A revision of the genus Psammogorgia Verrill, 1868 (Cnidaria, Anthozoa, Octocorallia) in the tropical eastern Pacific Ocean

Abstract The species of the genus Psammogorgia Verrill, 1868 from the shallow waters of the tropical eastern Pacific were mainly described from 1846 to 1870. Very few contributions were published subsequently. Recently, the genus was revisited with the addition of two new species. However, a comprehensive generic study is still missing for the eastern Pacific. Psammogorgia is characterised by having axes cores without mineralisation, mainly coarse irregular spindles and thorny, leafy or tuberculate clubs coenenchymal sclerites and the anthocodial armature with distinct collaret and points arrangements. Herein a taxonomic revision of the genus is presented based on type material which was morphologically analysed and illustrated using optical and scanning electron microscopy. Comparative character tables are provided for comparison among species in the genus, along with a taxonomic key. Moreover, the taxonomic status of each species was analysed. The genus Psammogorgia comprises six valid species and two varieties, and three lectotypes and a new combination are proposed to establish the taxonomic status of these species.


MCZ
Museum of Comparative Zoology, Harvard University, Boston, USA.

YPM
Yale Peabody Museum of Natural History, New Haven, USA.

Material and methods
The type specimens used in this study were analysed during visits to museums or acquired on loan from the MCZ, MNHN, NMNM, and YPM. For the species Psammogorgia fucosa (Valenciennes, 1846), the only type material available is a sclerite slide found in the MCZ. Depth of collection of the type specimens was not recorded; however, most of the types collected by F.M. Bradley were obtained by pearl divers between 8 and 12 m in depth (Verrill 1868b).
The taxonomic identification and description of the octocorals was based on external morphology: shape, size and colour of the colonies, and calyx structures, as well as on internal morphology: sclerites content, dominance, shape, size and arrangement. Terminology used in this study mostly follows Bayer et al. (1983). For microscopic study, fragments of the tips of the colonies were treated with 5% sodium hypochlorite to dissociate sclerites from the tissues. The structures were washed several times in distilled water and dehydrated with 100% ethanol and posteriorly dried in the oven (Breedy and Guzman 2002). For old specimens in bad conditions it was difficult to clean the sclerites. These samples were treated with hydrogen peroxide to remove remains of organic matter, but most sclerites from these samples were still dirty as shown by the Scanning Electron Microscope (SEM) micrographs. Notes on the colours of the colonies and sclerites based on dry type material and literature reports were taken, considering that colours are stable and persist after fixation of the Psammogorgia specimens.
In order to prepare the sclerome for imaging and measurements, different microscope preparations were made. For optic microscopy, sclerites were mounted in water or glycerine and photographed with an Olympus LX 51 inverted microscope. For SEM, sclerites were mounted on SEM stubs by double stick carbon tape and silver paint bridges between the tape and the stubs were made to increase the electronic conduction. The samples were then sputter-coated with gold, 30-60 nm layer, in an Eiko IB-5 Ion Coater and the pictures were obtained using a Hitachi SEM S-3700N. Unsorted optic microscope micrographs reveal colour details and sclerites composition while the SEM illustrations show details and sculpture of the sclerites. Not all sclerite types of a species are presented in the SEM figures. Measurements of the sclerites were obtained from the SEM images, and for P. fucosa from the optical micrographs the length of the sclerites was measured from one tip to the other and the width was taken from the most distant points across the sclerites, reporting the largest sizes found in the samples. Because type material was generally in bad condition, the anthocodial sclerite arrangement at the base of the polyps was not described in some cases. The diameter of the branches, branchlets, and stems was noted, taking the length of the calyces into account.
Designation of lectotypes was done for three species with unclear identity described by either Verrill or Valenciennes without type designation. Lastly, data on geographical distributions are based on our personal collections (Museo de Zoología, Universidad de Costa Rica, Naos Laboratory, Smithsonian Tropical Research Institut, Panamá, STRI), museum catalogues and published monographs.
