Holotype [ECOSUR 0145 (ECOSUR-OH-0213)] Xahuayxhol, Quintana Roo, México, 18°30'30"N, 87°44'02"W, August 2004, 1 m, reef lagoon, coralline rock, Coll. LFCP. Paratypes (3) ECOSUR 0146, 0147, 0148] the same data as for holotype (Fig. 1).

[ECOSUR P2641] Xcalak, Quintana Roo, México, sta. 4, 18°16'57"N, 87°49'8"W, in nightlight lift-net, August 2005, Coll. L. Vazquez. [USNM 15921] Sail Rock, Off Saint Thomas, 37 m, coral; [USNM 20296] Pillars of Hercules, English Harbor, Antigua; [USNM 15859] Puerto Rico; [USNM 20273] Barbados (Fig. 1); all as Notopygos crinita.

Holotype (ECOSUR 0145) mature male, complete, with 30 chaetigers, 3 cm total length, 1 cm wide. Body fusiform, orange to light brown, with reddish-brown branchiae. Pigmentation pattern complex, triangular and rhomboid forms covering the dorsum (Figs 2C, 4F). Prostomium semicircular with four eyes in pigmented strip, anterior eyes twice size of posterior ones (Fig. 2A). Median antenna in central position on prostomium, long and slender (1.1 mm long, Figs 2A, 4C); pair of lateral antennae placed on anterior prostomial margin, size similar to median antenna (1 mm long). Lips with lateral palps, shorter than lateral antennae (0.7 mm). Mouth ventral between peristomium and chaetiger 3.

Caruncle oval (2.9 mm long, 1.7 mm wide), with an elevated central lobe with about 20 folds (Fig. 4C). Row of circular projection protruding between each pair of folds in middle of caruncle (Figs 2B, 4C). Lateral lobes flattened with pigmented base and folding edge with 19 and 22 folds (Fig. 4C).

Branchiae from chaetiger 5 (Fig. 2I), present throughout body. Each branchia with main short stem, branching in several filaments of various thicknesses and lengths (Fig. 2E). First branchia with 11 branchial filaments, second branchia with about 20, middle one with about 40, posterior branchiae with 35–45 filaments up to the last chaetiger, where filaments are fewer. The large number of filaments causes a secondary ramification without a defined pattern.

Parapodia biramous, notopodium with double cirri and neuropodium with single ventral cirrus. Notopodial cirri differing; accessory cirrus (= branchial cirrus) simple with similar length along body (1.0–1.2 mm); dorsal cirrus with short, thick cirrophore (0.5 mm) in first chaetigers, subsequent ones with long slender cirrophore (1 mm) and cirrostyle (1.5 mm, Fig. 2F). Ventral cirri similar along body, cirrophore short (0.2 mm) and cirrostyle long (1 mm), decreasing towards last chaetigers.

Noto- and neurochaetae all asymmetrically furcated, slender (<0.03 mm), ratio of difference between short and long tines varies from three to four times (Fig. 2D). First chaetigers with some notochaetae with extra long tines, 10 to 30 times longer than short tines. Both neuro- and notochaetae include short and long types; shorter chaetae on exterior edge of chaetal lobe. Chaetae of first chaetigers with serrated margin. Some chaetae with an external “hard cover” that easily breaks up, giving the impression of being articulated (Fig. 2H).

Anus dorsal, on chaetiger 23. Posterior end margin with pair of distal lobes (0.5 mm long, 0.5 mm wide in the widest part, Fig. 2G).

Gametes: Gametes are located in the coelom. Oocytes are 40–57 μm in diameter (mean: 28.7±8.3 μm, n=20, one paratype female). Spermatozoids have a spherical head (~ 3 μm), ect-aquasperm type, aggregated in a mass (holotype).

Variation: Material examined varied in total length from 1.0 to 2.1 cm, in width from 0.3 to 0.5 cm, chaetigers from 23 to 26, and varies in the following features. Prostomium: median antenna similar length to lateral ones (from 0.4 mm to 1 mm), palps shorter (0.3–0.7 mm). In some worms the pigmented strip on the prostomium continues to the buccal lips, around the palps, and even onto the ventral body with a dark region, although in holotype this pigmentation is faded. Caruncle fold number varies from 13 in smallest to 20; in all specimens number of folds between elevated lobe and laterals is very similar (±2). Pigmented circular projections in mid-caruncle faded in some preserved specimens. Number of branchial filaments is size-dependent, smallest specimens having only three to nine, largest specimens having up to 25 filaments in median region. Branchiae from chaetiger 5 in both juvenile and adults.

