Early Miocene coral reef-associated bryozoans from Colombia. Part II: “Ascophora” Cheilostomatida

Abstract Bryozoans are common and diverse in fossil and modern coral reefs. However, studies of bryozoans in ancient reefs are generally limited, and even less is known about fossil bryozoan faunas associated with coral reefs in the Caribbean region. This is the second contribution describing the bryozoan assemblage from the early Miocene (Aquitanian) reefs of the Siamaná Formation in the La Guajira Peninsula, southern Caribbean. Here, we describe and illustrate 17 species of ascophoran-grade cheilostomes, including one new genus and three new species, Ditaxiporina colombiana n. sp., Poricella paulae n. sp., and Cycloavicularia parva n. gen. n. sp. Of the remaining fourteen taxa left in open nomenclature, one is considered confer and three affinis to species previously described, one is identified at family level, and nine at genus level. The Siamaná bryozoan fauna differs in species and colony-form composition from those associated with other paleoenvironments from Oligocene and Miocene localities of North America, the Caribbean, and Brazil. UUID: http://zoobank.org/043eadcf-0e39-4c1b-b207-f7628d6b5c84


Introduction
Shallow-water coral reefs are one of the most diverse ecosystems on Earth. Their structural framework provides a suitable habitat for diverse assemblages of organisms (Graham and Nash, 2013). Bryozoans are a common and diverse component of the benthic cryptic faunas associated with these ecosystems (Winston and Jackson, 1984;Cuffey, 2011;Di Martino andTaylor, 2014, 2015;Bastos et al., 2018;Ramalho et al., 2018). However, their roles in these ecosystems remain poorly known, and the species richness of the group is underestimated in most Recent and ancient reefs (Pearman et al., 2018). Although extensive work was previously undertaken on fossil bryozoan collections from the Caribbean region Cheetham and Jackson, 2000;Di Martino et al., 2018), early Miocene deposits, especially Aquitanian, are poorly represented. In addition, studies focused on bryozoans associated with coral reefs of this age are non-existent. This is the second part of a comprehensive taxonomic study of the bryozoan fauna from the early Miocene deposits of the Siamaná Formation in Colombia, interpreted as shallow-water coral reefs (Flórez et al., 2019a, b). In the first contribution, we described 15 species included in the order Cyclostomatida, as well as anascan-grade and Cribrilinidae Cheilostomatida.
Here, we describe 17 species of ascophoran-grade Cheilostomatida, and discuss the results of both contributions.

Geologic setting
The Siamaná Formation is part of the sedimentary infill of the Cocinetas Basin, at the foothills of the Cocinas, Jarara, and Macuira mountain ranges, in the La Guajira Peninsula, a remote area of northern Colombia ( Fig. 1.1). The formation has varying thickness ranging from 430 m in the type locality (Renz, 1960) to ∼20 m in the hills of Arroyo Ekieps ( Fig. 1.2). It consists of basal conglomerates overlain by sandstones and fossiliferous limestones interbedded with silty clays (Rollins, 1965;Teatin, 1991). Limestones in the upper part of the Siamaná Formation include coral reefs (Rollins, 1965), some of which grew bordering the SE of the Jarara paleoisland (current highlands, Fig. 1). The studied bryozoan samples were collected in the framestone of these reefs, which developed in shallow waters with low siliciclastic input and therefore low turbidity (Flórez, 2020). The Siamaná Formation unconformably overlaps the Eocene Macarao Formation and Jurassic metamorphic rocks (Rollins, 1965). Deep marine sediments of the lower Miocene Uitpa Formation unconformably overlie the Siamaná Formation at the basin margins; however, the transition between both formations can be conformable and gradational in the central part (Rollins, 1965).
