Beania hexamicorum Tilbrook, Hayward, and Gordon, 2001

Dick, Matthew H. & Grischenko, Andrei V., 2016, Rocky-intertidal cheilostome bryozoans from the vicinity of the Sesoko Biological Station, west-central Okinawa, Japan, Journal of Natural History 51 (3 - 4), pp. 141-266 : 166-182

Beania hexamicorum Tilbrook, Hayward, and Gordon, 2001

( Figure 7 (c–f))

Beania hexamicorum Tilbrook, Hayward, and Gordon, 2001, p. 50 , fig. 4(c, d).

? Beania sp. : Hayward 1988, p. 288, fig. 4(b).

Material examined

NSMT-Te 1069 ( MIN- 34), dried, on SEM stub; NSMT-Te 1070, two colony fragments, dried, MIN site; NHMUK 2016.5.13.12 ( MIN- 18), dried, on SEM stub; NHMUK 2016.5.13.13–14, two colony fragments, dried, MIN site.

Measurements

OpL, 0.49–0.58 (0.534 ± 0.026); OpW, 0.22–0.37 (0.292 ± 0.029) (n = 20, 1). AvL, 0.13–0.22 (0.158 ± 0.023) (n = 21, 1).

Description

Colony ( Figure 7 (c)) forming a small, unilaminar sheet, raised from surface of substratum and loosely attached to it by occasional thin rhizoids arising from basal side of zooids; tan in colour. Zooids ( Figure 7 (d)) oval, thin walled, lightly calcified, each linked to surrounding zooids by up to six evenly spaced tubular connections; distance between adjacent opesiae equal to or somewhat less than half the opesial width. Three or (less often) four short, erect spines distal to orifice; another small spine on each side lateral to orifice, erect or angled inward; three to nine longer, straight or slightly curved spines arising from opesial rim proximal to avicularium on each side, angled over opesia; additionally up to five straight, horizontally oriented basal spines on each side arising just below opesial rim, directed into spaces between adjacent zooids ( Figure 7 (d)). Basal spines variably present; some or most zooids in some colonies lack them ( Figure 7 (f)). Zooids dimorphic; one type (asterisks, Figure 7 (d, e)) has pair of relatively thick, straight or curved spines proximolateral to orifice, angled over proximal margin of orifice and meeting in midline, forming distinct suborificial strut, with orifice small and well defined; other type (circles, Figure 7 (d, e)) lacks these distinct spines and has larger, broader orifice defined by opercular margin. Avicularia ( Figure 7 (d–f)) single or paired proximolateral to orifice, arising from opesial rim, with short peduncle, bulbous chamber and narrow, laterally compressed rostrum with hooked tip. Many zooids have second pair of avicularia proximal to orificial pair, in the region 1/3–1/2 the length of zooid from distal end; one zooid ( Figure 7 (f)) has two additional pairs in this region.

Remarks

Our material resembles Beania hexamicorum from Vanuatu ( Tilbrook et al. 2001) in the following characters. Average zooid size is similar (Okinawa, 0.53 × 0.29 mm; Vanuatu, 0.57 × 0.31 mm); the avicularia are identical in shape and similar in average length (Okinawa, 0.16 mm; Vanuatu, 0.14 mm); zooids are rather closely spaced, connecting with neighbours by up to six evenly spaced tubes; there are similar complements of distal and lateral marginal spines; and zooids can produce more than one pair of avicularia (Okinawa, up to three pairs were observed; Vanuatu, up to five pairs). The main difference in the two populations is that zooids in our material can produce straight accessory spines from the basal side that project into the interzooidal spaces ( Figure 7 (d)); however, this character is variable, as not all zooids produced these basal spines ( Figure 7 (e)). While Tilbrook et al. (2001) did not mention zooidal dimorphism in B. hexamicorum , this would be an easy character to overlook; it is not possible to check from their illustration, as they figured only two zooids. Tilbrook et al. (2001) listed, as a synonym of B. hexamicorum , ‘ Beania sp. ’ reported from Mauritius by Hayward (1988), who considered his material too fragmentary either to reliably identify to species or to describe as new. While the avicularium shape is similar, Hayward (1988) did not mention more than a single pair of avicularia.

Occurrence

We found six colonies, all at the MIN site. Tilbrook et al. (2001) reported this species to be common on the undersides of pieces of coral rubble at Erakor Island, Efate, Vanuatu. Without verification of Hayward’ s (1988) record from Mauritius, we consider this species to have a western-Pacific distribution, with Vanuatu the only previously known locality.

Superfamily MICROPOROIDEA Gray, 1848 Family ONYCHOCELLIDAE Jullien, 1882

Genus Smittipora Jullien, 1882

Smittipora cordiformis Harmer, 1926

( Figure 8 (a, b))

Smittipora cordiformis Harmer, 1926 (part), p. 260, pl. 16, figs 14–18.

Smittipora cordiformis: Hayward and Ryland 1995, p. 543 , fig. 6(c). Tilbrook et al. 2001, p. 52, fig. 6(g). Tilbrook 2006, p. 74, pl. 12A.

Material examined

NSMT-Te 1071 ( MIN- 6), bleached, on SEM stub; NSMT-Te 1072, dried specimen, MIN site.

