Evaluating the genus Cespitularia MilneEdwards & Haime, 1850 with descriptions of new genera of the family Xeniidae (Octocorallia, Alcyonacea)

Abstract Several species of the family Xeniidae, previously assigned to the genus Cespitularia Milne Edwards & Haime, 1850 are revised. Based on the problematical identity and status of the type of this genus, it became apparent that the literature has introduced misperceptions concerning its diagnosis. A consequent examination of the type colonies of Cespitularia coerulea May, 1898 has led to the establishment of the new genus Conglomeratusclera gen. n. and similarly to the assignment of Cespitularia simplex Thomson & Dean, 1931 to the new genus, Caementabunda gen. n. Both new genera are described and depicted and both feature unique sclerite morphology, further highlighting the importance of sclerite microstructure for generic position among Xeniidae. Freshly collected material was subjected to molecular phylogenetic analysis, whose results substantiated the taxonomic assignment of the new genera, as well as the synonymies of several others.


Introduction
Members of the octocoral family Xeniidae form a major faunistic component on shallow Indo-Pacific coral reefs (e.g., Alderslade 2001, Janes 2013, 2015. They play a significant ecological role in coral reef ecosystems, exhibiting a rapid colonization rate (e.g., Tilot et al. 2008, Wild andNaumann 2013) as well as invasive capabilities (Ruiz-Allais et al. 2014). Uniquely among Octocorallia, in xeniids the pinnules along the margins of the polyp tentacles are commonly arranged in more than one longitudinal row. The number of pinnule rows and the number of pinnules in the outermost row have been considered taxonomically diagnostic (e.g., Hickson 1931a, Reinicke 1997). However, Halàsz et al. (2015) and subsequently McFadden et al. (2017) demonstrated that this character is not informative for species delineation among members of the xeniid genus Ovabunda Alderslade, 2001. The taxonomic literature on Xeniidae also considers several other morphological characters to be informative, such as colony shape, dimensions and coloration, as well as polyp retractability and pulsation in the live state (e.g., Reinicke 1997, 2015.
The majority of the described Xeniidae taxa have a high density of minute sclerites in their tissues, although some have only a few or none (e.g., Halàsz et al. 2014). This family has been considered to exhibit less diversity of sclerites than most other octocoral families, with the commonly held notion that most of the species feature relatively simple sclerites in the form of round platelets (Fabricius and Alderslade 2001). Consequently, most of the old taxonomic literature does not depict xeniid sclerites, although their size-range has occasionally been recorded (Halàsz et al. 2014 and references therein). Among the few studies that have included drawings of xeniid sclerites are those of Cespitularia mantoni Hickson, 1931, C. multipinnata Quoy & Gaimard, 1833(in Hickson 1931), and C. stolonifera Gohar, 1938(in Utinomi 1950 ) (see also Halàsz et al. 2014). With the use of scanning electron microscopy (SEM), the diverse microstructural features of xeniid sclerites have now become evident (e.g., Benayahu 1990, 2010, Reinicke 1997, Alderslade 2001, Janes 2008, Aharonovich and Benayahu 2011). Subsequently, several new genera have been described, such as Bayerxenia Alderslade, 2001, Ingotia Alderslade, 2001, Ixion Alderslade, 2001, Orangaslia Alderslade, 2001, and Yamazatum Benayahu, 2010. Alderslade (2001 established the genus Ovabunda Alderslade, 2001 for previously described species of Xenia Lamarck, 1816 with the corpuscular sclerite-type, while retaining those with a dendritic surface in the original genus. To date, the phylogenetic studies on Xeniidae support the hypothesis that their distinct sclerite microstructure justifies establishing generic boundaries within this family (Haverkort-Yeh et al. 2013. There is considerable confusion in the literature concerning the diagnosis of the xeniid genus Cespitularia. This genus was erected by Valenciennes in an unpublished manuscript and later published by Milne Edwards and Haime (1850). The type of Cornularia multipinnata Quoy & Gaimard, 1833 collected in Tonga (West-Pacific) was designated to be the type species of the genus; Quoy and Gaimard (1833) also described Cornularia subviridis from the same locality. According to Milne Edwards and Haime (1850), the genus Cespitularia features non-retractile polyps arranged in fasciculi (=longitudinal groups) and united along the greatest part of their length by dense tough tissue; their description does not note the presence of sclerites. Our attempts to trace the types of both these Cornularia species have failed and therefore they are considered lost. Later, May (1899: 89) synonymized the genera Cornularia Quoy &Gaimard, 1833 andSuensonia Brundin, 1896 (see ahead) under Cespitularia Valenciennes; his description too does not note the presence of sclerites.
