Ceriantharia (Cnidaria) from Australia, New Zealand and Antarctica with Descriptions of Four New Species Stampar, Sérgio N. Mills, V. Sadie Keable, Stephen J. Records of the Australian Museum 2020 2020-07-29 72 3 81 100 Stampar & Mills & Keable, 2020 Stampar & Mills & Keable 2020 [154,593,150,181] Anthozoa Cerianthidae Ceriantheopsis Animalia Ceriantharia 9 90 Cnidaria species microbotanica sp. nov.   Figs 8–10, Table 3     Holotype. Australian MuseumG18354, Botany Bay, west of Port Botany, New South Wales, Australia 33.98°S 151.20°E(  13/ii/1975), depth not recorded.   Paratypes. Botany Bay, New South Wales, Australia(  12/x/1995), all Smith-McIntyre grab,  AMG18356, 33.97°S 151.19°E,  15.5 m( 1 specimen),  AMG18357, 33.97°S 151.18°E,  16.3 m( 2 specimens),  AMG18358 33.96°S 151.18°E,  16.3 m( 1 specimen).   Diagnosis. Labial tentacles in two pseudocycles. Only directive mesenteries attached to siphonoglyph, presence of directive labial tentacle, M and m mesenteries with almost same length and very short mesenterial structures.   Variation. Elongated (up to 40 mmlong) and narrow ( 3–4 mmwidth) cerianthid; 20–38 brown marginal tentacles ( 3–4 mmin preserved specimens), arrangement 1212.1212.1212…, no visible pores on tentacle; 16–36 brown labial tentacles (up to 2 mmlong in preserved specimens), arrangement (2)131.3212.3212…, unpaired labial tentacle present; slightly smooth stomodeum extending over 1/6 to 1/7 of total body length, hyposulcus 2 mmlong, hemisulci 1 mmlong; siphonoglyph narrow, connected only to directives; free parts of sterile directive mesenteries almost the half length of siphonoglyph, without mesenterial filaments. Second protomesenteries almost reaching aboral pole, fertile, with very short cnido-glandular tracts (c. 20% of the mesentery). Third protomesenteries sterile, longer than 1/4 of P2, with craspedonemes at middle region. M and m-metamesenteries long, fertile; M1 and m1 almost reach aboral pore with bundles of craspedonemes and cnido-glandular tracts (c. 30% of the mesentery); B and b-mesenteries, sterile, B mesenteries 30% longer than b; see Fig. 9for schematic arrangement of mesenteries. The cnidome of the species ( Fig. 10) is composed of spirocysts, microbasic b-mastigophores (three types) and ptychocysts distributed as shown in Table 3.   Remarks. This species has a very unusual form, probably due to the small body size. The organization of the mesentery seems to have been restricted and it is not possible to verify a clear difference between the same typeof mesenteries, B or M. Still, the genus  Ceriantheopsisis the most suitable placement for this species, because of the mesenterial arrangement (with long and fertile P2). This species is unusual because of its small size and also seems endemic to a very restricted area. All specimens were collected in benthic surveys. In one of these studies, two estuaries, Botany Bay and Pittwater, were evaluated for comparative purposes with many samples ( Wilson et al., 1998). The distance between these two regions is only 50 km. Interestingly, samples of  Ceriantheopsis microbotanicaonly come from Botany Bay. Perhaps there is some strong biological or other reason that has restricted collections to date to this location. This is also potentially a very interesting species for studies of evolutionary developmental mechanisms (evo-devo) because its small size can be compared with the well-known biological model  Nematostella vectensis( Darling et al., 2005; He et al., 2019).   Distribution. Botany Bay, Sydney, Australia.   Etymology. The species name is derived from a mixture of the locality name (Botany Bay) and the size of the specimens (micro).    Holotypedescription( AMG18354). Elongated polyp, 38 mmlong, 4 mmdiameter just below marginal tentacles and 3 mmnear aboral end. Marginal tentacles 38, arranged in two pseudocycles, 3–4 mmlong and 0.5 mmin diameter near the base, brown with a lighter longitudinal line. The space between cycles of marginal and labial tentacles short and light brown. Labial tentacles 36, arranged in four pseudocycles, about 2 mmlong, brown, directive labial present, arrangement of marginal tentacles 1212.1212.1212… and labial tentacles (2)131.3212,3212…. Oral disk 4 mmwide, stomodeum 5 mmlong, light brown, siphonoglyph narrow and elongate with 2 mesenteries attached (directives), hyposulcus 1.7 mmwith short hemisulci 0.7 mmlong. Free parts of directive mesenteries rather short, without mesenterial filaments. Second protomesenteries almost reach aboral pole, fertile, bearing ciliated tract at first 1/4 of the mesentery. Third protomesenteries sterile, longer than 1/4 of the P2, with craspedonemes at first 1/4 of the mesentery. M and m-metamesenteries indistinct with the same length, fertile; M1 and m1 almost reach the aboral pore (9/10 of gastral cavity) with mesenteric filaments at first 1/4 of each mesentery; B mesenteries 30% longer than b mesenteries. 1975-02-13 Australia Port Botany -33.98 Australian Museum 721 151.2 Botany Bay 9 90 1 New South Wales holotype 1995-10-12 Australia Botany Bay 9 90 1 New South Wales paratype [179,744,415,439] AM Australia 16 -33.97 721 151.19 9 90 1 New South Wales paratype [121,697,444,469] AM Australia 16 -33.97 721 151.18 9 90 2 New South Wales paratype AM Australia 16 -33.96 721 151.18 9 90 1 New South Wales paratype