Liotipoma McLean & Kiel, 2007

Mclean, James Hamilton, 2012, New species and genera of colloniids from Indo-Pacific coral reefs, with the definition of a new subfamily Liotipomatinae n. subfam. (Turbinoidea, Colloniidae), Zoosystema 34 (2), pp. 343-376 : 347-352

Genus Liotipoma McLean & Kiel, 2007

Liotipoma McLean & Kiel, 2007: 259 .

TYPE SPECIES. — Liotipoma wallisensis McLean & Kiel, 2007 (by original designation).

DESCRIPTION

(REVISED FROM MCLEAN & KIEL, 2007)

Shell small (maximum diameter 6.8 mm), nonnacreous; aperture round; lip massively thickened and projecting, with inward extension, the tongue that partially blocks aperture in male shell; shell profile low, with projecting mid-whorl angulation and projecting subtending cord that forms lowermost projection of base. Sculpture axial and spiral; axial sculpture of raised ridges, overriding spiral sculpture; spiral sculpture of cords that terminate on outer face of final lip. Base with broad low cord in the umbilical area, the emergent cord, separated by narrow groove from prominently projecting subtending cord. Axial micro-sculpture of sharply raised lamellae throughout, strongly expressed as layers across thickened final lip. The calcified periostracum (intriticalyx) of most Liotiidae is also expressed in Liotipoma . Most specimens are sufficiently worn to not show the surface layer, but it clearly shows in the SEM view of Figure 12 E-G. Whorl diameter in some species expanding in final quarter whorl, mature lip arising abruptly, projecting, strongly thickened; lamellar deposition that forms final lip decreasing in diameter toward final position and showing terminations of spiral sculpture extending across thickened lip. Aperture nearly radial (only slightly oblique); umbilicus open in juvenile shell; umbilical wall with extension of axial sculpture, with inwardly projecting spines corresponding to axial ribs ( Fig. 12G ). Mature shell of Liotipoma species sexually dimorphic; umbilicus of male shell blocked with massive tongue, extending from inner edge of thickened lip. Female shell with open umbilical cavity, reduced tongue, bordered on outside by raised subtending cord, enlarged for brooding of larval stages.

Protoconch ( Fig. 1 ) diameter 320 µm, with fine longitudinal ridges and flared final expansion, positioned at same level as first teleoconch whorl. Axial sculpture arising in first teleoconch whorl next to protoconch in first quarter whorl, projecting at periphery (to give a spinose effect in umbilical and apical views) and clumped to project into umbilicus and clumped to form early subtending cord. Most of the figured specimens are sufficiently worn to obscure protoconch sculpture. The assumption is made that protoconchs of all species are like those shown in Figure 1 .

Operculum ( Fig. 2 ) calcareous, with deep central pit of ⅓ to ∕₄ its diameter; outer area raised, with radial, somewhat irregular rugose sculpture separated by deep radial channels; interior surface low conical, with narrow, raised multispiral volutions and long growing edge.

Radula unknown (live-collected specimens unknown).

DISTRIBUTION. — Central Indo-Pacific, sublittoral, reef-associated. Records for Liotipoma include Fiji, Wallis Island, Papua New Guinea, New Caledonia, Loyalty Islands (east of New Caledonia), and Vanuatu at Espiritu Santo. Three sympatric species are known from Lifou, Loyalty Islands ( L. mutabilis n. sp., L. dimorpha n. sp., and L. lifouensis n. sp.).

REMARKS

Liotipoma is characterised by the operculum with deep, broad central pit, conical inner surface with raised multispiral ridges; and by the shell with fine axial lamellae, the massive final lip produced by the abruptly expanded diameter of final whorl, with incremental lamellar layers decreasing in size; axial ribs are stronger than the spiral cord. The umbilicus in male shells is usually blocked by the massive extension of the inner lip, here called the tongue.

The surface sculpture of Liotipoma has axial lamellae and other sculpture comparable to that of Liotiidae . Without knowledge of the operculum, this genus would surely be placed in the Liotiidae . Most of the available specimens show some wear and encrustation.

Mature shells are large enough that illustration with SEM is not a necessity. An unusually clean, but immature (3.3 mm in diameter) specimen of L. solaris n. sp. is presented in Figure 12 E-G, showing intricate spines in the umbilical area that represent the termination of axial sculpture, as also expected in Liotiidae .

In most liotiid genera, whorl expansion stalls or retreats at the final stage,still allowing for an expanded lip. The species of Liotipoma differ in showing an increase in whorl expansion in addition to the whorl expansion resulting from the final projecting lip.

Shells of this genus are probably represented in other museum and private collections among undetermined micro-gastropods from Indo-Pacific localities,no doubt thought to be small species of Liotiidae .Live-collected specimens are unknown but the operculum is now known from single immature shells of three species, in which it is wedged in place ( Fig. 2 ).

SHELL CHARACTERS

Size

Maximum diameter ranges from 4.0 ( Liotipoma dimorpha n. sp., Fig. 6 E-H) to 6.8 mm ( L. magna n. sp., female shell, Fig. 9 ). This is usually a reliable species level character, with about a 1 mm allowance for variation in shell diameter.