Drawings of the type of Cornularia multipinnata Quoy & Gaimard (1833) (plate 22, figs 1-4), depict a colony with a distinct dome-shaped capitulum bearing polyps as well as a bare stalk with no polyps ( fig. 4), thus resembling Xenia (see e.g., Fabricius and Alderslade 2001). Cornularia subviridis (plate 22, figs 5-7) was described as a colony with three elongated stems arising from a common base, each bearing polyps along half of its length ( fig. 5). The depicted sclerites of this species are spindles (fig. 5'), but no information is given on those of C. multipinnata. Hickson's (1931) revision of the Xeniidae (p. 162) referred to this original description, but erroneously stated that C. multipinnata featured spindle-shaped sclerites and C. subviridis had Xenialike sclerites. Consequently, his conclusion that C. subviridis is probably X. umbellata would appear to be an error. Hickson's revision also indicated that Quoy & Gaimard (1833) had provided errata, arguing that their original drawing of the two Cornularia species had been switched, and thus figs 1-4 should refer to C. subviridis and figs 5-7 to C. multipinnata. It should be noted that although the colony shape depicted in plate 22, fig. 5 might be considered to be Cespitularia (see Fabricius and Alderslade 2001), doubts nonetheless exist because of the spindle-shaped sclerites ( fig. 5'). Such sclerites have never been recorded among Xeniidae and, therefore, doubt exists as to whether Cornularia multipinnata Quoy & Gaimard, 1833 should be assigned to the family Xeniidae. Until new xeniid material can be obtained from the original type locality (Tonga), the taxonomic status of Cespitularia sensu stricto Quoy & Gaimard (1833) cannot be unequivocally determined.
The genus Cespitularia Milne Edwards & Haime, 1850 was first revised by Kükenthal (1902), who diagnosed it as forming tree-like colonies, with polyps not positioned on a defined polypary. That revision listed the following species under the genus: C. subviridis (Quoy & Gaimard, 1833); C. multipinnata (Quoy & Gaimard, 1833) as well as the subsequently described species C. mollis (Brundin, 1896); C. coerulea May, 1898; and C. taeniata May, 1899. The revision by Hickson (1931) similarly diagnosed the genus as having dendritic branches with the margins of the capitulum not sharply defined, i.e., its polyps do not arise only from the summit of the branches but also from lower down, albeit gradually diminishing in number. Based on the problematical identity and status of the type of the genus Cespitularia, as detailed above, it is apparent that both of these revisions introduced further misperceptions concerning its diagnosis.
The ambiguity concerning the diagnosis of Cespitularia is further demonstrated in C. mollis (Brundin, 1896), originally described as Suensonia mollis, whose type locality is the Korean Straits (120 m depth). May (1899) assigned this species to Cespitularia, but Hickson (1931) stated that it "must be regarded as a distinct species" because of its geographical origin and depth of collection. Hickson (1931) also indicated that the sclerites of S. mollis are "twins, quadruplets and hour-glass shaped", but no drawings were presented. Although Utinomi (1950:81) stated that this species is "a member of Cespitularia", the type locality of S. mollis certainly departs from that of the tropical coral-reef systems. It can therefore be concluded that C. mollis is not a xeniid.
At present, the literature refers to 18 species of the genus Cespitularia (Cordeiro et al. 2018). Considering the fact that the type species of the genus Cespitularia is missing and presumed lost, we searched for the types of species that were originally assigned to the genus subsequent to the species noted above, i.e., from May (1898) onwards. Accordingly, the current study examined the following types: C. coerulea May, 1898, C. taeniata May, 1898, C. simplex Thomson & Dean, 1931, C. robusta Tixier-Durivault, 1966, and C. turgida Verseveldt, 1971. Freshly collected material was subjected to molecular phylogenetic analyses whose results also substantiated the taxonomic findings that have led us to assign new xeniid genera as well as to synonymize several others. Examination of diverse, related museum material provided data on intraspecific variation and the zoogeographical distribution of the taxa.