The age of the Siamaná Formation continues to be a subject of debate. Some works point to a late Oligocene age (Rollins, *Corresponding author   Ditaxiporina colombiana new species Figure 2.6-2.10; Table 2 Holotype. Diagnosis.-Colony erect, branching, uni-or biserial. Biserial internodes can be without fertile zooids. Zooids claviform. Orifice semicircular, proximal border formed by two vestigial costae. Frontal shield made of smooth gymnocyst, regularly perforated by circular pores arranged in six longitudinal rows. ?Three elliptical pores placed along each side of the zooid. Abfrontal surface smooth, lacking pores. Oral avicularia single or paired, with triangular rostrum oriented distomedially and complete crossbar. Ovicell unknown. Description.-Colony erect, articulated, internodes uni-or biserial. Zooids elongate and claviform (mean L/W 2.76); biserial internodes with up to five zooids, alternated with and separated by narrow grooves, forming a zig-zag line along the center of the internode, all zooids facing the same side. Orifice terminal, semicircular with a broad sinus; proximal rim formed by two short and raised vestigial costae, ?with pelmata and separated by a suture along the middle line. Gymnocyst smooth, convex, perforated by circular and conspicuous pores with a slightly raised rim. Pores aligned forming three curved and concentric 'Vs'; the outer series bearing 23-27 pores; the middle series, slightly smaller, having 17-19 pores; and the inner series, the smallest, with seven pores; the central area is generally imperforate, but a small, isolated pore may occur. Three elliptical to oval lateral pores along the outer lateral side of the zooid. Abfrontal surface smooth, imperforate, and convex. Avicularia small, single or paired, placed at the sides of the orifice; rostrum triangular, short, oriented distomedially; crossbar complete. Ovicell unknown. Oral spines absent.
Etymology.-Named after Colombia, in reference to the country where it was collected for the first time, plus the Latin suffix -ianus, belonging to.
Remarks.-The analyzed material shares the characteristics of two close genera of the subfamily Ditaxiporinae Stach, 1935: the fossil genus Ditaxiporina, and the recent genus Vasignyella Gordon, 1989, the latter genus transferred to the subfamily Vasignyellinae Braga, 1994 (Vieira et al., 2007). Both genera have species with unizooidal and/or multizooidal internodes. In the members of Vasignyella, the multizooidal internodes are infrequent and bear ovicellate zooids, the paired avicularia lack a crossbar and bear lateral pore chambers (Vieira et al., 2007, p. 51, 56). By contrast, the members of Ditaxiporina have multiserial internodes with or without fertile zooids, pelmata in the suboral costae, and single or paired avicularia with a complete crossbar (Gordon and Braga, 1994). Despite the scarcity of material and its poor preservation, it is possible to infer that the specimens belong to Ditaxiporina owing to the absence of ovicells or scars thereof in the multizooidal internodes. Two North American congeners are known from the early Oligocene, Ditaxiporina subseptentrionalis (Canu and Bassler, 1917), and Ditaxiporina bifenestrata . The former species differs from Ditaxiporina colombiana n. sp. in having tubular frontal pores and in the absence of the suboral vestigial costae, while the latter species differs in having the orifice proportionately much smaller and a single smaller avicularium without crossbar . The closest congener is D. septentrionalis (Waters, 1891), known from the Eocene of Italy (Gordon and Braga, 1994, fig. 10 Gordon, Tilbrook, andWinston in Winston, 2005 Genus Trypostega Levinsen, 1909 Type species.-Lepralia venusta Norman, 1864, from English Channel, Guernsey Island, Recent; by original designation.
Description.-Colony encrusting, multiserial, multilaminar. Autozooids distinct, separated by deep furrows, ovoidal to elliptical (mean L/W 1.39), arranged in alternating rows or irregularly. Frontal shield convex with a relatively flat center, smooth, perforated by 3-9, most often seven, circular or bean-shaped foramina of different sizes; suboral mucro developed in most zooids. Marginal areolar pores few and small. Pore-chamber windows large, circular to elliptical, visible in the lateral and distal walls of marginal zooids. Orifice terminal, D-shaped; two rounded, proximally placed condyles separating a semicircular anter from a slightly wider sinus with straight to slightly concave proximal border; 4-6 oral spine bases. One to three interzooidal avicularia placed mid-lateral or distolateral to each zooid, variable in shape and size, mainly oval, sporadically subspatulate, prominent, with short rostrum oriented distally or distolaterally. Giant interzooidal avicularia less frequent, with long, straight, parallel sided, rounded rostrum and pyriform to elliptical opesia. Crossbar not observed. Ovicell hyperstomial, globular and imperforate.
Etymology.-Named after researcher Paula Zapata-Ramírez (Universidad Pontificia Bolivariana), who obtained funds to undertake research on the Siamaná Formation coral reefs and collected the coral samples in 2011.