The specific name refers to the distribution area of the species.

Greater Caribbean basin in shallow waters, related to coralline areas, particular associations are unknown.

Notoygos caribea sp. n. is characterized by the complex pigmentation pattern covering the dorsum with triangular and rhomboid forms (Figs 2C, 4F), and by other features such as branchiae beginning on chaetiger 5, anus on chaetiger 23, and a prominent caruncle with a median keel with a series of highlighted points arranged in a a longitudinal row of circles. The juvenile specimen also shows the coloration pattern and the distinctive caruncle. The coloration pattern on the caruncle of some specimens is faded; however, it is possible to distinguish the serial projections on the mid-caruncle.

The most common species recorded in the Atlantic is Notopygos crinita. This species was briefly described by Grube (1855) from St Helena. He did not comment on pigmentation pattern and omitted the presence of the second dorsal cirri; furthermore, chaetae are described only as pale yellow, long and asymmetrically bifurcated. Unfortunately, the holotype of Notopygos crinita [ZMB Verm. 3330] in the Zoologisches Museum, Berlin is lost (Hartwich 1993), so new topotypical materials are needed for a complete redescription, but this is beyond the scope of this study. However, the differences in anus position (21 vs. 23 in Notopygos caribea sp. n.), size of the second cirri (indistinguishable vs. prominent in Notopygos caribea sp. n.), pigmentation pattern (unstated, as not denoting vs. complex in Notopygos caribea sp. n.) and caruncle (crenulated vs. well-defined structure in Notopygos caribea sp. n.) allowed us to separate the two species.

Kinberg (1910) recorded one specimen from St Helena as Notopygos crinita; however, the illustration shows one dorsal cirrus per notopodium and his description confirms this character. In addition, Kinberg stated that the specimen lacks the dorsal anus; thus we consider that this specimen does not belong to Notopygos, possibly a juvenile Chloeia.

Material from Puerto Rico on corals revised by Treadwell (1901) was identified as Notopygos crinita; however, in the description he refers to the row of small dark brown bead-like elevations on the median fold of the caruncle. The mention of this characteristic feature of the caruncle in the Treadwell specimens allows us to assume that the Puerto Rico specimens belong to Notopygos caribea sp. n.

In the Indo-Pacific region, eight Notopygos species have branchiae beginning on chaetiger 5 (Table 1):

1) Notopygos rayneri (Baird, 1870) from north-eastern Australia also has a complex pigmentation pattern but with white lines crossing in various directions, whereas Notopygos caribea sp. n. lacks white lines even in live specimens (Figs 2I, 5). 2) Notopygos flavus Haswell, 1878 from northern Australia lacks any pigmentation pattern. 3) Notopygos variabilis Potts, 1909 from the Maldives differs from Notopygos caribea sp. n. mainly in caruncle shape (Fig. 4A) and pigmentation pattern of live specimens, which is like a chessboard with orange spots (original description lacking illustration of pigmentation pattern). 4) Notopygos sibogae Horst, 1911 from Indonesia differs in that the pigmentation pattern includes a violet band around the notopodium and violet secondary cirri (original description lacking illustration of pigmentation pattern). 5) Notopygos cirratus Horst, 1911 from the Philippines differs in the pigmentation pattern grey with a dark band around the base of each notopodium and violet cirrophore, and in the intersegmentary location of the anus above an elevation. 6) Notopygos gigas Horst, 1911 from the south coast of Timor differs in the dissimilar anus location and branchiae shape, being three large stems in Notopygos gigas, while in Notopygos caribea sp. n. the branchial ramification lacks a defined pattern. 7) Notopygos horsti Monro, 1924 from northern Australia differs from Notopygos caribea sp. n. by having two series of circular projections on the caruncle median lobe (Fig. 4B) instead of only one (Fig. 4C) and by the intersegmental anus position. 8) Notopygos andrewsi Monro, 1924 from Christmas Island has a pigmentation pattern with crossed lines and raised longitudinal ridges and caruncle without pigmentation (Fig. 4D, G), different from Notopygos caribea sp. n.

In addition, Horst (1911) suggested that Notopygos gardineri Potts, 1909 (Amirante Islands) and Notopygos labiatus McIntosh, 1885 (Philippine Islands) have the branchiae beginning on chaetiger 5. In Table 1, these species were omitted because the original descriptions do not provide this information. Therefore, to confirm this assertion it will be necessary to re-examine the types as part of a review the genus, with additional material from the Indo-Pacific region.

