26 



A.V. SYSOEV 



Gymnobela adenica Sysoev, new species 



Figs 1 06 & 107 



MATERIAL, stn 185, 2 specimens (holotype No. 1993112 and 

 paratype No. 1993113). 



Description of holotype. The shell is small, broadly biconic, 

 thin, yellowish-white, and consisting of 5 remaining whorls. The 

 protoconch is missing, and the upper teleoconch whorls are 

 eroded. The whorls are angled below the periphery. The 

 subsutural slope is almost flat on the upper spire whorls and 

 concave on the body whorl. The uppermost part of subsutural 

 slope is slightly raised forming an indistinct subsutural fold. The 

 sutures are shallow. Growth lines are mostly indistinct, some of 

 them form clear, narrow, oblique folds regularly set on the upper 

 third of the subsutural fold and approximately twice as 

 numerous as main axial folds. The latter are strongly oblique, 

 narrow, with sharpened crests, and tuberculate at the place of 

 whorl angulation. The folds are separated by narrow intervals, 

 abruptly disappear on the subsutural slope and extend to the 

 lower suture on the spire whorls and to the upper part of the 

 shell base. There are 21 folds on the body whorl and 20 on the 

 penultimate. Spiral ribs (about 30 on the body whorl plus canal) 

 are strong, flattened and uniform except for narrower ones on 

 the canal. Intervals between the ribs are approximately equal to 

 ribs in width. The subsutural slope is densely covered with thin, 

 low, rounded and closely set riblets (about 14 on each of two last 

 whorls). The shell base with a distinct bend passes into a short 

 and straight canal. The aperture is rather small, subrectangular, 

 with the inner lip distinctly bent. The canal is narrow, attenuated 

 at its end. The anal sinus is moderately deep, broadly rounded, 

 its deepest point is situated in the middle of subsutural slope. H 

 = 9.5, Hb = 6.9, Ha = 5. 1 , D = 6.0 mm. 



The paratype is very similar to the holotype except for smaller 

 size (H = 7.1, D = 5.3 mm, 3 teleoconch whorls), smaller H/D 

 ratio, and longer folds formed by growth lines which often 

 occupy the whole subsutural slope. There are 24 main axial folds 

 on the body whorl. The last protoconch whorl preserved is 

 covered with typical diagonally cancellated sculpture. 



The species differs from other species of the genus in its small 

 broadly biconic shell with numerous strongly oblique axials and 

 short attenuated canal. 



Distribution. Gulf of Aden, 2000 m. 



Subgenus BATHYBELA Kobelt, 1905 



Type species: Thesbia nudator Locard, 1897 (subsequent 

 designation Dall, 1918) 



Gymnobela ( Bathybela) africana Sysoev, new species 



Figs 109-1 11 



Material, stn 1 18, 1 specimen (holotype, No. 19931 14) and 1 

 shell (No. 1993115). 



Description of holotype. The shell is large, broadly 

 fusiform, thin but solid, reddish-brown to light-brown, and with 

 a slightly glossy surface. It consists of 6 whorls, the protoconch is 

 missing. The whorls are obtusely angled above the periphery, 

 moderately convex below the angulation and slightly concave 

 above it. The sutures are rather shallowly impressed, clear, 

 straight or wavy in some places. The body whorl is large, 



occupies about 0.7 of the shell height; the shell base is weakly 

 convex, with a distinct bend passes into the straight canal. The 

 axial sculpture consists of narrow oblique folds, often with 

 sharpened crests. The folds begin in the lower part of the 

 subsutural slope and extend to the lower suture on the spire 

 whorls and only to the periphery on the body whorl. They are 

 most prominent in the place of the whorl angulation. There are 

 1 7 folds on the body whorl and 1 5 on the penultimate one. The 

 growth lines are indistinct on the whorl surface except the 

 subsutural slope, some of them are thickened and raised. The 

 thickened growth lines, however, do not form the regularly 

 arranged plicae on the subsutural slope which are characteristic 

 of many deep-sea Daphnellinae. The spiral sculpture is 

 represented by rather wide, flattened, wavy ribs unequal in size 

 and separated by narrow grooves. The subsutural slope is 

 smooth except for several very feeble spiral lines. The aperture is 

 broad, the inner lip forms a distinct bend, and the columella is 

 twisted. The anal sinus, judging from the growth lines, is shallow 

 and broad, its deepest point is situated immediately above the 

 middle of subsutural slope. The dried soft body has no 

 operculum. 



H = 54.7, Hb = 38.5, Ha = 30. 1 , D = 22.7 mm. 



The shell of the paratype is larger than in the holotype (H = 

 68.0, Hb = 48.2, Ha = 38.5, D = 30.0 mm). It was dead-collected 

 and the surface is rather worn. The paratype differs from the 

 holotype mainly in its shorter axial folds developed on the body 

 whorl only at the place of angulation and obsolete in the last 

 quarter of body whorl, and in the canal curved backwards. 



The new species is rather similar to Spergo sibogae Schepman, 

 1913 from Indonesia differing in much broader shell (H/D = 3.0 

 in S. sibogae and 2.3-2.4 in G. africana). It also shows some 

 similarity to Pontiothauma pacei E.A.Smith, 1906 from India 

 and Ceylon differing in somewhat more slender shell with short 

 axial folds and faint spiral sculpture. 



Distribution. East Africa eastward of Mombasa, 1789 m. 



Subgenus THETA Clarke, 1959 



Type species: Pleurotomella (Theta) Iyronuclea Clarke, 1959 

 (original designation) 



Gymnobela (Theta) daphnelloides (Dall, 1895) 



Figs 1 13 & 114 



Mangelia (Spergo) daphnelloides Dall, 1895, p. 683-684, pi. 31, 

 fig. 11. 



Type locality. 'Albatross', stn 3476 (Hawaiian Islands), 298 

 fms. 



Material, stn 118, 1 shell. 



The species was originally described within the subgenus Spergo 

 which is considered as a full genus by all modern authors. 

 However the species differs from the type species of Spergo, 

 Mangilia (Spergo) glandiniformis (Dall, 1895), in all important 

 conchological characters included by Dall in the original 

 diagnosis of the subgenus (the latter was based to a considerable 

 extent on the soft body characteristics which are presently 

 treated as insignificant for taxonomy at the generic level), i.e. in 

 having well developed sculpture and rather deep anal sinus. On 

 the other hand, the species is very similar to the group of species 

 assigned by Bouchet & Waren (1980) to the genus Theta. The 



