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Hexactinellid sponges often form structural habitats for other organisms and thus support high biodiversity. Two representative morphotypes of hexactinellid sponges were sampled by a remotely operated vehicle along a transect (depths of 2377–2758 m) on the Ko-Hakucho Guyot in the northwestern Pacific Ocean, both new to science. One new species,Flavovirens hemiglobusgen. et sp. nov., which is pedunculate and bears the main choanosomal spicules of diactins, is clearly attributed to the euplectellid subfamily Bolosominae. Its set of microscleres present (namely, predominating oxyhexasters and discasters, and rare discohexasters and staurodiscs) characterizes it as a new genus. The other new species,Chonelasma tyloscopulatumsp. nov., which is funnel in form without dichotomous branching tubes or lateral oscula and has firm body walls supported by a three-layered dictyonal framework, is clearly attributed to the euretid genusChonelasma(subfamily Chonelasmatinae). Its presence of surface pentactins, two types of scopules, and both oxy- and disco-tipped hexasters or hemihexasters as common microscleres, characterizes it as a new species. The placements are also supported by molecular phylogenetic evidence from nuclear 18S rDNA and 28S rDNA, and mitochondrial 16S rDNA and cytochrome c oxidase subunit I (COI) gene. More sampling efforts should be conducted to improve the understanding of the biodiversity of deep-sea seamount sponges.

Genus Tretopleura Ijima, 1927 Type species. Tretopleura candelabrum Ijima, 1927, Published as part of Shen, Chengcheng, Zhang, Dongsheng, Lu, Bo & Wang, Chunsheng, 2020, A new species of glass sponge (Hexactinellida: Sceptrulophora: Uncinateridae) from the Weijia Seamount in the northwestern Pacific Ocean, pp. 322-334 in Zootaxa 4878 (2) on page 325, DOI: 10.11646/zootaxa.4878.2.6, http://zenodo.org/record/4425032, {"references":["Ijima, I. (1927) The Hexactinellida of the Siboga Expedition. In: Weber, M. (Ed.), Siboga-Expeditie. Uitkomsten op zoologisch, botanisch, oceanographisch en geologisch gebied verzameld in Nederlandsch Oost-lndie 1899 - 1900 aan boord H. M. ' Siboga' onder commando van Luitenant ter zee 1 e kl. G. F. Tydemann. 106 Monographie VI. E. J. Brill, Leiden, pp. i-viii + 1 - 383, pls. I-XXVI."]}

Tretopleura weijicus sp. nov. (Figs. 1–6, Table 2) Material examined. Holotype: SIO-POR-090, SRSIO, Haima ROV DY41B, dive MCROV02, collected by Dong-sheng Zhang, Sep. 22, 2017, Weijia Seamount in the northwestern Pacific Ocean (12.3772°N, 156.2871°E), depth 1995 m, frozen at -20°C. Description. The holotype has a blade-like body form, bifurcating into mainly three branches at its top, with a slender peduncle attached to hard substrate and widening gradually towards the body (Fig. 1A). Four segments were sampled, including one piece of the blade-like body and three segments of the lower peduncle (Fig. 1B). Color of the specimen is light beige to white. The body segment is 695 mm long and 45–116 mm wide (Fig. 1B1). Both surfaces longitudinally bulge in the central axes of branches to 13–20 mm thick. The bulge is gradual to 7 mm high in the dermal surface while semicylindrical to 11 mm high in the atrial surface. Thus the transverse cross-section of the body is similar to the lateral view of a bowler hat (Fig. 1C). The edges of the blade-like body are moderately thick-walled lamellae to about 4 mm thick, usually rolling up to the dermal side and pitted by non-overlapping channels penetrating vertically into the body wall (Fig. 2A,B). Epirhyses and aporhyses in the edges of both surfaces are ovoid and in no regular arrangement (Fig. 2C 1,D1). There are evident transition areas between axial and marginal areas in the dermal surface where epirhyses elongate longitudinally and occur in closed-spaced longitudinal series (Fig. 2C2). Epirhyses, 233.1–(847.8)–1865.0 µm in maximum diameter of the cleaned framework, are covered by a lattice of loose dermal pentactins and hexactins (Fig. 2C 4; Table 2). Aporhyses, 267.5–(1065.6)– 2036.8 µm in maximum diameter of the cleaned framework, are more widely spaced and mostly have no overlying of atrial spicules (Fig. 2D 3; Table 2). The bulging areas of both sides are usually smooth and without channels (Fig. 2C 3,D 2). Three segments of the lower peduncle are 37–50 mm wide and totally 881 mm long (Fig. 1B 2). The basal part of the peduncle is cylindrical, and its bottom is relatively round and flat with a diameter of 57–70 mm (Fig. 1D). It should be noted that the basal part of the peduncle was densely covered by anchorate spicules (Fig. 1A,B). Further investigation