Remarks.-Three fossil species and a population group of Poricella are known from southern North America and the Caribbean: P. horrida (Canu and Bassler, 1923) from the Miocene of Florida, P. lidgardi (Taylor and Foster, 1994) from the Plio-Pleistocene of Tobago, P. mucronata (Smitt, 1873) from the Miocene to Recent of Gulf of Mexico and Caribbean, and 'Poricella miocenica' (McGuirt, 1941), originally described from the middle Miocene of Louisiana, and subsequently found in the middle Miocene of Florida and South Carolina (Cook, 1977). Poricella horrida is easily distinguishable from P. paulae n. sp. in having an elongate orifice with condyles very close to the proximal border, and large interzooidal avicularia with triangular rostrum, single foramen, and conspicuous marginal areolar pores. Poricella lidgardi differs from the new species in having 1-3 foramina, adjacent zooids connected by calcified buttresses, and in the lack of condyles, oral spines, and mucro. Poricella mucronata exhibits a significant variation in the number of frontal foramina and oral spines, in the presence/absence of the suboral mucro, and in the shape and size of avicularia (Powell and Cook, 1967;Cook, 1977;. However, some features appear to be more dominant than others, such as avicularia with truncate rostra and distal expansion, reduced number of foramina (generally three and always fewer than six), and almost equidimensional orifice.
Although 'Poricella miocenica' is closely related to P. mucronata, Cook (1977, p. 131) distinguished the former species based on its similarity with Miocene species from Africa and Europe. Poricella paulae n. sp. resembles 'P. miocenica' sensu Cook (1977) in having avicularia associated with the ovicell, in the size of the orifice, and the frequency and orientation of oval/elliptical avicularia. However, it differs in the greater number of foramina (3-9 versus 1-2), and in the broader variety of interzooidal avicularia. Among Miocene European congeners, Poricella paulae n. sp. shares some features with P. areolata (Reuss, 1874) from Austria (on the coral Porites incrustans) and P. pouyetae (Cook, 1977) from France. Both these species have elongate orifices, and P. pouyetae also shows conspicuous marginal areolar pores. In addition, P. areolata bears a single foramen, and despite P. pouyetae bearing seven foramina, as does P. paulae n. sp., these are located more centrally on the frontal shield. In the Siamaná Formation, Poricella paulae n. sp. was found growing on the corals Alveopora tampae, Acropora panamensis, Millepora sp., and Caryophylliidae, co-occurring with Hippopodina sp. indet., Cribrilaria multicostata Flórez, Di Martino, and Ramalho, 2021, Hippopleurifera sp. indet. 2, and an indeterminate cheilostome.
Remarks.-We place this specimen in the family Arachnopusiidae because of the relatively large size of the frontal surface foramina, the presence of oral spines and basal pore chambers, and the prominent ovicells (Gordon, 1984, p. 68). Among the genera of this family, it resembles Arachnopusia Jullien, 1888, in having recumbent ovicells with a frontal window exposing the endooecium; however, it differs in having autozooids with distinct outline, foramina lacking a ligula, and in the absence of suboral avicularia (Hayward and Thorpe, 1988). It also resembles Briarachnia Gordon, 1984, in having exposed endooecium, but Briarachnia lacks interzooidal avicularia. The poor preservation of the single specimen found in the Siamaná Formation prevents description of a new genus or species. Arachnopusiidae sp. indet. was found encrusting the coral Porites baracoaensis Vaughan, 1919.
Escharoides aff. E. martae Marcus, 1955 Figure 6; Table 6 aff. Description.-Colony encrusting, multiserial, unilaminar. Autozooids distinct, separated by deep grooves, oval to polygonal, slightly longer than wide (mean L/W 1.27). Frontal shield slightly convex, smooth, centrally imperforate, surrounded by a single row of circular marginal areolar pores separated by ridges. Orifice terminal, semicircular distally, hidden by the peristome proximally. Peristomial aperture shallow, two proximal sinuses formed by two robust, rounded, lateral denticles and a central ridge, bearing distally 6-7 oral spine bases (0.03 mm in diameter). Adventitious avicularia single or paired, similar in size, placed on raised, well-developed cystids outlined by a row of marginal areolar pores, located laterally adjacent to zooidal margins, at about half zooidal length; when paired, one placed more proximally than the other; rostrum triangular, oriented proximolaterally and obliquely to the frontal shield plane, crossbar complete. Ovicells not observed.