Measurements

AzL, 0.65–0.86 (0.791 ± 0.053); AzW, 0.34–0.53 (0.456 ± 0.049); OpL (to base of proximal lip), 0.17–0.20 (0.187 ± 0.007); OpW, 0.14–0.16 (0.151 ± 0.007) (n = 15, 1). AvL, 0.52–0.75 (0.623 ± 0.063); AvW, 0.24–0.34 (0.293 ± 0.026) (n = 15, 1). MatZL, 0.55–0.76 (0.694 ± 0.097); MatZW, 0.45–0.55 (0.492 ± 0.055); MatZOpL, 0.27–0.34 (0.306 ± 0.027); MatZOpW, 0.20–0.25 (0.221 ± 0.022) (n = 4, 1). Largest colony fragment 24 mm across.

Description

Colony ( Figure 8 (a)) forming a unilaminar, encrusting sheet; dried colony light reddish brown, with ‘salt-and-pepper’ appearance due to pigmented ectocyst over cryptocyst surrounded by white raised zooidal margins; operculum dark brown, appearing black; rachis and bifurcate base of avicularian mandible also dark brown. Zooids ( Figure 8 (a, b)) distinct, closely appressed, with suture line between them. Cryptocyst sunken, uniformly granulated, sides sloping from margin to lowest area in centre, proximal to opesia. Opesia of non-maternal zooids subterminal, elongate-D-shaped, sides nearly parallel; proximal margin with broad lappet flanked by narrow sinus on each side. Sunken inside distal curvature of opesia is a broad, straight or slightly convex shelf, occasionally forming a distinct, conical median projection. Opesia of internally brooding maternal zooids ( Figure 8 (b)) terminal, much larger than that of non-maternal zooids; elongate-Dshaped, with nearly parallel sides, or campanulate, widest proximally; proximal margin straight or slightly convex, sometimes with conspicuous lappet flanked by sinuses. Along distal curvature of maternal opesia is a smooth, curved, visor-like vestigial ooecium delineated laterally by a suture on each side ( Figure 8 (b), arrowhead). Avicularia interzooidal; shorter and narrower than autozooids, with elongate opening widest distally. Mandibular pivot is a comma-shaped slit on each side; opesial part of rostral opening surrounded by granulated cryptocystal shelf. Avicularia ( Figure 8 (a, b)) asymmetrical distally, one margin nearly straight and the other strongly curved. Avicularian mandible (not shown) with bifurcate base and long rachis about as long as avicularian cystid; proximal half of rachis has colourless, transparent, hemi-ovoid wing on each side. Spines lacking. Ancestrula not observed.

Remarks

This species is characterised by dimorphism between brooding and non-brooding zooids, and by having an asymmetrical avicularian rostrum. Autozooids in our specimens are larger (average L × W, 0.79 × 0.46 mm) than in populations in the Solomon Islands (L × W, 0.65 × 0.40 mm; Tilbrook 2006) and Great Barrier Reef (~0.55 × 0.40 mm; Hayward and Ryland 1995), and the avicularia are conspicuously smaller than the flanking autozooids. Harmer (1926, p. 261) noted in the original description that the opesia usually has ‘a conspicuous median tubercle present within its distal border’ and clearly shows this structure in his illustrations. We observed only one zooid in our specimens to have this median tubercle; most zooids have, in place of the tubercle, a straight or broadly convex thickening that appears as a low shelf, and some zooids lack any trace of a projection.

Occurrence

We found only two colonies, both at the MIN site. Smittipora cordiformis is broadly distributed in the Indo-West Pacific. Harmer (1926) originally described it from depths of 0–32 m in the Celibes, Indonesia, and reported other specimens from Burma ( Myanmar), Singapore or the Philippines, and the Adimarante Islands in the Indian Ocean. It has subsequently been reported from the Great Barrier Reef ( Hayward and Ryland 1995), Vanuatu ( Tilbrook et al. 2001) and the Solomon Islands ( Tilbrook 2006).

Superfamily CRIBRILINOIDEA Hincks, 1879 Family CRIBRILINIDAE Hincks, 1879

Genus Cribralaria Silén, 1941

Cribralaria curvirostris Silén, 1941

( Figure 8 (c, d))

Cribralaria curvirostris Silén, 1941, p. 122 , figs 182 and 183.

Material examined

NSMT-Te 1073 ( MIN- 7), bleached, on SEM stub; NSMT-Te 1074 ( MIN- 7-1), bleached on SEM stub; NSMT-Te 1075, six dried specimens, MIN site; NHMUK 2016.5.13.15-17, three dried specimens, MIN site.

Measurements

AzL, 0.53–0.67 (0.603 ± 0.039); AzW, 0.32–0.42 (0.361 ± 0.029) (n = 20, 1). OrL, 0.07–0.09 (0.081 ± 0.008); OrW, 0.16–0.20 (0.178 ± 0.012) (n = 20, 1). Exposed OvL, 0.11; OvL

including distal, endoozoidal part not evident in unbleached specimens, 0.16; OvW, 0.21 (n = 1). Largest colony observed 20 × 13 mm.