indicated that these two-toothed anchors were extraneous and probably sourced from a lophophytous Pheronematidae sponge which once grew on the base of this specimen and may have been dead for a long time to only leave its anchorate basalia implanting into and enwinding around the base. Skeleton. The choanosomal skeleton is a three-layered dictyonal framework consisting of an unchannelized primary middle layer and two channelized peripheral layers on both dermal and atrial sides (Fig. 3A). The dermal and atrial peripheral layers consist of hexactine dictyonalia joined irregularly by tip-to-ray fusion at any angle, with rays slightly curved (Fig. 3B,D). The meshes of both cortices are irregularly triangular to polygonal (Fig. 4A,C). The dermal cortex is thicker than the atrial cortex and has a more elongate form of channel apertures in rows (Fig. 3A). The primary middle layer is constructed of longitudinal strands consisting of a series of hexactin centers (Fig. 3C, 4E). Longitudinal stands are joined and supported by two types of connecting elements. One is irregularly appended hexactine dictyonalia, which are joined by ray tips fused to strands at any angle (Fig. 4F 1). Another is irregular-spaced transverse rays of the constituent dictyonalia of longitudinal stands, forming ladder-like connections (Fig. 4F 2). Synapticula are absent. The longitudinal strands, 24.0–(41.5)–58.0 µm thick, are about 1.5 times thicker than the radial or transverse beams (Table 2). Strands and beams are smooth. Beams in the dermal cortex, 20.0–(45.2)– 66.7 µm thick, are mostly thicker than those in the atrial cortex and primary layer (Table 2), but they are similar in average length (Table 2). There are rough and digitate spurs attached thoughout the skeleton (Fig. 4B,D). The dermal and atrial spurs in the edges of the blade-like body are abundant, curving to project candelabra-like outwards on the surfaces (Fig. 4B 1,B 2,D 1). Most of the spurs are conical with sharply or bluntly pointed ends. Besides, there is another form of spurs rarely in the dermal surface, which is cylindrical with swollen and rounded ends (Fig. 4B 2). The atrial spurs, 96.0–(184.0)–312.0 µm long, are slightly longer and much denser than the dermal ones (Fig. 4D; Table 2). Rough microhexactins are attached profusely thoughout the choanosomal skeleton (Fig. 4G). Sometimes microhexactins are fused tip-to-tip. The ectosomal skeleton is composed of a lattice of loose pentactins and hexactins with the blunt sixth distal ray outwards, overlying all choanosomal framework surfaces and entrances to epirhyses but not most of the openings of aporhyses (Fig. 2C 4,D 3). Uncinates are largely distributed horizontally on both surfaces and also project with the anterior end outwards. Sceptrules project vertically or obliquely on the surfaces with head outwards. Additionally, abundant sceptrules along with uncinates can be seen projecting vertically from the inwall of aporhyses with head outwards (Fig. 2D 3). Megascleres. Megascleres are dermal and atrial pentactins and hexactins, discoscopules, and uncinates (Fig. 5; Table 2). The dermalia and atrialia are classified into two categories, respectively. One is pentactins or subhexactins (Fig. 5A,B) referring to the triaxon spicules with a swelling (pentactine form) or a sixth distal ray very short, rounded-tipped and distinct from the other five rays rendering the spicule hexactine. The latter is named as subhexactin, as presented by Reiswig and Kelly (2011), to distinguish from the another category of dermilia and atrilia which includes general hexactins with six rays in similar shape (Fig. 5C,D). Herein, the pentactine and subhexactine forms are placed into one category due to their similarities in shape and continuous change in length of the sixth ray. Dermal pentactins or subhexactins (Fig. 5A) often have a bullet-like or spherical swelling (pentactine form) but may extend up to 53.6 µm long with clavate tip (subhexactine form); tangential rays are 87.0–(139.3)– 263.5 µm long and have conically pointed or rarely rounded tips, sometimes slightly inflated near the pointed tips; the proximal ray is 142.0–(307.9)–430.0 µm in length with conically pointed tips and 1.3–(2.3)–3.6 times longer than the tangential ones; the distal ray is 4.2–(8.2)–11.0 µm in diameter, slightly thicker than the proximal and tangential ones. Dermal pentactins or subhexactins are entirely microspined and rougher in the distal part of rays. Atrial pentactins or subhexactins (Fig. 5B) have a sixth distal ray which is a short cylindrical ray extending from 6.7 to 39.2 µm long with rounded tip (subhexactine form) or rarely only