Holotype. CASIZ 75783, ethanol preserved, Los Frailes, Baja California sur, México, 52 m, coll. R. Adcock, 18 June 1979.

Paratypes. MCZ 36106, dry, Paita, Piura, Perú, no more data available. USNM 56879, ethanol preserved, El Alto, Piura, Perú, 1860-1815 m but depth data dubious (F. M. Bayer’s note on label: ‘specimen probably from previous shallow station’), Anton Bruun Cruise, 18B, Sta. 766, 4°10'S, 81°27'W, 9 September 1966.

Baja California sur, México.

Ascending colony sparse growing, branching irregularly pinnate, and multiplanar, subdividing up to 11 times, some pseudo-anastomosis present. Prominent polyp-mounds up to 0.70 mm tall, dome-shaped, arranged irregularly, and closely placed on branchlets, and very distant on thick branches. Colony and sclerites white. Spindles and disc-spindles up to 0.14 mm in length, double discs up to 0.07 mm long, and 0.05 mm wide. Anthocodial rods absent.

Holotype 24 cm tall, and 20 cm wide, ascending, sparse growing, (Fig. 1A). Branching irregularly pinnate, and multiplanar, several pseudo-anastomosis occurs in branchlets and branches (Fig. 1A–B). Main stem 4 mm diameter at base, slightly compressed, and short, about 80 mm long arising from a fragment of holdfast, 0.6 mm diameter. Main stem gives off several branches and stumps. The three main branches, 3.0–4.0 mm in diameter, emerging at angles of 45–90°and producing secondary branches subdividing and giving off thin branchlets, up to 2.5 mm diameter, including polyp-mounds. Branchlets irregularly arranged, separated 5–16 mm, and giving off 2 or 3 lateral, secondary branchlets, of same thickness and arrangement. Colony branching up to 11 times. Unbranched terminal twigs blunt, and reaching up to 50 mm long (Figs 1A–B). Polyp-mounds prominent, up to 0.7 mm height and 1 mm in diameter, dome-shaped, with slit-like apertures, arranged irregularly, close together along the branchlets, and very distantly distributed or absent along the thick branches (Fig. 1B). Holdfast devoid of polyps. Colony white (Fig. 1A–B). Sclerites of coenenchyme white, mostly double discs (Fig. 1C). Spindles and disc-spindles, up to 0.14 mm long and 0.04 mm wide, with 4 or 5 whorls of warty tubercles, the ends mostly blunt (Fig. 3A). Double discs up to 0.07 mm long, and 0.05 mm wide (Fig. 3B). Crosses about 0.08x0.06 mm, scarce on samples (Fig. 3C). No anthocodial sclerites present in the samples.

Paratype MCZ 36106 reaches up to 34 cm tall, and 31 cm wide, the main stem 0.7 mm diameter, slightly compressed, and short, about 1.0 cm long arising from an oval holdfast 3.2 cm diameter, and 0.2 cm thick (Fig. 2A–B). Sclerites as in the holotype (Fig. 2C). The other examined specimens are smaller, but very consistent in all aspects with the holotype.

The morphology of the colony, i.e., irregular-pinnate branching and prominent polyps, immediately segregates the new species from the ampla-group, and suggest a similarity with daniana-, rubens- and siedenburgae-groups. Eugorgia beebei and Eugorgia siedenburgae differ from the species in the daniana-group, including Eugorgia mutabilis sp. n. (described below), firstly, in the colony growth, which is sparse and ascending in Eugorgia beebei sp. n. but bushy and profuse in Eugorgia siedenburgae, not flabellate as it is in the daniana-group species. Secondly, it differs in the branching patterns because branchlets in the daniana-group form flat pinnate fronds with pinnae projecting in the same plane. That is not the case in Eugorgia beebei and Eugorgia siedenburgae where the secondary branchlets stick out in several, irregular planes.

Eugorgia siedenburgae and Eugorgia rubens form monospecific groups, they differ especially in the colony growth. The rubens-group have pink, sparse and laterally branched colonies, and the siedenburgae-group, have bushy, bicolored colonies (Breedy and Guzman 2013).

