Alcyonidium bullitum, Seo & Chae & Winston & Zágoršek & Gordon, 2018

Seo, Ji-Eun, Chae, Hyun Sook, Winston, Judith E., Zágoršek, Kamil & Gordon, Dennis P., 2018, Korean ctenostome bryozoans-observations on living colonies, new records, five new species, and an updated checklist, Zootaxa 4486 (3), pp. 251-283 : 255-258

Alcyonidium bullitum n. sp.

( Figs 2 , 3 )

Etymology. Latin bullitus, bubbling up, alluding to the bubble-like kenozooids at the colony surface; suggested common name, the bubble Alcyonidium .

Material examined. Holotype: MBRBKH4. Paratype: MBRBKP4 , Junghwadong , Baengnyeong Island, 37.9230° N, 124.6987° E, intertidal, 17 May 2017 . Other: MBRBK 1696, Cheongpodae, Yellow Sea, 36.6344° N, 126.2997° E, encrusting on intertidal rock, 26 May 2017. Nakwoldo waters, Yeonnggwang, Yellow Sea, 35.1608° N, 126.1378° E, encrusting on crabs, 20 May 2011 .

Description. Gelatinous colony encrusting various substrata including sea grass, rocks, and live crabs, ranging in size from a few mm to several cm maximum diameter. Zooids elongate-oval to irregularly polygonal, quite transparent, translucent whitish outlines of retracted polypides visible inside, but grooves marking the walls that separate them are indistinct ( Figs 2C, D , 3C ). Zooid length, mean 0.551 mm in young colonies on sea grass blades ( Fig. 2 ), and 0.592 mm in larger colonies on stone (range 0.369–0.674 mm, N = 18). Zooid width, mean 0.333 mm (range 0.253–0.397 mm, N = 10). Orifice round, raised on low mound-like papilla at distal end of autozooid when retracted, expanding as a white circle almost the width of distal end of zooid as tentacle sheath begins to evert for zooid feeding. Retracted orifice width, mean 0.114 mm (range 0.107–0.142 mm, N = 21). As colonies grow, increasing numbers of small transparent and bubble-like kenozooids develop between autozooids in rows and sheets, filling in areas between adjacent sheets of autozooids as they fan outward, thus rapidly increasing colony size. Because of their roundness, small size (about one-sixth the length of an autozooid) and transparency, kenozooids resemble patches of tiny bubbles embedded in colony surface ( Figs 2B–E , 3F ). In some of kenozooids are tissue masses that may represent vestigial or developing polypides; others are clear, except at their walls. Tentacles 14–16, tentacle crown white, an equitentacled funnel in which individual tentacles are held straight, but which are capable of flicking inward and outward when feeding actively ( Figs 2C , 3A–C ). In zooids with expanded tentacle crowns, the thick transparent introvert and transparent setigerous collar extend almost to level of mouth. Mode of reproduction unknown; newly settled colonies present at Baengnyeong Island in May.

Remarks. Very small colonies found on a piece of sea grass (with space) is used otherwise in ms had only autozooids. Larger colonies encrusting intertidal rocks had numerous bubble-like kenozooidal areas between groups of autozooids ( Fig. 2 ). Very large colonies that encrusted crabs dredged from the Yellow Sea also had relatively few autozooids compared to the number of kenozooids; the colonies covered the exterior of the crabs, including their eyes and appendages ( Fig. 3B ). The species resembles the eastern Atlantic species Alcyonidium mytili Dalyell, 1848 in its initial transparency and some overlap in tentacle number ( A. mytili , range 13–18, mode 15; Cadman & Ryland 1996, De Blauwe 2009) and Alcyonidium hirsutum ( Fleming, 1828) (tentacle number larger, range 14–18, mode 17–18; Ryland 1985) in the presence of many kenozooids, but the kenozooids of the Korean species are round and bubble-like, not raised and sometimes conical as are those of A. hirsutum .

Eight species of Alcyonidium are known from Japan, distributed from Sagami Bay (c. 35° N) northwards to Hokkaido. Most have a robust, erect colony form but Alcyonidium nanum Silén, 1942 , A. nipponicum d’Hondt & Mawatari, 1986 and A. shizuoi d’Hondt & Mawatari, 1986 are encrusting. These, however, differ from A. bullitum n. sp. in several respects— A. nanum has about 20 tentacles, the orifice is wholly non-projecting, and there are no kenozooids; A. nipponicum has whitish colonies when alive, 15 tentacles, fusiform to oval zooidal outlines and very thick interior walls but no kenozooids; and A. shizuoi has 12–15 (mostly 13–14) tentacles, a wide-diameter peristome, and many interzooidal kenozooids that are quadrangular, not bubble-like. The zooids of these three species are proportionally less elongate than in A. bullitum n. sp. Another encrusting species has been described from the Straits of Johor, Singapore, a much more tropical environment than those of Korean localities (Tilbrook & Gordon 2015). Alcyonidium jauhar has, like A. bullitum , elongate transparent autozooids. Tentacle number is 15–16 and a few kenozooids occur, but the unilaminar colony does not undergo the massive development of kenozooids and aggressive overgrowth of substrata, including living crustaceans, found in A. bullitum .

Distribution. Yellow Sea: Baengnyeong Island to Cheongpodae on eel grass ( Zostera ), rocks and dredged crab carapaces, intertidal to 10 m.

Figures

FIGURE 2. Alcyonidium bullitum n. sp., Junghwadong, Baengnyeong Island (MBRBKH4). A. Live encrusting colony on intertidal rock. B. Higher-magnification view of same colony showing large orifice and outer area with bubble-like kenozooids. C. Close-up of white orifice and long tentacle sheaths of autozooids. D. View of preserved colony through compound microscope showing large dark-colored autozooids and many interspersed kenozooids. E. Part of colony with many transparent kenozooids, showing rock surface beneath. F. Compound-microscope image showing very large orifices of autozooids and a few small kenozooids. Scale bars: A = 3 mm; B, C = 1.2 mm; E = 0.60 mm; F = 0.30 mm.

FIGURE 3. Alcyonidium bullitum n. sp., Junghwadong, Baengnyeong Island. A. Very young colony encrusting sea grass with tentacle crowns expanded (MBRBKP4). B. Large multilayered colony enveloping a crab from deeper water, including its eye (BKF1). C. Another view of seagrass colony in A. D. Preserved rock-encrusting colony showing position of retracted polypides (BKF1). E. SEM image of dried surface of colony from enveloped crab, showing area with protruding orifices and tips of tentacle sheaths of many autozooids (BKF1). F. Part of crab-encrusting colony surface with mostly kenozooids, some still with bubble-like frontal membranes, others collapsed (BKF1). Scale bars: A, C = 0.50 mm; D = 0.60 mm; E, F = 0.10 mm.