a spherical swelling (pentactine form); tangential rays are usually long and gently taper to sharply pointed tips, 148.6–(431.3)– 698.3 µm in length, sometimes having one tangential ray very short but the paired one long and obviously thickened with bluntly pointed tip; the proximal ray is relatively short, 14.4–(118.6)–200.0 µm in length, with tapering and sharply pointed tip; all rays are 3.0–(5.6)– 8.3 µm in diameter. The tangential and proximal rays are microspined but the distal ray and the axial cross are smooth or sparsely spined. Dermal hexactins (Fig. 5C) are usually sword-like with short distal ray and very long proximal ray similar to dermal pentactins/subhexactins, while some are irregular and have all the rays unequally long. The distal rays, 28.0– (114.4)–195.0 µm long, are conically pointed or sometimes slightly inflated near the pointed tips; tangential rays are 87.8–(133.8)– 254.5 µm long; the proximal ray is 100.0–(317.4)–420.0 µm long; the ray width is 4.7–(6.9)–10.0 µm. Atrial hexactins (Fig. 5D) have an obviously short distal ray 18.0–(64.0)–122.0 µm in length; tangential rays are 107.8–(356.4)– 568.3 µm long with sharply pointed tips; the proximal ray is 211.1–(364.8)–501.0 µm in length, nearly equally long to tangential rays or more than 1.5 times longer than tangential ones rendering the hexactins sword-like; the proximal ray is 4.4–(10.4)–60.0 µm in width slightly thicker and rougher than the distal and tangential rays with sharply or rarely bluntly pointed tips. Atrialia are generally larger and more irregular than dermalia with considerable variation occurring in the relative lengths of each ray, leading to a lot of broken-rayed triaxon spicules when observed. Additionally, no regular pentactins without any swelling are observed. Uncinates (Fig. 5E) are basically straight, 853.9–(1709.9)– 15833.3 µm long and 5.0–(6.2)– 8.3 µm thick, sometimes slightly curved, with barbs curving out from the spicule surface. One end is full of well-developed barbs which are oriented towards the other end. The barbs of the other end are undeveloped and similar to forward-curved spines. Both tips are sharply pointed. Sceptrules (Fig. 5F) are discoscopules, 450.0–(632.3)–1192.0 µm long, usually have 4–7 thin, basically straight or slightly curved, and rough tines capped with small marginally toothed discs. The tapered shaft is rough and straight, occupying about 88% of the total length. The middle of the shaft is sparsely microspined, 4.8–(6.5)– 12.8 µm thick, while its terminal part bears procurved spines and ends in a sharply pointed tip. Sceptrules vary in the form of the head with the head length 59.2–(76.0)– 156.8 µm and neck width 6.7–(9.6)– 16.4 µm. Overall, one form often has a neck tapering to the shaft with 4–6 nearly parallel straight tines; another form has a short neck consisting of four swellings with 4–7 relatively divergent tines. Microscleres. Microscleres are only stellate discohexasters (Fig. 5G; Table 2). Their primary rays bear 4–11 secondary rays ending in small discs with 7–9 marginal spines. All rays are entirely ornamented with short recurved spines, but the spherical centrum remains smooth. Considerable variation occurs in the relative lengths of primary and secondary rays, the form of the terminal group, and the number of secondary rays. There are mainly two types of stellate discohexasters. Type I (Fig. 5G 1) has 6–11 relatively sigmoid secondary rays per primary ray, arranged with a central one in line with the primary rays and the others in a single whorl around it. The discohexasters of type I are 26.5–(31.8)– 36.3 µm in diameter, with their ratio of secondary to primary length being 1.2–(2.0)–2.8. Type II (Fig. 5G 2) has short primary rays bearing 4–6 relatively long, slightly curved, and tightly bunched terminal rays. The discohexasters of type II are 30.6–(40.8)–49.0 µm in diameter and their ratio of secondary to primary length is 1.7–(2.8)–4.0. Both are scattered in the whole specimen, but the former is more common. Ecology. The Weijia Seamount in the northwestern Pacific Ocean, depth 1995 m. The flat bottom of the peduncle is attached to a hard substrate beneath a thin sediment. Etymology. The species name, weijicus, refers to the location, the Weijia Seamount. Remarks. The new specimen described here is a sceptrule-bearing sponge, of which the primary choanosomal framework consists of multiaxial longitudinal strands joined and supported by irregularly-appended hexactine dictyonalia and irregularly-spaced transverse rays, without synapticula. Therefore it is attributed to the family Uncinateridae, rather than Aulocalycidae. Due to its