Stephanotheca fenestricella, Dick & Grischenko, 2016

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 : 204-208

Stephanotheca fenestricella sp. nov.

( Figure 21)

Etymology

The specific name is a noun in apposition formed from the Latin fenestra (window) and cella (chamber), referring to the well-delineated pseudoporous area atop the ovicell.

Material examined

Holotype: NSMT-Te 1123, one dried colony, in three parts, SES site; NSMT-Te 1124 ( SES- 52 ), part of same colony as NSMT-Te 1123, bleached, on SEM stub.

Measurements

AzL, 0.42–0.64 (0.508 ± 0.072); AzW, 0.27–0.45 (0.368 ± 0.055) (n = 15, 1). AzOrL, 0.083 – 0.115 (0.098 ± 0.006); AzOrW, 0.112 –0.125 (0.118 ± 0.005) (n = 15, 1). OvZOrL, 0.088 – 0.119 (0.104 ± 0.008); OvZOrW, 0.123 –0.144 (0.135 ± 0.007) (n = 11, 1). OvL, 0.30–0.34 (0.322 ± 0.017); OvW, 0.30–0.40 (0.362 ± 0.033) (n = 9, 1). One colony, 20 mm in maximum dimension.

Description

Colony forming a unilaminar, encrusting sheet; dried specimen light tan in colour. Zooids ( Figure 21 (a)) distinct, delineated by shallow grove and suture line flanked by opposing columns of areolae; shape quite variable, ranging from much longer than broad to nearly as broad as long. Frontal wall weakly convex, densely covered with small, infundibular pseudopores except in narrow zone around periphery; surface somewhat rugose, with scattered small tubercles. Six to 11 slit-like areolae along each lateral margin. Orifice terminal; with low, narrow rim distally and laterally, and smooth imperforate zone laterally and proximally; often with ‘necklace’ of four to six tubercles along margin of smooth zone. Primary orifice ( Figure 21 (b, c)) broader than long; dimorphic, markedly broader in ovicelled zooids than in those lacking capacity to form ovicell; with broadly concave proximal sinus between prominent, rounded condyles. Condyles smooth or weakly denticulate at tip. Avicularium ( Figure 21 (a, b)) single, in midline proximal to orifice. Rostrum elongate, separated from orifice by less than one rostral length; distal end slightly raised, pointing proximally; with complete, curved crossbar almost in middle; mandible acute, about twice as long as broad. Ovicell ( Figure 21 (a)) hyperstomial, conspicuous, slightly broader than long, closed by operculum. Ooecium covered with thick secondary calcification bearing scattered tubercles, except in flat, transversely oval area in centre that is covered with numerous circular or irregular pseudopores; pseudoporous area often ringed by tubercles; surficial sutures indicate contributions to secondary calcification from up to four neighbouring zooids. Zooids interconnect by row of uniporous septula ( Figure 21 (d)) in each of transverse and distolateral walls. Ancestrula not observed.

Remarks

Reverter-Gil et al. (2012) established Stephanotheca to accommodate a distinct group of species formerly placed in Schizomavella Canu and Bassler or other genera, and recognised several additional previously undescribed species that belong in this group. Generic characters for Stephanotheca include a frontal wall with pseudopores; broad orificial sinus flanked by distinct condyles; dimorphic orifices between maternal and non-maternal zooids; no oral spines; a usually median suboral avicularium; and a prominent ovicell closed by the operculum, with a well-defined central area having pseudopores. Stephanotheca fenestricella differs from the approximately 12 species currently placed in Stephanotheca ( Bock 2016) in having a narrow, acute median suboral avicularium with a distinctly longtriangular mandible. The other species have an oval suboral avicularium; a larger, triangular frontal avicularium displaced to the proximal end of the zooid; or a large, triangular suboral avicularium occupying most of the length of the zooid (Reverter- Gil et al. 2012; Cumming 2015).

At present, the distribution of Stephanotheca appears to be disjunct, with six species known from the Mediterranean, two from the eastern Atlantic and four from Australia, with no records between Australia and Europe ( Reverter-Gil et al. 2012; Cumming 2015). Our study area on Okinawa is likewise somewhat disjunct from northern Australia, lying in the East China Sea roughly 5000 km to the north-north-west. However, there are indications that additional Stephanotheca species occur in the tropical to temperate western Pacific. Canu and Bassler (1929) designated two varieties of Schizomavella ambita ( Waters 1889) , originally described from Australia, in the western Pacific: var. granulosa from 192 m depth in the Philippines and var. granulata from an unspecified depth at ‘Cape Tsiuka, Sea of Japan’ (actually within Tsugaru Strait, northern Japan, according to the accompanying coordinates). Reverter-Gil et al. (2012) transferred Schizomavella ambita Waters to Stephanotheca , and one or both of these varieties could represent a species in Stephanotheca . While the descriptions and illustrations in Canu and Bassler (1929) are poor, neither variety appears to have avicularia of the same shape as Stephanotheca fenestricella .