Eugorgia beebei and Eugorgia siedenburgae are very similar in sclerite content (Table 1), but they are different especially in the growth form and in the color. The conspicuous bushy colony immediately distinguished it from Eugorgia beebei; additionally, Eugorgia beebei has thicker branches and branchlets than Eugorgia siedenburgae; the polyp mounds are pointed and higher in the latter, and are more rounded in Eugorgia beebei. Branchlets in Eugorgia beebei are longer than in Eugorgia siedenburgae (Table 1).

We found the paratype in the MCZ (36106), labelled in Elisabeth Deichmann’s handwriting (Ardis Johnston, pers. comm.) as a variety of Eugorgia rubens, however, she certainly had not published anything on this genus, thus the variety or the species was never established. The specimen was part of an MCZ public exhibition, the only data we have are the locality. It is probable that this specimen examined by Deichmann came from the Zaca expedition of 1937 and 1938. We do not consider Eugorgia beebei as a variety of Eugorgia rubens because they differ in the traits that have been shown to be informative to separate species in the genus: color, branching pattern, colony growth and sclerite content (see Table 1), as mentioned above.

This new species of Eugorgia is named for explorer/naturalist William Beebe (1877–1962) who studied the marine fauna at numerous locations along the west coast of Central America from Mexico to Columbia during the Templeton Crocker Zaca expedition between 1937 and 1938. Beebe subsequently wrote the book, Book of Bays, which chronicles the five month expedition (Gould 2004).

Presently known from Piura, Perú and Baja California, but it is very likely that it exist along all along the geographic range. The depth range is 50–60 m, it is possible the range could extends deeper, but not as deep as reported for paratype USNM 56879, which is probably a mistake, as was remarked by F. M. Bayer (former USNM curator).

Holotype. UCR 2297, ethanol preserved, Burbujas, between Los Potreros and Playa Arenitas, Puerto Jiménez, Golfo Dulce, Costa Rica, 11 m, O. Breedy, 9 May 2013. Paratypes. UCR 2298, same data as the holotype. UCR 2272, 2276, fragments, ethanol preserved, Burbujas, 12 m, C. Sánchez, May 2012. UCR 2299, fragment, ethanol preserved, Roca Matapalo, Cabo Matapalo, Golfo Dulce, 20 m, O. Breedy, 6 February 2009. STRI 408, dry, Isla Seca Grande, Gulf of Chiriquí, Panamá, 20 m, H. Guzman, 26 August 2002. STRI 444, dry, Isla Jicarita, Gulf of Chiriquí, 20 m, H. Guzman, 29 August 2002. STRI 511, dry, Isla Ladrones, Gulf of Chiriquí, 15 m, H. Guzman, 14 April 2003. STRI 1073, Santa Cruz, Coiba Island, Panamá, 15 m, H. Guzman, 27 April 2007. STRI 1076, Twin Peaks, Coiba Island, 15 m, H. Guzman, 27 April 2007. STRI 1168, fragment, ethanol preserved, Bajo Hacha, Coiba Island, 20 m, O. Breedy, 16 April 2009. STRI 1122, ethanol preserved, La Blanca, Oxaca, Mexico, 46 m, R. Abeytia, 29 August 2004.

Puerto Jiménez, Golfo Dulce, Costa Rica, 11 m.

Broad, stout, flabellate colony, main branches sinuous, branching irregularly pinnate, subdividing 5–7 times, no anastomosis present. Prominent polyp-mounds closely spaced and irregularly distributed around branches and branchlets (Figs 4, 6A-C). Colony white, pale pink when alive (Fig. 6A–C), dark grayish when dry or ethanol preserved. Change in color after collection very conspicuous. Longitudinal grooves evident along branches and branchlets. Sclerites white. Spindles and disc-spindles up to 0.15 mm long, double discs mostly 0.05–0.08 mm long. Sclerite discs sharp, serrated and prominent. No anthocodial rods found.