Materials and methods
The study examined preserved type specimens obtained on loan from the British Museum of Natural History (BMNH); Muséum National d'Histoire Naturelle, Paris (MNHN); Naturalis Biodiversity Center, formerly Rijksmuseum van Natuurlijke Historie, Leiden (RMNH); Zoologisches Museum, Hamburg (ZMH); Zoologisches Museum Berlin (ZMB); Smithsonian National Museum of Natural History, Washington DC (USNM), and the Steinhardt Museum of Natural History at Tel Aviv University (ZMTAU).
Morphological features of the preserved colonies were recorded, comprising dimensions, branching and stalk length, and width of the stalk at the colony base. The number of rows of pinnules and number of pinnules on the aboral side of the tentacles were counted under a dissecting microscope, whenever possible from multiple polyps. The length of the anthocodiae, consisting of the polyp body and extended tentacles, and the dimensions and shape of the pinnules were also recorded (see also Halàsz et al. 2014). To examine the sclerites, the tissue samples were treated with 10 % sodium hypochlorite followed by repeated rinses in distilled water. Wet preparations of the clean sclerites from polyps and the colony base were examined under a Nikon Optiphot light microscope at 400× magnification. Observed differences led to preparation of SEM mounts from both regions; otherwise only those from the polyp were used (see Aharonovich and Benayahu 2011); each stub usually contained numerous sclerites and samples were coated with Pd/Au and viewed under a Quanta 200 FEG (Field Emission Gun) ESEM at 5-20 kV. SEM was used to examine sclerites of almost all the studied material; in certain cases, wet preparations were prepared and examined under the light microscope (×200-400). Both SEM and wet preparations were prepared from the same colonies in order to correctly visualize the unique structure of the corresponding sclerites. The zoogeographical species distributions were determined by the examination of types and other material.
Freshly collected material used for molecular and morphological studies was collected by YB in Yonaguni Is., Ryukyu Archipelago, Japan (in 2010); Green Is., Taiwan (2012) and Nosy Be, Madagascar (2015). Xeniidae colonies tend to release large quantities of mucus, especially when being detached from the reef and brought onboard, which is particularly relevant to the taxa studied here. This usually causes rapid colony disintegration and poor condition of museum material. Therefore, upon collection samples were immediately preserved in 95 % ethanol and subsamples were removed and preserved in absolute ethanol for molecular studies and then placed on ice in cool boxes until brought to the laboratory. In order to ensure appropriate preservation, the fixatives were replaced twice within 24 hours after collection, and throughout all preservation steps, the bottles were shaken to enhance infiltration of the fixative into the tissues.
DNA was extracted from ethanol-preserved tissue samples using the Qiagen DNEasy Blood & Tissue kit, and three gene regions were subsequently amplified by polymerase chain reaction (PCR) using previously published primers and PCR protocols (McFadden et al. 2011). For most specimens, we amplified the octocoral-specific mitochondrial mutS homolog (mtMutS) using primers ND42625F (McFadden et al. 2006) and mut3458R (Sánchez et al. 2003); cytochrome oxidase I (COI) and the adjacent intergenic region, igr1, using primers COII8068F (McFadden et al. 2004) and HC02198 (Folmer et al. 1994); and a fragment of 28S rDNA using primers 28S-Far and 28S-Rar (McFadden and Ofwegen 2013). The L-INS-i method in MAFFT (Katoh et al. 2005) was used to align sequences to a reference dataset consisting of previously published sequences for other genera of xeniids and three outgroup taxa, Coelogorgia, Paralemnalia, and Rhytisma (McFadden et al. 2014). Pairwise measures of genetic distance (Kimura 2-parameter) among sequences were computed using MEGA v.5 (Tamura et al. 2011). jModelTest2 (Darriba et al. 2012) was used to select appropriate models of evolution for maximum likelihood analyses that were run using GARLI 2.0 (Zwickl 2006). Analyses were run for each gene region alone, and for a combined dataset with all three genes concatenated. Each gene was treated as a separate data partition with different models of evolution applied to each (mtMutS: HKY+G; COI: TIM2+I+G; 28S: GTR+I+G). Bayesian analyses of the concatenated alignment used MrBayes v. 3.2.1 (Ronquist et al. 2012) with the same data partitions and evolutionary models applied, except that GTR+I+G was substituted for TIM2+I+G. MrBayes was run for 5,000,000 generations (until standard deviation of split partitions < 0.01) with a burn-in of 25 % and default Metropolis coupling parameters. Diagnosis. Colonies soft with a short but distinct stalk, ramified into primary branches and occasionally into secondary ones. Polyps monomorphic, found along the branches, sometimes down on the stalk; most are non-retractile. Sclerites of a wide diversity of forms and dimensions, many lacking a distinct repetitive morphology. They include spheres, spherules, and small dumbbell-like sclerites. They are commonly cemented together, forming heterogeneous morphologies of various shapes and sizes. Occasionally, the aggregates form plate-like structures, embedded with spheres and/or spherules. The abundance of sclerites can vary greatly; in some specimens they are rare and then mostly found only at the colony base, and occasionally they may be found in all parts of the colonies, or may even be entirely absent. Zooxanthellate.