Description

Colony forming a unilaminar, encrusting sheet; glistening white in colour. Zooids ( Figure 8 (c)) oval, distinct. Costal shield high, convex, with 15–19 (usually 16–18; modal number, 17) well-defined costae, including suboral pair; adjacent costae separated by three to six (usually five) conspicuous, kidney-shaped intercostal foramina. Paired costae forming proximal margin of orifice are thicker than others, and each has three to five minute denticles along distal edge. Orifice much broader than long, with smooth, raised distal rim. Avicularia ( Figure 8 (c, d)) large, interzooidal, the chambers approximately square in outline; located between distal end of one zooid and proximal end of the next; sometimes lacking from extensive portions of colonies. Rostrum long; narrow and acute distally; directed distolaterally; slightly curved around proximal end of succeeding autozooid; opesia oval or pear shaped; crossbar incomplete, with pivot consisting of pair of condyles. Ovicell ( Figure 8 (d)) endozooidal; ooecium formed by, and sunken in, cystid of distal avicularium; ooecium visible externally only as slightly convex crescentic area distal to orifice; entire ooecium evident only in bleached specimens. Zooids interconnect via uniporous septula, at least two in transverse wall and three to five in each distolateral wall. Ancestrula not observed.

Remarks

Silén’ s (1941) illustrations of this species show a suture running along the midline of each costa, equidistant between two flanking columns of intercostal foramina. This does not make intuitive sense, as one would expect a suture instead between each pair of adjacent costae, indicating lateral fusion of the costae. However, the condition shown by Silén is evident in various cribrimorphs as the frontal shield develops during zooidal ontogeny, with a column of pores and half of each adjacent costa developing as a unit and later fusing with adjacent units. Ontogenetically mature zooids of C. curvirostris show the suture running through the midline of a column of pores, as expected.

Occurrence

This species occurred only at the MIN site, where it was abundant ( Table 1). The only previous report of C. curvirostris is from 120 m depth east of Chichijima (~ 27.083°N, 142.183°E) in the Ogasawara (Bonin) island group ( Silén 1941), roughly 900 km due east of our study area.

Genus Puellina Jullien, 1886

Puellina harmeri Ristedt, 1985

( Figure 9)

Puellina harmeri Ristedt, 1985, p. 26 , figs 1, 6(a–e), 7(a–k), 8(a–j) and 9(a–d).

Puellina harmeri: Dick et al. 2006, p. 2212 , fig. 6(a).

Cribrilaria harmeri: Hayward 1988, p. 290 , pl. 3c.

? Puellina vulgaris Ryland and Hayward, 1992, p. 244 , fig. 12(b, c).

Material examined

NSMT-Te 1076 ( MIN- 9), dried (unbleached), on SEM stub; NSMT-Te 1077, specimen MIN- 9/1, bleached, on SEM stub; NSMT-Te 1078 ( MIN- 30), ancestrula, bleached, on SEM stub.

Measurements

AzL, 0.25–0.36 (0.314 ± 0.030); AzW, 0.18–0.29 (0.226 ± 0.027) (n = 20, 1). Non-ovicelled zooids: OrL, 0.04–0.06 (0.050 ± 0.009); OrW, 0.06–0.08 (0.062 ± 0.007) (n = 7, 1). OvL, 0.09–0.13 (0.110 ± 0.012); OvW, 0.11–0.12 (0.116 ± 0.006) (n = 12, 1). AvRosL: adventitious avicularia, 0.15–0.21 (0.182 ± 0.018) (n = 12, 1); marginal vicarious avicularia, 0.13, 0.14 (n = 2, 1). Largest colony observed 8 mm across.

Description

Colony forming an irregular, unilaminar, encrusting sheet. Frontal shield ( Figure 9 (a)) slightly convex, with 14–16 costae (mode, 15), including suboral pair; raised boss at bend of costal spines variably present within and among zooids. Adjacent costae separated by three to seven (usually five or six) intercostal foramina, including the papilla foramen; papilla foramen about as large as largest of other intercostal foramina. Suboral pair of costae often with tips raised, forming a pointed boss. Suboral lumen single; small, about same size as largest of intercostal pores. Orifice D-shaped, varying within same colony from broader than long to longer than broad. Non-ovicelled zooids with seven closely spaced oral spines; ovicelled zooids with two spines on each side of orifice. Avicularia of two types: interzooidal ( Figure 9 (b)), budded at growing edge, with broad base contacting substratum, later surrounded by autozooids; and adventitious ( Figure 9 (c)), sparsely present in some parts of colony, abundant in other parts, budded from and recumbent on marginal gymnocyst, single or paired lateral to orifice, pointing distally. Rostrum of both types variable in length, sometimes longer than ovicell; narrow, sides nearly parallel, edges variable in sculpturing, smooth or serrate even within same colony. Ovicell prominent ( Figure 9 (b, c)), closed by operculum. Ooecium smooth, globose, often with slight median ridge or boss proximally. Ancestrula ( Figure 9 (d)) tatiform, with 12 spines evenly distributed around opesial margin; ancestrula buds a triplet of daughter zooids, distally and distolaterally; daughter zooids similar to but smaller than subsequent zooids, with seven oral spines.