Type species. Echinogorgia arbuscula Verrill, 1866 by subsequent designation (Verrill 1868b). Diagnosis. Colonies bushy to flabellate. Branching lateral, dichotomous, irregularly dichotomous, or subpinnate. Branches round or slightly flattened. Axis horny, chambered central core filled with organic non-mineralised fibres. Calyces on all sides of branches, flat, slightly raised or prominent. Polyp apertures slit-like or swollen. Anthocodial sclerites mostly large, elongated, warty, spinose or slender spindles, with or without median waist, in collaret and points arrangements at base of tentacles. Sclerites of coenenchyme thick, warty spindles; radiates, and crosses. Clubs warty or foliate-like with variation of those types mostly present at calyx rims and external coenenchyme. Colony colours dark red, red, orange, pink and white. Sclerites colours red, pink, orange, yellow, various hues of these, and/or colourless.
Distribution. The genus has been reported from the eastern Pacific, Californian province, the Indian Ocean and the north Atlantic.
Remarks. Axes analysis of the species of Psammogorgia show chambered central cores filled with organic non-mineralised fibres (e.g., Fig. 1). (Verrill, 1866) STRI 269 A central core chambers filled with organic non-mineralised fibres B detail of organic non-mineralised fibres.
Description. (see also Verrill 1866Verrill , 1868bBayer 1956). The lectotype is a bushy, irregularly dichotomous dry colony, 12 cm long and 9.5 cm wide. The colony is of a red orange colour ( Fig. 2A, B). Nine stems arise from an oval encrusting holdfast which is ~ 4.5 cm in diameter ( Fig. 2A). The holdfast is covered by a thin layer of coenenchyme with polyps. Most of the stems are 3.0-3.2 mm in diameter bifurcating a few mm above the base, two of them raising up to 2 cm before subdividing in several branches 2-4 mm in diameter including calyces. The colony branches up to eight times. The branches emerge at angles of 45-90°, ascending parallel and slightly curved at the end. Terminal branchlets are 2.5-10 mm long ( Fig. 2A). The calyces are with rounded somewhat tapered tips. Calyces are closely arranged around the branches, mostly in 2-3 longitudinal rows on each side of the branches; somehow in quincunx (arrangements of five) as Verrill (1868b) mentioned (Fig. 2B). The calyces are prominent, up to 1 mm tall and around 2 mm diameter, composed of eight marginal swollen lobes around the polyp apertures, which is evident when polyps are withdraw or in dry condition (Fig. 2B). Calyces present a concentration of thorny, irregular spindles and wart-clubs around the borders. The coenenchyme is moderately thick, granulose and brittle in the dry lectotype. Coenenchymal sclerites are dark red, red, orange and of lighter hues (Fig. 2C), and of different forms: irregular spindles with acute or bifurcated ends, some being slightly curved (Figs 2C, 3A), 0.14-0.20 mm long and 0.06-0.07 mm wide. Warty radiates are 0.07-0.13 mm long and 0.065-0.085 mm wide (Fig. 3B); and some warty crosses up to 0.11 mm by 0.1 mm. Wart-clubs are 0.09-0.18 mm long and 0.049-0.12 mm wide, variable in form and with a larger end expanded and covered with thorny warts (Fig. 3C). They are concentrated at the calyx rims and the base of the anthocodia. The anthocodial armature is well developed. It is composed of spiny spindles arranged in a collaret and points, 0.13-0.17 mm long (0.20-0.26 mm long according to Verrill (1868b)) and 0.02-0.045 mm wide (Fig. 3D); its flat spindles are with small tubercles and scattered warts.
Variability. Most of the type material of the form typica of P. arbuscula is constituted of small colonies 5-15 cm long and 3-7 cm wide or fragments of colonies, the largest specimen being MCZ 7009 (28 cm long and 20 cm wide), with unbranched ends up to 15 cm long. Stems can reach up to 4 mm diameter, branches up to 3.5-3.8 mm in diameter and branchlets up to 2.0-2.6 mm in diameter. The sclerites content is consistent among the types. When alive, the colonies are dark red and the polyps are bright yellow (Verrill 1868b) (Fig. 4).