Systematics
Etymology. The generic name is derived from Latin conglomerātus, which refers to anything composed of heterogeneous materials or elements and sclera from Greek meaning sclerite. Here it denotes the sclerites that resemble the geological structures termed conglomerates, a feature comprising rounded to sub-angular clast of granules, pebbles or cobbles cemented together. Gender female. Figures 1A  yan, Green Is., 22°40'56"N, 121°30'06"E, 3-25 m depth, coll. Y. Benayahu, 12 July 2005; ZMTAU Co 33006, details as before, seven specimens, Co 33008, details as before; ZMTAU Co 33030, Dabaisha, Green Is., 22°38'25"N, 121°29'04"E, 10-25 m depth, coll. Y. Benayahu (Thomson & Dean, 1931) with expanded polyps D C. simplex (Thomson & Dean, 1931)    Notes to previous description. The original description of C. coerulea by May (1898) referred to a colony from Kokotoni, Zanzibar. Later, May (1899) repeated the description, referring to colonies collected from that location in 1889 by Stuhlmann and from Zanzibar in 1885 by Sander, deposited in Hamburg and Berlin museums, respectively. During a visit by the senior author to ZMH two colonies were found labeled as the type of C. coerulea, both collected in Kokotoni, Zanzibar, 24 July 1895 (leg. Stuhlman). Similarly, in a subsequent visit to ZMB two colonies were found, labeled as syntypes of C. coerulea, collected in Zanzibar, 1895 (leg. Sander). Both ZMH and ZMB colonies are considered to be the original syntypes of that species and are re-described below.

Conglomeratusclera coerulea (May, 1898)
Description. ZMH C 2518 consists of two colonies; the first is 8.5 cm high by 4.2 cm wide and the second 5 cm high by 4 cm wide ( Figure 1A). The polypary of these colonies is branched and their tips are bent. They bear non-retractile polyps, with some occurring towards the upper part of the colony's base. The polyp body is up to 8 mm long and the tentacles are up to 3 mm long; the latter bear one row of pinnules and 16-18 pinnules along each edge. The pinnules are short, pointed and evenly placed along  the tentacle, with a narrow space of less than a pinnule width between adjacent ones. The preserved colonies are pale gray-almost white. Sclerites could not be found in the upper part of the branches or in the polyps. However, the lower part of the branches, including the base of the colonies, feature conglomerates, comprised of spherules and small dumbbell-like sclerites, mostly cemented ( Figure 2). The spherules are about 0.002-0.006 mm in diameter (Figures 2A, E-G), with a rather rough surface-texture. The abundance of the dumbbells (Figures 2B-D, F) may exceed that of the spheroids. The former vary in size, with a length of 0.003-0.006 mm. The conglomerate nature of the sclerites exhibits a large morphological variation as demonstrated in Figure 2. The syntype ZMB Cni 3671 ( Figure 1B) resembles syntype ZMH 2518, except for the size of the colonies. Most of the polyps of the former are expanded, well-preserved, and thus recognizable on the branches of the colony. The sclerites are similar, conglomerated spheres and spherules along with some double-heads (Figure 3), but are less   common in the tissues compared to ZMH C 2518. Under the light microscope wet preparations of the tentacles removed from ZMB Cni 3671 revealed some conglomerates along with spheres of various sizes.