blade-like and branching body form, the presence of epirhyses and aporhyses and the absence of diarhyses, the specimen belongs to the genus Tretopleura. The two currently valid species of Tretopleura occur in the tropical western Pacific Ocean at depths of 1500- 2080 m. Also, the new specimen was collected from the Weijia Seamount in the northwestern Pacific Ocean at a depth of 1995 m. T. candelabrum was collected as curved plate-form fragments, and loose spicules were unavailable. It is named after its candelabra-like atrial spurs, which also characterize the new specimen. The dermal spurs of T. candelabrum are thickened and often fused as compound clubs while such swollen dermal spurs are not found in the new specimen. T. styloformis was collected integrally as a blade-like body, of which the spiculation was described but the skeleton was not mentioned. Pentactins with a spherical swelling were observed in both specimens [shown as Fig. 3.10B in Tabachnick (1988) and Fig. 5A,B in this paper]. Besides, regular pentactins without a swollen distal ray [Fig. 3.10A in Tabachnick (1988)] were described in the T. styloformis, but not in the new specimen. Moreover, there are two types of discohexasters in the new specimen, of which the type II (Fig.5G 2 in this paper) is similar to those of T. styloformis [Fig. 3.11 in Tabachnick (1988)]. The type I (Fig.5G 1 in this paper) in the new specimen is smaller and more common with relatively sigmoid secondary rays, but not shown in the T. styloformis. In addition, although uncinates which are abundant on both surfaces of the new specimen were not shown by Tabachnick (1988), their presence was included in the diagnosis by Reiswig (2002) after further review.

Genus Rhizophyta gen. nov. urn:lsid:zoobank.org:act: B71AF3A9-527F-454E-9AC7-0074CC189FE0 Type species. Rhizophyta yapensis gen. et sp. nov. Diagnosis. Body is fungus-like, pedunculate, rhizophytous with completely everted, laterally directed atrial cavity. Choanosomal spicules of the main body are diactins and hexactins. Dermalia and atrialia are pinular hexactins and rare pentactins. The internal spicules of the peduncle are diactins fused into a rigid skeleton by synapticulars. External spicules of the peduncle are loose pentactins forming a veil. Microscleres are toothed stellate discohexasters. Etymology. The new genus name, Rhizophyta, reflects the rhizophytous attachment method (fixation by rootlike outgrowths instead of spicule tuft or basal plate). Remarks. Due to the presence of a long peduncle and absence of hypodermal pentactins, the new specimens most closely match the diagnosis of Euplectellidae: Bolosominae. Although the surface pentactins veiling the peduncle resemble similar structures formed by hypodermalia in the Rossellidae, there are no smaller megascleres accompanying them, so they are best interpreted as homologous to dermalia rather than hypodermalia. Furthermore, our molecular evidence (see below) clearly rules out any affinity to Rossellidae. The rhizophytous method of fixation is quite rare among extant Hexactinellida and has to our knowledge never been reported for bolosomine euplectellids – as far as we are aware, only two rhizophytous euplectellids have been described before, namely Regadrella rhizophora and R. pedunculata, which are venus-flower-basket-like forms with a very short "peduncle", currently classified in Corbitellinae (see Tabachnick & Lévi 2004; Reiswig & Kelly 2018). The new species cannot be accommodated in any of the currently known ten genera of Bolosominae. The overall body shape combined with pinular dermal and atrial hexactins suggest affinities to the monotypic genus Neocaledoniella Tabachnick & Lévi, 2004. However, the new species is clearly distinguished from it by the presence of regular discohexaster microscleres rather than a combination of calycocomes and graphiocomes. Furthermore, recent investigation of a newly collected specimen of Neocaledoniella caulophacoides (Tabachnick, 2002) allowed for the first time examination of the base of its peduncle, showing that it has a basiphytous method of fixation (CS, unpublished observation). The presence of no other microscleres than discohexasters is uniquely shared with Bolosoma Ijima, 1904 among known pedunculate euplectellids. However, besides from differing in body shape (no everted, laterally directed atrial cavity and shorter, thicker stalk), Bolosoma species are characterized by the presence of anchorate discohexasters (codonhexasters) and their derivatives (missing in the new species). Our molecular evidence (see below) also does not support any affinity of the new species to Bolosoma.

