Brookula Iredale, 1912

Absalão, Ricardo S., Miyaji, Cintia & Pimenta, Alexandre D., 2001, The genus Brookula Iredale, 1912 (Gastropoda, Trochidae) from Brazil: description of a new species, with notes on other South American species, Zoosystema 23 (4), pp. 675-687 : 677-681

Genus Brookula Iredale, 1912

Brookula Iredale, 1912: 219 .

TYPE SPECIES. — Brookula stibarochila Iredale, 1912: 220 by original designation (holotype’s photograph in Clarke 1961: pl. 1, fig. 5).

DIAGNOSIS. — Shell small, globose-turbinate, thin, umbilicate, with inflated whorls. Protoconch smooth or sculptured with anastomosing ribs forming microscopic pits or with irregular wart-like concretions. Axial sculpture dominant; raised spiral sculpture welldefined, but weaker, in some species overriding and forming beads at intersections with axial ribs; fine incremental growth lines are present. Suture deeply constricted. Aperture rounded, slightly oblique, with a slightly thickened lip and complete peritreme.

REMARKS

The genus Brookula was created by Iredale (1912), based on Brookula stibarochila , to include certain species that he could not place in any other genus of Cyclostrematidae . Cyclostrema conicum Watson, 1886 , was a member of that group. Clarke (1961) divided the species of Brookula into three subgenera: Brookula sensu stricto; Vetulonia Dall, 1913 (type-species: Vetulonia galapagana Dall, 1913 ); and Benthobrookula Clarke, 1961 (type-species: Brookula (Benthobrookula) exquisita Clarke, 1961 ).

Warén (1992) regarded Brookula as belonging to the family Trochidae , subfamily Eucyclinae (sensu Hickman & McLean 1990: 74, 75) and raised the taxon Benthobrookula Clarke, 1961 to generic level, considering it as probably related to Lissotesta Iredale, 1915 , because of the protoconch type shared by both taxa. However, Warén (1992: 170) expressed doubts whether that type of protoconch is a “synapomorphy or caused by modification in the larval development”. The subfamily Eucyclinae is largely characterized by the radulae (diagnosis in Hickman & McLean 1990), but we have no information about radulae from local Brazilian Brookula species. In the other hand, the radulae of B. powelli ( Clarke 1961: pl. 4, fig. 9) seems to fit well within the definition given by Hickman (1998: 680) for this subfamily. Therefore, we follow Hickman & McLean (1990) in considering the genus Brookula as included in the subfamily Eucyclinae , but regard all species herein treated as belonging to the genus Brookula sensu lato, because of the insufficiently well-established supraspecific classification, even in a conchological sense.

Among the South American species of Brookula , there are two or perhaps three recognizable kinds of protoconch sculpture. Brookula calypso , B. powelli and B. exquisita have protoconchs consisting of a surface covered by very low, irregular wart-like concretions ( Fig. 1B, D, F ). This kind of protoconch ornamentation differs from that found in the three species discussed in this paper ( B. conica , B. pfefferi , and B. spinulata n. sp.), which consists of very fine and densely crowded anastomosing ribs, forming microscopic pits in a somewhat alveolar pattern ( Figs 2F, G ; 4 E-G; 5G). A third pattern seems to be present in the topotype of B. stibarochila (figure in Warén 1992: 224, fig. 23B), which shows an apparently smooth protoconch surface.

Beside the Brazilian species reported herein, additional species from southwestern Atlantic and adjacent Antarctic waters have been, elsewhere, referred to Brookula . We give a brief summary of some of them:

1. Cyclostrema liratula Pelseneer, 1903 and Cyclostrema humile Pelseneer, 1903 , were includ- ed in Brookula by Carcelles (1953). However, these species do not fit the genus Brookula as defined herein, since they lack axial sculpturing and have only spiral sculpture. Both species were referred to Lissotesta Iredale, 1915 by Warén (1992);

2. Brookula crassicostata ( Strebel, 1908) . Described from 54°43’S, 064°08’W, 36 m. According to a syntype (ZMH), B. crassicostata shows no trace of spiral sculpture, having only low and strong rounded ribs. This species was illustrated by Castellanos & Landoni (1989: 12, fig. 1a, b, c) and, according Warén (in litt.) this species fits in the Liotella Iredale, 1915 concept; 3. Brookula decussata ( Pelseneer, 1903: 19, pl. 5, fig. 48). Described from the Bellingshausen Sea (70ºS, 080º48’W, 500 m). The type for this species has not been located, and our comparisons to the Brazilian species are based on the original description and figure;