Occurrence

We found a single colony at the SES site, the only known locality.

Superfamily SCHIZOPORELLOIDEA Jullien, 1883 Family SCHIZOPORELLIDAE Jullien, 1883

Genus Stylopoma Levinsen, 1909

Stylopoma duboisii ( Audouin, 1826)

( Figure 22)

Flustra ? duboisii Audouin, 1826, p. 239 .

Stylopoma duboisii: Tilbrook 2001, p. 8 , fig. 2(c–f).

? Stylopoma duboisii: Hirose 2010, p. 129 , pl. 221A, B.

See Tilbrook (2001) for synonyms following his revision of the genus.

Material examined

NSMT-Te 1129 ( MIN- 21), bleached, on SEM stub; NSMT-Te 1130, two dried specimens, SES site.

Measurements

AzL, 0.43–0.61 (0.506 ± 0.043); AzW, 0.23–0.39 (0.317 ± 0.041) (n = 20, 1). OrL (without sinus), 0.06–0.08 (0.074 ± 0.005); OrW, 0.10–0.12 (0.108 ± 0.004); OrSinL, 0.02–0.04 (0.028 ± 0.005) (n = 20, 1). OvDm, 0.46–0.54 (0.511 ± 0.026) (n = 7, 1). AvRosL, 0.04–0.06 (0.051 ± 0.005) (n = 8, 1). Largest fragment observed 10 mm across.

Description

Colony forming a unilaminar, encrusting sheet; occasional frontally budded zooids occur on colony surface. Zooidal ( Figure 22 (a)) boundaries delineated by marginal areolae and suture line. Frontal wall weakly convex, minutely granulated, covered with numerous small, infundibular pseudopores, except in peristomial region; five to seven slit-like areolae along each lateral margin. Primary orifice ( Figure 22 (b)) D-shaped, with deep, U-shaped proximal sinus having parallel sides; sinus occasionally wider proximally, somewhat drop-shaped. Condyles occupy entire flat proximal orificial margin on each side, reaching opening of sinus or nearly so, serrate on top, with rounded tip. Orifice completely surrounded by thickened, slightly elevated, granulated peristomial rim, sometimes with blunt umbo on one or both sides proximolateral to orifice. Small, single avicularium ( Figure 22 (a, b)) on raised chamber on either side proximolateral to orifice; rostrum inclined to frontal surface, crossbar complete; mandible a small, equilateral triangle, directed distolaterally; many zooids lack an avicularium. No large vicarious avicularia observed. Ovicell ( Figure 22 (c)) hyperstomial, conspicuous; with transverse opening ( Figure 22 (d)) at base; distal margin of opening thickened, with semicircular area above lacking pseudopores; labellum appears to be straight, entire; aperture D-shaped. Ooecium entirely covered with infundibular pseudopores; texture granulated like frontal wall. No spines. Ancestrula not observed.

Remarks

Stylopoma duboisii is very similar to S. velatum Tilbrook et al., 2001 . According to Tilbrook (2001), the latter has a more semicircular orifice that is distinctly broader than long, but this difference is negligible; the average width/length ratios of the orifice exclusive of the sinus calculated for the two species from Tilbrook’ s (2001) measurements are 1.4 and 1.5, respectively, and orifice shape varies considerably even within our specimens. Average zooid size is essentially indistinguishable among S. duboisii (L, 0.50; W, 0.35), S. velatum (L, 0.52; W, 0.36) (Tilbrook 2001), and our specimen (L, 0.51; W, 0.32). Tilbrook (2001, fig. 11(d, e)); shows the adventitious avicularium in S. velatum to have a small chamber and to lie close to the orifice; in S. duboisii and our specimen, the chamber is larger relative to rostrum size; the rostrum is more elevated and tends to lie outside the peristomial rim. A key difference between the two species is a D-shaped aperture and entire, straight labellum (see Tilbrook 2001 for the meanings of ‘labellum’ and ‘aperture’) in the ooecial opening in S. duboisii versus an oval aperture and split labellum in S. velatum . Although Tilbrook’ s (2001) illustration of the ooecial opening for the latter species is not clear, our specimen clearly has a D-shaped aperture, and the labellum appears to be entire.

Occurrence

We found two colonies at SES and one at MIN. Tilbrook (2001) lists the range of S. duboisii sensu stricto (i.e. after his revision of the genus) as extending from the Red Sea to Malaysia, New Guinea and the Philippines; and the range of S. velatum as the western Pacific, including the South China Sea, Great Barrier Reef, Vanuatu and Tahiti. The occurrence of S. duboisii at Okinawa constitutes a northward range extension in the western Pacific. Hirose (2010) reported a single specimen of S. duboisii from Sagami Bay, Pacific coast of central Honshu, Japan; while his identification seems compatible with S. duboisii , his illustration consists of two light micrographs, and this record needs confirmation by SEM.