Metamicropora areolae ( Sakakura, 1935 )

Arakawa, Shinji, 2016, Taxonomy of Some Microporids (Bryozoa: Cheilostomata) from the Pacific Coast of Japan, Species Diversity 21 (1), pp. 9-30 : 25-27

publication ID	https://doi.org/ 10.12782/sd.21.1.009
publication LSID	lsid:zoobank.org:pub:61308999-8455-4892-8464-423FFBACF0A1
DOI	https://doi.org/10.5281/zenodo.5526925
persistent identifier	https://treatment.plazi.org/id/DA5F87F2-4662-FFDD-FF68-F893FC24F957
treatment provided by	Felipe
scientific name	Metamicropora areolae ( Sakakura, 1935 )
status

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Metamicropora areolae ( Sakakura, 1935) ( Figs 10–12 View Fig View Fig View Fig , 13A View Fig )

Verminaria areolae Sakakura, 1935: 12 , pl. 2, fig. 5, text-fig. 3; Hayami 1970: 324, pl. 36, fig. 4; Hayami 1975: 89 (only listed); Nishizawa and Sakagami 1986: 84, pl. 11, fig. 3; Arakawa 1995: 80 (only listed); Nishizawa 1997: 147, 152 (only listed).

Microporina areolae: Sakakura 1936: 264 .

Microporina elongata View in CoL (not of Hincks, 1880): Silén 1942: 65, pl. 3, fig. 12, text-figs 76–78; Hirose 2010: 45, pl. 78A–C. Micropora areolae: Arakawa 1999: 56 .

Material examined. NMNS PA 16846 View Materials (two fragments, A, B), and SGBC-0105, Station 1748, Hakurei-Maru cruise GH80-2; NMNS PA 16845 View Materials (two colonies, A, B, the latter with ancestrula, on mollusc shell), 16847 (on mullusc shell), 16848 (on mullusc shell), 18158 (inner surface of frontal shield) and 18159, and SGBC-0002 (on mullusc shell), -0407 (on mullusc shell, not coated with metal), Jizodo Formation, Pleistocene, Nishiyatsu, Chiba Prefecture, Japan; NMNS PA 16849 View Materials and SGBC-0370 (on mullusc shell), Jizodo Formation, Pleistocene, Oi, Chiba Prefecture, Japan; NMNS PA 18157 View Materials (lateral and basal walls), Yabu Formation , Pleistocene , Neriki , Chiba Prefecture, Japan; SGBC-0410 (on mollusc shell, not coated with metal), Jizodo Formation , Pleistocene, Nagara Dam, Chiba Prefecture, Japan . See Table 1 View Table 1 for coordinates and depths of cruise samples.

Measurements (in milimetres). NMNS PA 16845, 16846, 16847, and 16848; SGBC-0002, -0105, -0370 and -0398. Autozooids (n =515, 10): ZL, 0.49–1.49 (0.780±0.124); ZW, 0.25–0.79 (0.396±0.0073; OrL, 0.06– 0.12 (0.082±0.010); OrW, 0.11–0.22 (0.162±0.020). Avicularia (n =184, 10): AvL, 0.07–0.18 (0.124±0.018); AvW, 0.05–0.12 (0.075±0.012).

Description. Colony encrusting, unilaminar, oπen becoming multilaminar; maximum size in largest dimension estimated to be more than 20 mm (SGBC-0407). Zooids irregularly hexagonal or rectangular. Frontal shield cryptocystal, flattened, finely granulated, with scattered frontal pores, surrounded by raised rim ( Fig. 10A View Fig ); frontal pores occluded, with three or more slit-like openings each ( Fig. 10C View Fig ). Six to nine pairs of circular opesiules present, closed by thin internal layer with radially arranged slits, or cribriform; distalmost pair generally larger than the others ( Fig. 10A, C, D View Fig ). Orifice semicircular, without oral spines. Operculum smooth ( Fig. 10B View Fig ). Paired tubercles lateral to orifice, derived from proximal gymnocyst of next-distal zooids ( Fig. 11 View Fig A–D). Avicularium, when present, situated distal to orifice, interzooidal, directed distolaterally, with complete pivot bar; rostrum acute to frontal plane, mandibular opening semicircular to rounded triangular ( Fig. 11A, B View Fig ). Ancestrula similar to later zooids; rhomboidal or hexagonal, with one pair of large, irregularly shaped opesiules and a few additional smaller ones; ancestrula budding three daughter zooids, one distally and two distolaterally ( Fig. 12A, B View Fig ). Zooids interconnected by six or more basal uniporous septula in each lateral wall ( Fig. 12C View Fig ) and several basal septula (some of them pauciporous) in transverse wall ( Fig. 12D View Fig ). Ovicells absent.

Distribution. Sagami and Tokyo Bays ( Sakakura 1935; Silén 1942; Nishizawa 1997; Hirose 2010) and the continental shelf east of the Boso Peninsula (station 1748, Hakurei- Maru cruise GH80-2). The recorded depth range is from 65 m (station 1748, this study) to more than 100 m ( Silén 1942).

Fossils of this species have been collected from Miocene to Pliocene deposits in Hokkaido, Miyagi, and Ishikawa Prefectures ( Hayami 1970, 1976; Nishizawa and Sakagami 1986), and from Pleistocene deposits in Chiba Prefecture ( Sakakura 1935; Arakawa 1995; Nishizawa 1997). It is one of the predominant species among cheilostome bryozoans in the Pleistocene Jizodo Formation ( Arakawa 1995).

Remarks. Silén (1942) advanced Sakakura’s (1936) discussion and concluded that Verminaria areolae is synonymous with Microporina elongata ( Hincks, 1880) from southern Africa. However, Silén’s conclusion is incorrect, as it was based on Waters’ (1889) misinterpretation that Micropora variperforata is synonymous with M. elongata . Those two species are distinct, as Brown (1952: 128) discussed in detail. The opesiules of M. elongata are occluded with calcification lacking any small openings ( Hincks 1880: pl. XVI, fig. 4).

On the other hand, Silén (1942) correctly described that the tubercles lateral to the orifice in this species are derived from the next-distal zooids. Similar structures are evident in Verminaria oblonga (Busk, 1859) , Calpensia rebeshovensis Zágoršek, 2010 and Micropora finisterrae , although the tubercles in these species are situated distal to the orifice of the proximal zooid ( Bishop 1987; Zágoršek 2010; Moyano 1994b). The occurrence of such tubercles thus seems to be polyphyletic.