Rhizophyta yapensis gen. et sp. nov. (Figs. 1���4, Table 2) urn:lsid:zoobank.org:act: 2211A05A-53D7-4563-82DE-86BBBB1BB33B Material examined. Holotype: SIO-POR-083, SRSIO, Jiaolong HOV DY 38III, dive JL148, collected by Bo Lu, June 4, 2017, Yap Trench in the northwestern Pacific Ocean (8.0582��N, 137.5233��E), depth 4160 m, preserved in 95% ethanol. Paratype A: SIO-POR-075, SRSIO, Jiaolong HOV DY 37I, dive JL109, collected by Bo Lu, May 15, 2016, Yap Trench (9.90045��N, 138.3995��E), 4779 m, 95% ethanol. Paratype B: SIO-POR-084, SRSIO, Jiaolong HOV DY 38III, dive JL148, collected by Bo Lu, June 4, 2017, Yap Trench (8.0579��N, 137.5227��E), 4159 m, frozen at -20?. Paratype C: SIO-POR-085, SRSIO, Jiaolong HOV DY 38III, dive JL148, collected by Bo Lu, June 4, 2017, Yap Trench (8.0582��N, 137.5224��E), 4159 m, 95% ethanol. Description. The new species is presented by four fungus-like specimens with everted, laterally directed atrial cavity. The holotype (Fig. 1A1���A 3) has a disc-like main body borne on a long, thin, slightly curved peduncle. The basal part of the peduncle is solid and features root-like outgrowths (rhizophytous method of fixation). The specimen was collected intact, but the peduncle was intentionally broken for storage and shipping. Total length of this specimen is 284 mm, of which the main body is 29 mm high, the peduncle is 233 mm long, and the root-like structure is up to 22 mm long. The main body is hanging from the upper part of the peduncle to one side; it is 60�� 37 mm in diameter and up to 30 mm thick. The peduncle is solid, not hollow. It varies in diameter from 4.0 mm just below the main body to 1.0 mm at its narrowest point in the upper third and enlarges to 5.0 mm near the base. The exhalant or atrial surface of the main body (Fig. 2A) is relatively smooth, with very fine lattices (Fig. 2B) of loose megascleres (Fig. 2C) covering the subatrial exhalant canal openings, which are up to 2 mm in diameter. The inhalant or dermal surface (Fig. 2D) is more transparent, with a conspicuous network of white strands of radiating choanosomal diactins surrounding large inhalant canals, which are easily visible through the overlying thin and quite regular lattices (Fig. 2E) of loose megascleres (Fig. 2F). A marginal fringe is not evident at the junction of dermal and atrial surfaces. Spicules of the body are entirely unfused. The entire length of the peduncle and the main roots at the base are covered by a veil of loose pentactins with proximal rays directed inside (Fig. 2 G���I). The thin lateral roots branching off from the main roots are smooth (Fig. 2G). The roots are solid and consist of diactins fused by short synapticulars (Fig. 2J). Color of the specimen in ethanol is white. Paratype A (Fig. 1B1���B 2) was collected broken with a tattered main body borne on a thin peduncle split into two pieces. It is 587 mm long, of which the main body is 46 mm high, the peduncle is 502 mm long, and the rootlike structure is up to 39 mm long. The peduncle varies in diameter from 2.8 mm just below the main body to 1.6 mm at its narrowest point and enlarges to 5.6 mm near the base. Color of the specimen is white in situ while yellowish brown after sampling due to mixing with sediment. A sea anemone (Relicanthus sp.) was attached to the peduncle in situ. Paratype B (Fig. 1C1���C 3) was sampled with its main body and a section of peduncle 119 mm long. The main body is 25 mm high and 44�� 26 mm in diameter. The diameter of the peduncle is 1.9 mm just below the main body and 1.0 mm at its narrowest point. The specimen is colored light yellow by mixing with sediment. Paratype C (Fig. 1D1���D 3) was collected with its main body and a section of peduncle 161 mm long. The main body is 28 mm high, 54�� 46 mm in diameter, and up to 21 mm thick; it was sampled intact but later cut in half. The diameter of the peduncle is 3.2 mm just below the main body and 1.5 mm at its narrowest point. Color of the specimen in ethanol is