Hincksina flustroides ( Hincks, 1877 )

Berning, Björn, Spencer Jones, Mary E. & Vieira, Leandro M., 2021, Revision of the European species of the genus Hincksina Norman, 1903 (Bryozoa, Cheilostomatida, Flustridae), Zootaxa 5081 (3), pp. 333-352 : 335-337

Hincksina flustroides ( Hincks, 1877)

( Fig. 1 )

Membranipora flustroides Hincks, 1877: 213 ; 1880a: 151, pl. 19, fig. 2.

Hincksina flustroides (Hincks) : Ryland & Hayward 1977: 86, fig. 32; Hayward & Ryland 1998: 152, fig. 37.

Hincksina flustroides subsp. crassispinata Calvet : De Blauwe 2009: 190, fig. 175, 176.

? Hincksina flustroides (Hincks) : Fernández-Pulpeiro 1983: 472; Haya & Anadón 1989: 111, fig. 2.

not Hincksina flustroides (Hincks) : Waters 1898: 678, pl. 49, fig. 12; Calvet 1902: 31, pl. 1, fig. 3; Norman 1909: 286; Gautier 1962: 49, fig. 8; Prenant & Bobin 1966: 200, fig. 62; Hayward 1974: 370; Arístegui Ruiz 1984: 56, fig. 11; Harmelin 1988: pl. 1, figs 4, 5; Zabala & Maluquer 1988: 80, text-figs 86, 87. pl. 3, fig. A; Chimenz Gusso et al. 2014: 103, fig. 40a, b.

Material examined. Lectotype (here designated): NHMUK 2016.6.9.2 (formerly part of NHMUK 1899.5.1.582), Antrim, Hincks coll., one colony on bivalve shell. Paralectotypes: NHMUK 1899.5.1.582a, b, Guernsey, Hincks coll., two colonies on slide, one on bivalve shell, the other on serpulid tube, plus six colony fragments in Canada balsam; NHMUK 1899.5.1.583a, b, Antrim, Hincks coll., two small colonies on bivalve shells, on slide. NHMUK 1911.10.1.348, Guernsey, Norman coll., one colony on interior of Glycymeris shell; NHMUK 1911.10.1.349, Antrim, Norman coll., two colonies on bivalve fragments; NHMUK 1911.10.1.350, Guernsey, Norman coll., several colonies on echinoid and bivalve fragments; NHMUK 1919.6.25.20, Antrim, Norman coll., several free colony fragments on slide; NHMUK 1919.6.25.21, Antrim, Norman coll., several free colony fragments in Canada balsam, on slide; NHMUK 1919.6.25.22, Antrim, Norman coll., several free colony fragments on slide. Non-type material examined using SEM: NHMUK 1963.3.24.2, one colony encrusting polychaete tubes on a bivalve shell, on slide, Salcombe, 7–9 m (4–5 fathoms), March–April 1896, leg. S.F. Harmer, figured in Ryland & Hayward (1977: fig. 32), and Hayward & Ryland (1998: fig. 37). Non-type material examined optically: NHMUK 1897.5.1.510, Guernsey, John Bracebridge Wilson coll., one colony on bivalve shell; NHMUK 1899.5.1.22, Ilfracombe, Hincks coll., several colonies on rocks.

Description. Colony encrusting, unilaminar, multiserial ( Fig. 1A ), forming light brown circular or lobed patches. Autozooids oval to rectangular (ZL 431±49, 369–523, 20; ZW 251±24, 210–293, 20), arranged in irregular series, separated by shallow grooves ( Fig. 1B ), skeleton whitish translucent when dried. Vertical walls with two or more uniporous septula per neighbouring zooid. Gymnocyst reduced to practically absent, sometimes exposed in proximal, lateral and distal corners, and/or as a very narrow band along the distolateral zooecial margin, cryptocyst not developed, opesia therefore extensive (OpL 363±48, 300–471, 20; OpW 186±24, 140–222, 20). Opercular region laterally framed by a pair of vertically directed, cylindrical or slightly flattened oral spines in both auto- and ovicellate zooids; frontal membrane in mature zooids overarched by 8–12 (most often 9–10) cylindrical to flattened subclavate mural spines of variable width ( Fig. 1B, D ), the distal ones may be bifid while the proximal spines are generally smaller and shorter as well as more cylindrical ( Fig. 1B ), lateral spines of variable length and either leaving a central gap in some zooids or exceeding beyond the zooidal midline in others; all spines jointed at their base.

