaetiger 10 excluding parapodia, 65 chaetigers (Fig. 17A); three parapodia previously dissected, anal cirri missing, dissections avoided to prevent further damage. Additional material (AMNH 1930 and AMNH 1950) consists of several males, all in good condition, one male (AMNH 1950) selected for description (Figs 2A, 17B), 28.5 mm long, 2.8 mm wide at chaetiger 10 excluding parapodia, 73 chaetigers.

Body pale or yellowish, brownish pigmentation in anterior chaetigers (Fig. 17A–B).

Prostomium 1.3x wider than long, subpentagonal, anterior margin deeply incised, dorsal groove present (Fig. 17A–C).

Antennae lanceolate, 1.5x longer than prostomium, not extending beyond palps (Figs 2A, 17A–C).

Eyes rounded, subequal, in trapezoidal arrangement, anterior and posterior pair overlapped, blackish, as wide as basal diameter of antennae, lenses visible, posterior not covered by achaetous ring (Figs 2A, 17A–C).

Achaetous ring as long as chaetiger 1, anterior margin convex (Figs 2A, 17A–C).

Most tentacular cirri detached, remaining smooth (Figs 2A, 17A–C).

Pharynx everted in holotype (Fig. 17E) and in non-type specimen (Fig. 17F–G). Jaws amber, 7 teeth along cutting edge (Fig. 18G). Maxillary ring cylindrical, oral ring frustum-shaped, 1.8x longer and 1.4x wider than maxillary ring (Fig. 17E–G).

Maxillary ring: I= 0; IIa= 11 and IIb= 12 cones in arc; III= 10 cones in round; IVa= 16 and IVb= 18 cones in round (Fig. 17E–G). Oral ring: V= 0; VIa-b= 1 rounded papilla; VII–VIII= 0 (Fig. 17E–G). 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. 17A–B).

Pre-natatory region with parapodia resembling atokous ones (Figs 2A, 18A–B). Dorsal cirrus basally slightly swollen in anterior chaetigers and becoming filiform toward posterior chaetigers; 3.6x longer than neuroacicular ligule in chaetigers 7 and 14 (Fig. 18A–B); upper lamella present from chaetiger 14 (Fig. 18B). Dorsal ligule digitiform, progressively relatively longer toward middle chaetigers; as long as neuroacicular ligule in chaetiger 7, 1.4x longer than in chaetiger 14 (Fig. 18A–B). Notopodial prechaetal lobe absent (Fig. 18A–B). Median ligule subconical, progressively relatively longer toward middle chaetigers; 1.5x longer than neuroacicular ligule in chaetiger 7, 1.7x longer in chaetiger 14 (Fig. 18A–B). Neuroacicular ligule subconical, progressively relatively longer toward middle chaetigers (Fig. 18A–B). Neuropodial superior and inferior lobes absent (Fig. 18A–B). Neuropodial postchaetal lobe digitiform in anterior chaetigers, lamelliform and shorter than neuroacicular ligule thereafter. Ventral ligule subconical, 0.7x length of neuroacicular ligule in chaetigers 7 and 14 (Fig. 18A–B). Ventral cirrus slightly basally swollen in anterior chaetigers and becoming filiform toward posterior chaetigers; 2.2x longer than neuroacicular ligule in chaetiger 7 (Fig. 18A).

Natatory region with dorsal cirrus filiform, crenulations absent; twice longer than neuroacicular ligule throughout (Figs 2C; 18C–D). Dorsal ligule subconical in anterior chaetigers, basally swollen thereafter; 0.7x length of neuroacicular ligule thereafter (Figs 2C; 18C–D). Notopodial prechaetal lobe rounded, lamelliform; half as long as neuroacicular ligule in anterior chaetigers, as long as thereafter (Figs 2C; 18C–D). Median ligule subconical, progressively relatively shorter toward posterior chaetigers; as long as neuroacicular ligule throughout (Figs 2C; 18C–D). Neuroacicular ligule subconical, mucronate, progressively relatively shorter toward posterior chaetigers, distally slightly flattened (Fig. 18C–D). Neuropodial inferior lobe present throughout (Figs 2C; 18C–D). Neuropodial postchaetal lobe transformed into flabelliform ventral lamella, half as long as neuroacicular ligule throughout (Figs 2C; 18C–D), reaching and fusing with ventral ligule, forming a ligule (Figs 2C; 18C–D). Ventral ligule subconical; 0.4x length of neuroacicular ligule throughout (Figs 2C; 18C–D). Ventral cirrus filiform; 0.4x length of neuroacicular ligule in anterior chaetigers, 0.6x length thereafter (Figs 2C; 18C–D); upper and lower lamella appearing in anterior chaetigers and disappearing toward posterior ones, upper and lower ones obovate and subequal (Fig. 18C).