Holotype 30 cm tall, and 47 cm wide; colony broad, flabellate, very flexible. Branching irregularly pinnate. Main stem 6 mm diameter, laterally flattened, and short, 14 mm long. Holdfast oval, 40 mm diameter without polyps. Main stem subdividing in 5 sinuous main branches. Main branches slightly flattened on plane of colony, 3–4 mm in diameter emerging at angles of about 45°, bifurcating and diverging producing five flat pinnate fronds of long pinnate branchlets (Fig. 4A–B). Pinnae short, up to 8 mm long, and 1.5–2 mm diameter including polyp-mounds, close together 1–3 mm apart. Branching up to 7 times. Unbranched terminal twigs blunt, and reach up to 8 mm long (Fig. 4A–B). Longitudinal grooves distinct along branches and pinnate branchlets, evident in living and preserved specimens. Polyps white (Fig. 4B). Polyp-mounds prominent, up to 0.7 mm height and 0.8 mm in diameter, arranged mostly in lateral rows along the branchlets and separated by the longitudinal grooves, and more sparsely and irregularly distributed along the thicker branches (Fig. 4B). Colony white to pale pink when alive, gray to dark grayish in ethanol/dry preservation (Fig. 4A). Change in color very conspicuous possibly by liberation of black pigments after collection. Sclerites of coenenchyme white. Sclerite discs conspicuous mostly sharp, serrated and prominent (Fig. 4C, 5A–B). Disc-spindles 0.08–0.12 mm long, and up to 0.06 wide with 4–5 whorls of discs (Fig. 5B); spindles and disc-spindles, longer and thinner up to 0.15 mm long and 0.05 mm wide, with 5–7 whorls of warty tubercles, the ends acute, blunt, or both (Fig. 5A). Double discs up to 0.08 mm long, and 0.05 mm wide with prominent discs (Fig. 5B), some almost complete (Fig. 5B). No crosses, capstans or anthocodial sclerites present in samples.

The specimens present some variation in sclerite color, white sclerites being dominant, but some pale yellow hues could be observed in the samples. In all other aspects they agree with the holotype, including the change of color from bright white alive or recently collected to grayish when fixed. It is interesting that after collection, the specimens discharge a black pigment that turns the water black or the alcohol, and the colony becomes gray. The specimens from Mexico represent the deeper record; they have been observed down to 50 m, meaning that the range of depth extends from 40 to 50 m as it is for Eugorgia rubens, Eugorgia siedenburgae, and Eugorgia beebei, but the morphology of the colony and sclerites remain the same described for Eugorgia mutabilis. Current flow and depth are some of the environmental factors that could influence interspecific variability in octocorals (Fabricius and Alderslade 2001), but in this case no effect was observed. The morphology of the colony and sclerite content are persistent along the depth range.

The species was mentioned before as a variety of Eugorgia daniana: ‘a white variety has been observed in shoals in Costa Rica and Mexico occurring together with the red form’ (Breedy et al. 2009). However, after examination of many specimens from various localities and depths, we found enough differences with respect to Eugorgia daniana, and to the other species in the group, especially in the color and the conspicuous sclerites, to establish Eugorgia mutablilis as a new species.

The new species is found on rocky substrates, in general with other species of gorgonians, including Eugorgia daniana, but in some places, it is the only Eugorgia present (Fig. 6A–C). Other gorgonians found normally inhabiting the same localities are Pacifigorgia irene, Pacifigorgia stenobrochis, Leptogorgia alba, and Carijoa riseii, which were very abundant in the type locality. A variety of associated invertebrates were found on the holotype and paratype UCR 2298, including ophiuroids, Ophiotrhix sp., and crustaceans, shrimps, Periclimenaeus sp. and abundant crabs, Orthochela sp.

The specific epithet is from Latin, mutablilis, changeable, in allusion to the change in color after collecting.

Eugorgia mutabilis belongs to the daniana-group with a characteristic flabellate colony composed of flat pinnate fronds, and irregular pinnate-branching pattern, and prominent polyp mounds. The white color of the colony and sclerites of Eugorgia mutabilis separates it from the rest of the group. However, the new species is similar to Eugorgia daniana in some features, e.g. maximum number of branches, branchlet distance, polyp distribution (see Table 1), but the sclerite composition is very different. The dominant sclerites in Eugorgia mutabilis have very sharp crested discs that are very consistent in all specimens revised from Mexico, Costa Rica and Panama, and along the depth range. These type of sclerites are distinct also from the ones in Eugorgia beebei, and in Eugorgia siedenburgae.

Records from Costa Rica, México and Panamá suggest a wide distribution, at least from Mexico to Panamá, but this has to be further explored. The deepest record in Panama is 35 m, in Costa Rica 25 m, and in Mexico 50 m. Thus, the occurrence of this species from 11 to 50 m deep also suggests a large bathymetric range of distribution.