white. Spicules. Dermalia and atrialia are pinular hexactins (Fig. 3 A���C) and rare pentactins (Fig. 3 D���F). Choanosomal megascleres are hexactins and diactins (Fig. 3 H���I). Peduncle and root internal spicules are diactins fused by short synapticulars (Fig. 2J). Dermal spicules of the peduncle are pentactins (Fig. 2 H���I, Fig. 3J). Microscleres are toothed stellate discohexasters with flower-shaped (perianthic) tufts of secondary rays (Fig. 3G). Spicule dimensions are given in Table 2. ......continued on the next page Pinular dermal hexactins (Fig. 3A) have thorny pinular rays and entirely rough tangential and proximal rays, which are various in shape and size. The pinular ray is quite variable in shape with spindle-like or ovoid ends. It is 63.8���232.3 (131.7) ��m long, the tangential rays are 147.5���220.0 (181.8) ��m long, and the proximal ray is 72.4��� 370.0 (158.8) ��m long. The ratio of proximal ray length to tangential rays length ranges from 0.3 to 2.1 with an average of 0.9. There are 38% pinular hexactins with a relatively shorter proximal ray (1.4 times the length of tangential rays. Most dermal hexactins are regular with tangential rays of equal length. However, some (1%) have only one pair of tangential rays equal and one of the unequal tangential rays is similar to a pinular ray. Atrial hexactins (Fig. 3B) are similar to the dermal ones but have longer proximal rays. The pinular ray of atrial hexactins is 31.3���173.0 (128.0) ��m long, the tangential rays are 133.3���230.0 (179.7) ��m long, and the proximal ray is 106.0���571.0 (309.8) ��m long. The ratio of proximal ray length to tangential rays length ranges from 0.6 to 2.7 with an average of 1.7. There are 12% hexactins with a relatively shorter proximal ray (~60% of tangential rays length), while 76% have it> 1.4 times the length of tangential rays. The hexactins in the transition of main body and peduncle (Fig. 3C) are smaller in size, but thicker in ray width relative to ray length. They have a longer proximal ray of which 68% is more than 1.4 times longer than the tangential ray. Their pinular rays are 45.5���97.5 (70.8) ��m long, the tangential rays are 82.8���173.7 (118.9) ��m long, and the proximal ray is 102.9���371.7 (182.0) ��m long. Dermal and atrial pentactins are rare and have spined tangential and proximal rays and smooth axial crosses (Fig. 3 D���F). There are two kinds of pentactins differing in size both as dermalia and atrialia, of which the smaller one is quite rare (Fig. 3D). Moreover, among atrial pentactins there is another type with relatively longer proximal ray (Fig. 3E). The tangential rays of dermal pentactins in the main body are 45.9���287.3 (145.4) ��m long and the proximal ray is 38.7���201.3 (97.2) ��m long. Atrial pentactins are bigger than dermal pentactins with the tangential rays 90.0���207.5 (159.3) ��m long and the proximal ray 66.7���181.6 (120.8) ��m long. Dermal pentactins in the transition of main body and peduncle (Fig. 3F) have thicker and rougher rays, longer proximal rays with a length of 89.2���266.8 (159.2) ��m, while relatively shorter tangential rays with a length of 60.0���139.1 (108.4) ��m. A few dermal pentactins have missing or undeveloped rays and are irregular tetractins, stauractins or tauactins (not shown). Forty-two percent of choanosomal hexactins (Fig. 3H) have equal rays. Others have rays of unequal length: 44% have one ray relatively shorter than others and 14% have one pair of rays evidently longer than the other two equal pairs. The rays of choanosomal hexactins are on average 86.8���182.0 (137.1) ��m long and 10.5���23.8 (19.5) ��m wide. They all bear spines; ray tips are rough and abruptly pointed. Choanosomal diactins (Fig. 3I) are slightly curved, with a generally inconspicuous central swelling, and can be roughly classified into two types according to the shape of terminal ends: One type has rounded, occasionally inflated, and rough terminal ends with less rough or even smooth caps, and smooth