Remarks. -Canu and Bassler (1920) introduced (as Peristomella) the species Escharoides falcifera and E. laticella from the Eocene, and E. erecta from the Oligocene of North America. Cheetham, Sanner, and Jackson (2007) described E. guraboensis from the late Miocene-early Pliocene, and Osburn (1914) described E. costifer from the late Pliocene-Recent of the Caribbean region. All of these species differ from Escharoides aff. E. martae in the position and orientation of the lateral avicularia, which are placed more distally and closer to the orifice and are directed laterally, distally or distolaterally. Although these fossil specimens closely resemble the Recent E. martae from Brazil in the location, shape, and direction of the avicularia and size of autozooids, the nominal species has a more developed peristome lacking a central ridge, sparse and prominent calcified granules on the frontal shield, and larger avicularia; in addition, the mean of zooidal length/zooidal width ratio of our specimens is lower than in the Recent material (1.27 vs. 1.60). Even though E. aff. E. martae may have lost the ornament of the frontal shield by dissolution or mechanical abrasion, as seen in other Escharoides species (Berning, 2006), the preserved morphology of the peristome distinguishes it from the nominal species.  Remarks.-The definition of this genus has been puzzling since its introduction in 1917 (Tilbrook, 2006, p. 257;Berning, 2013, p. 8;Ramalho et al., 2015, p. 126). The absence of ovicell description in the original diagnosis of Hippomenella has led over the years to the inclusion in this genus of species with bifenestrate ectooecium, a diagnostic feature of Hippopleurifera (Berning, 2013). In addition, discovery of fossil specimens exhibiting a combination of characters of the two genera (Di Martino and Taylor, 2015, p. 18), as in the material from the Siamaná Formation, increases the uncertainty. Here, we follow the amended diagnosis of Hippomenella in Berning (2013), and provide an open classification for three species: one placed in Hippomenella (based on a wider umbonuloid area, up to six oral spines, and adventitious avicularia) and two in Hippopleurifera (based on a reduced umbonuloid area, more than seven oral spines, and ovicells with bifenestrate ectooecium).
Remarks.-Our specimens consist of small colony fragments, each with only a few poorly preserved autozooids. We placed them into the genus Hippomenella based on the wide area of imperforate frontal shield, the presence of suboral and lateral avicularia, and the number of oral spines. Canu and Bassler (1920) introduced the species Hippomenella transversora and ?Hippomenella pungens from the North American Oligocene; Hippomenella sp. indet. resembles both species in general appearance. However, H. tranversora has up to six oral  spines, ooecium with an elongate pore, a small, triangular avicularium transversally directed, and lacks suboral avicularia, while ?H. pungens has two symmetrical avicularia placed below the level of the orifice. Canu and Bassler (1920) also described seven species of ?Hippomenella from the North American Eocene, among which Hippomenella sp. indet. resembles ?H. punctata in the suboral placement of the avicularia, but lacks the larger avicularium placed laterally to the orifice. ?Hippomenella infratelum Canu and Bassler, 1919, known from the Caribbean early Miocene, lacks oral spines and differs from Hippomenella sp. indet. also in having an elliptical avicularium with a complete crossbar placed more proximally on the autozooid. In the Siamaná Formation, Hippomenella sp. indet. was found on the corals Caryophylliidae and Acropora sp., co-occurring with Figularia bragai Flórez, Di Martino, and Ramalho, 2021, Hippopleurifera sp. indet. 2, Gemelliporidra aff. G. magniporosa, and an indeterminate cribrilinid.
Description.-Colony encrusting, multiserial, unilaminar. Autozooids distinctly separated by deep grooves, elliptical to subhexagonal, slightly longer than wide (mean L/W 1.22). Frontal shield slightly convex, central U-shaped area imperforate, flanked by 3-4 rows of circular, elliptical, or drop-shaped areolar pores (0.04 mm long × 0.03 mm wide) sloping inwards and separated by ridges. Orifice slightly longer than wide with arched anter separated from a smaller concave poster by two blunt condyles; 8-10 distolateral oral spine bases in non-ovicellate zooids, four in ovicellate zooids; suboral peristome well developed. Adventitious avicularia present or absent, one or two; one placed on the lateral margin of the zooid among the rows of areolar pores at about the same level of the orifice condyles, with triangular rostrum oriented laterally to proximolaterally, crossbar complete; in about half of the zooids, a second, smaller, oval to elliptical avicularium, apparently without crossbar, was observed, also placed over the rows of areolar pores, but generally on the opposite side of the zooid with respect to the oral avicularium, and more proximally. Ovicell hyperstomial, globular, slightly flattened centrally, surrounded by a row of marginal pores with radial ridges in between; ectooecium surface with radial ribs and two large drop-shaped fenestrae (0.04 mm long × 0.03 mm wide).