Remarks and comparison. The Psammogorgia arbuscula typica is different in calyx structure, size of sclerites and colour from the varieties P. arbuscula var. dowii and P. arbuscula var. pallida (see Tables 1, 2). These other varieties lack the prominent and swollen calyces present in P. arbuscula typica. Psammogorgia gracilis and Psammogorgia hookeri have prominent calyces however, there are many other differences that separate them from P. arbuscula (Tables 1, 2). Psammogorgia gracilis has thinner and longer branchlets as well as shorter spindles, longer wart clubs, and shorter anthocodial sclerites (Tables 1, 2). Psammogorgia hookeri has smaller bushy colonies with a typical coral red colour, different from the larger colonies of P. arbuscula. In general, P. hookeri has star-like sclerites absent in the later, and smaller sclerites than in P. arbuscula. Bayer (1958) treated specimen MCZ 4022 as the holotype for the species however, Verrill did not designate a holotype. Verrill´s 1866 original description of Echinogorgia arbuscula is general, and he did not describe specimen MCZ 4022 specifically. We consider specimen YPM 573 more representative of the species and designate this as the lectotype to clearly establish the taxonomic status of P. arbuscula.   (Verrill, 1866). A In situ colony, 13 m deep, Rocas Corcovado, Osa Peninsula, Costa Rica. Photograph: Manu San Felix, National Geographic Pristine Seas. Table 1. Comparative features of Psammogorgia colonies from the tropical eastern Pacific, according to analyses of type material from museums (YPM, MCZ, MNHN), and taxonomic descriptions by Verrill (1868bVerrill ( , 1870 and Bayer (1958). Diameter of the branches includes calyces. Measurements in millimetres. Description. The syntype YPM 1787 is a small, 5.8 cm long dark red colony of two dichotomous branches. A 1.1 cm long stem arises from an oval holdfast ~ 1 cm in diameter (Fig. 5A). The holdfast is covered by a thin layer of coenenchyme without polyps. The stem is 2.0 mm in diameter and bifurcates, subdividing in two branchlets up to 3.5 cm long. The branchlets are of the same diameter as the stem, with rounded tips. The branchlets bifurcate at angles of 45°, ascending parallel and are slightly curved. Terminal branchlets are 6-35 mm long (Fig. 5A). The coenenchyme is granulose and brittle. Coenenchymal sclerites are of different forms: irregular spindles with acute or bifurcated ends, some are slightly curved (Fig. 6A), 0.14-0.21 mm long and 0.05-0.09 mm wide. Warty radiates and crosses are 0.13-0.15 mm long and 0.10-0.11 mm wide (Fig. 6B). Wart-clubs are 0.11-0.18 mm long and 0.05-0.085 mm wide at the expanded head being variable in form with a larger end expanded and covered with thorny warts and leaf-like projections (Fig. 6C). Coenenchymal sclerites are of various colours: orange, red, and darker (Fig. 5C). Table 2. Comparative features of sclerites of Psammogorgia species in the tropical eastern Pacific Ocean according to an analysis of type material from museums (YPM, MCZ, MNHN) and taxonomic descriptions by Verrill (1868bVerrill ( , 1870, Bayer (1958), Breedy and Guzman (2014), and Breedy et al. (2020). The calyces are arranged all around the branches, not very close, slightly raised up to 0.5 mm tall as small mounds composed of eight marginal lobes with small polyp apertures at the summits (Fig. 5B). Thorny, irregular spindles and some wart-clubs appear often, around the calyx aperture. The anthocodial armature is well developed and composed of spiny spindles arranged in a collaret and points, 0.12-0.20 mm long and 0.032-0.056 mm wide (Fig. 6D); its flat rods are with small tubercles and scattered warts. Anthocodial sclerites are red and orange (Fig. 5C).

