Flustrellidra armata, Grischenko, Andrei V., Seo, Ji Eun & Min, Bum Sik, 2010

Grischenko, Andrei V., Seo, Ji Eun & Min, Bum Sik, 2010, Flustrellidra armata (Bryozoa: Ctenostomatida) — a new species from the southern shoreline of Korea, Zootaxa 2684, pp. 25-35 : 27-32

Flustrellidra armata sp. nov.

( Figs 2–4 )

Diagnosis. Colony erect, branching, bilamellar, arising from an encrusting, unilaminar basal portion, the erect flabellate lobes undulating along their margins, which are lined by kenozooids with conical spines. Autozooids elongate, arranged alternately, with subterminal transversely oval bilabiate orifice; interspersed with small kenozooids with simple, pointed spines, 1–6 along each lateral margin. Mature zooids with one to three similar kenozooids separating maternal and daughter zooids. Large, vicarious kenozooids with long spines scattered throughout colony, their spines tubular, weakly branched. Encrusting basal portion composed of spineless, inflated kenozooids of irregular shape.

Type material. Holotype: NIBRIV0000100504, one intact colony, collected 30 August 1996 at rocky shore of Mijo by J. E. Seo, H. J. Kil and J. H. Yoo. Paratype: NIBRIV0000100505, one intact colony, same data as for holotype.

Additional material examined. One specimen, intertidal, Mipo, 23 December 1976, collected by J. W. Lee. One specimen, intertidal, Mipo, 10 December 1981, collected by J. E. Seo. One specimen, intertidal, Samcheonpo, 23 September 1984, collected by B. J. Rho, J. H. Park, S. Shin, and J. E. Seo. Twenty-six specimens, intertidal, Mokdo, 11 August 1995, collected by J. E. Seo. Three specimens, intertidal, Mijo, 30 August 1996, collected by J. E. Seo, H. J. Kil and J. H. Yoo. Four specimens, intertidal, Sangju, 30 August 1996, collected by J. E. Seo, J. H. Yoo, and H. J. Kil. Two specimens, intertidal, Cheokdo, 13 June 1999, collected by J. E. Seo. Twenty-two specimens, intertidal, Daechilgido, 13 June 1999, collected by J. E. Seo. Thirty-three specimens, intertidal, Jangji, 18 August 2000, collected by J. E. Seo, S. J. Seo, and Y. H. Gong. One specimen, intertidal, Seosang, 3 November 2002, collected by J. E. Seo. Three specimens, intertidal, Songgo, 18 August 2000, collected by J. E. Seo, S. J. Seo, and Y. H. Gong. Three specimens, depth 10–15 m, rocky bottom, Jisimdo, 17 October 2007, collected by B. S. Min using SCUBA. Seventy-three specimens, depth 10–15 m, rocky bottom, Naedo, 17 October 2007, collected by B. S. Min using SCUBA. Fifty-three specimens, depth 10–15 m, rocky bottom, Oedo, 17 October 2007, collected by B. S. Min using SCUBA. Seventy-five specimens, depth 20 m, rocky bottom, Namyeodo, 19 October 2007, collected by B. S. Min using SCUBA.

Etymology. The species name derives from the Latin armatus (protected), referring to the armament of colony provided by numerous kenozooidal spines.

Description. Colony erect, branching, flexible, with numerous strap-shaped to flabellate lobes, rounded and undulate at growing margins ( Fig. 2 A, B); up to 12.5 cm in height, but usually 6.5–8.5 cm; attached to substratum by encrusting, unilaminar basal plate, up to 1.4 x 2.2 cm in size. Up to 7 closely appressed stalks arranged in parallel planes can arise from single basal plate ( Fig. 2 B). Branches of independent trunks mutually interlaced, giving bushy appearance to colony. Young colonies are yellowish, grayish, or pale brown, with whitish zone comprising 3–5 generations of developing zooids on periphery of terminal branches. Mature colonies brownish to flesh-coloured, with dark-brown to reddish fringing zone of marginal kenozooids along entire periphery, except for stalk. Branches slender, 5–17 mm wide, 1.1–1.8 mm thick (without spines). Lobes bilamellar without interposed medullary kenozooidal layer.

Zooids oval to rounded-rectangular, elongate, arranged alternately in distinct series. Grooves distinct between young zooids, when not occupied by kenozooids ( Fig. 4 A). Frontal surface smooth, inflated, semitransparent, yellowish to brownish, chitinous. Orifice ( Fig. 4 B) subterminal, raised, transversely elongate, bilabiate, roughly oval to rectangular in outline, with thickened, chitinous proximal labium, brown in color. Along each lateral zooidal margin are small kenozooids with circular to oval base and a sharp simple spine directed upwards or slightly tilted toward zooid. Young zooids ( Fig. 4 A, B) have 1–2 pairs of distal kenozooids, each with a sharp spine pointing upwards, flanking orifice; 1–3 similar kenozooids successively developing more proximally along each lateral margin ( Fig. 4 C, D).

