Myxilla (Burtonanchora) asigmata ( Topsent, 1901 )

Goodwin, Claire E., Berman, Jade & Hendry, Katharine R., 2019, Demosponges from the sublittoral and shallow-circalittoral (<24 m depth) Antarctic Peninsula with a description of four new species and notes on in situ identification characteristics, Zootaxa 4658 (3), pp. 461-508 : 494-495

Myxilla (Burtonanchora) asigmata ( Topsent, 1901)

( Figure 19 )

Synonymy: Myxilla asigmata ( Topsent, 1901) ; Myxilla (Myxilla) asigmata ( Topsent, 1901) ; Myxilla spongiosa var. asigmata ( Topsent, 1901) ; Lissodendoryx asigmata Topsent, 1901 ; Lissodendoryx spongiosa var. asigmata Topsent, 1901 .

Specimens. BELUM. Mc 2015.555 and BELUM. Mc 2015.558 Danco Island (64°43.416’S, 62° 35.799’W), depth 5– 19 m; collected by C. Goodwin and E. Priestley, 14/02/2015 . BELUM. Mc 2015.562 and BELUM. Mc 2015.574 Port Lockroy (64°49.572’S, 63° 29.390’W), depth 12–17 m; collected by C. Goodwin and E. Priestley, 14/02/2015 . BE- LUM.Mc2015.586 BELUM. Mc 2015.590 BELUM. Mc 2015.591 BELUM. Mc 2015.592— Port Circumcision, Pieter- man Island (65°10.471’S, 64° 08.070’W), depth 5–9 m; collected by C. Goodwin and E. Priestley, 15/02/2015 . Port Circumcision , Pieterman Island (65°10.471’S, 64° 08.070’W), depth 5–9 m; collected by C. Goodwin and E. Priest- ley, 15/02/2015 . BELUM. Mc 2015.642 Rocks near San Martin Islands (65°41.297’S, 65° 20.091’W), depth 6–21 m; collected by C. Goodwin and E. Priestley, 17/02/2015 . BELUM. Mc 2015.669 , BELUM. Mc 2015.670 and BELUM. Mc 2015.675 Dalgleish Bay, Porquoi-pas Island (67°42.390’S, 67° 44.155’W), depth 15–17 m; collected by C. Goodwin and E. Priestley, 20/02/2015 . BELUM. Mc 2015.676— Jenny Island (67°43.325’S, 68° 20.590’W), depth 6–16 m; collected by C. Goodwin and E. Priestley, 21/02/2015 . BELUM. Mc 2015.808 Neptune’s Bellows, Decep- tion Island (62°59.607’S, 60° 33.601’W), depth 7–18 m; collected by C. Goodwin and E. Priestley, 26/02/2015 .

External morphology. In situ appearance ( Figure 19A ): Thick very bright, almost neon, orange crust of variable dimensions—our specimens ranged from 5 to 20 cm in diameter. Some specimens have an irregular surface with many small mounds, others are smoother. Often one or two large oscules (~ 1 cm diameter) are visible.

Preserved appearance. Firm crust with light brown interior and dark, chocolate brown, exterior. Surface very smooth. Alcohol coloured pale orange.

Skeleton ( Figure 19B ): Reticulate choanosomal skeleton with ascending columns of 4–6 styles joined by thinner bundles 2–4 spicules in width. Dense ectosomal palisade of tylotes. Chelae throughout the tissue.

Spicules: Measurements from BELUM.Mc2015.586.

Styles ( Figure 19C ): 433(524)560 by 15(20) 24 µm Smooth styles with an abrupt point. Often gently curved.

Tylotes Figure 19D ): 239(283)299 by 7(11) 13 µm. Ends only slightly tylote and bearing a crown of 4–6 large spines.

Myxillid chelae ( Figure 19E ): 53(61) 69 µm with three pointed teeth at each end.

Remarks. Only two species of Myxilla (Burtonanchora) recorded locally have only one category of chelae as microscleres: M. asigmata ( Topsent, 1901) and M. lissostyla ( Burton, 1938) . Myxilla lissostyla has much smaller chelae (11µm) and larger styles (800 µm). The type specimen of Myxilla asigmata has similarly sized chelae (60–70 µm) and tylotes (380 by 7–8 µm) but larger styles 715–775 by 20 µm. The style sizes in our other specimens ranged from 530 to 647 µm so they consistently had smaller styles than the type. However, a wide range of style sizes, from 300 to 900 µm, have been reported by other authors (see Rios & Cristobo 2007). The number of teeth reported on the chelae is also variable: most authors report three, but Topsent described this as variable and Rios & Cristobo (2007) report five in their specimen.

Distribution. We found this species to be widespread and recorded it from Deception Island down to Jenny Island in the South. At some sites it was very abundant, notably Port Circumcision, Pieterman Island. Myxilla asigmata is widespread in the Antarctic and Subantarctic: Bellingshausen Sea ( Topsent 1901); Booth-Wandel Island ( Topsent 1908); Weddell Sea ( Topsent 1913); Gauss Station ( Hentschel 1914); South Georgia ( Burton 1932); Wilkes Land and South Shetland Islands ( Koltun 1964); MacRobertson Land and Enderby Land ( Koltun 1976); Weddell Sea ( Barthel et al. 1990); Ross Sea ( Pansini et al. 1994); Lazarev Sea ( Gutt & Koltun 1995); Bransfield Strait ( Rios & Cristobo 2007).

Figures

FIGURE 19. Myxilla (Burtonanchora) asigmata (Topsent, 1901). BELUM.Mc2015.586. A. In situ appearance. B. Choano- somal skeleton, scale bar 1000 µm. C. Style.D. Tylote. E. Chelae. Spicule scale bars all 10 µm. F. Spicules viewed under light microscope, scale bar 1000 µm.