center; the other has conically pointed terminal ends and spines scattered across the whole spicule. Choanosomal diactins are 536.98���5200.0 (1766.8) ��m long and 3.71���13.5 (8.7) ��m wide. Diactins of the peduncle and roots (Fig. 2J) are fused by short synapticulars to form a rigid framework; they are larger than the main body diactins and smooth or somewhat verrucous. Dermal spicules of the peduncle are pentactins forming a veil (Fig. 2 H���I, Fig. 3J). They have spines in the axial cross, spined tangential and proximal rays, less rough and tapered or rounded ends of tangential rays, and short proximal rays. The tangential rays are 268.3���670.0 (456.2) ��m long and the proximal ray is 30.2���99.4 (60.9) ��m long. Microscleres (Fig. 3G) are toothed, stellate, perianthic discohexasters. They have short primary rays bearing 6���9 secondary rays ending in small discs with 6���8 marginal teeth. The primary rays are thick and mainly smooth while the secondary rays are thin and rough. The discohexasters are 56.7���108.6 (82.6) ��m in diameter, primary rays are 6.0���11.1 (7.7) ��m long, secondary rays are 19.6���43.0 (31.9) ��m long. The general spiculation of the holotype and paratypes is the same. However, some spicules differ in specific shapes. Choanosomal diactins of paratype A have rounded or conically pointed terminal ends with relatively smooth caps, and the shape of their centers varies with inconspicuous, one or two swellings (Fig. 4A). The discohexasters of paratype C have 9���14 terminal rays per primary ray with 9���13 marginal teeth per disc (Fig. 4 B��� C). Etymology. The species name, yapensis, refers to the location of collection, the Yap Trench. Remarks. The slight differences in spiculation between the four specimens could indicate ongoing speciation within the new genus. However, we consider these differences, combined with the geographical proximity of the specimens, to be too minor to provide evidence of full formation of separate species or subspecies (see also molecular results below). Instead, we interpret them as regular intraspecific variation., Published as part of Shen, Chengcheng, Dohrmann, Martin, Zhang, Dongsheng, Lu, Bo & Wang, Chunsheng, 2019, A new glass sponge genus (Hexactinellida: Euplectellidae) from abyssal depth of the Yap Trench, northwestern Pacific Ocean, pp. 367-378 in Zootaxa 4567 (2) on pages 370-377, DOI: 10.11646/zootaxa.4567.2.9, http://zenodo.org/record/2595030

Subfamily Bolosominae Tabachnick, 2002 Emended definition (after Tabachnick 2002): Basiphytose or rhizophytous Euplectellidae with peduncle. Remarks: Although erection of a new subfamily for Rhizophyta gen. nov. would have been a possibility, we refrained from it because classification of euplectellids according to attachment mode is clearly artificial (Dohrmann et al. 2017). We nevertheless retain the obviously paraphyletic Bolosominae (see below and Dohrmann et al. 2017) here for purely practical purposes, pending major revision or abolishment of euplectellid subfamily division., Published as part of Shen, Chengcheng, Dohrmann, Martin, Zhang, Dongsheng, Lu, Bo & Wang, Chunsheng, 2019, A new glass sponge genus (Hexactinellida: Euplectellidae) from abyssal depth of the Yap Trench, northwestern Pacific Ocean, pp. 367-378 in Zootaxa 4567 (2) on page 369, DOI: 10.11646/zootaxa.4567.2.9, http://zenodo.org/record/2595030, {"references":["Tabachnick, K. R. (2002) Family Euplectellidae Gray, 1867. In: Hooper, J. N. A. & Van Soest, R. W. M. (Eds.), Systema Porifera: A Guide to the Classification of Sponges. Kluwer Academic / Plenum Publishers, New York, pp. 1388 - 1434. https: // doi. org / 10.1007 / 978 - 1 - 4615 - 0747 - 5 _ 146","Dohrmann, M., Kelley, C., Kelly, M., Pisera, A., Hooper, J. N. A. & Reiswig, H. M. (2017) An integrative systematic framework helps to reconstruct skeletal evolution of glass sponges (Porifera, Hexactinellida). Frontiers in Zoology, 14, 18. https: // doi. org / 10.1186 / s 12983 - 017 - 0191 - 3"]}