Shell height

Most shells thought to represent females are noticeably higher in profile that those of male shells. These distinctions are evident from the dimensions provided in the captions for the illustrations.

Whorl count

Whorl count ranges from 2.6 to 3.3 teleoconch whorls, as determined in apical view.Smaller species generally have fewer whorls.

Count of axial ribs for final whorl

Axial ribs on the final whorl (not including the closely spaced lamellae of the body whorl and the massive final lip) number from 21 to 33. Counts can be made from spire views or from basal views. Some specimens exhibit sudden changes in the spacing of axials (e.g., L. magna n. sp., Fig. 8 A-D); others may have more closely spaced axials in the pre-terminal condition. This character is considered least reliable as a species level character, in view of the sudden changes observed in some specimens.

Peripheral spines

In most species, the peripheral spines produced by axial sculpture in basal view are directed slightly forward; in some they are pointed straight out, and in one specimen of one species ( L. lifouensis n. sp., Fig. 10 A-D), the spines are directed backward, but this does not apply to the second specimen illustrated here in which the spires are directed straight out ( Fig. 10 E-H). This is therefore unreliable for species distinctions.

Plane of aperture and plane of tongue

In basal view, it is apparent that the plane of the nearly radial aperture may or may not coincide with the plane of the outer edge of the tongue, the extension of the lip that blocks the umbilicus of the male shells. This is regarded as variable within the species.

Shape of tongue

In basal view the tongue is roughly triangular in outline. This is also regarded as variable within species. In one species ( L. lifouensis n. sp., Fig. 10 ), the tongue is longer and narrower than in others, and this is considered a species-level character.

Whorl expansion

In basal or spire views, species differ in the extent of whorl expansion in the final whorl. Some species have very little whorl expansion (e.g., L. solaris

n. sp., Fig. 11 A-D) and others have a more notable whorl expansion ( L. splendida n. sp., Fig. 13 A-D).

Relative strength and positioning of basal cords Some species have the emergent cord and subtending cord broad ( L. mutabilis n. sp., Fig. 4 ), in others the first basal is narrow ( L.dimorpha n. sp., Fig. 6 ). These distinctions are regarded as highly consistent for species determination.

SEXUAL DIMORPHISM

All species of Liotipoma are considered to be sexually dimorphic, although the available material of most species includes a recognisable female shell in only four of the eight species ( L. wallisensis , L. mutabilis n. sp., L. dimorpha n. sp., L. magna n. sp.). Female shells are unknown for the species L. lifouensis n. sp., L. solaris n. sp., L. splendida n. sp., and L. clausa n. sp.

Specimens considered as male shells have the massive tongue extending to block the umbilicus. This is not formed in female shells, which have an open umbilicus with an angular edge for the retention of egg masses and larval stages, with further protection provided by the extended body of the female.The female shell for two species better known from the male shell are shown for L. wallisensis n. sp. ( Fig. 3 E-H), and L. mutabilis n. sp. ( Fig. 4 ). In these two species the female shell seems to be worn and resorbed in the umbilical area, which is considered to have been the result of having a large egg mass and brood.

The tongue, a massive lip projection that blocks the umbilical cavity of the male shell of specimens of most species of Liotipoma gives it a predation resistant advantage over that of most species of Liotiidae , in which the open umbilical wall is thinshelled, and often is the site of drill holes made by naticid or muricid gastropods, as is evident in the drilled shells of many species.

The number of mature shells for all species of Liotipoma is limited to the material at hand, which in some species consists of very few or single specimens. Male shells are much more common than female shells and some species are known only from male shells. The few known female shells generally have a higher profile than that of male shells, which serves to expand the umbilical cavity and increase the volume available for brooding. Descriptions of the species are based on male shells, with a supplementary description of the female shells for the species in which it is now recognised.

Most species of Liotipoma have a similar general appearance, having a subdiscoidal profile with a peripheral angulation, usually two low cords on the shoulder and four cords on the base, crossed by axial ribs that form spinose projections at the periphery and extend across the shoulder and form beaded cords on intersecting the basal cords.

ARRANGEMENT OF LIOTIPOMA SPECIES

The type species in which the only known female shell is badly worn is treated first, followed by another species, in which two worn female shells are known. This is followed by two species that have the male and female shells in good condition. Species represented by male shells are treated last.

Figures

FIG. 12. — Liotipoma solaris n. sp., male shells: A-D, paratype (LACM 3109), Horseshoe Reef, Bootless Bay, Port Moresby, Papua New Guinea, 25 m, H 2.4, D 3.9 mm; E-G, SEM of immature male shell (LACM stn 85-138), Cape Washington, westernmost end of Kandavu, Fiji, 18 m, H 1.5, D 3.3 mm. Scale bars: 1 mm.