Remarks

Our specimen matches well the original description of this species from the Philippines (Ristedt 1985), although Ristedt reported slightly more (15–17) costae per zooid. The origin of the ooecium is variable in this species; the ooecial fold can be formed either by the distal zooid ( Figure 9 (c)), by a distal kenozooid visible from above, or by a distal kenozooid with no frontal part visible from above ( Figure 9 (b)) ( Ostrovsky 1998, 2013), with all three variants sometimes occurring in the same colony.

It is not clear how P. harmeri differs from Puellina vulgaris Ryland and Hayward, 1992 , originally described from the Great Barrier Reef, Australia. Judging from the original description, the latter species differs from the former only in having slightly smaller zooids and a shorter avicularian rostrum. Rostrum length is not a reliable character, however, as it varies within colonies, both in material reported as P. harmeri (e.g. Dick et al. 2006, p. 2212, fig. 6(a, c, e, g)) and that reported as P. vulgaris (e.g. Tilbrook 2006, p. 95, pl. 15E). Ryland and Hayward (1992) did not describe the ancestrula for P. vulgaris . The original description for P. harmeri indicates a tatiform ancestrula with 12 spines (Ristedt 1985), as was observed in both the Hawaii ( Dick et al. 2006) and Okinawa populations. Specimens from the Solomon Islands identified as P. vulgaris have a tatiform ancestrula with 14 spines ( Tilbrook 2006), although the avicularia, zooid measurements and range in number of costae are quite similar to those in our specimens. Tilbrook et al. (2001) also reported P. vulgaris as quite common at Vanuatu, but did not observe the ancestrula in that population. Without a better idea of the range of variation in nominal P. harmeri and P. vulgaris , it is premature to declare them synonymous, but the possibility cannot be ruled out.

Occurrence

Puellina harmeri was uncommon in the study area; we found six colonies, all at the MIN site. This is a widely distributed, shallow-water, tropical to subtropical, Indo-West Pacific species, previously reported from the Philippines (Ristedt 1985), Mauritius ( Hayward 1988) and Hawaii ( Dick et al. 2006). This range encompasses that of the similar and possibly synonymous species P. vulgaris , reported from the Great Barrier Reef ( Ryland and Hayward 1992), Vanuatu ( Tilbrook et al. 2001) and the Solomon Islands ( Tilbrook 2006).

Superfamily CATENICELLOIDEA Busk, 1852b Family CATENICELLIDAE Busk, 1852b

Genus Vasignyella Gordon, 1989

Vasignyella otophora ( Kirkpatrick, 1890)

( Figure 10 (a))

Catenaria otophora Kirkpatrick, 1890, p. 17 , Plate 5, fig. l(a–c).

Savignyella otophora: Harmer 1957, p. 763 , pl. 51, figs 19–21.

Vasignyella otophora: Gordon 1989, p. 453 , figs 13–15. Ryland and Hayward 1992, p. 247, fig. 14(a). Tilbrook et al. 2001, p. 60.

Material examined

NSMT-Te 1079 ( MIN- 4), dried, on SEM stub; NSMT-Te 1080, dried fragments, MIN site.

Measurements

AzL, 0.94–1.13 (1.016 ± 0.060); AzW, 0.23–0.27 (0.249 ± 0.016) (n = 8). OrL, 0.124; OrW, 0.101 (average values, n = 2, 1).

Description

Colony consisting of zooids in branching uniserial series; recumbent, loosely attached to substratum by rhizoids budded from proximal basal side of dilated portion of zooids. Branching pattern irregular, with zooids giving rise to two (up to three?) daughter zooids from basal side near distal end of dilatation, or anywhere along lateral margin. Zooids clavate, with narrow cauda comprising one-quarter to two-fifths of total zooid length gradually expanding to form dilated portion; zooids often appear curved due to bend in frontal direction at point where cauda meets dilatation. Frontal wall gymnocystal, smooth, with one or two longitudinal series of frontal pseudopores on each side (one along frontolateral margin, and another more medially); pseudopores conspicuous, circular, infundibular. Five or six large, circular, uniporous septula along each lateral margin. Orifice small, oval, longer than broad; terminal. Proximal margin of orifice formed by two flattened, truncated costal spines with suture line between them. Oral spines lacking. Avicularia small, paired, lateral to orifice; rostrum raised, facing laterally; mandible triangular. Ovicells not observed.

Occurrence

We found two small colonies, both at the MIN site. Originally described from Tizard Bank ( Spratly Islands), South China Sea ( Kirkpatrick 1890), Vasignyella otophora has a broad Indo- West Pacific distribution, ranging from the Sudanese Red Sea ( Dumont 1981) eastward to Samoa ( Gordon 1989). Our specimen at Okinawa represents the farthest northern record of this distinctive species.

Superfamily HIPPOTHOOIDEA Busk, 1859 Family HIPPOTHOIDAE Busk, 1859

Genus Hippothoa Lamouroux, 1821

Hippothoa petrophila sp. nov.

( Figure 10 (b–h))

? Hippothoa flagellum: Dick et al. 2006, p. 2216 , fig. 7(a, b).