Caudal region with parapodia resembling atokous ones (Fig. 18E–F). Dorsal cirrus filiform, 9x longer than neuroacicular ligule (Fig. 18E). Dorsal ligule subconical, half as long as neuroacicular ligule throughout (Fig. 18E– F). Medial ligule subconical, progressively relatively longer toward posterior chaetigers; as long as neuroacicular ligule in anterior chaetigers, 1.7x longer than thereafter (Fig. 18E–F). Neuroacicular ligule subconical, pointed tip, progressively relatively shorter toward posterior chaetigers. Ventral ligule digitiform, 0.4x length of neuroacicular ligule throughout (Fig. 18E–F). Ventral cirrus filiform, extending beyond tip of neuroacicular ligule; 1.8x longer than neuroacicular ligule in anterior chaetigers, 5x longer thereafter (Fig. 18E–F).

Aciculae proximal end dark brown and distal end amber throughout, amber in posteriormost chaetigers (Fig. 18A–F). Notoaciculae present in first two chaetigers. Notoaciculae narrower than neuroaciculae in anterior chaetigers, becoming as wide as in following chaetigers (Fig. 18A–F).

Both noto- and neurochaetae resembling atokous ones in pre-natatory region (Fig. 18H–I), replaced with paddlelike, short-bossed 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. 17D).

Description of atoke. Largest one used for description (LACM-AHF 7411), 26 mm long, 2 mm wide excluding parapodia, 45 chaetigers; another specimen (LACM-AHF 7410) in fair condition, 22 mm long, 1.2 mm wide excluding parapodia, 66 chaetigers.

Body pale or yellowish; brown pigmentation present, with a brown, cordiform spot in posterior margin of prostomium, between eyes, and dorsal striate pattern in anterior chaetigers (Fig. 19A).

Prostomium1.5x wider than long, subpentagonal,anterior margin deeply incised,dorsal groove present(Fig.19A).

Antennae lanceolate, twice longer than prostomium, not extending beyond palps (Fig. 19A).

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. 19A).

Achaetous ring as long as chaetiger 1, anterior margin convex (Fig. 19A).

Tentacular cirri smooth (Fig. 19A), posterodorsal cirri extending backwards to chaetiger 16.

Pharynx dissected. Jaws brown with 4 teeth extended along cutting edge and 3 ensheathed (Fig. 19C). Shape and size of both maxillary and oral rings difficult to interpret since the pharynx was not everted.

Maxillary ring: I= 0; IIa= 16 and IIb= 16 cones in ellipse; III= 9 cones in round; IVa= 18 and IVb= 19 cones in ellipse. Oral ring: V=0; VIa-b= 1 rounded papilla; VII-VIII=0. Ridge pattern of areas VI–V–VI, λ-shaped.

Paired oesophageal caeca absent.

Dorsal cirri filiform, progressively relatively longer; 3.6x longer than neuroacicular ligule in chaetiger 1, 9.2x longer in chaetiger 10, 8.6x longer in chaetiger 29, 10.3x longer in chaetiger 44, 16.9x longer in chaetiger 59 (Fig. 19D–H).

Dorsal ligule subconical, progressively shorter and becoming digitiform toward posterior chaetigers, present throughout chaetigers; 2x longer in chaetiger 10, 1.3x longer in chaetiger 29, 0.5x length in chaetiger 44, 1.2x longer in chaetiger 59 (Fig. 19D–H).

Notopodial prechaetal lobe absent throughout (Fig. 19D–H).

Median ligule subconical, progressively shorter toward posterior chaetigers; 2.2x longer in chaetiger 10, 1.6x longer in chaetiger 29, 1.2x length in chaetiger 44, 2.6x longer in chaetiger 59 (Fig. 19D–H).

Neuroacicular ligule subconical throughout, progressively relatively shorter toward posterior chaetigers. Neuropodial superior and inferior lobes absent (Fig. 19A–D).

Neuropodial postchaetal lobe digitiform in first two chaetigers, lamelliform and shorter than neuroacicular ligules thereafter, disappearing toward most posterior chaetigers (Fig. 19D–H).

Ventral ligule subconical to digitiform throughout, progressively shorter toward posterior chaetigers; 2.2x longer than neuroacicular ligule in chaetiger 1, as long as in chaetiger 10, 0.7x length in chaetiger 29, 0.5x length in chaetiger 44, 1.3x longer in chaetiger 59 (Fig. 19D–H).

