Arachnopusia aff. pusae Marcus, 1955

Ramalho, Laís V. & Calliari, Lauro, 2015, Bryozoans from Rio Grande do Sul Continental Shelf, Southern Brazil, Zootaxa 3955 (4), pp. 569-587 : 577-578

Arachnopusia aff. pusae Marcus, 1955

( Fig. 5 A–D)

Arachnopusia pusae Marcus, 1955: 294 , figs 46–50.

Material examined. Parcel do Carpinteiro, Rio Grande do Sul, Brazil: MNRJ-1173, (fertile), am28 point 2, 32°08.402’S, 51°28.045’W, 28 August 2009; MNRJ-1174, am28 point 2, 32°08.402’S, 51°28.045’W, 28 August 2009; MNRJ-1175, am22 parcel 1, 32°13.716’S, 51°46.101’W, 21 meters depth, 0 2 February 2009; MNRJ-1201, am21 P1 Bento, 32°16.674’S, 51°47.330’W, 25 meters depth; MNRJ-1202, am24 station 2, 32°09.406’S, 51°28.318’W, 31 July 2009; MNRJ-1203, am25 station 2, 32°09.173’S, 51°28.099’W, 0 7 Aug 2009; MNRJ-1204, am28 point 3, 32°07.472’S, 51°26.435’W, 28 August 2009; MNRJ-1209, am30 station 0 1, 32°14.300’S, 51°46.630’W, 25 meters depth; MNRJ-1210, #113, (Geo Costa I), 32°15.900’S, 51°46.970’W. Hermenegildo, Rio Grande do Sul, Brazil: MNRJ-1205, HT#22 33°44.213’S, 53°14.414’W, 15.4 meters depth, June 2011, Coll. FURG; MNRJ-1206, HT#22b, 33°44.213’S, 53°14.414’W, 15.4 meters depth, June 2011, Coll. FURG; MNRJ- 1207, H#20, 33°41.254’S, 53°10.116’W, 17 meters depth, June 2011, Coll. FURG; MNRJ-1208, H#24, 33°45.073’S, 53°16.029’W, 16 meters depth, June 2011, Coll. FURG.

Description. Colony encrusting, uni- or bilamellar; autozooids square to oblong (461–631 (540) µm long x 338–369 (350) µm wide) disposed in quincunx to irregularly. Frontal shield usually with four to eight ligulate foramina (frequently 6) ( Fig. 5 A–B). Aperture wider than long (108–169 (143) µm long x 138–215 (168) µm wide), aperture rim well developed proximally, concave. Three to -four oral spines with the most proximal larger and located almost at the median-lateral region of aperture; apertural plate well developed, wider than long, smooth, and a convex proximal edge ( Fig. 5 C).

One to two (usually one) avicularia located proximo-laterally to aperture or almost median, on the rim apertural; rostrum triangular (77–108 (96) µm long) and curved at one side, directed to the inner side and slightly downwards. It can occur a large avicularium on the frontal wall of autozooid located at the proximal region directed to laterally or straight to upwards.

Oecium hood-shaped, wider than long (108–246 (190) µm long x 200–246 (220) µm wide), with a crescent band of ectooecium, smooth, uncovered frontally; oecium without avicularia or protuberances ( Fig. 5 D).

Geographic distribution. Rio Grande do Sul–Parcel do Carpinteiro and Hermenegildo (present study).

Remarks. Almost 41 species of Arachnopusia are valid today. Hayward & Thorpe (1988) mentioned that this genus has a wide distribution in cold temperate and polar waters of the southern hemisphere. However, three Arachnopusia species are recorded in tropical waters from Brazil, A. pusae Marcus, 1955 , A. monoceros (Busk, 1854) , and A. haywardi Vieira et al., 2010 . The species A. monoceros was recorded for São Paulo state (see Vieira et al. 2010); it has larger autozooids (790 µm long x 390 µm wide), 10-15 rounded ligulate foramina, one oral median avicularium directed distally, and an oecium bearing one or two small avicularia. Other species is A. haywardi that has one single oral spine, small proximal avicularium directed distally, small avicularia on the oecium, and 6–16 ligulate foramina. The most similar species is Arachnopusia pusae described by Marcus (1955) from Espirito Santo state; it is very similar in the presence of 4–8 ligulate foramina and disposition of the avicularia, but some differences were observed. Marcus described longer zooids (700–800 µm long x 350–450 µm wide), avicularia on the oecium (varied number), and did not mention or illustrate the oral spines. However, material from Rio Grande was not so well preserved and the absence of avicularia on oecia could be masked due to the poor preservation state of this material. Unfortunately, material described by Marcus (1955) was not found and the comparisons were made using his descriptions and illustrations. Thus, we cannot confirm the identification of these specimens, leaving them as affinity A. pusae Marcus, 1955 . New samples from this area or nearby will need to be analysed to better understand these specimens. The other species described for the southern hemisphere (see Hayward & Thorpe 1988, principally) are distinguished from our species principally by more numerous foramina on the frontal shield, avicularia on oecium, and the presence of oral avicularia.

Figures

FIGURE 5. Arachnopusia aff. pusae Marcus, 1955 (A, C: MNRJ- 1174; B, D: MNRJ- 1173). A, colony fragment with infertile zooids; B, colony fragment with ovicellate zooids in the distal region; C, close-up of autozooids, showing ligulate foramina in the frontal shield, oral avicularia (eroded), oral-spine bases and well-developed concave apertural plates below distal orificial rims; D, fertile zooids with ooecia. Scalebars: A, B, 500 µm; C, D, 200 µm.