The type material of Cespitularia taeniata (ZMH C 2519) comprises two flaccid colonies and two additional fragments ( Figure 1C). The colonies are 3-4.5 cm high by 2-2.5 cm wide. Their polyparies consist of short branches bearing non-retractile polyps; some polyps were also found on the upper part of the stalk. The tentacles feature one row of 16-18 pointed pinnules, evenly placed along the edges with a free space between adjacent ones. Sclerites were found in the base of the colonies and the branches (Figure 4) but none in the polyps. They are conglomerates comprised mainly of spherules ( Figure 4A) and some predominantly of spheres ( Figure 4B), the latter measuring up to 0.018 mm in diameter. In addition, some cylinder-like small sclerites featuring round tips are also found, measuring 0.002-0.003 mm ( Figure 4C). It should be noted that the aggregates tend to disintegrate during the sclerite preparation and therefore their actual dimensions cannot be determined.
A colony labeled as ZMH C 2375 ( Figure 1D) features tentacles with 12-14 pinnules and sclerites similar to ZMH C 2519. ZMH C 2375 is listed in the museum's catalog as the "Typus von Ammothea bauiana May, 1898" along with a note that Gohar had corrected the identification in 1938 to C. taeniata. Both colonies, ZMH C 2519 and ZMH C 2375, are light gray-beige. Conglomeratusclera taeniata was described by Thomson and Dean (1931: 33) as being "near to but distinct from Cespitularia coerulea". The current findings indicate that there are only some small morphological differ- ences in the colony and polyp dimensions between the two species, and therefore, the above statement appears reasonable. Utinomi (1950) described the C. taeniata specimen identified by him as having 10-12 pinnules, slightly lower in range compared to the 12-14 pinnules of C 2375. The current examination of the types of both C. coerulea and C. taeniata revealed that despite the erroneous statement that they have no sclerites, they feature quite similar sclerites. It is therefore suggested that the similarity between the two species indicates that the above-reported morphological differences in the number of pinnules of the two types represent intra-specific variation. The sequencing results obtained in the current study along with the morphological findings further substantiate this conclusion, as colonies with a single row of 8-22 pinnules share similar DNA sequences (see ahead). Therefore, it is concluded that C. coerulea and C. taeniata sensu stricto should be synonymized, and both are now designated under Conglomeratusclera coerulea.
Remarks. The original descriptions of Cespitularia coerulea by May (1898, 1899) indicated an absence of sclerites in the colony. In contrast, the current findings dem-  onstrate the presence in the syntypes of a novel type of sclerite, depicted here for the first time. These sclerites are composed of agglomerated calcite-constructed minute substructures of various morphologies, mostly spherules, spheres, and double heads appearing in different arrangements. They were probably overlooked in previous stud-  ies due to their minute size and also occasional low abundance. Moreover, the unusual irregular sclerite morphology with almost no definite structure (Figures 2-4), may have caused the misinterpretation concerning their potential as octocoral sclerites to be used as diagnostic characters for taxonomic purposes.
Since the original description of C. coerulea a number of studies have assigned specimens to that species. Thomson and Henderson (1906) identified a multibranched colony from Zanzibar, with one row of pinnules and no sclerites. Later, Thomson and Mackinnon (1910) described a similar colony from Cargados Carajos (Mauritius), noting that when alive the colony was "vivid grass green, but after preservation it faded to cream", a feature that has been widely observed in the current study (see below). Thomson and Dean (1931) identified C. coerulea from Kawas- sang, Indonesia, obtained in the course of the Siboga Expedition, featuring a single row of pinnules and no sclerites, with no mention of the number of pinnules in the polyps. Next, Roxas (1933) identified the same species from Sabang, near Puerto Galera, Mindoro, Philippines, with one row of 14-18 pinnules and no sclerites. Interestingly, that study of Roxas's study was the first to indicate number of the pinnules in that species. In general, the above octocoral samples are in agreement with the original description by May (1898), but all the above authors nonetheless failed to detect any sclerites.