Material examined

Holotype: NSMT-Te 1081 (MIN-8/1; Pleurocodonellina microperforata also present). Paratypes: NSMT-Te 1082 ( MIN- 30; Poricella spathulata and ancestrula of Puellina harmeri also present), lightly bleached, on SEM stub; NSMT-Te 1083 ( MIN- 31), lightly bleached, on SEM stub; NHMUK 2016.5.13.18 ( MIN- 14), on SEM stub.

Etymology

The specific name is a Latinised adjective from the Greek petra (rock) and philos (loving), referring to the apparent preference of this species in colonising bare rock substrata rather than calcareous substrata.

Measurements

Az dilatation L, 0.26–0.38 (0.298 ± 0.031); W, 0.14–0.20 (0.171 ± 0.018) (n = 19). Cauda L, 0.18–1.50 (0.693 ± 0.433) (n = 13); cauda W (at centre between dilatations), 0.023 –0.031 (0.026 ± 0.003) (n = 15). AzOrL, 0.055 –0.069 (0.063 ± 0.005); AzOrW, 0.043 –0.057 (0.052 ± 0.004) (n = 18). Ovicelled zooid exclusive of ovicell: L, 0.15; W, 0.14 (n = 1). OvL exclusive of marginal lamina, 0.15; OvW, 0.13 (n = 1). Zooeciule L, 0.060 –0.085 (0.075 ± 0.07) (n = 5).

Description

Colony unilaminar, encrusting, composed of zooids in branching uniserial series; zooidal dilatations (hereafter, ‘zooids’) connected by narrow, stolon-like caudae (hereafter, ‘caudae’) to form branching ( Figure 10 (b)) and sometimes anastomosing ( Figure 10 (c)) network spreading over broad areas of substratum relative to zooid size; cauda often long, up to 6 times length of zooid. Zooids ( Figure 10 (b–d, h)) hyaline, elongate-oval in outline. Frontal wall transversely convex, with transverse striae; cancelli evident between striae on unworn zooids, giving a lattice pattern; striae proximal to orifice angled proximally in chevron pattern ( Figure 10 (d, e)). Rounded median keel extends from proximal margin of orifice at least to middle of zooid and often to proximal end. Zooids produce up to three daughter zooids, one distally and one from each lateral margin; lateral daughter zooid may be produced only on one side. Some zooids produce zooeciule from proximolateral margin on one or both sides; zooeciules ( Figure 10 (d, h)) short, cylindrical, roughly same diameter as caudae, length about one-half zooid width; opening circular and usually turned frontally. Zooeciules generally uncommon, but zooids lacking zooeciules may show a zooecium scar – a small, circular external opening – proximolaterally on one or both sides. Orifice ( Figure 10 (d, e)) raised; oriented parallel to frontal plane; longer than broad; with deep, U-shaped sinus ( Figure 10 (e)) flanked by small brackets; small, knob-like condyles in angles of sinus brackets; small, circular pseudopore in orificial rim just proximal to sinus. Ovicelled zooid ( Figure 10 (f)) budded distolaterally from autozooid on one side only (n = 5); zooid exclusive of ovicell less than half as long as autozooid, connected by a short cauda; orifice D-shaped, with broad, shallow sinus. Ovicell closed by operculum; surrounded by calcified marginal lamina. Smooth ectooecium appears to bear small central pseudopore and sometimes has a median carina. Lateral pore chambers ( Figure 10 (g)) leading to autozooidal caudae are large, conical. We were unable to observe form of pores or pore chambers leading to zooeciules. Distal communication pore single, median. Presumed ancestrula ( Figure 10 (h)) kenozooidal (hemispherical, without orifice), giving rise to single daughter zooid similar to but smaller than subsequent zooids.

Remarks

Gordon (1984) provided descriptions for and summarised differences among Pacific species of uniserial Hippothoa having zooids with a long cauda, including H. flagellum Manzoni, 1870 ; H. calciophila Gordon, 1984 ; H. distans MacGillivray, 1869 ; H. divaricata Lamouroux, 1821 ssp. pacifica Gordon, 1984 ; and H. peristomata Gordon, 1984 . Other studies ( Ryland and Gordon 1977; Gordon and Hastings 1979; Hastings 1979; Moyano 1986) have also provided information on this group, and here we mention only a few key characters distinguishing H. petrophila from these other uniserial, caudate species.

Hippothoa petrophila is defined by the following suite of characters: small dilatations (~ 0.3 mm long); long caudae, up to 6 times dilatation length; frontal wall with keel and transverse striations; cruciate branching pattern, although not all zooids produce a daughter cauda on both sides; a large, conical pore chamber and smaller pore or pore chamber in each lateral wall, with the former giving rise to a daughter cauda and the latter to a zooeciule (some zooids have a large pore chamber only on one side; zooeciules and presumably the connections that give rise to them may be present on one side only, or lacking); a single distal communication pore, as occurs in H. calciophila and H. flagellum ( Gordon 1984, p. 109, fig. 10(a, d)); ovicelled zooids smaller than autozooids and connected to the latter by a short cauda; ovicell with a thickened marginal lamina; and a kenozooidal ancestrula, without orifice, giving rise to a single daughter zooid. Hippothoa petrophila also appears to preferentially inhabit bare rock substrata; in our samples, it occurred only on small patches of rock not encrusted with coralline algae or heavily encrusted with other calcareous organisms.