Zooids in mature colony regions ( Fig. 4 E, F) interspersed with single or double series of 4–6 kenozooids each, with parallel or alternating arrangement and with pointed, straight or slightly tilted spines; in addition, there are 1–3 small kenozooids, each with a minute, slightly curved spine, between maternal and daughter zooids. Thus, old zooids can be entirely surrounded by small kenozooids. With age and increasing chitinization, all kenozooidal spines acquire a dark-brown color that contrasts with the zooidal surface. Large vicarious kenozooids scattered throughout colony, these oval, hexagonal, or rhombic in shape with strongly convex frontal surface ( Fig. 3 B); occasionally arranged as compact groups in limited areas on colony surface ( Fig. 3 A). A hollow, tubular spine ( Fig. 3 A–C, F, G), dark brown in color, sharply contrasting with brownish colony surface, originates from center of each vicarious kenozooid. Spines straight to slightly curved in middle, orientated vertically or tilted slightly distally or distolaterally. Majority of spines weakly branching terminally into 2–5 short spurs, without secondary branches; some lack distinct ramifications and have a slightly pointed or blunt tip. Most spines gradually taper from base to tip, but some are enlarged in middle and appear spindle-shaped; others are entirely elongate-cylindrical. Occasionally, a spine narrows moderately in middle and is secondary enlarged near tip, at point of ramification. Bases of large kenozooids flanked by 2–5 minute kenozooids along each lateral margin, each with short, pointed spine directed laterally and upwards. Marginal kenozooids very irregular in shape and size, arranged along entire lateral and terminal margins of branches ( Fig. 3 D–F). At terminal end of growing branches, kenozooids fringe the zone of developing zooids ( Fig. 3 B). Along margins, kenozooids of opposite layers develop complementarily, side by side ( Fig. 3 D), and partly overlap each other; each has a conical spine with pointed tip, oriented 20–80° from frontal plane.

Encrusting basal plate and stalk of colony ( Fig. 4 G, H) composed entirely of inflated kenozooids that are hexagonal, oval, roughly quadrangular, or irregular in shape, with distinct raised boundaries, not intercalated with small, spinous kenozooids. Polypide with 18 tentacles.

Measurements. ZL, 0.62–1.03 (0.81 ± 0.09). ZW, 0.32–0.51 (0.39 ± 0.05). OrL, 0.14–0.23 (0.18 ± 0.02). OrW, 0.27–0.35 (0.31 ± 0.02). Kz(s)L, 0.05–0.20 (0.12 ± 0.04). Kz(s)W, 0.04–0.15 (0.09 ± 0.03). Kz(l)L, 0.45–0.83 (0.64 ± 0.12). Kz(l)W, 0.35–0.58 (0.45 ± 0.06). Kz(m)L, 0.22–0.43 (0.31 ± 0.07). Kz(m)W, 0.18– 0.35 (0.27 ± 0.06). Kz(bp)L, 0.37–0.63 (0.51 ± 0.07). Kz(bp)W, 0.26–0.43 (0.33 ± 0.05). Kzs(s)L, 0.13–0.42 (0.25 ± 0.09). Kzs(l)L, 0.67–1.62 (1.19 ± 0.27). Kzs(m)L, 0.30–0.97 (0.53 ± 0.19).

Remarks. Flustrellidra armata most resembles its Japanese congener F. stolonifera ( Okada, 1921) in having a similar erect, branching, strap-shaped colony form; zooids interspersed by small lateral kenozooids with sharp, simple spines; and very large vicarious kenozooids bearing tubular branching spines. However, F. armata differs from the latter in the following combination of characters: (1) the number of minute, spiny kenozooids separating neighboring zooids along the lateral margins successively increases in F. a r m a t a with age from one or two to five or six, whereas F. stolonifera has only one pair of angular kenozooids flanking the orifice, and rarely one additional pair proximolaterally; (2) the double series of kenozooids between zooids in mature regions of the F. a r m a t a colony is absent in F. stolonifera ; (3) the proximal kenozooids that separate maternal and daughter zooids of F. a r m a t a have not been reported in F. stolonifera ; (4) branch margins of F. armata are fringed along their whole length with marginal kenozooids having a conical spines, while the margins are edged with spineless zooids in F. stolonifera ; (5) spines of the vicarious kenozooids of F. a r m a t a are scarcely branched and only at the very tip, without secondary ramification, whereas the homologous spines in F. stolonifera are divided into two to six tine-like branches (see Okada 1921, text-fig. 1; Mawatari 1953, text-fig. 3).

An eastern-Pacific species, F. s p i n i f e r a ( O’Donoghue & O’Donoghue, 1923), also forms erect colonies, having strap-shaped bilamellar lobes and large kenozooids with long, sparsely branched spines (holotype specimen illustrated by d’Hondt 1983, pls 1, 2), some of which are superficially similar to those in F. a r m a t a. However, the spine branches are always longer and the ramification is deeper than in the vicarious kenozooidal spines of F. armata . In addition, all kenozooids of F. spinifera are of the same type, located distally to each zooid, whereas in F. a r m a t a large vicarious kenozooids are scattered over the colony surface and small, circular kenozooids with a simple spine are always present.