Remarks.-Although the specimens studied here share some features with the type species of Hippomenella (see Berning, 2013) (e.g., the wide umbonuloid area and the presence of dimorphic adventitious avicularia), we assigned them to Hippopleurifera based on the characters of the ectooecium, which is bifenestrate, and the presence of 10 or more oral spines (Tilbrook, 2006;Ramalho et al., 2015). Twelve species of Hippopleurifera are known from the American continent, ten are fossil and two are Recent. Cheetham (1962b) introduced H. mcbeanensis, and Canu and Bassler (1920)  Among the Oligocene-Miocene to Recent species, Hippopleurifera sp. indet. 1 resembles H. costulata in having a bifenestrate ooecium with radial ribs, and in the shape, size, and orientation of the oral avicularium; however, the latter species differs in having a single row of areolar pores, 4-6 oral spines, and in the absence of dimorphic avicularia. The bifenestrate ooecium and arrangement of the areolar pores also resemble H. capitimortis; however, in this species the ectooecium lacks the ribs, the fenestrae bear a proximal tongue, and the avicularia are absent or smaller in size and placed far from the orifice. In the Siamaná Formation, Hippopleurifera sp. indet. 1 was found encrusting the hydrocoral Millepora sp. and Caryophylliidae, as well as coralline algae covering the coral Porites sp., co-occurring with Gymnophorella hadra and Antropora guajirensis Flórez, Di Martino, and Ramalho, 2021.
Description.-Colony encrusting, multiserial, unilaminar. Autozooids distinct by shallow interzooidal grooves, subhexagonal, rounded distally, slightly longer than wide (mean L/W 1.27). Frontal shield almost flat to slightly depressed, granular, central area imperforate, 3-4 rows of areolar pores. Orifice longer than wide, arched anter separated from the smaller and narrower poster (proximal border straight to slightly concave) by two blunt, rounded condyles; nine distolateral oral spine bases. One or two small, adventitious avicularia with raised, acutely triangular rostrum, oriented proximally to proximolaterally; when paired, avicularia placed symmetrically close to the lateral zooidal margins, almost at zooidal mid-length; occasionally a similar, slightly larger adventitious avicularium located laterally at the same level of the orifice, oriented lateroproximally; crossbar complete. Ovicells not observed.
Remarks.-The absence of ovicells in our specimens increases the uncertainty of its classification. However, we place this species in the genus Hippopleurifera based on the relatively reduced imperforate frontal area, the high number of oral spines, and the absence of dimorphic avicularia (Tilbrook, 2006;Ramalho et al., 2015). Among the eight species known from the American continent (see Remarks of Hippopleurifera sp. indet. 1), Hippopleurifera sp. indet. 2 resembles the Recent Caribbean species Hippopleurifera belizae , in the shape and location of the avicularia, as well as in its general aspect, but differs in the number of oral spines (9 instead of 6-8), and the morphology of the orifice, which is hoof-shaped instead of D-shaped. In the Siamaná Formation, Gemelliporidra aff. G. magniporosa (Canu and Bassler, 1923) Figure 11.1-11.3; Table 11  Description.-Colony encrusting, multiserial, unilaminar. Autozooids distinctly separated by a narrow groove or a thin thread, subrectangular to irregularly pentagonal, almost as long as wide (mean L/W 1.07). Frontal shield flat to slightly depressed, granular, evenly perforated by regularly spaced, circular pseudopores (diameter 0.02-0.04 mm), except for a reduced imperforate area below the orifice. Orifice terminal, anter semielliptical, sinus rounded V-shaped, condyles rounded triangular. Small, triangular structures, seemingly oriented proximolaterally, placed at the distal zooidal margins, interpreted as putative adventitious avicularia. Ovicell hyperstomial, globular, occupying most of the frontal surface of the next distal zooid, up to the proximal margin of the orifice; apparently perforated by closely spaced pseudopores, smaller than those of the frontal shield.