Uniserial, caudate congeners differ from Hippothoa petrophila in the following key characters (other characters may differ as well). Hippothoa flagellum has smooth zooids lacking a keel, and only one pore chamber in each lateral wall (zooeciules replace daughter caudae, rather than supplement them). Hippothoa distans has smooth zooids, ovicelled zooids larger than autozooids, a perforate central area on the ovicell, and a tatiform rather than a kenozooidal ancestrula. Hippothoa calciophila has longer dilatations (0.37–0.40 mm), generally shorter caudae and ovicelled zooids as large as autozooids. Hippothoa divaricata has ovicelled zooids about as large as autozooids, and has two distal communication pores ( Gordon 1984, p. 109, fig. 10(c)). Hippothoa peristomata has somewhat larger dilatations, a shallow orificial sinus flanked proximally by a pair of low tubercles, and only one pore chamber in each lateral wall, and apparently lacks zooeciules; while ovicelled zooids are smaller than autozooids as in H. petrophila , the ovicell lacks the thick surrounding marginal lamina seen in the latter.

Specimens from Hawaii Island identified as H. flagellum ( Dick et al. 2006) may actually be H. petrophila . In the Hawaiian population, colonies are attached to rock substrata, as they were on Minna Island in our study area, and show the following additional similarities to Okinawan material: the dilatations have transverse striations and a median keel; the orifice is similar in position and shape, with a deep, U-shaped proximal sinus; caudae can be up to several times as long as dilatations; ovicelled zooids are smaller than autozooids and budded distolaterally; the ovicell has a thick marginal lamina; and zooeciules are present. The nature of the interzooidal connections and distribution of zooeciules need to be reexamined in Hawaiian specimens to check their identity.

Occurrence

This species was common at the MIN site, the only known locality. Its actual abundance was difficult to document, because colonies are composed of small, widely spaced zooids.

Family CHORIZOPORIDAE Vigneaux, 1949

Genus Chorizopora Hincks, 1879

Chorizopora brongniartii ( Audouin, 1826) sensu lato

( Figure 11 (a, b))

Indo-Pacific records:

Chorizopora brongniarti: Canu and Bassler 1930, p. 14 . Sakakura 1935, p. 18.

Chorizopora brongniartii: Gordon 1984, p. 113 , pl. 44C. Hayward 1988, p. 326. Scholz and Cusi 1991, p. 412, pl. 3, fig. 4. Ryland and Hayward 1992, p. 249, fig. 13(c). Liu et al. 2001, p. 540, pl. 36, figs 5 and 6; Tilbrook et al. 2001, p. 64, fig. 8(c). Kaselowsky 2004, p. 62. Tilbrook 2006, p. 102, pl. 17B–D. Dick et al. 2006, p. 2217, fig. 7(c, d).

Material examined

NSMT-Te 1084 ( MIN- 32), bleached, on SEM stub.

Measurements

AzL, 0.34–0.44 (0.388 ± 0.029); AzW, 0.24–0.31 (0.268 ± 0.019) (n = 15, 1). OrL, 0.055 – 0.067 (0.061 ± 0.004); OrW, 0.083 –0.099 (0.092 ± 0.005) (n = 15, 1). Average OvZOrL, 0.063; OvZOrW, 0.103 (n = 3, 1). AvL, 0.073 –0.089 (0.081 ± 0.005); AvW, 0.083 –0.108 (0.096 ± 0.007) (n = 15, 1). OvL, 0.208 –0.209 (0.208 ± 0.001); OvW, 0.162 –0.172 (0.168 ± 0.005) (n = 3, 1). Largest colony observed 3 mm across.

Description

Colony forming a unilaminar, encrusting sheet. Zooids ( Figure 11 (a)) vitreous, translucent; distinct, separated by shallow groove and interzooidal foramina between tubular connections; variable in outline. Frontal wall gymnocystal, moderately convex, with smooth texture and shallow transverse ribbing; ribbing chevron-shaped distal to small mammillate umbo. Umbo approximately in centre of zooid, separated from proximal orificial margin by distance greater than orifice length. Orifice ( Figure 11 (b)) raised; broader than long; widest in middle, recurving to meet straight proximal margin; condyles lacking. Orifice weakly dimorphic; that of ovicelled zooids slightly but discernably broader than that of non-ovicelled zooids. Small, roughly triangular kenozooid ( Figure 11 (a, b)) proximal to most zooids; central, marginated frontal opening of variable shape. Small interzooidal avicularium ( Figure 11 (b)) distal to each zooid; rostrum oval, angled at about 45° to frontal plane, with small distal hook; crossbar complete; opesial area proximal to crossbar semicircular; mandible rounded-triangular. Ovicell ( Figure 11 (a)) hyperstomial, conspicuous; opening with thickened rim; closed by operculum. Ooecium longer than broad, and associated with distal avicularium; ectooecium with longitudinal ribbing following ovicell contour; pseudopores lacking. Spines lacking. Ancestrula not observed.