Ventral cirrus filiform, extending beyond tip of neuroacicular ligule in posteriormost chaetigers; 5.8x longer than neuroacicular ligule in chaetiger 1, 2.8x longer in chaetiger 10, 2.2x longer in chaetiger 29, 2.5x length in chaetiger 44, 4.8x longer in chaetiger 59 (Fig. 19D–H).

Aciculae dark brown in anterior and middle chaetigers, amber in posterior chaetigers (Fig. 19D–H). Notoaciculae present in first two chaetigers (Fig. 19D). Notoaciculae narrower than neuroaciculae in anterior chaetigers, becoming as wide as in following chaetigers (Fig. 19D–H).

Notochaetae both short-bossed heterogomph spinigers and falcigers; spinigers in all chaetigers, pectinate, teeth minute, decreasing in size toward tip; falcigers appearing from chaetigers 14–17, pectinate, basal teeth minute and greatly increasing in size toward distal blade, distal teeth extending beyond blade tip, blade tip rounded (Fig. 19I), shaft becoming slightly stouter toward posterior chaetigers.

Supracicular neurochaetae short-bossed heterogomph spinigers and long-bossed heterogomph falcigers; spinigers with blades as in notopodial ones; falcigers pectinate, basal teeth minute and greatly increasing in size toward distal blade, distal teeth extending beyond blade tip (Fig. 19J), blades becoming wider toward posterior chaetigers.

Infracicular neurochaetae both long-bossed heterogomph spinigers and falcigers; spinigers with blades as in notopodial ones; falcigers pectinate, basal teeth minute and greatly increasing in size toward distal blade (Fig. 19K– L), distal teeth extending beyond blade tip, blade tip rounded throughout (Fig. 19K–L), blades becoming narrower toward posterior chaetigers, uppermost falcigers with longer and wider blades than lowermost ones (Fig. 19K–L).

Pygidium minute, bilobate; anal cirri filiform, as long as last six chaetigers (Fig. 19B).

Remarks. Salazar-Vallejo & Jiménez-Cueto (1997) examined the holotype and mentioned it consisted of two portions and missing the pharynx, but neither the holotype nor additional AMNH materials examined have such damage. Also, the latter authors thought that ‘pre-pygidial portion’ was in the process of regeneration, perhaps by the distinct size especially when they are compared with chaetigers from pre-natatory and natatory regions; however, the presence of this feature in all epitokes of Ceratonereis herein described and the lack of chaetae in such chaetigers suggest it is an epitoke-related modification and not posterior portions undergoing regeneration.

Hartman (1956) regarded C. singularis as a junior synonym of C. mirabilis without further explanation. Also, Hartman (1956) suggested, without explanation, that Nereis singularis Treadwell, 1943, a species collected from Newfoundland Basin, might be another synonym. The holotype (USNM 20092; 8 mm long, 0.5 mm wide at chaetiger 10 excluding parapodia, 52 chaetigers, longest tentacular cirri reach chaetiger 11) and the paratype (AMNH 2129; 7 mm long, 0.5 mm wide at chaetiger 10 excluding parapodia, 29 chaetigers, specimen friable) of Nereis singularis Treadwell, 1943, were examined (Fig. 20). After a close examination of the type series, N. singularis was found to be a Platynereis species based on the following features: 1) anterior margin of prostomium entire (Fig. 20A–B, D); 2) palpophores globose (Fig. 20A–B); 3) presence of rod-like paragnaths in the pharynx (observed in holotype after whole-mounting specimen and using a compound microscope); 4) parapodial processes of similar relative size along the body, especially dorsal ligules; 5) presence of symmetrical homogomph spinigers and falcigers in middle and posterior chaetigers; and 6) notopodial and neuropodial falcigers with blades having a distal incurved hook with a tendon fused to the blade (Fig. 20E). Therefore, the synonymy of N. singularis with C. mirabilis is rejected, and the new combination Platynereis singularis (Treadwell, 1943) is proposed; future works could address if it is a valid species or not.

Perkins (1980) redescribed Ceratonereis singularis based on type material and additional specimens from other localities from Eastern Pacific coasts, but also included Atlantic material, regarding C. singularis as an amphiamerican species. However, his Atlantic specimens resemble C. maya n. sp. as well as the material identified as C. singularis by Salazar-Vallejo & Jiménez-Cueto (1997); further comments are in remarks of C. maya n. sp. above. The species have been recorded in several localities of the Caribbean Sea (Dean 2012), but they likely belong to C. maya n. sp.

Distribution. Mexican Pacific.