Brookula pfefferi Powell, 1951

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 : 681-685

Brookula pfefferi Powell, 1951

( Figs 3; 4)

Brookula pfefferi Powell, 1951: 104 , pl. 5, fig. 8. — Carcelles 1953: 170. — Castellanos & Landoni 1989: 8, pl. 5, fig. 5.

Brookula strebeli Powell, 1951: 104 , pl. 5, fig. 7. — Carcelles 1953: 170. — Castellanos & Landoni 1989: 7, 8, pl. 5, fig. 7.

Brookula sinusbreidensis Numanami & Okutani, 1991: 39 , figs 2-6.

Brookula delli Numanami, 1996: 55 , figs 30A-E.

TYPE MATERIAL. — Holotype of B. pfefferi ( BMNH 1961.368); holotype of B. strebeli ( BMNH 1961.369); described from off the mouth of Stromness Harbor, South Georgia (from 54°04’S, 036°27’W to 53°58’S, 036°26’W, 155-178 m); holotypes of B. sinusbreidensis (NSMT-Mo 69595) and B. delli (NSMT-Mo 70613); both described from Breid Bay, Antarctica.

TYPE LOCALITY. — Off mouth of Stromness Harbour, South Georgia, from 54°04’S, 036°27’W to 53°58’S, 036°26’W, 155- 178 m.

MATERIAL EXAMINED. — Holotypes of Brookula sinusbreidensis and Brookula delli ; holotype photographs of Brookula pfefferi and Brookula strebeli and:

PADCT. [1], 27°18.28’S, 047°08.77’W, 228 m, 28.XI.1997 ( MZSP 32503 : # 6601) ; [5], 27°48.07’S, 047°24.04’W, 175 m, 29.XI.1997 ( MZSP 32504 : # 6606) ; [1], 26°30.99’S, 046°15.27’W, 474 m, 02.XII.1997 ( MZSP 32505 : # 6622) .

REVIZEE. [5], 25°53.58’S, 045°42.13’W, 256 m, 15.XII.1997 ( MZSP 32506 : # 6651) ; [1], 25°51.04’S, 045°47.30’W, 206 m, 15.XII.1997 ( MZSP 32507 : # 6652) ; [1], 24°17.68’S, 043°48.20’W, 314 m, 09.I.1998 ( MZSP 32508 : # 6660) ; [2], 24°00.95’S, 043°55.54’W, 135 m, 09.I.1998 ( MZSP 32509 : # 6662) ; [1], 24°49.70’S, 044°44.97’W, 153 m, 12.I.1998 ( MZSP 32510 : # 6676) .

REDESCRIPTION

Shell trochiform, reaching 1.8 mm in height, 1.6 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 three-quarter whorls, with convex profiles. Axial sculpture consisting of narrow, orthocline ribs (38 on last whorl of holotype), ribs continuing through base of shell, reaching umbilical region; microscopic axial lines present through interspaces. Spiral sculpture formed by prominent, thin, irregularly spaced, revolving threads (11 on last whorl of holotype), threads crossing axial ribs and present on base (10 on base of holotype), forming two or three moderately strong cords surrounding umbilicus. Aperture rounded, holostomate. Umbilicus circular, deep. Outer lip thin.

REMARKS

Clarke (1961: 358) stated that B. strebeli and B. pfefferi “[...] are so similar to each other that they appear to represent the same species”. In fact, it is not possible to distinguish the type of B. strebeli ( Fig. 3B) from the type of B. pfefferi ( Fig. 3A). Powell (1951), when describing the species, stated that B. pfefferi is umbilicate, while B. strebeli is imperforate; however, an umbilicus is clearly present in the holotype of B. strebeli ( Fig. 3B); besides that, any known Brookula species lack an umbilicus. Secondarily, there are also subtle differences in the ornamentation and h/w ratio, but those are due to intraspecific variation ( Fig. 3 A-C, E; Table 2).

Brookula sinusbreidensis Numanami & Okutani, 1991 and Brookula delli Numanami, 1996 fit the concept herein adopted to B. pfefferi ; the number of spiral threads in the holotypes of both taxa is encompassed by the intraspecific variation present in B. pfefferi (compare Figs 3; 4 A-C in this work and Numanami & Okutani 1991: 39, figs 2-6 and Numanami 1996: 56, fig. 30A-D). The apparent weaker axial and spiral sculpture in the holotype of B. sinusbreidensis is due to its erod- ed surface. The protoconchs of the types of both B. sinusbreidensis and B. delli are a little larger than the protoconch of B. pfefferi (1.75, 1.75 and 1.5 whorls, respectively) but the sculpture pattern in B. delli ( Numanami 1996: fig. 30C, E) is identical to that in B. pfefferi ( Fig. 4 E-G). The protoconch sculpture in B. sinusbreidensi ( Numanami & Okutani 1991: 39, fig. 6) described as smooth by the author is due to the general eroded state of the shell.

The spiral threads on the base of B. pfefferi may be evanescent cords, or cords regularly spaced near the umbilical region ( Fig. 4 A-C and Numanami 1996: fig. 30D). Brookula pfefferi bears three or four cords surrounding the umbilicus, one or two of them entering the umbilicus, the others surrounding it. Those cords distinguish B. pfefferi from B. calypso , B. decussata , and B. conica , since these species lack umbilical cords (as noted by Clark 1961: 357 for B. calypso ).

Although the Brazilian material could not be distinguished from the type of B. pfefferi on the basis of sculpture (see cline variation in Fig. 3 A-C, E and Fig. 3D, F), e.g., axial ribs varying from 27 to 40, spiral sculptures in the last whorl varying from 6 to 12 and base spirals varying from 6 to 11; it does have a consistently lower h/w ratio (1.01, sd = 0.04, Table 1) than that of the types of B. pfefferi (1.11), B. strebeli (1.15), B. sinusbreidensis (1.16) and B. delli (1.17) ( Table 2). For now, until more material from both the type localities and the Brazilian continental shelf becomes available for study, we have determined the Brazilian specimens as B. pfefferi .