Color. When alive, the color of colonies ranges from vibrantly bluish-purple, light green, light yellow-beige, light cream to almost white (see Figure 5A, B). The alcohol-preserved colonies lose their vibrant colors and mostly become pale cream, gray, or beige.
Morphological variation. In the current study, examination of the colonies from Green Is., Yonaguni Is. and Madagascar was based on both morphological characters (colony shape, pinnule count, and sclerite features), along with DNA sequencing; the latter enabled us to construct a phylogenetic tree (Figure 6). In general, the colony shape of all the colonies listed in Material Examined was in agreement with the syntypes shown above, except for colony size. All colonies exhibited one row of pinnules along the margins of the polyp tentacles, with a variable number of pinnules, ranging from 8 to 22 per row. In some colonies the tentacles were partially or completely withdrawn or the pinnules fully contracted, probably due to the preservation process. In several cases the polyps were fully expanded and in others partially or fully contracted. The following findings denote the number of pinnules found in some of the sequenced colonies (Figure 6), demonstrating the variability in pinnule count. The respective colonies from Green Island are ZMTAU Co 35717: 8,Co 35747: 8,Co 35774: 8,Co 35709: 15,Co 35758: 15,Co 35693: 16,Co 35756: 20,Co 35760: 20,; colonies with fully contracted pinnules Co 35706, Co 35708, Co 35710, Co 35731, Co 35752, Co 35765, and Co 35766. Colonies from Yonaguni Is are ZMTAU Co 35131: 9-12 pinnules, Co 35132: 12-14 and Co 35134: 11-13. Colonies from Madagascar: ZMTAU Co 36013: 10-13 pinnules and Co 36129: 12-13.
The sclerites of the colonies noted above featured the full array of morphologies, mostly corresponding to that of the syntypes (Figures 2-3). To demonstrate the vast variation in shape and size of the sclerites, SEM images of sclerites of several sequenced colonies are presented for the Taiwan material: ZMTAU Co 35692 (Figure 7   and Madagascar Co 36129 (Figure 15), and Co 36013 (Figure 16). Figures 7-16 demonstrate the morphological variability of the sclerites, with all being conglomerates comprised mainly of spheres and spherules and occasionally dumbbells. The SEM images revealed that their outer surface is sometimes bristly (Figures 7B-D, 8B, 13A-B, 14, 15A, 17) but commonly rather smooth ( Figures 8A, 10A-B, 11A-B, 15B, 16). It is interesting to note that the spheres are sometimes embedded in a calcareous lamella-like structure ( Figure 7A). Dumbbells were revealed in some colonies ( Figures 8B, 12B, 14, 15C, 17) as well as twisted dumbbells (Figures 9, 11C, 12B). Similarly, as noted above for the syntypes, the above SEM images indicate that the aggregates tend to disintegrate during sclerite preparation and therefore their actual dimensions cannot be determined. The molecular results indicate that despite the differences in pinnule count and sclerite morphology, all the colonies should be assigned to the same species ( Figure 6). Consequently, the pinnule count is of no diagnostic value for species delineation within Conglomeratusclera. C. coerulea thus accommodates colonies with one row of pinnules on the margins of the polyp tentacles, but featuring a remarkable range of pinnule numbers (see above). In addition, the variable sclerite morphologies found in the different colonies (Figures 7-16) both encompass and exceed the range observed among the syntypes of C. coerulea (Figures 2A-B). The current results provide further support for the recent findings of McFadden et al. (2017) who argue that the pinnule count used in the taxonomy of Xeniidae, explicitly in the genus Ovabunda (see references in Halàsz et al. 2014), is not indicative of species boundaries. It should be noted that in contrast to the relatively uniform morphology of Ovabunda sclerites recorded across the four genetic clades presented by McFadden et al. (2017), colonies of C. coerulea exhibit an unprecedented and bewildering array of sclerite morphologies (Figures 2A, B, 7-16). Material that was examined, but not sequenced, comprised both freshly collected colonies and museum specimens. Their colony and polyp morphologies, including the pinnule counts, are in agreement with the findings presented above. Noteworthy are some colonies for which SEM or light microscopy could not detect any sclerites. There are several suggested reasons for this: (1) actual lack of sclerites; (2) their low incidence which led to a failure to detect them by SEM; or (3) preservation procedures, such as acidic conditions that may have caused sclerite dissolution.