Ecology. The majority of colonies of F. a r m a t a collected intertidally support a diverse association of other sessile benthic forms. Most colonies observed were covered with hydroids, sponges, tubes of sabellid polychaetes, barnacles, ascidians, brachiopods, green and red algae (including articulate coralline algae), and other bryozoans, including species of Lichenopora , Alcyonidium , Cauloramphus , Figularia , Hippothoa , Watersipora , Fenestrulina , Microporella , Pacificincola , Celleporaria , and Celleporina . Among the bryozoans, colonies of Celleporaria were the most frequent and abundant, forming thick nodules around the branch stems of F. a r m a t a. Occasionally, errant polychaetes, pycnogonids, and the shells of juvenile gastropods and oysters were noticed between the appressed branch trunks of colonies.

We observed in the field that populations of F. a r m a t a are patchy in the upper subtidal zone but have a high of coverage of substrata on rocky bottoms at depths of 10–20 m at some sites. These deeper colonies likewise provide a habitat for a variety of subtidal benthic organisms. We saw dozens of caprellid and other amphipod crustaceans associated with colonies of F. a r m a t a. The majority of colonies were densely covered by hydroids, green and red algae (both encrusting and articulate coralline algae), sponges, barnacles, tubes of sabellid polychaetes, and other bryozoans, including species of Crisia , Lichenopora , Alcyonidium , Cellaria , Beania , Catenicella , Escharoides , Pacificincola , Celleporaria , and Celleporina . In some cases, we found juvenile mytilids, oysters, decapods, errant polychaetes, and pycnogonids between branches of of F. a r m a t a colonies, and groups of small scleractinians attached to the basal region of colonies.

Distribution. Flustrellidra armata is currently known along more than 300 km of the southern shoreline of the Korean Peninsula, facing the western passage of the Korea Strait, between Mipo (35°36’ N, 129°27’ E) in the northeast and Mokdo (34°10’ N, 126°34’ E) in the southwest. Accordingly, F. a r m a t a can be categorized as a Pacific-Asian, low-Boreal to Subtropical, intertidal to upper-subtidal species.

Figures

FIGURE 2. Colony morphology of Flustrellidra armata n. sp. A, holotype colony, NIBRIV 0000100504. B, paratype colony, NIBRIV 0000100505. Scale-bars: 1 cm.

FIGURE 3. Flustrellidra armata n. sp. NIBRIV 0000100504. A, distal view of terminal end of branch showing zone of developing zooids, marginal kenozooids, and a compact group of closely arranged vicarious kenozooids with long, stout tubular spines, pointed or weakly ramified at tips; B, frontal view of terminal end of branch with deep zone of developing zooids, marginal kenozooids, and two vicarious kenozooids with a long tubular spine having a blunt or forked tip; C, distal view of terminal end of branch, showing spinous marginal kenozooids and tubular kenozooidal spines in the opposite layers; D, close-up of marginal kenozooids with conical spines directed forward at various angles, fringing the zone of developing zooids; E, lateral margin of branch showing one or two distolateral pairs of spiny kenozooids between immature zooids; also evident are marginal kenozooids with pointed, conical spines; F, region of mature zooids near lateral margin of branch, showing zooids separated by two series of small spiny kenozooids; marginal kenozooids with pointed spines; and a vicarious kenozooid with a long, tubular spine, weakly bifurcate at tip; G, highermagnification view of vicarious kenozooid in F, which bears a tubular spine with slightly forked tip and is surrounded by minute kenozooids with short, laterally directed spines; H, base of vicarious kenozooidal spine, flanked proximolaterally by minute spinous kenozooids arising from the two lateral autozooids (each indicated by the large orifice). Scale-bars: A, 1 mm; B – D, 0.5 mm. E – G, 0.2 mm; H, 0.1 mm.

FIGURE 4. Flustrellidra armata sp. nov. NIBRIV 0000100504. A, immature zooids from region near colony margin, interspersed with distolateral kenozooids flanking orifice, with long pointed spines tilted forward; B, immature zooids intercalated with one to three pairs of distal and lateral kenozooids with sharp, elongate spines; C, zooids separated by series of lateral oval kenozooids, some twinned, with sharp spines slightly tilted over frontal surface; D, zooids separated by three to four pairs of lateral kenozooids with sharp spines, with occasional minute, spiny kenozooids proximally; E, mature zooids separated laterally by double series of small kenozooids with sharp spines slightly curved over frontal surface; F, zooids from old colony region, separated laterally and proximally by single to double series of minute kenozooids with short, pointed spines; G, general view of basal plate and stalk of colony, composed entirely of kenozooids of irregular shape; H, close-up of kenozooids from encrusting basal plate. Scale-bars: A, D, G, 0.5 mm; B, C, E, F, H, 0.2 mm.