Remarks.-Six fossil species of Margaretta were recorded from the American continent in addition to M. buski. Canu and Bassler (1920) introduced (as Tubucellaria) the species M. fallax, M. nodifera, and M. parviporosa from the Eocene of Alabama, Florida, and North Carolina, respectively, and M. vicksburgica from the Oligocene of Alabama. Margaretta cf. M. buski differs from all these species in having smaller zooids (<1 mm long); in addition, M. nodifera has zooids with tuberosities. The Eocene species M. congesta  and the Miocene species M. pentaceratops Di Martino, Taylor, and Portell, 2017, both from Florida, differ from M. cf. M. buski in having eight rows of smaller and densely packed zooids and peristome with five spiniform processes, respectively. Margaretta cf. M. buski resembles the Miocene to Recent M. cereoides (Ellis and Solander, 1786), known from the Mediterranean and East Atlantic, in general appearance, including the shape and arrangement of autozooids; however, it differs in having bipartite basis rami instead of undivided, and three zooids per whorl instead of four or five (Harmer, 1957). The early Miocene Siamaná specimen differs from the holotype of the nominal species (see Di Martino et al., 2017, fig. 49) in having curved but not inturned fertile peristomes, which also has been observed in specimens from the Miocene Pirabas Formation of Brazil   fig. 3). However, the limited amount of material available prevents determination of whether this is a genuine morphological difference or a diagenetic effect. The small fragments of Margaretta cf. M. buski were found in sediment cemented to the corals Goniopora hilli and Acropora panamensis, co-occurring with Nellia cf. N. tenella (Lamarck, 1816), Ditaxiporina colombiana n. sp., Mecynoecia sp., Catenicella sp., Reteporellina sp., and Glabrilaria sp. Hippopodina sp. indet. Figure 12; Table 13 Occurrence.-Early Miocene, Siamaná Formation, Arroyo Ekieps, Colombia.
Description.-Colony encrusting, multiserial, unilaminar. Autozooids separated by deep furrows and a narrow thread, rounded polygonal, longer than wide (mean L/W 1.38). Frontal shield convex, finely granular, evenly perforated by numerous (∼130), circular pseudopores, ∼0.02 mm in diameter. Larger, fusiform pores at the distal corners of the zooids sometimes visible. Orifice terminal, hoof-shaped, two robust condyles separating a semicircular anter from a shallow, broad sinus with proximal border flat or slightly concave. Adventitious avicularium single, sometimes absent, lateral to the orifice, originating at the same level as the orifice proximal margin and extending for the total length of the orifice; rostrum raised, narrow and acutely triangular, oriented distolaterally or medially; crossbar complete. Ovicells not observed.
Remarks.-In the fossil record of North America two species of Hippopodina are known from the Eocene of Georgia and Florida (USA): H. stephensi Cheetham, 1962b, and H. vibraculifera Canu and Bassler, 1917, respectively. The former species differs from Hippopodina sp. indet. in often having paired adventitious avicularia, placed and directed proximolaterally to the orifice, while the latter species has avicularia placed distally and oriented proximally.
In addition, five Recent species are known from off North America: H. pulcherrima (Canu and Bassler, 1928) from the Western Atlantic; H. bernardi Lagaaij, 1963, from the Gulf of Mexico; H. irregularis Osburn, 1940, from the Caribbean Sea; H. tahitiensis Leca and d'Hondt, 1993, allegedly from the Caribbean Sea, India, and Africa; and H. californica Osburn, 1952, from the Pacific coast of the USA. However, Hippopodina californica and H. irregularis lack avicularia; H. bernardi has a centrally imperforate frontal shield; H. tahitiensis bears single or paired, small, drop-shaped avicularia placed distolaterally and oriented distally; and H. pulcherrima, the most common in the Caribbean region (Tilbrook, 1999), has a narrower sinus and single or paired avicularia, located beside the orifice and oriented proximomedially.
Three species of Hippopodina are known from the earlymiddle Miocene of other geographic regions: H. lappi David, 1965, from France lacks avicularia; H. emerensis Abbas and El-Senoussi, 1979, from Egypt has adventitious avicularia on either side of the orifice; and H. indicata Di Martino and Taylor, 2015, found in coral reefs from East Kalimantan, has similar adventitious avicularia but originating more proximally and with the rostrum pointing to the orifice condyles. Our specimens resemble the Recent species H. iririkiensis Tilbrook, 1999, recorded in the Indo-West Pacific, Australia, and the Mediterranean Sea in the shape, location, and direction of the single avicularium; however, in H. iririkiensis, avicularia are often paired, Hippopodina sp. indet. has larger zooids (1.12 × 0.82 mm vs. 0.9 × 0.62 mm), and the proximal margin of the orifice is flatter. However, the limited amount of material available and the lack of ovicells in our specimens prevented us from confirming its conspecificity with previously described species and from describing a new species. In the Siamaná Formation, Hippopodina sp. indet. was found encrusting the coral species Porites anguillensis and Millepora sp., co-occurring with Poricella paulae n. sp.
Diagnosis.-As for the type species.