Species
Remarks and comparison. The calyces in this specimen are more separated and do not have swollen polyp apertures as in P. arbuscula typica. Verrill (1868b) mentioned a more flabellate colony but YPM 1787 is not flabellate having only a few branches. Verrill (1868b) did not provide data approximately the size of sclerites of this variety, uniquely pointing out that the sclerites resemble the ones of P. arbuscula typica. We found that the sclerites of the only specimen of this variety are smaller and similar to, the ones of P. arbuscula typica. Specimen YPM 8684 corresponds to several colony fragments belonging to P. teres, P. arbuscula and an undetermined species.
Distribution. Tropical eastern Pacific: only reported from the type locality, Pearl Islands, Panamá. Description. The syntype MCZ 729 is a yellowish flabellate, 10.5 cm long and ~ 9 cm wide colony. Two main stems arise from a holdfast that is 1.6 cm in diameter nd devoid of polyps (Fig. 7A). The stems are less than 1 cm tall and 2.5 mm in diameter, subdividing irregularly in secondary branchlets of 2-3 mm diameter with rounded tips (Fig. 7A). The branchlets emerge at angles of 45-180° and spread irregularly in one plane. The colony branches up to 15 times. Terminal branchlets are up to 40 mm long (Fig. 7A). The polyps occur all around the branches, 1-1.5 mm apart on branchlets and 1.5-2.5 mm apart on the branches. The calyces are almost flat with a few being ~ 0.02 mm tall with oval or round polyp-apertures. Thorny, irregular spindles  and wart-clubs occur around the calyx rim (Fig. 7B). The coenenchymal sclerites are mostly irregular tuberculate spindles (Figs 7B, 8A) with acute or bifurcated ends or combinations of both ( Fig. 8A) with colours varying from pale pink to mostly colourless (Fig. 7B). These sclerites are 0.15-0.23 mm long and 0.04-0.09 mm wide. Wart clubs are 0.11-0.14 mm long and 0.05-0.06 mm wide with warts or with wide tubercles (Fig. 8B). Crosses various intermediate forms and radiates are 0.08-0.16 mm long and 0.07-0.12 mm wide with tubercles (Fig. 8C). The anthocodial armature is composed of slightly bent spiny orange-red sclerites arranged in a collaret and points, 0.11-0.23 mm long and 0.02-0.045 mm wide (Figs 7B, 8D).
The syntypes YPM 1785a, b are two fragments of a lighter colour than MCZ 729 (Fig. 9B). The largest fragment is 5.6 cm long and composed of four branchlets with 2-3 mm in diameter; flat calyces all around the branches (Fig. 9A). All sclerites, including the anthocodials, are pale yellow to colourless. Sclerites from the syntypes are more ornamented than in specimen MCZ 729 but mostly colourless (Fig. 9B). The coenenchymal sclerites are mostly irregular, tuberculate warty spindles with acute or bifurcated ends or combinations of both; being 0.13-0.18 mm long and 0.035-0.08 mm wide. Clubs have a few warts or with wide tubercles being 0.11-0.16 mm long and Remarks and comparison. Verrill´s material at MCZ includes two specimens, MCZ 729 (4916) and YPM 1785, both with similar sclerites but different in external morphology. One is a small colony and the other is a small fragment in bad condition. According to Verrill´s description (Verrill 1868b) the type material has a "corallum more or less flabelliform, branching dichotomously, branchlets round, sometimes as large as the main stem, usually smaller. Cells a little raised forming low verrucae". However, Verrill did not measure the specimens. YPM 1785 is different from Verrill's description while MCZ 729 (4916) matches some details of his description. Orangered anthocodial sclerites are present in MCZ 729, as well as at the P. arbuscula var. pallida description by Verrill (1868b), in contrast with the colourless rods in specimen YPM 1785. Also, pale pink, colourless, and transparent coenenchymal sclerites match his description (Fig. 7B). In terms of sclerite sizes, Verrill's description better matches MCZ 729 with larger sclerite sizes than the smaller YPM 1785 ones. As Verrill suggested, with this and dowii variety, we opt to keep P. arbuscula var. pallida as a variety.
Distribution. Tropical eastern Pacific: only reported from the type locality at Pearl Islands, Panamá.
