Pyropelta ovalis Beck, 2023

Chen, Chong & Sigwart, Julia D., 2023, The lost vent gastropod species of Lothar A. Beck, Zootaxa 5270 (3), pp. 401-436 : 413-415

Pyropelta ovalis Beck , sp. nov.

Figs 6–8

[ZooBank LSID: urn:lsid:zoobank.org:act:C80CB17D-A870-4A2B-9CA7-008C93EE6D05 ]

Type material. Holotype [MNHN-IM-2000-38678] and one paratype in MNHN [Paratype 1: MNHN-IM-2000- 38679], two paratypes in NSMT [Paratype 2: NSMT-Mo 79406; Paratype 3: NSMT-Mo 79407], two paratypes in SMF [Paratype 4: SMF 370354 ; Paratype 5: SMF 370355 ].

Type locality. North Fiji Basin (White Lady). STARMER II, PL21 .

Material examined. The type material and: BIOLAU, BL08, 1 specimen, soft parts only [NSMT-Mo 79408]; STARMER II, PL14, 2 specimens [NSMT-Mo 79409]; STARMER II, PL20, 7 adults and 8 juvenile specimens [ SMF 370356 ] .

Distribution. North Fiji Basin [and Lau Basin] in bathyal, sulfide-rich areas.

Etymology. Species name refers to the oval form of the shell.

Description. Shell ( Figs 6A–C, E, F ) medium sized for genus, moderately thick, of opaque white colour; outer surface heavily eroded which is caused by acidic hydrothermal solutions. Surface characterized by concentric and irregular steps of thin shell layers; outermost layer, if present, with fine naps of irregular distribution (discernible by SEM only); in most specimens the horse-shoe-shaped scar of shell muscle is visible from outside due to the transparency of the shell; apex slightly posterior to the centre, shell profile low; protoconch lost in all specimens. Inner shell surface smooth except the heavily marked muscle scar. Shell structure consists of a multitude [of] thin prismatic layer[s].

Dimensions. Holotype: length 5.4 mm, width 3.6 mm, height 1.0 mm; paratype 1: length 5.2 mm, width 3.7 mm, height 1.2 mm.

Radula ( Fig. 7C, D ). Rhipidoglossate with about 45 transverse rows of teeth, formula 50-60 x 5 x 1 x 5 x 50-60, transverse rows of teeth roughly M-shaped; rachidian tooth with a broad base, laterally equipped with weak ridges, rachidian cusp reduced, rachidian shaft ends bluntly; rachidian base forms a hump with the bases of the first laterals; first laterals with overhanging cusps bearing 4–5 inner coarse denticles; cusps of second, third and fourth laterals with finely denticulated inner edges; fifth lateral claw-like and with 8–9 coarse denticles at cusps, base with distal flap, short pin-like first marginal teeth probably functions like a lateromarginal plate; marginal teeth with slender shafts and well-denticulated short and stiff cusps, outermost marginal teeth more flabelliform.

Soft parts ( Figs 6A, D , 7A , 8 ). Cephalic lappets lacking, cephalic tentacles of equal size and equipped with micropapillae, snout with oral disc and small lateral lappets; foot with flat sole and a marginal bulge on which anteriorly the slit of the foot gland is discernible; foot sides bear a broad epipodial lobe which is posteriorly accompanied with two appendages and shows somewhat broadened area anteriorly, posterior appendages arise from areas above the epipodial lobe. Pallial margin thickened and entirely fused to the shell, outermost area densely covered with micropapillae (can be seen by SEM only); on right ventral side of the pallial margin, 25–28 small secondary gill leaflets are located, each leaflet consists of a basal (anterior), thickened, partly ciliated part and a distal (posterior), non-ciliated flap; pallial cavity shallow and short at left neck side (inhalant opening), ciliary bundles function as sensory control of incoming hydrothermal solutions, at right neck side, a densely ciliated area causes the exhalant flow of solutions, mantle skirt above neck extremely thin and translucent. Shell muscle horseshoe-shaped, with left and right arm of about equal size, inner bounds irregular. Half of the visceral mass is occupied by the hermaphrodite gonad whereas the ovary covers the testis in the posterior and left area; at the centre, a loop of the intestine shines through; the right area includes the digestive gland and a somewhat granular area interpreted here as the right kidney; the rectum penetrates the pericardium and ends at the right side of the pallial cavity; rectum contents include flaky material and some mineral particles; apparently, the ducts of the right kidney and the gonad are fused and end in a common uro-genital papilla towards the end of the right shell muscle arm. More detailed anatomical information requires dissections; therefore, data on the digestive system, left and right kidneys as well as the circulatory and nervous systems cannot be given here.

Remarks. Pyropelta ovalis sp. nov. is similar to P. bohlei (from Edison Seamount, West Pacific) with respect to the radular characters. However, P. ovalis sp. nov. is different to P. bohlei in the following characters: the shell is larger and not vitreous, the radula has a rachidian shaft that ends bluntly instead of tapering and the cusps of the marginal teeth have short and stiff denticles instead of long and flexible ones; with respect to soft parts, the diagnostic characters of P. ovalis are: arms of shell muscle of equal size, much higher number of secondary gill leaflets (up to 28), leaflets comparatively small and not reaching to the pallial cavity ( Beck 1996).

Figures

FIGURE 6. Pyropelta ovalis sp. nov., shell and soft parts.A. Paratype 2 (shell length 5.5 mm; anterior to the left), ventral view. B–C. Holotype (shell length 5.4 mm; anterior to the left). B. Apical view. C. Lateral view. D. Paratype 3 (shell length 5.1 mm, anterior to the left), Soft parts removed from shell in dorsal view (cf. Fig. 8). E–F. Paratype 1 (shell length 5.2 mm; anterior to the left). E. Apical view on shell. F. Ventral view on shell; note the heavily marked horseshoe-shaped scar of shell muscle.

FIGURE 7. Pyropelta ovalis sp. nov., soft parts and radula.A. Soft parts in oblique ventral view; arrow points to the opening of the anterior foot gland. B. Gill lamellae at ventral right side of soft parts (cf. Fig. 8), arrow indicates the ciliated and thickened base of gill lamella anterior to the non-ciliated flap. C. Radula. D. Half of the central field of radula. [Scale bars:A, 1 mm; B–C, 50 μm; D, 20 μm.]

FIGURE 8. Pyropelta ovalis sp. nov., soft parts depicted in dorsal view, gill lamellae shown by transparency. (Abbreviations cf. material and methods).