Holotype (juvenile) [BMNH 1885.12.1.12] Bermuda, 32°07' N, 65°04'W, Sta. 36, “Challenger”, April 1873, 55 m. Broken into two parts, damaged (Fig. 1).

[UMML 22.909] Near Jamaica, 17°27'N; 78°10'W, Sta. 1256, “R/V Pillsbury”, July 1970, 590 m. [UMML 22.903] Venezuela, 10°57'N, 66°18'W, Sta. 739, “R/V Pillsbury”, July 1968, 257m, juvenile (Fig. 1).

Adult specimen (UMML 22.909) complete with 23 chaetigers, damaged, gut exposed, broken, posterior end in poor condition; body fusiform; 3 cm total length, 1 cm wide in the widest part. Prostomium semicircular without pigmented areas, four eyes. Median antenna lost, in central position of prostomium, lateral antennae and palps of similar length (0.7 mm). With stain, ventral surface of buccal lips conserved the stain displaying a glandular zone (Fig. 3A). Mouth placed ventrally in chaetiger 3.

Caruncle oval (1.9 mm length, 0.8 mm wide), elevated lobe with about seven folds in the middle, a rectangular projection between each fold pair. Lateral lobes narrow, with a slightly folded edge, without pigmentation (Fig. 3B).

Branchiae from chaetiger 6, present throughout body. Each branchia as a tuft of slender branchial filaments. First branchiae with a main stem, with seven branchial filaments; in median chaetigers with a main short stem, branching in four stems with five to seven branchial filaments each (Fig. 3D).

Parapodia biramous, notopodium with double cirri and neuropodium with single ventral cirrus. Accessory cirrus simple, long (2 mm); main cirrus with robust short cirrophore (0.5 mm length) and slender and long cirrostyle (1.5–2.0 mm) in all chaetigers (Fig. 3E). Ventral cirri of similar length (1 mm) along the body, last one smallest (0.7 mm).

Chaetae in noto- and neuropodia of two sizes, short and long. All neurochaetae slender (<0.04 mm wide), long notochaetae (Fig. 3C) twice as thick as short notochaetae. All chaetae asymmetrical furcates; ratio of difference between small and large tines is similar in all chaetae, varying from three to four times.

Anus dorsal in the intersegment 18–19. Posterior end margin with pair of short distal lobes.

Gametes: Unknown.

Greater Caribbean, 55 to 590 m.

Notopygos megalops is characterized by branchiae beginning on chaetiger 6, with four main stems on median chaetigers; anus dorsal in the intersegment 18–19 and a short caruncle in comparison with other Notopygos species. The caruncle has a wide median lobe with seven wide folds and narrow lateral lobes. McIntosh (1885) indicated that only the cirrophore has a buff pigmentation; the material reviewed, including the holotype, lacks pigmentation, so we cannot corroborate this statement. McIntosh emphasized the serrations of neurochaetae, and the material examined enabled us to clarify that serrations are present in both noto- and neurochaetae on the first chaetigers.

The main attributes that permit us to associate the juvenile described in the original description with the adult forms are the caruncle, the position of the first branchiae, branchial branching, largest notochaeta and the stout cirrophore. McIntosh (1885: 18) described the caruncle as a “usual folded structure, a little more lax than in Chloeia”. In Chloeia the lateral lobes usually are narrower than in Notopygos, which generally are large and flattened. The caruncle in Notopygos megalops has narrow lateral lobes, and relaxed folds in the median lobe (Fig. 3B).

Hartman (1959) suggest that Notopygos megalops is a synonym of Notopygos crinita. Ebbs (1966) pointed out the differentiation in the details of branchial branching discussed by MacIntosh (1855) to differentiate the two species; however, he considered that the differences in chaetae were only minor variations as in other amphinomids. Thus, he supported the statement by Hartman. Salazar-Vallejo (1997), despite having reviewed the holotype of Notopygos megalops, followed Hartman’s opinion and regarded it as a junior synonym of Notopygos crinita.

Only two species of the genus have branchiae beginning on chaetiger 6: Notopygos megalops and Notopygos hispidus Potts, 1909 from the Seychelles. The latter has a complex pigmentation pattern, and a well-developed caruncle with expanded lateral lobes, with about 20 folds and continuous projection between folds in the elevated lobe. In addition, the anus is on chaetiger 21. We consider that there are sufficient features to distinguish Notopygos megalops from the other Notopygos species; thus, we regard it as a valid species.

The caruncle in juvenile specimens is not completely developed; however, the branchiae beginning on chaetiger 6 and the large size of the notochaetae permit species identification.