Diagnosis. Colony dull reddish. Colonies bushy and irregularly dichotomous. Stems short and up to 12.5 mm in diameter. Branchlets up to 4.5 mm in diameter. Calyces flat, sparsely distributed all around the branches. Coenenchymal sclerites red, pink or colourless, mostly spindles up to 0.22 mm long; wart-clubs, up to 0.18 mm long; and warty radiates. Anthocodial spindles red, up to 0.21 mm long. Description. Valenciennes´ figured type was originally presented in natural size (Fig. 10A). Verrill (1868b) reported this dull reddish specimen to be 25.4 cm long and 22.8 cm wide, with the branches ~ 3.8 mm wide. Approximately five stems arise from the holdfast, the thicker being around 12.5 mm in diameter. The colony branches up to 12 times. The branches are irregularly dichotomous, emerging at angles of 45-120°, mostly ascending in parallel and bifurcating at distances of 12.5 to 50.8 mm. The end branchlets are mostly crooked, scarcely tapering and obtuse or clavate at the tips with a diameter of 3-4.5 mm. Branchlets tips are ~ 12.7 to 25.4 mm long (Fig. 10A). The calyces occur all around the branches but not close to each other (Fig. 10A).
The coenenchymal sclerites vary remarkably in diversity of colour, size and form as Verrill has pointed out. Verrill found white, yellowish, light red, deep red and amethystine intermingled sclerites while we observed transparent, red and pink sclerites in the MNHN slide. The MNHN sclerites show a diversity of sclerites that is typical of the genus: mostly irregular warty spindles with acute, blunt or bifurcated ends, and several irregular forms (Figs 10B, 11). These sclerites measure 0.10-0.19 mm in length (reaching 0.22 mm according to Bayer (1858)) and 0.04-0.095 mm in width. Spindles commonly lack the naked median space as they are densely covered with warts. Few wart-clubs are found in the sample, 0.10-0.18 mm long and 0.04-0.06 mm wide at the expanded head. Radiates are densely covered by warts measuring 0.09-0.11 mm in length and 0.055-0.07 mm in width (Fig. 11). Anthocodial spindles are red, long, slender, and covered with small warts measuring 0.10-0.21 mm long and 0.01-0.02 mm wide (Fig. 11).
Remarks and comparison. Verrill´s description of sclerites was based on the MNHN sclerite slide that was sent to him at the MCZ for analysis, probably by R.A. Kölliker (Bayer 1958). We have also analysed sclerites from the slide, showing details that are difficult to compare with those of other species. Though, we found larger sizes of the sclerites than sizes given by Verrill (1870), as also observed by Bayer (1958). This species is similar to P. teres, in many aspects (see analysis below). It is indeed possible that P. fucosa is a synonym of P. teres; however, without a specimen to examine we prefer to keep the status of P. fucosa as dubious.
Distribution. Tropical eastern Pacific: only reported from the type locality at Mazatlán, México.
Description. The lectotype colony is red and 10 cm long and ~ 6 cm wide. Branching is irregularly dichotomous. The holdfast is absent. The branches emerge at angles of 45-90°, ascend parallel and slightly curve. The main branch of the colony is 2.5 mm in diameter subdividing into long, slender, ascending branchlets, 1.5-1.6 mm in diameter. Branches are round, slender, some extending up to 6.3 cm, undivided or bifurcating at the ends. Branches subdivide up to nine times while terminal branchlets are up to 60 mm long with rounded slightly tapered tips. (Fig. 12A). The calyces are densely arranged around the branches, slightly raised, swollen and are around 0.3 mm tall and 1 mm in diameter (Fig. 12B). The calyces have wart-clubs and some irregular spindles around the calyx rim and the base of the anthocodiae. Coenenchymal sclerites are red, orange or of lighter hues (Fig. 12A-C); including slim spindles with acute ends that may bifurcate (Figs 12C, 13A). Spindles are 0.12-0.24 mm long and 0.04-0.07 mm wide. Wart-clubs are 0.11-0.25 mm long and 0.04-0.08 mm wide at  the expanded head (Fig. 13B). Warty radiates and crosses are 0.08-0.10 mm long and 0.055-0.07 mm wide (Fig. 13C); and some warty crosses up to 0.10 mm by 0.09 mm. Anthocodial armature is well developed with orange and pale yellow spiny spindles arranged in collaret and points (Fig. 12A-C), measuring 0.11-0.20 mm long and 0.03-0.04 mm wide (Fig. 13D) and flat spindles with small tubercles and scattered warts.
