Amathia medullaris Mawatari, 1972

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 : 275-279

Amathia medullaris Mawatari, 1972

( Fig. 18 )

Bowerbankia medullaris Mawatari, 1972: 300 , figs 1, 2.

Bowerbankia (Crassicaula) medullaris: Kubanin 1992: 26 .

Material examined. MBRBK1708 , 36.6334° N, 126.2997° E, Cheongpodae , West Sea, 26 May 2017 . MBRBK 1709 , Daejin port, East Sea, 38.2957° N, 128.2533° E, 3 June 2017 .

Description. Colony encrusting brown alga Stephanocystis hakodatensis (Yendo) (formerly Cystophyllum hakodatense ), on which it produces tufts of squat rounded sac-like zooids on stipes and fruiting bodies. Colony divided into two regions, an inner thick medullary region of branched stolons and single layer of almost spherical autozooids. At colony edges stolons thin and closely adherent to algal substratum, with erect autozooids sometimes biserially arranged along them ( Fig. 18E ). More-developed parts of colonies swell into thick complex mat of stolons and zooids, entire mat surrounding substratum but not tightly adherent to it ( Fig. 18A ). Zooidal orifice quadrate, polypide with distinct gizzard (note zooids in Fig. 18E ). Zooids of Korean specimens with 10 evenly spaced tentacles all the same length ( Fig. 18A, C, E ). Eggs and embryos ( Fig. 18B, D, G ) yolky yellow color and brooded in zooids in which polypides had degenerated into brown bodies.

Remarks. The colonies found by us match the original description of Mawatari (1972) except in two details. All the polypides in Korean colonies had 10 tentacles, whereas eight tentacles and orange eggs were described in the Japanese material. Since the eggs of our specimens were somewhat orange-yellow this detail may not matter, but tentacle number (eight or ten) is a significant species-specific character in all known Amathia species. Because species in this genus are so constrained in terms of tentacle number, if living Japanese specimens can be confirmed to have eight tentacles, the Korean material likely represents a new species. Amathia medullaris differs from all other known species in its production of a medullary region. Other 10-tentacled species, e.g. Amathia imbricata from the east and west Atlantic, may have thickly interwoven networks of stolons and zooids in well-grown colonies, but do not show the structural zonation found in A. medullaris .

Kubanin (1992) created the subgenus Crassicaula for this species, based on the differences in its morphology in comparison with other species then classified in Bowerbankia . This distinction needs to be evaluated through further study.

Distribution. Korea: Yellow Sea, East Sea. Also Peter the Great Bay, Russian coast of Japan Sea, and Hokkaido, Japan. Intertidal.

Figures

FIGURE 18. Amathia medullaris Mawatari, 1972 (MBRBK1708). A. Portion of a live colony encrusting the alga Stephanocystis hakodatense. B. Cluster of zooids, many containing yellow embryos. C. Another view of live colony on alga with expanded (10-tentacled) tentacle crowns. D. Closely spaced squat zooids, with developing embryos. E. View of growing tip of a colony, with zooids aligned on stolon, but not massively clustered as in older areas of colony. F. Compound-microscope view of retracted zooids showing walls of tubes and part of a setigerous collar. G. More-magnified view of two zooids, both brooding embryos. Scale bars: B, E = 0.30 mm; D = 0.13 mm; G = 0.15 mm.