Etymology.-From the Latinized form of the Greek kyklos, meaning circle, plus the morphologic term avicularia, alluding to the circular, adventitious avicularia placed on the zooidal 'shoulders.' Remarks.-We place this new genus in the family Teuchoporidae based on the following characters: frontal shield evenly perforated, peristome moderately high, presence of small adventitious avicularia, and a conspicuous and perforated ooecium that is proximally encroached by the peristome (Harmer, 1957;Poluzzi, 1977;Gordon, 1984). This family includes three genera: Teuchopora Neviani, 1895b (type), "Coleopora" Canu andBassler, 1927, andLagenicella Cheetham andSandberg, 1964. Cycloavicularia n. gen. differs from Teuchopora and "Coleopora" in having adventitious avicularia while lacking the proximal peristomial denticle. It differs also from Lagenicella in having polygonal rather than vase-shaped zooids, and in the lack of imperforate, hood-like projections rimming the peristomial ovicells. Cycloavicularia n. gen. also shows some similarities with members of the family Exechonellidae Harmer, 1957, which, however, usually lack or have inconspicuous ovicells (Gordon, 1984). The type species of this new genus closely resembles the Recent Brazilian species Marcusadorea pinheroi Almeida et al., 2017, in its overall appearance, size of the zooids and ovicells, and density and distribution of pseudopores, but differs in having avicularia. Its allocation in Marcusadorea, however, would not be justified because Marcusadorea jamaicensis Vieira, Migotto, and Winston, 2010, the type species of the genus and family Marcusadoreidae Winston, Vieira, and Woollacott, 2014, has an irregularly perforated frontal shield, marginal areolar pores are distinct from the pseudopores, and peristomial avicularia are sometimes present (Vieira et al., 2010), while Cycloavicularia parva n. gen. n. sp. has an evenly perforated frontal shield and distinctive, small, adventitious avicularia in the distolateral corners of the zooids.
Description.-Colony encrusting, multiserial, unilaminar. Autozooids almost indistinct, boundaries apparently concealed by secondary calcification, subrhomboidal to oval, slightly longer than wide (mean L/W 1.19). Frontal shield smooth, generally slightly depressed, but raised suborally, imperforate except for 2-4 small marginal areolar pores. Orifice bell-shaped, almost as long as wide, bearing two robust, triangular condyles; four distolateral oral spine bases; proximal border with a poorly developed or poorly preserved umbo. Adventitious avicularium single, placed on one side of the frontal shield slightly below the orifice; rostrum rounded triangular, directed proximolaterally, seemingly with pivotal condyles. Ooecium broken, apparently small and circular in outline.
Remarks.-We place this specimen in Pleuromucrum based on the shape of the orifice, the imperforate frontal shield with few, sparse marginal pores, the presence of frontal triangular avicularia, oral spines and suboral umbo, and the proportionally small ooecium in respect to autozooid size (Di . The smooth appearance of the frontal shield (in Pleuromucrum it is usually nodular) is likely due to preservation, which also prevents species-level assignment. In the Siamaná Formation, Pleuromucrum sp. indet. was found encrusting coralline algae.
Description.-Colony erect, rigid. Branches cylindrical to slightly flattened, 0.32-0.50 mm wide. Autozooids distinct,  Journal of Paleontology 96(2):274-303 294 separated by raised ridges, subrhomboidal, arranged alternately in three longitudinal rows on the frontal side of the branch, more than twice as long as wide (mean L/W 2.10). Primary orifice hidden by a proximally well-developed peristome with a U-shaped sinus medially. Frontal shield slightly convex, perforated by a pair of marginal areolar pores placed proximally at about one-third of the total length of the zooid.
Remarks.-Based on its general appearance, including the arrangement of zooids, the well-developed suboral processes, and the monomorphic suboral avicularia, we assign these specimens to Rhynchozoon. However, the poor preservation prevents the comparison with congeners and nomenclature remains open. In the Siamaná Formation, Rhynchozoon sp. indet. was found encrusting the hydrocoral Millepora alcicornis Linnaeus, 1758, and the scleractinian Colpophyllia willoughbiensis, co-occurring with Calpensia caribensis and Copidozoum sp. indet.