Remarks and comparison. This species differs from the others by having long, slender and ascending branchlets, which are thinner than in the other species of the genus (Table 1). Verrill (1868b) pointed out the abundance of wart-clubs in this species when compared to P. arbuscula and P. teres. According to Verrill, the specimen he described was slender, flabelliform with subparallel and elongated branchlets, measuring12.7 cm long and 10.2 cm wide. The material left (YPM 813a) matches Verrill´s description and illustration. Therefore, we designate this specimen, YPM 813a, as the lectotype of P. gracilis.

Psammogorgia hookeri Breedy & Guzman, 2014
Diagnosis. Colonies coral red, small, bushy, multiplanar and irregularly dichotomous. Coenenchyme granular. Coenenchymal sclerites: wide, irregular spindles with acute or bifurcated ends, and combinations of both; warty and irregular radiates, crosses and conspicuous star-like radiates. Colours of coenenchymal sclerites reddish, coral red, and lighter. Calyces prominent, swollen and closely placed. Thorny, irregular spindles, and wart-clubs around the calyx rim up to 0.16 mm long. Anthocodial spindles, thin and spiny, in collaret and points arrangements, yellowish, and pale pink in colour. We refer to Breedy and Guzman (2014) for a full description of the species.
Distribution. This species has only been reported for Perú, Isla Gallán, Paracas National Reserve at 25 m depth, and from Bahía Independencia at unknown depth (Fig. 14).
Diagnosis. Colonies white, flabellate and branching in one plane, profuse irregularly dichotomous with occasional anastomosis. Calyces slightly raised, not close together with spiny lobes around polyp apertures. Thorny, irregularly-shaped spindles, and wart clubs around the calyx rims; wart clubs up to 0.26 mm long. Coenenchyme granular. Coenenchymal sclerites white, irregular spindles with acute or bifurcated ends or combinations of both as well as warty and irregular radiates. Anthocodial spindles orange, thin and spiny, in collaret and points arrangements. We refer to Breedy et al. (2020) for a full description of the species.
Distribution. This species has only been reported from its type locality in the upper mesophotic habitats of the Hannibal Bank at 63 m depth. Verrill, 1868 Figures 15, 16 Psammogorgia teres Verrill, 1868b: 416-417;Hickson 1915: 554;Kükenthal 1919: 237-238;Kükenthal 1924: 108;Harden 1979: 120. Colonies red or orange when preserved but brighter when alive. Colonies bushy and branch laterally and irregularly dichotomous. Stems vary from few mil-limetres up to 5 cm long, and 6 mm in diameter. Holdfasts encrusting with thin coenenchyme, often with polyps. Calyces flat, sparsely distributed all around the branches. Calyces with thorny, irregular spindles and wart-clubs around the calyx rim. Coenenchyme compact. Coenenchymal sclerites red, orange or colourless, mostly irregular warty spindles with acute or bifurcated ends and asymmetrical forms with prominent warty tubercles up to 0.20 mm long; wart-clubs with wide heads, up to 0.16 mm long; warty radiates and crosses. Anthocodial spindles pale yellow or colourless, flat or spiny, up to 0.26 mm long and in collaret and points arrangements. Coenenchymal sclerites red, orange and colourless, anthocodial rods pale yellow and colourless.