4. Brookula rossiana Dell, 1990: 102 , fig. 169 and Brookula antarctica Dell, 1990: 102 , fig. 170. Both described from the Ross Sea, at 362 m. Although the original description of B. rossiana fits very well in our concept for B. pfefferi , considering the scope of variation we found in the latter, we do not feel secure to consider them co-specific since we could not exam the holotype of B. rossiana and the original figure provided by Dell (1990) does not allow a precise evaluation of their conchological characters. On the other hand, the description of B. antarctica suggests it to be distinct enough to be consider as a valid species; 5. Brookula lamonti Clarke, 1961: 357 , pl. 4, fig. 3. Described from the Scotia Sea, around 96 km south of South Georgia, at 3758 m. Although the holotype (MCZ 225963) is only a shell fragment, some parts of the shell sculpture, the aperture (partly broken), and the umbilicus are still visible. The narrow umbilicus and the somewhat posteriorly angled aperture are the distinctive characters, although the sculpture pattern shows no distinctions from B. pfefferi ;

6. Brookula calypso ( Melvill & Standen, 1912: 345, fig. 3). Described from Burdwood Bank, 54°25’S, 057°32’W (at 102 m). We illustrate the holotype ( RSM 143.599 ) ( Fig. 1A, B ) ; 7. Brookula powelli Clarke, 1961: 355 , pl. 3, fig. 7; pl. 4, figs 1, 9. Described from the mid- Argentine Basin, around 1609 km east-southeast of Buenos Aires, at 4587 m. We illustrate the holotype ( MCZ 224960 ) ( Fig. 1C, D ). There are also paratypes at MCZ and NMC ;

8. Brookula exquisita Clarke, 1961: 356 , pl. 3, fig. 8; pl. 4, fig. 2. Described from around 96 km south of South Georgia, at 3758 m. We illustrate the holotype ( MCZ 225964 ) ( Fig. 1E, F ). There is also a paratype at NMC 4742 .

Brookula conica ( Watson, 1886) ( Fig. 2 )

Cyclostrema conicum Watson, 1886: 122 , pl. 8, fig. 9.

Brookula conica – Rios 1994: 39, pl. 12, fig. 128.

TYPE MATERIAL. — Three syntypes ( BMNH 1887. 2.9.432).

TYPE LOCALITY. — Off Pernambuco, Brazil, stn 120, 08°37’S, 034°28’W, 1235 m. — Stn 122, 09°05’S, 034°50’W, 640 m.

MATERIAL EXAMINED. — The photograph of the syntype herein figured and:

PADCT. [15], 28°00.05’S, 046°59.67’W, 490 m, 29.XI.1997 ( IBUERJ 1519 : # 6608) ; [50], 27°10.38’S, 047°27.54’W, 129 m, 09.XII.1997 ( IBUFRJ 10872 : # 6635) ; [20], 24°17.13’S, 044°12.15’W, 163 m, 10.I.1998 ( MNRJ 8423 ) ; [25], 25°15.76’S, 45°04.62’W, 124 m, 21.XI.1997 ( MORG 41033 : # 6577) ; [2], 23°35.82’S, 041°42.42’W, 143 m, 15.XI.1997 ( MZSP 32480 : # 6541) ; [225], 24°12.74’S, 044°58.98’W, 79 m, 20.XI.1997 ( MZSP 32481 : # 6571) ; [3], 24°42.61’S, 044°43.42’W, 155 m, 20.XI.1997 ( MZSP 32482 : # 6573) ; [25], 25°15.76’S, 45°04.62’W, 124 m, 21.XI.1997 ( MZSP 32483 : # 6577) ; [5] (24°42.30’S, 045°18.83’W, 84 m, 21.XI.1997 ( MZSP 32484 : # 6579) ; [2] 25°17.66’S, 046°21.16’W, 81 m, 26.XI.1997 ( MZSP 32485 : # 6587) ; [55], 26°23.55’S, 046°39.49’W, 175 m, 27.XI.1997 ( MZSP 32486 : # 6595) ; [68], 27°48.07’S, 047°24.04’W, 175 m, 29.XI.1997 ( MZSP 32487 : # 6606) ; [14], 28°00.05’S, 046°59.67’W, 490 m, 29.XI.1997 ( MZSP 32488 : # 6608) ; [2], 23°57.99’S, 043°52.56’W, 133 m, 07.XII.1997 ( MZSP 32489 : # 6627) ; [51], 27°10.38’S, 047°27.54’W, 129 m, 09.XII.1997 ( MZSP 32490 : # 6635) ; [1], 25°49.30’S, 046°34.00’W, 128 m, 11.XII.1997 ( MZSP 32491 : # 6642) .

