Exochella cryptodontia, Min, Bum Sik, Seo, Ji Eun, Grischenko, Andrei V. & Gordon, Dennis P., 2017

Min, Bum Sik, Seo, Ji Eun, Grischenko, Andrei V. & Gordon, Dennis P., 2017, Intertidal Bryozoa from Korea — new additions to the fauna and a new genus of Bitectiporidae (Cheilostomata) from Baengnyeong Island, Yellow Sea, Zootaxa 4226 (4), pp. 451-470 : 462-464

Exochella cryptodontia n. sp.

( Figs 24–26 )

Etymology. The species name alludes to the cryptic, minutely toothed proximal margin of the primary orifice (Greek odon, tooth).

Material examined. Holotype: NIBRIV0000325941, Hwadong, Baengnyeong Island, 37.9192° N, 124.7002° E, southeastern coast, 24 November 2007, low tide, collected by B.S. Min and A.V. Grischenko . Paratype: NIBRIV0000711264, Dumujin, 37.9738° N, 124.6170° E, northwestern coast, 25 November 2007, low tide, collected by B.S. Min and A.V. Grischenko. Other material: Woosuk University collection—Baengnyeong Island: Hwadong (47 colonies), Junghwadong (3 colonies), Dumujin (106 colonies), Jinchon-ri (7 colonies), Gobongpo (8 colonies), Yeonhwa-ri (23 colonies); mostly on rocky substrata, but also on plastic debris, shell and crustose coralline algae ( Clathromorphum ). Cheongsan Island (1 colony) on a small rock.

Description. Colony encrusting, unilaminar, small, to 40 mm in diameter. Autozooids at growing margin subhexagonal, with the angles rounded distally and proximally, and acute laterally; the overall shape less angular in older autozooids with heterozooids; arranged regularly in quincunx. Umbonuloid frontal shield not very convex, more or less smooth, with 5–7 conspicuous areolar pores along each margin. Primary orifice deep-set, proximal rim bearing 9–10 minute peg-like teeth along the proximal rim as seen from interior view. Oral spines usually 3, sometimes 4, on the distal rim of marginal zooids, proximal of which is a peristome that surrounds the rest of the orifice; middle part of peristome forming a bridge, creating a relatively large pseudospiramen, at the bottom of which the almost-concealed, minutely toothed border is just visible proximally; proximal margin of peristomial rim high, somewhat spout-like, sloping steeply to frontal shield. Oral spine bases mostly completely concealed in older or ovicellate zooids, although sometimes one can be seen adjacent to an avicularian rostrum projecting from a neighboring zooid. Avicularia paired or single, each budded from an areolar pore at widest part of zooid, the acute rostrum directed more or less laterally or slightly obliquely proximolaterally, the palatal foramen and avicularian opesia relatively large, separated by a complete crossbar. Ooecium recumbent on distal zooid, occupying much of its frontal shield, convex, smooth, subumbonate, forming a low arcuate rim around the distal margin of the maternal orifice, opening above secondary orifice. A pair of basal pore-chambers present in distal half of each zooid, with 1–2 mid-distally. Ancestrula not seen.

Measurements. ZL, 276–427 (333) µm; ZW, 152–295 (235) µm; OrL, 80–91 (84) µm; OrW, 87–112 (99) µm; AvL, 75–101 (91) µm; AvW, 37–53 (45) µm; OoL, 142–169 (153) µm; Oo,W 149–180 (164) µm.

Remarks. We found E. cryptodontia n. sp. not only at Baengnyeong Island but also at deeper localities (27–42 m) among the islands of the southwestern coast of South Korea. In both areas the species is relatively common and abundant, so it is surprising that it appears not to have been previously encountered.

Four species names have been applied to Recent Exochella from northeast Asia and a median pseudospiramen is lacking in all four. Two of them are endemic to the region. These are Exochella japonica Ortmann, 1890 , which has a median peristomial process flanked by a pair of pseudosinuses and what may be lateral linear ridges on the ooecium, and Exochella areolata Okada & Mawatari, 1937 , which also has a median process, but this is not flanked by pseudosinuses (cf. Kubanin 1975). The other two species names— Exochella tricuspis ( Hincks, 1881) and Exochella longirostris Jullien, 1888 —pertain to taxa first described from Bass Strait, Australia and Magellanic South America, respectively. Published illustrations of these species (not all using SEM) from the northeast Asian region (e.g. Mawatari 1965; Rho & Lee 1980; Seo & Min 2009) certainly closely resemble those based on topotypic material but subtle differences are evident. Since neither of these species has been noted as hull-fouling or invasive, it is possible, if not likely, that populations from northeast Asia may not be conspecific. Close comparison of Asian material from Asia and austral regions using SEM needs to be carried out. One useful character is the internal configuration of orificial structures, such as depicted by Levinsen (1909) and Gordon (1989).

A fifth form from northeast Asia is Exochella longirostris var. quadricella Sakakura, 1935 from the Pleistocene Dizodo beds of Boso Peninsula, Honshu, Japan. Sakakura noted that the number of basal porechambers was four (hence var. quadricella ) compared to three in E. longirostris ; it remains to be determined whether var. quadricella should be raised to species rank.

Like E. cryptodontia n. sp., Exochella conjuncta ( Brown, 1952) has a single pseudospiramen; this has been illustrated by SEM ( Gordon 1989). The latter species differs most obviously from E. cryptodontia in having a proportionally smaller, less spout-like proximal peristome and a non-denticulate inner rim.

Figures

FIGURES 24 – 26. Exochella cryptodontia n. sp., Hwadong (except for 25, from Cheongsan Island). 24, Frontal view of ovicellate zooids, with three umbonate ooecia occupying virtually the entire frontal shield of each next-distal zooid; scale bar, 200 µm. 25, Interior of a frontal shield showing the clearly delimited umbonuloid area with a toothed distal margin; scale bar, 100 µm. 26, Differentiating zooids at the colony margin showing distal oral-spine bases and the formation of the peristomial pseudospiramen; arrows indicate the denticulation on the inner proximal margin of the orifice; scale bar, 200 µm.