Scutopus schanderi, Saito & Salvini-Plawen, 2014

Saito, Hiroshi & Salvini-Plawen, Luitfried v., 2014, Four new species of the aplacophoran class Caudofoveata (Mollusca) from the southern Sea of Japan, Journal of Natural History 48 (45 - 48), pp. 2965-2983 : 2967-2969

Scutopus schanderi sp. nov.

( Figures 2–3 )

Type locality

Western Wakasa Bay , between Kanmuri-jima Island and Ine Port, Tango Peninsula, southern Sea of Japan, 35°39.20 ′ N, 135°21.47 ′ E, 69 m.

Type depository

Department of Zoology, National Museum of Nature and Science, Tsukuba.

Etymology

This species is named for the late Dr. Christoffer Schander (University of Bergen, Norway) who contributed much to increase our knowledge on aplacophoran molluscs.

Material examined

Holotype. NSMT-Mo 78588, ethanol preserved specimen, a part of sclerites and radula are mounted on slide glasses, body length 14.7 mm, 35°39.20 ′ N, 135° 21.47 ′ E, 69 m, 2 September 2010. Paratypes. #1: NSMT-Mo 78589, body length 12.0 mm, from type locality; #2–3: NSMT-Mo 78590–78591, body length 6.5– 10.8 mm, 35°45.11 ′ N, 135°20.43 ′ E, 96 m, 2 September 2010; #4–9: NSMT-Mo 78592–78597, body length 5.2–10.3 mm, 35°44.97 ′ N, 135°22.40 ′ E, 101–102 m, 2 September 2010; #10: NSMT-Mo 78598, body length 6.8 mm, 35°45.03 ′ N, 135° 20.21 ′ E, 95 m, 13 August 2012; #11–12: NSMT-Mo 78599–78600, body length 6.7– 9.0 mm, 35°45.20 ′ N, 135°20.20 ′ E, 96–98 m, 25 October 2012.

Description of holotype

Animal 14.7 mm long, slender, almost uniform in diameter along body; 0.7 mm in foregut or pharyngeal region (neck or prothorax), 0.75 mm in anterior midgut region (anterior trunk or metathorax), and 0.6 mm in prepallial region ( Figure 2A ). Boundary between foregut and midgut regions usually demarcated by groove and by transition of internal colouration to dark greenish colour in midgut. Anterior midgut and midgut sac region with distinct groove of midventral suture line. Pedal shield (buccal plate, oral shield) postoral, but flanking mouth opening laterally ( Figure 2E ).

Dominant sclerites covering dorsal, lateral and large part of ventral surfaces of midgut region, midgut sac region, and prepallial region roughly oar-blade shaped, pointed at tip, thin, flat, weakly keeled on midline near tip, often with 1–2 longitudinal fine grooves on each side of median keel, up to 100 µm long × 40 µm wide in anterior midgut sac region ( Figure 3H ), gradually increasing in size posteriorly ( Figure 3I ), up to 138 µm long × 46 µm wide in prepallial region ( Figure 3J ). Sclerites of peribuccal region minute, oval, flat, 17–26 µm long × 11–12 µm wide ( Figure 3A, B ), elongating posteriorly and narrowing distally in more posterior sclerites. Sclerites in foregut region of two types: one similar to dominant sclerites, but with distinct waist, up to 80 µm long × 28 µm wide ( Figure 3C, E ), the other more slender, with width of base narrower than widest point of distal half ( Figure 3D ). Sclerites along midventral suture narrow in distal half, widening in proximal half, pointed at tip, keeled on midline near tip, measuring up to 115 µm long × 25 µm wide ( Figure 3F ). Similar but wider sclerites provided with lateral sides of those narrow sclerites ( Figure 3G ). Posterior margin of pallial region with narrow lanceolate sclerites that are broadly keeled in distal half, up to 165 µm long × 23 µm wide ( Figure 3K ). Small narrow lanceolate sclerites, up to 90 µm long × 14 µm wide ( Figure 3L ), inside pallial margin.

Radula large, c. 680 µm long, distichous, arranged in eight transverse rows, heavily sclerotized except for posteriormost two pairs; each tooth gaff- or hookshaped, c. 280 µm long, with 16–18 small, pointed median denticles ( Figure 2F, G ).

Additional description from paratypes

Colour of living animals through translucent body wall dark green in midgut region and light brown with numerous yellowish green maculations in midgut sac area ( Figure 2B ). Brownish colour of sclerotized radula observable through body wall ( Figure 2C , arrow). Greenish colouration faded out in preserved specimens ( Figure 2A, D ). Radula teeth less sclerotized in small specimen ( Figure 2H , paratype #5).

Remarks

The genus Scutopus is considered to be the most conservative representative in the Caudofoveata because of a postoral pedal shield, ventral suture line of fusion of the mantle edges in most species, body wall musculature, distichous radula without any lateral cuticular apparatus, and, in males, the pallial mucous tracts. So far, only four species of the genus Scutopus are known from three areas: S. ventrolineatus Salvini- Plawen, 1968 and S. robustus Salvini-Plawen, 1970 from the Eastern Atlantic ( Salvini-Plawen 1968, 1970); S. megaradulatus Salvini-Plawen, 1972 from the Caribbean Sea; and S. chilensis Salvini-Plawen, 1972 from off the East Pacific Chilean coast. The new species Scutopus schanderi most resembles S. robustus in possessing heavily sclerotized radula teeth with denticles up to the tip, but differs from the latter by having fewer radula denticles in adult individuals: 16–18 in S. schanderi , 20–22 (13–22) in S. robustus ; other characters in contrast to the 8–12 mm long, more stoutish S. robustus are also the wider, subparallel-sided dominant sclerites, the presence of the midventral mantle suture and the slender body shape in S. schanderi .

Figures

Figure 2. Scutopus schanderi sp. nov. (A) holotype, NSMT-Mo 77588, preserved condition; (B) paratype #11, NSMT-Mo 78599, specimen in life; (C) paratype #10, NSMT-Mo 78598, specimen in life, anterior body, showing observable radula through body wall (arrow); (D) paratype #2, NSMT-Mo 78590; (E) pedal shield of paratype #2; (F) radula of holotype; (G) same, tip of posteriormost tooth; (H) radula of paratype #5, NSMT-Mo 78593. Scale bars: 1 mm for A, B, D; 0.5 mm for C; 200 µm for E; 100 µm for F, H; 50 µm for G.

Figure 3. Scutopus schanderi sp. nov. Sclerites of holotype. (A, B) peribuccal region; (C–E) in foregut region; (F, G) at ventral suture; (H) in anterior midgut sac region; (I) in posterior midgut sac region; (J) in prepallial region; (K) at posterior margin of pallial region; (L) inside of posterior margin of pallial region. Scale bar: 100 µm.