Stomachetosella decorata, Grischenko & Dick & Mawatari, 2007

Grischenko, Andrei V., Dick, Matthew H. & Mawatari, Shunsuke F., 2007, Diversity and taxonomy of intertidal Bryozoa (Cheilostomata) at Akkeshi Bay, Hokkaido, Japan, Journal of Natural History 41 (17 - 20), pp. 1047-1161 : 1118-1120

Stomachetosella decorata new species

( Figure 28 )

Diagnosis

Frontal wall moderately convex, finely granulated, with a small central umbo; covered uniformly with small pores when young, with large marginal pores when mature. Primary orifice semicircular, with straight or slightly convex proximal margin. Secondary orifice cormidial, with raised, complete peristome having a short mid-proximal sinus. Ovicell hyperstomial, broad, rapidly submerged with secondary calcification, granulose, without pores, with a small, central nodule.

Etymology

The species name refers to the frontal wall decorated with nodular umbones in mature zooids.

Material examined

Holotype: ANC, colony on rock (NHM 2006.2.27.89). Paratypes: ACW, colony on rock (NHM 2006.2.27.90); BAC, young colony on bivalve shell (NHM 2006.2.27.91); ANC, young colony on rock (NHM 2006.2.27.92). Additional material: 59 specimens.

Description

Colony encrusting, unilaminar, coherent, irregularly circular; maximum dimension observed was 1.7 cm; red when alive. Zooids ( Figure 28A–E ) hexagonal, oval, or rectangular, 0.42–0.63 mm long (0.53¡ 0.06 mm), 0.30–0.43 mm wide (0.35¡ 0.04 mm), separated by raised adjacent vertical walls. Frontal wall moderately convex, finely granulated; when young, covered sparsely and uniformly from margin to margin with small pores, with a small, sharp central umbo ( Figure 28B, C ) or two or three scattered umbones ( Figure 28E ); with age and secondary calcification, central umbo becomes stout and prominent, central pores reduced in number, marginal pores enlarged, infundibular, often occluded along margins. Primary orifice ( Figure 28A ) semicircular, broad, about 0.12–0.14 mm long, 0.15– 0.16 mm wide; proximal margin straight to slightly convex, condyles and sinus lacking, deeply submerged, visible only in developing zooids near colony margin. Secondary orifice cormidial ( Figure 28C ); irregularly circular, transversely oval, or rounded-triangular, 0.12–0.16 mm long (0.15¡ 0.01 mm), 0.14–0.19 mm wide (0.16¡ 0.01 mm); peristome complete, raised, consisting of sharp, curved lateral flanges meeting distally with raised proximal margin of distal zooid; with a short mid-proximal sinus. Ovicell ( Figure 28B ) hyperstomial, broad, rapidly submerged ( Figure 28D ) with secondary calcification, 0.15–0.20 mm long (0.18¡ 0.01 mm), 0.19–0.26 mm wide (0.22¡ 0.02 mm), granulose, imperforate, often with a small nodule in central position. Interzooidal communication via pore chambers. Ancestrula proper not observed; obscured by small, possibly frontally budded zooids ( Figure 28F ) that are irregular in form.

Remarks

The genus Stomachetosella has moderately high diversity in the northwestern Pacific. According to previous reports ( Androsova 1958; Kluge 1962; Gontar 1980; Grischenko 1997), at least eight species have been recorded in this region, including S. cruenta ( Busk, 1854) , S. sinuosa (Busk, 1960) , S. limbata ( Lorenz, 1886) , S. magniporata ( Nordgaard, 1906) , S. incerta ( Kluge, 1929) , S. pachystega ( Kluge, 1929) , S. tuberculata Androsova, 1958 , and S. sienna Dick and Ross, 1988 . Stomachetosella decorata n. sp. can be distinguished from all of these congeners by the frontal umbo in combination with large, occluded pores, and the broad, submerged ovicell with a small, central umbo.

In the northern hemisphere, only one species of Stomachetosella , S. distincta Osburn, 1952 , described from the Beaufort Sea near Point Barrow, Alaska, has a similarly umbonate ovicell and frontal wall. However, the distribution of frontal pores is different in S. distincta ; its primary orifice has a sinus; and zooid size is significantly larger (0.65–0.85 mm long, 0.45–0.65 mm wide) and not overlapping with Stomachetosella decorata n. sp.

The form of the secondary orifice of S. decorata is almost identical to that of S. sinuosa ( Busk, 1860) , previously reported from Akkeshi Bay ( Mawatari and Mawatari 1981b). The latter also has a sinuate, peristomial secondary orifice and immersed hyperstomial ovicells; however, the primary orifice is sinuate, rather than straight or slightly convex, and the ovicell has a central pore.

Distribution

Stomachetosella decorata is known only from Akkeshi Bay.

Figures

Figure 28. Stomachetosella decorata n. sp. (A) NHM 2006.2.27.92; (B, E, F) NHM 2006.2.27.90; (C, D) NHM 2006.2.27.89. (A) Colony margin with developing zooids; (B) zooids with developing ovicells close to colony edge; (C) immature zooids; (D) mature zooids with immersed ovicells; (E) mature zooids with immersed ovicells, infundibular occluded frontal pores and scattered umbones; (F) ancestrular region. Scale bars: 0.5 mm.