Ovicell endozooidal in proximal part of distal autozooid, ooecium continuous with the proximal gymnocyst, forming a short but broad hemispherical cap (OvL 102±16, 73–148, 20; OvW 157±14, 133–198, 20), proximal margin raised centrally, often producing a central peak ( Fig. 1D ).

Avicularia interzooidal, infrequent, situated between autozooids in a linear series, forming on a rectangular cystid with the gymnocyst well-developed in the corners; avicularium oval and only slightly longer than wide, the part proximal to condyles usually slightly wider (AL 132±16, 100–154, 15; AW 102±13, 80–124, 15), emplaced on an elevated rim with the rostrum slightly oblique to frontal surface and usually pointing distally or less often distolaterally ( Fig. 1C ); mandible roughly semicircular, wider than long (ML 57±7, 48–69, 9; MW 83±9, 68–95, 9), hinged on a pair of very short triangular condyles delimiting a semicircular proximal area, a narrow immersed shelf framing the entire opesia, lower side of mandible marked by a large transversely oval lucida (a less well-sclerotised area) proximally.

Kenozooids may occasionally be present, replacing an autozooid or avicularium.

Ancestrula and early astogenetic colony not well preserved in the present material; ancestrula tatiform, presumably of pyriform shape (280 x 200 µm).

Remarks. Of the type localities mentioned by Hincks (1877, p. 213), material exists in the NHMUK collection only from Antrim and Guernsey. The lectotype and paralectotypes were accordingly chosen from these specimens. As Hincks furthermore stated that A.M. Norman also recognised the species as new and suggested the species name flustroides , specimens from the Norman collection have to be considered as syntypes as well; these are therefore added to the paralectotypes.

The synonymy list is not exhaustive. As will be shown below in detail, a number of different morphotypes from European waters have hitherto been assigned to Hincksina flustroides , which, in the absence of SEM images and precise descriptions, makes it difficult to assess its true geographic range of distribution. Based on the type material studied here, which is particularly characterised by ooecia that are produced by the distal autozooid (not by the distal avicularium), as well as by avicularia that are only slightly longer than wide, H. flustroides is, at present, only known with certainty from western Great Britain, the Channel, and the southern North Sea.

Colonies washed ashore in Belgium, and assigned to H. flustroides subsp. crassispinata Calvet by De Blauwe (2009, p. 190, figs 175, 176), belong to H. flustroides . While the avicularia are identical, the colonies show differences in spine density, however, and particularly the one in fig. 175 has flattened, club-shaped spines throughout, giving it a different appearance. As spine morphology is subject to variation within a colony, and because clubshaped (as well as bifid) spines are also present in the types of H. flustroides ( Fig. 1B ), this morphotype is here regarded as intraspecific variability (see also the Remarks on Hincksina synchysia n. sp. below).

The specimens reported by Haya & Anadón (1989, p. 111, fig. 2) from northern Spain are also very similar to H. flustroides as regards the avicularium morphology, and are very likely conspecific (O. Reverter-Gil, pers. comm. 2021). Without having seen their material, however, it is not possible for us to decide whether they are indeed identical [the same applies to the material reported by Fernández-Pulpeiro (1983)].

All other Hincksina colonies reported from eastern Atlantic regions located further south and from the Mediterranean Sea differ in several aspects from H. flustroides and are rather similar to Hincksina synchysia n. sp. (see below). In Hincksina sp. from southern Portugal ( Souto et al. 2014, p. 136, fig. 3E, F) as well as in some of the specimens reported from Madeira by Norman (1909; NHMUK 1911.10.1.346), from the Canary Islands by Arístegui Ruiz (1984, p. 56, fig. 11), and from the eastern Mediterranean island of Chios by Hayward (1974; NHMUK 2009.10.12.4; see below), the avicularia are more elongated and the mandibles rather triangular than in H. flustroides . Thus, while the southern limit of distribution of H. flustroides remains unclear at present, it is likely to be absent from the Mediterranean Sea and the Atlantic coast of southern Iberia.

Figures

FIGURE 1. Hincksina flustroides (Hincks, 1877). A. overview of lectotype (NHMUK 2016.6.9.2). B. Oblique view on autozooids (NHMUK 1963.3.24.2), note the presence of bifid as well as broad and slender mural spines, and the jointed spines bases (dark areas between mural rim and calcified spines). C. Close-up of avicularium (lectotype, NHMUK 2016.6.9.2). D. Ovicellate zooids (NHMUK 1963.3.24.2). Scale bars: A, 500 µm; B, 100 µm; C, 50 µm; D, 200 µm.