Arbocuspis bellula ( Hincks, 1881 )

Vieira, Leandro M., Almeida, Ana C. S. & Winston, Judith E., 2016, Taxonomy of intertidal cheilostome Bryozoa of Maceió, northeastern Brazil. Part 1: Suborders Inovicellina, Malacostegina and Thalamoporellina, Zootaxa 4097 (1), pp. 59-83 : 72-73

Arbocuspis bellula ( Hincks, 1881)

( Figs. 24–25 )

Membranipora bellula Hincks, 1881: 149 , pl. 8, fig. 4. [ Australia]

Electra bellula: Marcus, 1937: 37 (in part), pl. 6, figs. 14B, D. [Not pl. 6, figs. 14A, C, E–F] [ Brazil: São Paulo] Electra bellula: Marcus, 1941: 16 (in part), fig. 6 (in part). [ Brazil: Paraná]

Electra bellula: Winston, 1982: 120 , fig. 33. [ USA: Florida]

Electra bellula: Vieira et al., 2008: 12 (in part). [ Brazil: São Paulo and Paraná]

Material examined. UFPE 0 51, UFPE 0 52, UFPE 0 88, UFPE 102, Riacho Doce, Maceió, Alagoas, Brazil, 9º34'42" S, 35º39'19" W, intertidal, on algae, Sargassum spp., coll. 31 March 2007 by L.M. Vieira. UFPE 0 53, UFPE 0 54, Jatiúca, Maceió, Alagoas State, Brazil, 9º39'10" S, 35º41'40" W, intertidal, on algae, Sargassum spp., coll. August and September 2003 by L.M. Vieira. UFPE 0 60, UFPE 0 61, UFPE 0 65, Pratagy (Sereia), Maceió, Alagoas State, Brazil, 9º33'55" S, 35º38'40" W, intertidal, on algae, Sargassum spp., coll. 0 7 September 2007 by A.G.A. Borba Jr. UFPE 104, Jatiúca, Maceió, Alagoas, Brazil, 9º39'10" S, 35º41'40" W, intertidal, on algae, Sargassum spp., coll. 0 9 September 2003 by L.M. Vieira; UFPE 106, coll. 13 August 2007 by L.M. Vieira; UFPE 108, coll. 0 9 September 2003 by L.M. Vieira. Additional specimens: NMHUK 1888.4.16.25, Electra bellula, H.N. Ridley det., Pernambuco, Brazil, on algae. NHMUK 1888.4.16.26, Electra bellula var. bicornis , Pernambuco, Brazil. NMHUK 1969.1.20.5, Electra bellula, E. Marcus det., Santos, Brazil, on algae.

Description. Colony encrusting, uniserial to narrowly multiserial, colony form ranging from linear runners with parallel rows to mat-like branched diffuse colonies, lightly calcified, glassy and translucent, white. Zooids elongate, 0.284–0.371 mm (0.326 ± 0.030) long and 0.148–0.179 mm (0.161 ± 0.010) wide, with distal oval pyriform opesia, about 0.136–0.191 mm (0.166 ± 0.016) long, and narrower proximal gymnocyst. Proximal gymnocyst extended, occupying half of zooid length, about 0.105–0.210 mm (0.160 ± 0.027) long, surface smooth; a large branching spine placed close to proximal rim of opesia, arched over and above the frontal membrane; one or two smaller sharp spines, which may become long and curved, placed lateroproximal to the large spine; one to eight spines with variable length occur on proximal gymnocyst. Cryptocyst a narrow shelf on the inner margin of the gymnocyst. A pair of curving pointed spines occurs at the distal end of the opesia (but belongs to the distal zooids), on either side of the operculum. Colonies develop from a single ancestrula with a smaller gymnocyst than later zooids and with eight spines.

Remarks. Nikulina (2010) erected a new genus, Arbocuspis , to accommodate three species— viz. Membranipora bellula Hincks, 1881 , Membranipora bellula var. bicornis Hincks, 1881 and Membranipora bellula var. multicornis Hincks, 1881 —with branching spines that bend across the opesia. Arbocuspis bellula is very common on the Brazilian coast, frequently found attached to Sargassum spp. algae, forming uni- to multiserial delicate colonies, slightly calcified and occasionally branched. The spines on gymnocyst are usually small and strong, but very long and lightly sclerotized spines are often present.

Marcus (1937) recorded A. bellula (under the name Electra bellula ) from the São Paulo coast, as showing several morphological variations. His description included encrusting and erect colonies in four different forms with distinct autozooidal shapes and number of spines. The first encrusting form (acc. Marcus 1937: pl. 6, fig. 14A) has a gymnocyst lacking spines, except for one to three unbranched spines placed at the proximal end, very close to the opesia. Three unbranched spines close to opesia were figured in erect colonies ( Marcus 1937: pl. 6, fig. 14F), in which colonies have two additional spines at the distal end of the opesia, one in each side of the operculum. These two forms are also characterized by a crenulated rather than smooth opesia rim, such as was figured in other colonies ( Marcus 1937: pl. 6, figs. 14B–D). Osburn (1940) described similar colonies from Puerto Rico under the name Electra bellula var. ramosa , which is here considered a distinct species (see below).

Among the other morphotypes figured by Marcus (1937, pl. 6, figs. 14B–D), one ( Marcus 1937, pl. 6, fig. 14C) belongs to Arbocuspis bicornis ( Hincks, 1881) (see below). Specimens examined by Marcus at the NHMUK (1969.1.20.5) have one branched spine overarching the opesia and are assigned to A. bellula . The specimen from Pernambuco identified as Electra bellula var. bicornis (NHMUK 1888.4.16.26) has a medial branched spine and it belongs to A. bellula .

Colonies of A. bellula from Alagoas have zooids with a variable number of spines, variants of the typical form described by Hincks (1881, pl. 8, fig. 1), with one to three pairs of spines on the gymnocyst. Specimens found on Sargassum are lightly calcified, uni- or biserial, rarely multiserial; usually a branched spine occurs over the opesia, and two to four pairs of additional spines are found on the gymnocyst. The second and third pairs of spines are usually longer and slender; a single spine placed close to the branched spine can also be found. In specimens found on red algae only two pairs of smaller spines at the distal end of the opesia may occur, on either side of the operculum, and another two spines variable in size, smaller and stronger than those from colonies encrusting Sargassum spp. were found. These single spines at the proximal gymnocyst (except those between the branched spines) were not observed in A. bicornis .

Distribution. Arbocuspis bellula is found on algae; it is likely a widespread (tropical and subtropical) species complex. This is the first record of the species in Alagoas.

Figures

FIGURES 24 – 27. Species of Arbocuspis from Maceió: 24 – 25, Arbocuspis bellula, Maceió, Alagoas Brazil; 24, group of zooids on algae; 25, close-up of three autozooids showing the frontal spines; 26 – 27, Arbocuspis bicornis, Maceió, Alagoas, Brazil; 26, group of zooids on red algae; 27, close-up of the autozooids showing the frontal spines.