Psammogorgia teres
Description. The lectotype is a red orange dry colony, which was brighter when alive (Verrill 1868b), with 25 cm long and 20 cm wide (Fig. 15A, B). The colony is bushy and laterally branched with an irregularly dichotomous pattern which branches up to 12 times (Fig. 15A, B). The stem is 5 mm long and is 6 mm in diameter, arising from an oval holdfast with around 3.1 cm in diameter that bifurcates in two main branches. These branches are 5-6 mm thick at the base diminishing toward the tips to branchlets of around 3 mm in diameter (Fig. 15A). The branches emerge at angles of 45-90°, ascending mostly parallel to each other and bifurcating the same way. Branchlets are mostly perpendicular to the branch of origin and slightly curved. Terminal branchlets are 5 to 60 mm in length (Fig. 15A). Calyces occur all around the branches, being flat and with a polyp rim 0.4-1.0 mm in diameter and, mostly separated be-  tween each other by 0.5-4.0 mm with an average of 3.5 mm (Fig. 15B). Calyces have concentration of thorny, irregular spindles and wart-clubs appearing usually around the calyx rim. The coenenchyme is compact with a finely granulated surface. The coenenchymal sclerites are very variable in size and form, being red, orange or colourless and mostly composed of irregular warty spindles with acute or bifurcated ends, and some asymmetrical forms with prominent warty tubercles (Figs 15C, 16A). Spindles are 0.11-0.20 mm long and 0.07-0.12 mm wide. Wart-clubs have wide leafy heads and are 0.07-0.16 mm long and 0.045-0.10 mm wide (Fig. 16B). Warty radiates are 0.07-0.13 mm long and 0.06-0.09 mm wide (Fig. 16C); and some crosses, 0.95-0.11 mm by 0.08-0.11 mm (Fig. 16C). The anthocodial armature is well developed and composed of pale-yellow to colourless spiny spindles and flat warty sclerites arranged in collaret and points, measuring 0.13-0.24 mm in length and 0.02-0.04 mm in width (Figs 15C, 16D).
Remarks and comparison. While the largest anthocodial sclerite measured in the lectotype was 0.24 mm long, Verrill (1886b) mentioned a slightly larger length of 0.26 mm. This is in accordance to the anthocodials of other specimens revised in this study. The syntype YPM1556b closely fits Verrill´s (1868b) description of the colony and the sclerites. For this reason, we designate this as the lectotype to clearly establish the species identity.
Psammogorgia teres has a colony morphology similar to that of P. fucosa (Table 1), but it has different sclerite sizes and colours in comparison with the type's sclerite slide (Table 2). In P. teres, spindles and wart-clubs are shorter while anthocodials and radiates are larger than in P. fucosa ( Table 2). Anthocodials of P. fucosa are red but colourless in P. teres, which is a diagnostic feature of this species.
In comparison with P. arbuscula and P. gracilis, P. teres differs in the external morphology represented by colonies with thicker branches and flat calyces; and relative abundance and sizes of sclerites (Tables 1, 2).
Distribution. The species occurs in Pearl Islands, Panamá (type locality) and also in in the Chiriquí Gulf, Panamá. However, the species presents a wider regional distribution in the tropical eastern Pacific. It was sampled by us, along the Pacific coast of Costa Rica, El Salvador, Nicaragua, and Ecuador, and encountered in collections from the Pacific coasts of México and Colombia.

Conclusions
The genus Psammogorgia comprises six species and two varieties belonging to two morphological species-groups: Psammogorgia arbuscula group consisting of P. arbuscula, P. gracilis, P. hookeri and P. pax. and the Psammogorgia teres group consisting of P. teres and P. fucosa. We have explored and collected Psammogorgia species in Costa Rica, El Salvador, Nicaragua and Panamá, and have revised collections from Colombia, Ecuador, México and Perú. We found P. arbuscula and P. teres from these localities; nonetheless, P. gracilis and the two varieties of P. arbuscula were not found as additional records. Regarding P. digueti, after our analysis of a specimen in the MNHN we conclude that it belongs to a different genus and its status has to be revised. Lastly, P. hookeri and P. pax seem to be endemic to their regions, the first one from Perú and the other from mesophotic habitats off the Pacific coast of Panamá. However, without more explorations and further records, the geographic distribution and species richness of Psammogorgia is incomplete.
Key to the valid species of the genus Psammogorgia Verrill, 1868 reported from the tropical eastern Pacific