Conglomeratusclera robusta (Tixier-Durivault, 1966) Figures 26-28
Cespitularia robusta Tixier-Durivault, 1966: 335-356;Janes 2008: 604-605. Description. Examination of the type material of Cespitularia robusta Tixier-Durivault, 1966 (MNH00000167) revealed five colonies (Figure 26), all in agreement with their original description. The tentacles bear two rows of pinnules along each side with an indication of a third row; the outermost row features 12-15 pinnules. The sclerites depicted in the original description are spheres and spherules, also in the form of aggregates (p. 356: fig. 321 C-N). The SEM images of the sclerites (Figure 27) reveal mor- phologies similar to those found in C. coerulea (see above), and therefore led us to assign the species to Conglomeratusclera n. gen instead of Cespitularia. Subsequent examination of C. robusta (RMNH Coel 38672), identified by Janes (2008), similarly confirmed his findings but based on the sclerite SEM images of that colony (Figure 28), the generic assignment is likewise changed to Conglomeratusclera.
The colonies assigned by us to C. coerulea feature one row of pinnules along the margins of the tentacles, whereas C. robusta has two rows. In order to determine whether a difference in pinnule-row count is indeed diagnostic for species delineation in Conglomeratusclera, corresponding fresh colonies with two pinnule-rows should be sequenced. Therefore, for the time being only the generic status of C. robusta is changed, making it the second species in the new genus.
Caementabunda gen. n. http://zoobank.org/899AF711-D0A6-43F7-A3A6-75F481DF29A6 Type species. Cespitularia simplex Thomson & Dean, 1931 Diagnosis. Colonies quite flaccid with a distinct but short encrusting base bearing primary lobes, sometimes divided into secondary ones. Non-retractile monomorphic polyps found on the lobes and occasionally down on some parts of the base. The spherical-oval sclerites are composed of a myriad of densely packed chip-like microscleres. Zooxanthellate.
Color. Live colonies are brown with yellow polyps (Figures 5C-D).
Remarks. The original description of the type by Thomson & Dean (1931: 34) is in agreement with the current findings, and indicates 10-12 pinnules compared to 12-14 noted by us. The sclerite size of 0.01 mm as given in the original description is incorrect and was later corrected by Verseveldt (1971). The latter study provides a better description of the sclerites as oblong, pear-like or angular in shape, 0.015-0.021 mm in diameter. The light microscopy used in the past clearly could not have revealed the unique surface microstructure of that species ( Figure 30D).
Examination of the type of Cespitularia turgida Verseveldt, 1971 (RMNH Coel 6607) revealed Caementabunda-type sclerites (Figure 31). In the original description Verseveldt (1971: 62) presented a comparison between the type of C. simplex and his new species and noted the number of pinnules in the single row of both species being 10-12 in the latter vs. 5-6 in the former. The current examination of the type of C. turgida has confirmed the original morphological findings, while we also present here for the first time images of its sclerites.
Dr. Zena Dinesen (Department of Agriculture, Fisheries and Forestry, Queensland) provided us with an unpublished taxonomic manuscript dealing with some Xeniidae of Flinders Reefs, Great Barrier Reef. Under the collection numbers BMNH   (Thomson & Dean, 1931), BMNH 1982. A spheroid sclerites B densely packed chips-like microscleres of spheroid's surface. 1982.11.17 and 1982.11.18 there are colonies labeled as paratypes of Efflatounaria flindensis Dinesen. Recently Dr. Dinesen confirmed that these two colonies are provisional paratypes of unpublished species presented in her manuscript. Our examination of the colonies revealed Caementabunda-type sclerites (BMNH 1982(BMNH .11.17: figure 32, 1982 figure 33). In addition, it confirmed the unpublished morphological description of the material which states that the pinnules: "Mostly very contracted, difficult to measure, in one row on each side of the tentacle with 5-12 (6-9) pinnules per row". Hence, the pinnule number corresponds to the original types of both C. simplex and of C. turgida. Similarly, examination of ZMTAU Co 35757 from Taiwan revealed Caementabunda-type sclerites ( Figure 34) and 10-12 pinnules in a row, and ZMTAU Co 36127 and Co 36122 from Madagascar both had Caementabunda-type sclerites (Co 36122: figure 35) and 7-11 pinnules, thus falling within the range stated above. Based on these findings, it is concluded here that pinnule count is not diagnostic for species delineation in the newly-described genus Caementabunda. Similarly, it is concluded that Cespitularia turgida is a junior synonym of Caementabunda simplex and thus that both should be accommodated within this new genus.

