Mixtoscutella, Grischenko & Gordon & Taylor & Kuklinski & Denisenko & Spencer-Jones & Ostrovsky, 2022

Grischenko, Andrei V., Gordon, Dennis P., Taylor, Paul D., Kuklinski, Piotr, Denisenko, Nina V., Spencer-Jones, Mary E. & Ostrovsky, Andrew N., 2022, Taxonomy, ecology and zoogeography of the Recent species of Rhamphostomella Lorenz, 1886 and Mixtoscutella n. gen. (Bryozoa, Cheilostomata), Zootaxa 5131 (1), pp. 1-115 : 82-83

Genus Mixtoscutella n. gen.

Type species: Cellepora ovata Smitt, 1868 , by original designation.

Diagnosis. Colony encrusting, multiserial, unilaminar.Frontal shield mixed, comprising a much-reduced umbonuloid area beneath suboral avicularium, corresponding externally to suboral avicularium, and extensive, uniformly pseudoporous lepralioid area. Primary orifice with or without lyrula, with condyles. Secondary orifice cormidial, with very low peristome. Suboral adventitious avicularium always present. Large adventitious avicularia present in some species. Ovicell hyperstomial, often becoming less prominent due to secondary calcification overgrowing ooecium; with pseudopores. Mural pore chambers and multiporous septula present. Basal wall fully calcified, without protuberances.

Etymology. The name refers to the mixed nature of the frontal shield.

Species included. Mixtoscutella ovata ( Smitt, 1868a) , M. ussowi ( Kluge, 1908a) , M. cancellata ( Smitt, 1868a) , M. harmsworthi ( Waters, 1900) , and M. androsovae ( Gontar, 1979) .

Remarks. Apart from two species examined in detail ( M. ovata and M. ussowi ) and transferred from Rhamphostomella ( Figs 27 , 28 ), we illustrate here three other taxa, including two little-known species ( Fig. 29 ), that display a combination of characters (mixed frontal shield and suboral avicularium) warranting their placement in Mixtoscutella .

Mixtoscutella androsovae ( Gontar, 1979) [= Smittina androsovae Gontar, 1979 (p. 244, fig. 4)] is known only from its type locality at Cape Nerpochka on the Pacific side of Simushir Island, middle Kuril Islands, from 30 m depth (paratype, ZIRAS 2 /43716) ( Fig. 29A–C ) .

The high-boreal-Arctic species, M. harmsworthi ( Waters, 1900) [= Schizoporella harmsworthi Waters, 1900 (p. 65, pl. 9, figs 10–12)], widely distributed in Arctic seas (see Kluge 1962 for details) has been detected in Avacha Gulf, eastern Kamchatka (ZIRAS 52/50568, KIENM Collection, RV Nazarovsk, Stn 141, 11 May 1988, 53°41.0ʹ N, 160°04.0ʹ E, depth 75 m) ( Fig. 29D–F ).

The rarely reported M. cancellata (Smitt, 1868) [= Escharella porifera forma cancellata Smitt, 1868a (p. 9, 75, pl. 24, figs 40, 41)], originally described from Spitsbergen (see also Nordgaard 1906; Kluge 1962; Kuklinski 2002b), has been documented from Point Barrow, Alaska ( Osburn 1953) and the Chukchi Sea ( Gontar 2010), and was recently found on the western slope of the Kamchatka Peninsula, Sea of Okhotsk (ZIRAS 1/50572, KIENM Collection, RV Agat, Stn 1–K–1, 1 June 2008, 58°00.0ʹ N, 155°43.0ʹ E, depth 285 m) ( Fig. 29G–I ).

Figures

FIGURE 27. Mixtoscutella ovata (Smitt, 1868). ZIRAS 36/50120 (western Kamchatka, Sea of Okhotsk). A. Colony margin with young and developing zooids (arrows, sites of ooecial development). B. Zooidal orifice, showing condyles, and suboral avicularium. C, D. Non-ovicellate zooids in young part of colony. E. Ovicellate zooids in older part of colony, showing ovicells, and suboral and adventitious avicularia. F. Ooecium covered by secondary calcification, except in proximal triangular area with pseudopores. G. Area of colony with ovicellate zooids and adventitious avicularia. H. Longitudinal section through frontal shield, showing interior of umbonulomorph suboral area and adjacent pseudoporous lepralioid shield. I. Interior of frontal shield with umbonuloid component, ring scar, areolae (smaller lateral openings in upper part of zooid), pseudopores and ooecial pore (arrow). J. Internal view of primary orifice with condyles. K. Basal surface of colony. L. Interior of frontal shield, showing blurred ring scar and exterior wall microstructure of umbonuloid component. M. Lateral view of zooid, showing frontal shield, suboral avicularium and lateral wall with mural pore chambers. Scale bars: A, D, G, K, 500 μm; B, F, I, J, 100 μm; C, E, 250 μm; H, L, 50 μm; M, 200 μm.

FIGURE 28. Mixtoscutella ussowi (Kluge, 1908). ZIRAS 14/50567 (Korfa Gulf, eastern Kamchatka, Bering Sea). A. Colony margin with developing zooids and ooecia. B. Distal view of two zooids, showing details of orifice and suboral avicularia. C. Orifice of non-ovicellate zooid, showing condyles and suboral avicularium. D. Group of non-ovicellate zooids. E. Zooids with developing ovicells close to colony periphery. F, G. Ovicellate zooids in older part of colony, showing ovicells with ooecia covered by secondary calcification and sutures between secondary calcification arising from distal and distolateral zooids. H. Transverse section through frontal shield, showing interior of proximal margin of orifice, umbonulomorph suboral area with adjacent pseudoporous shield, and cavity of suboral avicularian chamber. I. Interior of frontal shield, showing primary orifice with condyles and elongate suboral umbonuloid component surrounded by pseudoporous lepralioid shield. J. Internal view of primary orifice. K. Basal surface of colony. L. Interior of frontal shield, showing blurred ring scar and umbonuloid component surrounded by pseudoporous lepralioid area. M. Lateral view of zooid, showing frontal shield and lateral wall with mural pore chambers. Scale bars: A, D, G, K, 500 μm; B, E, F, 250 μm; C, H–J, 100 μm; L, 50 μm; M, 200 μm.

FIGURE 29. Known species of Mixtoscutella from the northern Pacific.A–C. M. androsovae (Gontar, 1979). Paratype, ZIRAS 2/43716 (Cape Nerpochka, off Pacific side of Simushir Island, middle Kuril Islands). D–F. M. harmsworthi (Waters, 1900). ZIRAS 52/50568, KIENM Collection (Avacha Gulf, eastern Kamchatka, Pacific Ocean). G–I. M. cancellata (Smitt, 1868). ZIRAS 1/50572, KIENM Collection (western Kamchatka, Sea of Okhotsk). A. Colony margin. B. Group of non-ovicellate zooids. C. Interior of frontal shield, showing small umbonuloid component and lepraliomorph area. D. Zooids with ovicells (one ooecium broken). E. Ovicellate zooids, showing details of orifice and suboral avicularium. F. Interior of frontal shield, showing umbonuloid component and lepraliomorph area. G. Colony margin. H. Ovicellate zooids, showing details of orifice and suboral avicularium. I. Interior of frontal shield, showing umbonuloid component and lepraliomorph area. Scale bars: A, B, D, E, G, H, 250 μm; C, F, I, 100 μm.