Remarks

Various authors (e.g. Gordon 1984; Hayward and Ryland 1999; Tilbrook et al. 2001; Hayward and McKinney 2002) have considered Chorizopora brongniartii to have a worldwide distribution in temperate to tropical waters. Due to the improbability of populations maintaining genetic continuity over vast areas (such as between the Atlantic and Pacific), however, this nominal species undoubtedly represents a species complex ( Dick et al. 2006; Tilbrook 2006), with small but consistent differences among geographically separate populations representing interspecific variation. Various Pacific populations identified as C. brongniartii show such distinguishing characters. In specimens from Hawaii Island ( Dick et al. 2006), the avicularium typically associated with the ovicell is lacking or highly reduced; zooids lack a frontal tubercle; and the ancestrula differs ( Dick et al. 2006) from that reported ( Hayward and Ryland 1999) for British C. brongniartii . In specimens from the Kermadec Ridge, New Zealand, the kenozooid proximal to zooids is often converted to an avicularium, and the frontal umbo is close to the orifice and comprises a sharp, spinous process. In a specimen from the Solomon Islands ( Tilbrook 2006), non-ovicelled zooids have the orifice nearly as long as broad, and zooids are completely surrounded by kenozooids, some of which are replaced by small interzooidal avicularia. While our specimens from Okinawa are probably not conspecific with C. brongniartii (Audouin) , their identity will best be resolved in the context of a global generic revision.

Occurrence

We detected two small colonies, both at the MIN site. Nominal Chorizopora brongniartii was previously reported in Japan from the Pleistocene Jizodo Formation, Boso Peninsula, Chiba Prefecture ( Sakakura 1935) .

Superfamily Arachnopusioidea Jullien, 1888 Family Arachnopusiidae Jullien, 1888

Genus Poricella Canu, 1904

Poricella spathulata ( Canu and Bassler, 1929)

( Figure 11 (c))

Hiantopora spathulata Canu and Bassler 1929, p. 116 , pl. 11, fig. 12.

Tremogasterina spathulata: Cook 1977, p. 136 , text-figs 1(b) and 8(a), pl. 5A. Ryland and Hayward 1992, p. 249, fig. 13(e).

Poricella spathulata: Tilbrook et al. 2001, p. 65 , fig. 10(b). Tilbrook 2006, p. 113, fig. 16(b). Dick et al. 2006, p. 2218, fig. 7(e, f). Gluhak et al. 2007, p. 413, figure 18(a–d).

For additional synonyms and records, see Cook (1977) and Tilbrook (2006).

Material examined

NSMT-Te 1085 (REEF-3), bleached, on SEM stub.

Measurements

AzL, 0.39–0.52 (0.453 ± 0.039); AzW, 0.22–0.35 (0.293 ± 0.033) (n = 15, 1). OrL, 0.11–0.14 (0.122 ± 0.010); OrW, 0.11–0.16 (0.133 ± 0.011) (n = 13, 1). OvL, 0.18; OvW, 0.24 (n = 1).

Description

Colony forming a unilaminar, encrusting sheet; our specimen 3 mm in diameter. Zooids distinct when young; boundaries indistinct with age. Frontal wall convex, texture coarsely granulated, perforated by five to eight large, lunate foramina, each surrounded by smooth infundibular area; three to five slit-like areolae along each lateral margin. Average orifice width slightly greater than length; semicircular anter separated from equally broad poster by small, low, proximomedially directed condyles. Distal margin with two pairs spines. Scattered between zooids are conspicuous avicularia arising from marginal pores; rostrum on raised chamber parallel or angled to frontal plane, usually flared and spatulate distally; hinge bar complete or incomplete; rostrum variable in direction. No large vicarious avicularia observed. One incompletely formed ovicell present in our specimen. Ancestrula not observed.

Remarks

With its infundibular, lunate frontal pores and spatulate avicularia, this is so distinctive a form that previous authors reporting it have often not included detailed descriptions. Illustrations representing different geographical populations (e.g. Cook 1977; Ryland and Hayward 1992; Tilbrook et al. 2001; Dick et al. 2006; Tilbrook 2006) indicate differences among populations, such as in spine number, orientation of the adventitious avicularia, degree of distal flare of the mandible, presence or absence of large vicarious avicularia, and number of frontal foramina.

Poricella spathulata is common in certain tropical and semitropical habitats, especially inner reef flats ( Tilbrook et al. 2001). It was the most common bryozoan species at Vanuatu ( Tilbrook et al. 2001), and likewise at Heron Island, Great Barrier Reef, where it occurred in over half the samples examined ( Ryland and Hayward 1992). Dick et al. (2006) found it to be abundant at Kealakekua Bay, Hawaii Island, on the undersides of coral-rubble fragments on an intertidal cobble beach subject to high temperatures at low tide.

Occurrence

We found only a single dead colony at the REEF site. This species is broadly distributed in the Indo-Pacific region. Cook (1977) summarised records from the Red Sea, Indian Ocean, South China Sea, Philippines and north-east Australia; it has also been reported from Vanuatu ( Tilbrook et al. 2001), the Solomon Islands ( Tilbrook 2006), Hawaii ( Dick et al. 2006) and Taiwan ( Gluhak et al. 2007).

Family EXECHONELLIDAE Harmer, 1957

Genus Exechonella Duvergier, 1924

Exechonella sp. A

( Figure 11 (d))

Material examined

NSMT-Te 1086 ( SES- 10), bleached, on SEM stub.