Figure 34. Caementabunda simplex
revealed Caementabunda-type sclerites. Likewise, RMNH Coel 38673 from Seychelles (see Janes 2008) and ZMTAU Co 31642 ( Figure 36) feature this type of sclerite, as do USNM 60793 and 60794 collected in the Philippines (USNM 60793: Figure 37). Based on the current findings all of these colonies were assigned to the new genus.
Molecular phylogenetic results. Sequences of mtMutS (582 bp), igr1+COI (767 bp) and 28S rDNA (755 bp) were obtained from 46 individuals of Conglomeratusclera and nine individuals of Caementabunda from three different geographical locations: Madagascar; Green Is., Taiwan; Yonaguni Is., Japan (GenBank accession nos. MH071812-MH071969). All phylogenetic analyses of individual gene regions as well as the concatenated alignment (2104 bp) recovered trees in which specimens of Conglomeratusclera and Caementabunda formed two separate, well-supported clades (Figure 6). The average pairwise genetic distance (K2p) among individuals belonging to the two different clades was 3.6%, a value comparable to or higher than that observed among most other genera of xeniids ( Figure 6).
All individuals of Conglomeratusclera shared identical sequences at mtMutS and COI, with just two exceptions: a single individual from Taiwan (ZMTAU Co35731) that differed by 0.2% at mtMutS; and one from Madagascar (ZMTAU Co36055) Figure 36. Caementabunda simplex (Thomson & Dean, 1931), ZMTAU Co 31642. Spheroid sclerites. (Thomson & Dean, 1931), USNM 60793. Spheroid sclerites. that differed by 0.4% at COI. Variation at the 28S rDNA locus ranged from 0-1.5%. Although a group of nine Conglomeratusclera colonies from Taiwan shared a 28S genotype that differed from all others by three nucleotide substitutions (0.4%), there was no significant bootstrap or a posteriori support for them as a separate clade, and no obvious morphological differences to suggest that they might represent a different species.

Figure 37. Caementabunda simplex
All Caementabunda specimens also shared identical mtMutS and COI sequences, with the exception of a single individual (ZMTAU Co 36076) that differed by 0.1% at COI. At 28S rDNA pairwise genetic distances (K2p) among individuals ranged from 0-0.8%, and a group of three specimens from Madagascar (ZMTAU Co 36065, Co 36076, Co 36122) differed from all others by three nucleotide substitutions. There was, however, no significant support for this clade, and no apparent morphological differences between these individuals and others of C. simplex.

Conclusions
Morphological and molecular phylogenetic analyses support the reassignment of the former species Cespitularia coerulea and C. simplex into two separate genera; Conglomeratusclera n. gen. and Caementabunda n. gen., respectively. They are distinguished by differences in sclerite microstructure as well as genetic distances comparable to those among other well-defined genera of the family Xeniidae. In addition, the findings justify synonymy of C. taeniata and C. turgida with each of these two new genera, respectively. We are at present only able to distinguish a single species in each of the new genera, based on both morphology and genetics. It should be noted that the status of C. robusta as a second species of Conglomeratusclera remains to be verified genetically. A recent study of the xeniid genus Ovabunda found a lack of congruence between the morphological characters traditionally used to diagnose species, in particular the number of rows of pinnules and pinnules per row, and genetic evidence of species boundaries (McFadden et al. 2017). In that case, evidence from multiple segregating nuclear markers was necessary to delineate species that shared identical or very similar mitochondrial haplotypes. Therefore, it is possible that data from additional genetic markers might detect further differences among those individuals with variant 28S rDNA genotypes that we have assigned here to Conglomeratusclera coerulea and Caementabunda simplex. As currently circumscribed, both of these new genera and in particular the respective species occur over a wide geographic range from the south-western Indian Ocean (Madagascar) to Japan.