Penetrantia taeanata, 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 : 269

Penetrantia taeanata n. sp.

( Figs 9C–F , 12 , 13 )

Spathipora [sp.]: Seo et al. 2016: 9.

Penetrantia [sp.]: Seo et al. 2016: 9.

Etymology. The species is named for the Taean Coast area of the Yellow Sea where it was discovered.

Material examined. Holotype: MBRBKH8, Cheongpodae, Taean Coast National Park, Korean east coast, 36.6334° N, 126.2997° E, intertidal, 16 June 2017 . Paratype: MBRBKP8, same data as holotype .

Description. Colonies boring into mollusk shells, composed of linked kenozooidal stolons which penetrate upper layers of shell, sometimes reaching surface as series of tiny elevated pores (tubulets), and buried saclike zooids, with rounded orifices at shell surface usually on both sides of stolon branches ( Figs 9C–F , 13B–C ). Main stolon branches develop side branches at almost 90° angles to principal stolons. Side branches larger than stolonate processes of Immergentia , about 15–20 µm wide ( Fig. 13D, E ). On shell surface, well-preserved colony borings look like narrow branching tracks with round to teardrop-shaped orifice holes on either side; densest colonies appear as jumble of closely spaced holes. Zooids tubular with roundly tapering proximal ends; c. 140–180 µm long, 50 µm wide, budding at distal ends from peduncles, perpendicular or diagonal to shell surface. Although orifices on both sides of stolon at shell surface may appear to be almost opposite each other, the resin cast shows they are offset, sometimes in a very neat herringbone fashion ( Figs 9C, D , 12B, D , 13A ). Gonozooids not seen.

Remarks. Our specimens resemble those of Penetrantia densa Silén, 1946 in the presence of the round apertures of zooids outside the line of the main stolon or branches, but zooids are smaller and openings can be even closer together in Penetrantia taeanata n. sp., which is the commonest boring ctenostome species at the intertidal site at Cheongpodae. Immergentia cheongpodensis n. sp. is less abundant at the same locality, but overall about one-third of the dead shell material collected at this site had borings of one or both species. They were most commonly found in bivalves, particularly oyster shells, but also noted in a few gastropod shells.

Distribution. Korea: Cheongpodae, Yellow Sea.

Figures

FIGURE 9. Light micrographs of various uncataloged shell-borings of Immergentia cheongpodensis n. sp. and Penetrantia taeanata n. sp. from Cheongpodae. A. Immergentia, frontal view of tear-drop-shaped excavations on bivalve shell. B. Highermagnification view of Immergentia excavations on same shell. C. Penetrantia, characteristic ‘railroad-track’ arrangement of seemingly paired openings either side of stolon traces in a densely bored shell. D. Borings of both species in the same shell, scattered, smaller openings of Immergentia colonies are visible in the upper less-bored half of the image. E. More-magnified Penetrantia colonies showing zooid openings and stolon traces. F. Translucent shell back-lit to show presence of Penetrantia zooid chambers beneath the openings at the shell surface. Scale bars: A = 2 mm; B = 1 mm; C = 4 mm; D = 0.20 mm.

FIGURE 12. Penetrantia taeanata n. sp., Cheongpodae, various uncataloged shells. A. Low-magnification appearance of a densely growing colony. B, C. Higher-magnification views showing that, while the openings at the shell surface may look paired, the actual zooids are offset diagonally in a herringbone pattern. D, E. Variations in angle of zooid chambers within the shell. F. Part of stolon showing tubulets. Scale bars: A = 1 mm; B, C = 0.50 mm; D–F = 0.10 mm.

FIGURE 13. Penetrantia taeanata n. sp., Cheongpodae. A. Cast of a densely growing colony in an area heavily bored by endolithic filaments. B, C. Casts of zooids with roundly tapering to nearly pointed proximal ends and cuticular-wall striations. D. Cast of zooid showing the peduncle that connects it to the principal stolon. E. Stolon with zooid bud. Scale bars: A = 0.50 mm; B–D= 0.10 mm; E = 0.05 mm.