REVIZEE. [1], 25°51.04’S, 045°47.30’W, 206 m, 15.XII.1997 ( MZSP 32492 : # 6652) ; [9], 25°43.50’S, 046°02.50’W, 155 m, 15.XII.1997 ( MZSP 32493 : # 6653) ; [1], 24°17.68’S, 043°48.20’W, 314 m, 09.I.1998 ( MZSP 32494 : # 6660) ; [150], 24°00.95’S, 043°55.54’W, 135 m, 09.I.1998 ( MZSP 32495 : # 6662) ; [4], 24°26.48’S, 044°06.55’W, 500 m, 10.I.1998 ( MZSP 32496 : # 6664) ; [30], 24°17.13’S, 044°12.15’W, 163 m, 10.I.1998 ( MZSP 32497 : # 6666) ; [3], 23°55.40’S, 044°24.45’W, 107 m, 10.I.1998 ( MZSP 32498 : # 6668) ; [22], 24°07.42’S, 044°42.22’W, 101 m, 11.I.1998 ( MZSP 32499 : # 6669) ; [2], 24°32.91’S, 044°27.46’W, 260 m, 11.I.1998 ( MZSP 32500 : # 6671) ; [1], 24°40.75’S, 044°50.82’W, 137 m, 12.I.1998 ( MZSP 32501 : # 6677) ; [1], 25°10.00’S, 044°56.65’W, 167 m, 12.I.1998 ( MZSP 32502 : # 6681) .

REDESCRIPTION

Shell trochiform, reaching 1.8 mm in height, 1.83 mm in width; spire elevated, umbilicate, color white. Protoconch globose, around one and a half whorls, about a half emerged from first teleoconch whorl, and sculptured with fine, densely crowded anastomosing ribs forming microscopic pits in a somewhat alveolar pattern. Teleoconch with up to two whorls, with convex profiles. Suture deep. Axial sculpture consisting of heavy, narrow, slightly prosocline axial ribs (19 on last whorl of syntype, illustrated herein), ribs continuing through base of shell, reaching umbilical region; microscopic axial lines present through interspaces. Spiral sculpture formed by about 20 (last whorl + base) prominent, thin, regularly spaced, revolving cords, cords crossing axial ribs; spirals forming no stronger cords surrounding umbilicus. Aperture rounded, holostomate. Umbilicus large, circular, deep. Outer lip thin.

REMARKS

Brookula conica is the only member of the genus previously recorded off Brazil, and seems to be one of the few Brookula species associated with tropical environments.

The type series of B. conica includes three syntypes, two of them broken (K. Way in litt.). Although we had access to a photograph of only one of the type specimens of B. conica ( Fig. 2A ), which is glued on a piece of cardboard and does not show the spire, protoconch, or sculpturing, the original description and illustrations ( Watson 1886) provide good representation of this species. This allowed us to recognize a large number of shells of B. conica from different localities along the Brazilian coast, and to redescribe the species. Our redescription includes several characters not mentioned by Watson (1886), such as the protoconch microsculpture ( Fig. 2F, G ), minor details of the shell sculpture ( Fig. 2E ), and an evaluation of the variability in shell shape (h/w varying from 0.9 to 1.11, see Table 1). We found that the number of axial ribs varies from 15 to 27 ( Table 1), which fits well with the number (15- 25) reported by Watson (1886).

Brookula conica can be distinguished from all other species previously reported from the South Atlantic by the absence of keels or spiral cords bordering or entering the umbilicus ( Fig. 2B ).

Figures

FIG. 1. — Holotypes of Brookula species from southeast South American coast; A, B, Brookula calypso Melvill & Standen, 1912 (RSM 153599); A, apertural view; B, protoconch detail; C, D, Brookula powelli Clarke, 1961 (MCZ 224960); C, apertural view; D, protoconch detail; E, F, Brookula exquisita Clarke, 1961 (MCZ 225964); E, apertural view; F, protoconch detail. Scale bars: 200 µm.

FIG. 2. — Brookula conica (Watson, 1886); A, syntype (BMNH 1887.2.9.432); B-G, Brazilian material (all from MZSP 32495); B, basal view; C, apertural view; D, apical view; E, sculpture detail of last adult whorl; F, protoconch; G, protoconch sculpture detail. Scale bars: A-F, 100 µm; G, 20 µm.

FIG. 4. — A-D, F, G, Brookula pfefferi Powell, 1951; A, C, from MZSP 32504; B, D, F, G, from MZSP 32506; E, holotype of B. strebeli Powell, 1951; A-C, basal view of three specimens showing the variation on the spiral cords; D, apical view; E-G, protoconch sculpture detail. Scale bars: A-C, 250 µm; D-G, 100 µm.