Brookula bohni, Schwabe, Enrico & Engl, Winfried, 2008

Schwabe, Enrico & Engl, Winfried, 2008, Description of two new deep­water species of the genus Brookula Iredale, 1912 (Mollusca, Gastropoda, Trochoidea), with a revision of the genus for the Subantarctic and Arctic Sector of the Atlantic Ocean *, Zootaxa 1866, pp. 187-204 : 196-198

Brookula bohni sp. nov.

( Figs 7–8 )

Type material

Holotype ( ZSM Mol 20070895), leg. Katrin Linse, February 4 2002, ANT XIX/3 (ANDEEP I).

Paratypes, one from type locality ( ZSM Mol 20021185). Two paratypes ( ZSM Mol 20021177) Antarctica , Drake Passage, St. PS 61 / 042–02 (59°40.29’S 57°35.43’W to 59°40.42’S 57°35.27’W), 3680–3683 m, Katrin Linse, January 27 2002, ANT XIX/3 (ANDEEP I). Besides the SEM­mounted holotype, all other specimens are fixed and preserved in 96% ethanol.

Type locality: Antarctica , South Shetlands, St. PS 61/043–08 (60°27.12’S 56°05.10’W to 60°27.18’S 56°04.80’W), 3959–3961 m ( Fig. 8 ).

Etymology: The species is named after our friend Jens Michael Bohn (ZSM), a holothurian specialist and participant of the relevant expeditions. We selected his surname because his nickname is “ Bohni ”.

Description: Shell minute, up to 1.30 mm long, 1.28 mm wide ( Fig. 7A ), globosely turbinate, fragile, translucent white in color, with inflated whorls slightly depressed at the shoulder, slightly expanded laterally, low spired, spire angle ranging from 80° (smallest paratype) to 85° (holotype). Protoconch ( Fig. 7D ) of 1.25 whorls, 280 µm in diameter, 100 µm high, globose, sculptured with fine anastomosing threads, forming microscopic pits of irregular arrangment. Teleoconch ( Figs 7A, C ) of up to 2.75 whorls with convex profile. Suture incised. Last adult whorl globose, slightly depressed at shoulder. Aperture oval, peritreme holostomate, although very weak at periphery of preceeding whorl; with thick inner, thin outer lip. Shell base roundly inflated. Umbilicus ( Fig. 7B ) tightly open, circular, deep. Axial sculpture of narrow ribs, ranging from 29 (largest paratype) to 31 on last whorl in holotype, 25 on penultimate whorl. Ribs regularly spaced, rounded, low, interspaces about three times rib width. Spiral sculpture of numerous flat threads, seven on first teleoconch whorl, about 12 on last adult whorl, narrower than axial ribs, crowded in upper and lower half of whorl, centrally absent (in the two small paratypes) or interrupted by distinctly separated slightly higher spirals, not overlaying the axial ribs distally. Nine flat spirals, two spiral cords (with inner being largest), which surround umbilicus, at shell base. Operculum circular, multispiral, with centric nucleus.

Comparisons: Brookula spinulata Absalão, Miyaji & Pimenta, 2001 differs in 1) its coarse sculpture with spinulate projections at the axial ribs, 2) the presence of fine axial lines between the spiral threads, 3) the lower number (6 vs 12) of spirals on the last body whorl, despite the general larger size, 4) the lower number (20 vs 29–31) of axial ribs.

Brookula calypso (Melvill & Standen, 1912) differs in 1) having cancellate sculpture, built up by regularly arranged axial ribs and spiral threads, 2) the presence of small axial threads between the axial ribs, 3) having a slightly larger protoconch (295 vs 280 µm) although it has only one whorl, 4) having a larger spire angle (90 vs 85°), 5) having a shallow suture.

Brookula powelli Clarke, 1961 differs in 1) shell proportions (0.81–0.93 vs 0.91–1.11, SL/SW ratio), 2) the lesser acute spire angle (min. 93.5 vs max. 85°), 3) the wider umbilicus (440 vs 135 µm), 4) the larger protoconch (one whorl of c. 350 µm vs 1.25 whorl of 280 µm), 5) the higher number of axial ribs at last whorl (37 vs 29–31), 6) the round vs oval aperture.

The oval aperture and the characteristic sculpture make the species easily separable from the remaining Antarctic congeners.

Figures

FIGURE 7: A – D, Holotype of Brookula bohni sp. nov. (ZSM Mol 20070895) Antarctica, South Shetlands, St. PS 61 / 043 – 08 (60 ° 27.12 ’ S 56 ° 05.10 ’ W to 60 ° 27.18 ’ S 56 ° 04.80 ’ W), 3959 – 3961 m. A, Ventral view of the complete shell. B, View of the shell base showing the narrow opening of the umbilicus. C, Apical view to show the protoconch and the teleoconch whorls. D, Detail of fig. C to show the fine protoconch ornamentation. Scale bars: 100 µm.

FIGURE 8: The geographic distribution of Brookula bohni sp. nov. with a 2500 m depth contour in light grey.