FIG. 1. — Protoconchs of Liotipoma McLean & Kiel, 2007 spp.: A, B, juvenile shell from Santal Bay, Lifou, Loyalty Islands (MNHN, stn 1434), shell diameter 2.4 mm: protoconch (A) and early whorls (B); C, protoconch of Liotipoma solaris n. sp., Cape Washington, western end of Kandavu, Fiji (LACM 85-138). Scale bars: A, 0.1 mm; B, 0.5 mm; C, 0.1 mm.

FIG. 2. — Opercula of three immature, sexually indeterminate species of Liotipoma McLean & Kiel, 2007; opercula wedged in place in all three specimens; A, B, L. wallisensis McLean & Kiel, 2007, off Wallis Island (MNHN, stn DW523), H 1.9, D 3.5 mm; C, D, inner and outer views of same operculum from immature specimen from Wallis Island, showing attached portion of columella, after breaking it free in order to show interior view; diameter of operculum 1.2 mm; E, F, L. solaris n. sp., Herald Pass, Great Astrolabe Reef, Fiji (LACM, stn 85-135), H 1.5, D 1.9 mm (SEM views of tilted specimen with operculum; apertural view is photo of coated specimen); G, Liotipoma sp., off Pointe Lefèvre, Santal Bay, Lifou, Loyalty Islands (MNHN, stn 1435), H 2.4, D 3.7 mm (specimen missing apical whorl). Scale bars: 1 mm.

FIG. 6. — Liotipoma dimorpha n. sp., male shells: A-D, holotype (MNHN 24761, stn 1442), Santal Bay, Lifou, Loyalty Islands, 47 m, H 3.0, D 4.3 mm; E-H, paratype (MNHN 24763, stn 1331), Grand Koumac Reef, Koumac Sector, New Caledonia, 55-57 m, H 2.6, D 4.0 mm. Scale bars: 1 mm.

FIG. 9. — Liotipoma magna n. sp., female shells: A-D, paratype (MNHN 24768,stn DS105), off NW side Tutuba Island, Espiritu Santo, Vanuatu,92 m,H 3.6, D 5.7 mm;E-G, paratype,off W side Tutuba Island (MNHN 24769,stn DS105),off NW side Tutuba Island,Espiritu Santo, Vanuatu, 92 m, H 3.4, D 5.3 mm. Scale bars: 1 mm.

FIG. 8. — Liotipoma magna n. sp., male shells: A-D, holotype (MNHN 24766, stn DS103), off W side Tutuba Island, Espiritu Santo, Vanuatu,70-80 m, H 3.6, D 6.8 mm; E-H, Paratype (MNHN 24767, stn DS104),80 m off W side Tutuba Island,Espiritu Santo, Vanuatu, H 3.4, D 5.3 mm. Scale bars: 1 mm.

FIG. 10. — Liotipoma lifouensis n. sp., male shells: A-D, holotype (MNHN 24770, stn 1434), male shell, Santal Bay, Lifou, Loyalty Islands,5-20 m, H 2.6, D 4.3 mm; E-H, paratype (MNHN 24771, stn 1432), male shell, Shelter Reef,Santal Bay, Lifou, Loyalty Islands, 12-32 m, H 2.9, D 4.3 mm. Scale bars: 1 mm.

FIG. 11. — Liotipoma solaris n. sp., male shells: A-D, holotype (LACM 3107, stn 91-188), Diamond Seamount, Great Astrolabe Reef, Fiji, 20-25 m, H 2.5, D 4.0 mm; E-H, paratype (LACM 3108, stn 91-188), Diamond Seamount, Great Astrolabe Reef, Fiji, 20-25 m, H 2.1, D 3.5 mm. Scale bars: 1 mm.

FIG. 13.— A-D, Liotipoma splendida n. sp.holotype,male shell (MNHN 24772,stn 1269), Doiman Reef,Touhou Sector,New Caledonia, 15-20 m, H 3.2, D 5.1 mm; E-H, Liotipoma clausa n. sp. Holotype, immature male shell (LACM 3110, stn 91-189), Herald Pass, Great Astrolabe Reef, Fiji, 15 m, H 3.0, D 4.2 mm. Scale bars: 1 mm.

FIG. 4. — Liotipoma mutabilis n. sp., male shells: A-D, holotype (MNHN 24757, stn 1435), Pointe Lefèvre, Santal Bay, Lifou, Loyalty Islands, 5-30 m, H 3.4, D 5.7 mm; E-H, paratype (MNHN 24758, stn 1436), Gaatcha Bay, Santal Bay, Lifou, Loyalty Islands, 10-20 m, H 3.0, D 5.1 mm. Scale bars: 1 mm.

FIG. 3. — Type species of Liotipoma McLean & Kiel, 2007, L. wallisensis McLean & Kiel, 2007, male and female shells: A-D, holotype, male shell (MNHN 24754, stn DW523), off Wallis Island, NE of Fiji, 455-515 m (depth for this and the following specimen probably represents down slope fall from shallow water), H 2.0, D 4.1 mm; E-H, paratype, female shell (MNHN 24756, stn DW601), off Wallis Island, 350 m, H 2.6, D 4.4 mm. Scale bars: 1 mm.