Porella donoghueorum Dick, Grischenko & Mawatari, 2005

Min, Bum Sik, Seo, Ji Eun, Grischenko, Andrei V. & Gordon, Dennis P., 2017, Intertidal Bryozoa from Korea — new additions to the fauna and a new genus of Bitectiporidae (Cheilostomata) from Baengnyeong Island, Yellow Sea, Zootaxa 4226 (4), pp. 451-470 : 461

Porella donoghueorum Dick, Grischenko & Mawatari, 2005

( Figs 19–23 )

Porella donoghueorum Dick, Grischenko & Mawatari, 2005: 3735 , fig, 12C–H (cum syn.).

Material examined. NIBRIV0000325937, Yeonhwa-ri, Baengnyeong Island. Other material: Woosuk University collction—Baengnyeong Island: Junghwadong (3 colonies), Dumujin (6 colonies), Jinchon-ri (9 colonies), Yeonhwa-ri (50 colonies); mostly on rocky substrata, but also on shell and crustose coralline algae ( Clathromorphum ).

Description. Colony encrusting, unilaminar, up to 10 mm in diameter, whitish. Zooids contiguous, arranged regularly in quincunx, more or less rounded-hexagonal, squat or only slightly elongate. Frontal shield more or less smooth, convex, rising to suboral umbonate area associated with avicularian chamber. Internal umbonuloid area of shield occupying about half shield length. Up to 8–9 relatively large areolar pores occur around the margin, fewer, larger pores apparent in older zooids. Primary orifice somewhat sunken below peristomial rim, its proximal margin with a relatively broad short, truncate convexity that simulates a lyrula but lacks alae; a short condyle evident in each proximolateral corner. Oral spines 4, relatively short, in developing zooids at colony margin, mostly becoming immersed in calcification. Median suboral avicularium set in proximal peristomial rim, rostrum rounded-triangular, with relatively large palatal foramen; crossbar complete. Avicularian chamber originating from an areolar pore on each side, the cystid with a proximal pair of pores that are retained as further calcification merges the cystid into the zooidal frontal shield. Occasional additional frontal avicularia in older part of colony. Ooecium recumbent, with membranous ectooecium and smooth skeletal endooecium, occupying about half the frontal area of the distal zooid; proximal rim of ooecium continuous with peristome as a combined secondary orifice; ooecium opening into space above primary orifice, below level of peristome. A well-developed pair of distolateral pore-chambers present.

Measurements. ZL, 297–391 (332) µm; ZW, 180–260 (220) µm; OrL, 63–76 (71) µm; OrW, 113–126 (120) µm; OoL, 101–142 (113) µm; OoW, 129–172 (152) µm.

Remarks. The species bears a striking resemblance to some species of Aimulosia Jullien, 1888 from the Australasian region , especially Aimulosia marsupium ( MacGillivray, 1869) and Aimulosia costata ( Powell, 1967) . Prior to transferral to Aimulosia by Gordon (1989), these species had been included in Porella ( Hamilton 1898; Brown 1952; Powell 1967; Gordon 1984). Gordon’s (1989) grounds for transferring MacGillivray’s species from Porella to Aimulosia were based on examination of the type species of Aimulosia , Aimulosia australis Jullien, 1888 , from magellanic South America. It has a short, rounded projection in the proximal margin of the orifice ( Gordon 1989, pl. 25F, G; Hayward 1995, p. 276). For this reason, Jullien (1888) included Aimulosia in the Smittinidae (as Smittidae), as did Gordon (1984, 1989). The species from the Australasian region also clearly resemble A. australis in the external appearance of the frontal shield and ooecium. Indeed , Waters (1904) believed MacGillivray’s species was identical. They are not, but they are clearly morphologically similar. Subsequently , Gordon et al. (2009) included Aimulosia in the Buffonellodidae Gordon & d’Hondt, 1997 , characterized by a lepralioid frontal shield and the same external characters that are also seen in A. australis . Although Buffonellodes Strand, 1928 has a sinusoid orifice, the short rounded lyrulate structure in A. australis does not preclude a relationship with Buffonellodes and related genera—Berning et al. (2014) described how Pseudoflustra Bidenkap, 1898 includes both lyrulate and non-lyrulate species.

The ooecium in both Porella and Aimulosia has the same structure, comprising a membranous ectooecium and a smooth imperforate endooecium, and the two genera are so close one must ask what separates them. The answer is, the frontal shield, which is lepralioid in Aimulosia (Buffonellodidae) and umbonuloid in Porella (Bryocryptellidae) , the latter noted by ( Hayward & Ryland 1999). The interior of the frontal shield in A. australis , A. marsupium and Buffonellodes rimosa Jullien, 1888 (the type species of Buffonellodes and Buffonellodidae ) is lepralioid (D. Gordon, pers. observ.), whereas it is indeed umbonuloid in P. donoghueorum . But the question remains whether the type of frontal shield is adequate to separate Porella and Aimulosia , or even Bryocryptellidae and Buffonellodidae , as it is now known that some clades contain both types of frontal shield (e.g. Adeonidae and Smittinidae ), with transitional forms between the two (e.g. Gordon 2000), in presumed ancestor-descendant relationships. Dick et al. (2005) described the ancestrula of P. donoghueorum , which is oval, with a transversely Dshaped orifice surrounded by eight spines.

Figures

FIGURES 19 – 23. Porella donoghueorum Dick, Grischenko & Mawatari, 2005, Jinchon-ri. 19, Part of a colony with several ovicellate zooids; scale bar, 400 µm. 20, Close-up of ovicellate zooids; scale bar, 200 µm. 21, Differentiating zooids at growing margin with distal oral-spine bases and incipient avicularian chamber; scale bar, 100 µm. 22, Newly formed avicularium with a pair of conspicuous pores; scale bar, 100 µm. 23, Interior of frontal shield showing an area of umbonuloid exterior microstructure; scale bar, 50 µm.