Discussion
The study area comprises patch reefs distributed in a shallow lagoon and in the discontinuous coral barrier enclosing the lagoon (Flórez, 2020). These coral communities thrived in tropical waters, at depths of 2-30 m, with low turbidity, low energy, and limited siliciclastic input (Flórez et al., 2019a, b;Flórez, 2020). Associated with them, we found 32 bryozoan species this paper). New species account for 31% (10 species) of the whole assemblage. Three new species belong to the family Cribrilinidae, and one each to Antroporidae, Microporidae, Onychocellidae, Steginoporellidae, Catenicellidae, Arachnopusiidae and Teuchoporidae. The new genera, Atoichos Flórez et al., 2021, in Onychocellidae;Gymnophorella Flórez et al., 2021, in Steginoporellidae; and Cycloavicularia n. gen. in Teuchoporidae, also have been introduced to accommodate three new species.
Two species are identified as confer and another three as affinis to preexisting species. The remaining species (53%) were left in open nomenclature, one identified at family level and 15 at genus level. This high percentage of undetermined species is due to the poor preservation caused by weathering, dissolution and recrystallization, and/or mechanical abrasion, which resulted in the loss or alteration of key skeletal features. It is well known that tropical Cenozoic carbonates, especially coral reefs, experience rapid cementation (Macintyre, 2011), and severe diagenetic alterations greatly affecting aragonitic organisms, even to the complete disappearance of the aragonitic component. Taylor and Di Martino (2014) found that 27% of tropical cheilostome species encrusting the underside of platy corals were aragonitic and 30% bimineralic. These results suggest that species richness may suffer a great loss in this tropical paleoenvironment, although it has also been observed that in some particular conditions the originally aragonitic skeletons of bryozoans can be preserved by calcitization (Di Martino et al., 2016). Furthermore, the preservation of bryozoan colonies may also be affected by the diagenetic processes affecting their aragonitic substrates, such as scleractinian corals (as in this case) or mollusks .
The relative proportions of cyclostomes (6%) and cheilostomes (94%) follow the general pattern observed in the Caribbean region from the Miocene to the Pleistocene , and in Recent coral-associated bryozoan faunas .
Species richness varies greatly among the three sampling localities: 75% of species were found in Arroyo Ekieps, 25% in Uitpa, and 3% in Flor de La Guajira (Appendix 2). The highest species richness in Arroyo Ekieps is associated with a higher structural complexity compared to the small patch reefs in Arroyo Uitpa and Flor de La Guajira. A single species, Hippopleurifera sp. indet. 1, was found in Flor de La Guajira, and was also present in Arroyo Uitpa. The remaining species are exclusive to each locality.
Except for the three newly introduced genera, Atoichos, Gymnophorella , and Cycloavicularia n. gen., the genera found in the Siamaná Formation have been observed previously in the Great Caribbean Region, Gulf of Mexico, and north of Brazil, either exclusively in the fossil record or contemporary environments, or both. For eight genera, the age range was extended back to the early Miocene (Aquitanian) (Fig. 17). Glabrilaria stands-out among these, because it has only recently been found in the Caribbean region associated with Recent deep-sea coral banks  and off the Amazon River mouth in bryozoan reefs .
The Neogene bryozoan fauna associated with shallowwater paleoenvironments from the Gulf of Mexico and the Caribbean Basin is relatively well studied Di Martino et al., 2018). In other tropical regions from South America, such northern Brazil, studies are incipient and knowledge of early Miocene bryozoans is partial (Zágoršek et al., 2014;Ramalho et al., 2015Ramalho et al., , 2019Aguilera et al., 2020). However, compared to these faunas, in which erect and free-living species are dominant (Cheetham and Jackson, 1996;Ramalho et al., 2015Ramalho et al., , 2019Di Martino et al., 2018), the Siamaná bryozoan assemblage shows a different ecological pattern and taxonomic composition at the genus level. In addition to the assemblage being older (Aquitanian), with the exception of the Brazilian fauna, these differences may be attributed to the reefal paleoenvironment, which favors cryptic, encrusting species colonizing the coral framework, as also observed in other tropical regions (Di Martino andTaylor, 2014, 2015). Nonetheless, genera such as Margaretta and Nellia are present throughout the regions over time.
Compared to other bryozoan faunas associated with Miocene coral reefs, the species richness in the Siamaná Formation is significantly lower (e.g., 123 species were reported from Indonesia [Di Martino andTaylor, 2014, 2015] and 56 species from the Mediterranean [Hamdane and Moissette, 2002]). These differences may be an effect of sampling effort in fresh exposures. In addition, the greater bryozoan diversity of the Indonesian reefs can be explained by the high input of siliciclastic sediment that facilitates the preservation of the material (Di Martino et al., The bryozoan fauna of the Siamaná Formation highlights the remarkable diversity of cryptic species in the ancient coral reefs of the Southern Caribbean region.