Remarks

The budding pattern in our single young colony does not clearly indicate which zooid is the ancestrula, if it remains. With the large, marginated foramina, well-developed peristome, and subcircular orifice with weak condyles, this species clearly belongs in Exechonella , although diagnostic characters such as ovicells and avicularia are absent. The zooids are moderately large: the larger complete zooid in Figure 11 (d) measures 0.76 by 0.66 mm, and zooids in mature colonies would be larger. One orifice measured 0.202 mm long by 0.204 mm wide. The suboral flange and blunt projections on the peristomial rim are unusual, as no other species reported from the Indo-Pacific region has them.

Occurrence

We found only a single young colony at the SES site.

Superfamily LEPRALIELLOIDEA Vigneaux, 1949 Family LEPRALIELLIDAE Vigneaux, 1949

Genus Celleporaria Lamouroux, 1821

Celleporaria calva Tilbrook, 2006

( Figure 12)

Celleporaria calva Tilbrook, 2006, p. 140 , pl. 25D–F.

Material examined

NSMT-Te 1087 ( SES- 23), bleached, on SEM stub; NSMT-Te 1088 ( MIN- 25), bleached, on SEM stub; NSMT-Te 1089, three dried specimens, MIN site; NHMUK 2016.5.13.19-21, three dried specimens, MIN site.

Measurements

Colony without oral spines. AzL, 0.49–0.80 (0.642 ± 0.091); AzW, 0.34–0.55 (0.433 ± 0.066) (n = 16, 1). OrL, 0.13–0.18 (0.149 ± 0.013); OrW, 0.16–0.19 (0.175 ± 0.010) (n = 13, 1). Spatulate vicarious avicularium: AvRosL, 0.48; AvRosW at crossbar, 0.14 (n = 1).

Colony with oral spines. AzL, 0.50–0.77 (0.643 ± 0.083); AzW, 0.39–0.58 (0.474 ± 0.056) (n = 11, 1). OrL, 0.14–0.15 (0.143 ± 0.005); OrW, 0.17–0.19 (0.178 ± 0.006) (n = 8, 1). OvL, 0.30–0.34 (0.312 ± 0.027); OvW, 0.34–0.36 (0.351 ± 0.011) (n = 3, 1). Rostrum of spatulate vicarious avicularium, three size categories: Small – L, 0.18–0.24 (0.204 ± 0.031); W at crossbar, 0.07–0.08 (0.077 ± 0.008) (n = 3, 1). Medium – L, 0.32–0.39 (0.351 ± 0.035); W at crossbar, 0.14–0.19 (0.157 ± 0.025) (n = 3, 1). Large – L, 0.513; W at crossbar, 0.225 (n = 1). Largest colony observed 30 mm across.

Description

Colony encrusting, flat, sheet-like; unilaminar at margin, but frontal budding occurs in interior ( Figure 12 (b)); colour off- white. Marginal zooids ( Figure 12 (a)) distinct, delineated by groove; with age ( Figure 12 (b, d)), boundaries less distinct. Frontal wall convex, uniformly coarsely granulated; with 10 to 12 areolae around periphery, at margin or offset some distance from margin; sometimes with a few pseudopores scattered in central area. Primary orifice hoof-shaped, broader than long, with straight proximal margin; condyles small, blunt, rounded, somewhat distal to proximal margin. Raised rim ( Figure 12 (c)) around proximal margin of orifice, sometimes forming slight point. Suboral avicularium lacking. In one of two colonies examined by SEM, most zooids show a pair of short, ephemeral, tubular distal oral spines or spine bases ( Figure 12 (c)); other colony entirely lacks spines. No adventitious avicularia observed. Scattered interzooidal avicularia ( Figure 12 (a, b)) occur, of several sizes, with the largest more than twice as long and broad as the smallest. Chamber of newly budded large avicularium about half the size of an autozooid, with marginal pores and granulated surface; with age, avicularian cystid becomes immersed. Crossbar complete; rostrum wide at crossbar, narrowest just distal to crossbar, and flared, spatulate, often somewhat scoop-shaped distally, with edge around distal curvature weakly serrate. Rostrum of smallest interzooidal avicularia scarcely spatulate. Ovicell ( Figure 12 (d)) hyperstomial, with large, circular to oval opening. Ooecium thick-walled, globose, slightly broader than long, largely obscuring primary orifice; covered by secondary calcification with same texture as frontal wall, arising from two or three neighbouring zooids and showing sutures on the ooecial surface. Ancestrula not observed.

Remarks

Most species in Celleporaria have a suboral avicularium associated with the peristome or orificial margin; C. calva is unusual in lacking suboral or any other adventitious avicularia. Other diagnostic characters include the hoof-shaped primary orifice; lack of a welldeveloped peristome; spatulate interzooidal avicularia of several sizes; and the unusual globose ovicell with a large opening. The original description ( Tilbrook 2006) also indicates that this species lacks oral spines; however, while this was true of the colony from the SES site, most marginal zooids in a colony from the MIN site had a pair of short, ephemeral oral spines or spine bases.

Occurrence

We found one specimen at SES and seven at MIN . Celleporaria calva was previously known only from the Solomon Islands ( Tilbrook 2006).