Dracoderes toyoshioae, Yamasaki, Hiroshi, 2015

Yamasaki, Hiroshi, 2015, Two new species of Dracoderes (Kinorhyncha: Dracoderidae) from the Ryukyu Islands, Japan, with a molecular phylogeny of the genus, Zootaxa 3980 (3), pp. 359-378 : 371-375

Dracoderes toyoshioae sp. nov.

[New Japanese name: Toyoshio tatsutogekawa] ( Figs 6 , 7 ; Tables 5 , 6 )

Material examined. Holotype: Exoskeleton from adult female (ZIHU-04990) used for DNA extraction, collected 23 May 2010 at station 3 ( Fig. 1 ), mounted in Fluoromount G®. Sequences: 18S (1776 bp), GenBank accession number LC 032118 ; COI (658 bp) for holotype, LC 032119 .

Type locality. Off northern Maeshima Island, Okinawa, Japan (26° 19.550'N, 127° 29.660'E).

Diagnosis. Dracoderes with middorsal subcuticular structure (and spine?) on segment 1; paradorsal subcuticular structures (and spines/tubules?) on segments 2–9, alternately laterally displaced; paradorsal acicular spines at least on segment 5; ventrolateral acicular spines on segment 1; lateral accessory tubules on segment 2; lateral accessory subcuticular structures (and spines/tubules?) on segments 2–7; lateroventral tubules on segment 5; lateroventral subcuticular structures (and spines/tubules?) on segments 2–10.

Etymology. The specific epithet toyoshioae is from TR.V. Toyoshio-maru, a research and training vessel for Hiroshima University since 1948. Since 2008, I have collected many kinorhynch specimens from this vessel, including this species.

The Japanese name ‘Toyoshio tatsutogekawa’ alludes to TR /V Toyoshio-maru and the Japanese name of the genus.

Description. Adult with head, neck, and eleven trunk segments ( Fig. 6 A–C). See Table 5 for measurements. Table 6 indicates the positions of cuticular structures (sensory spots, acicular spines, tubules, and glandular cell outlets).

Head consists of retractable mouth cone and introvert. Mouth cone present, but inner and outer oral styles could not examined. Introvert with spinoscalids and trichoscalids, exact numbers and arrangement of which were not examined.

Neck with four dorsal and five ventral placids ( Fig. 6 A, B). Ventral placids closely together; dorsal placids at intervals occupied by cuticular folding ( Fig. 6 A, B).

Trunk with eleven segments; segment 1 consists of complete cuticular ring, segments 2–11 consist of one tergal and two sternal plates ( Fig. 6 A, B). Thickened cuticle forms pachycyclus at anterior margin of all segments ( Fig. 7 A–E). Paradorsal acicular spine on segments 5 ( Figs 6 A, 7C). Lateral accessory tubules on segment 2 ( Figs 6 B, 7B). Lateroventral tubules on segment 5 ( Figs 6 B, 7B, E). Ventrolateral acicular spine on segment 1 ( Figs 6 B, 7B). Subcuticular structures at base of all spines and tubules. In addition, subcuticular structures middorsally on segment 2, paradorsally on segments 2–4 and 6–9, in lateral accessory position on segments 3–7, and lateroventrally on segments 2–4 and 6–10 ( Figs 6 A, B, 7A–E). An acicular spine or tubule possibly arises from each subcuticular structure in the natural state, but spines/tubules have certainly been lost during collecting, DNA extraction, or mounting. Paradorsal acicular spine and subcuticular structures on segments 2–9, laterally displaced alternately right and left ( Figs 6 A, 7A, C). Cuticular hairs present in central to posterior part of all segments ( Fig. 7 B–E). Secondary pectinate fringe could not be observed.

Segment 1 with middorsal and ventrolateral subcuticular structures ( Figs 6 A, B, 7A, B). Acicular spine from one of ventrolateral subcuticular structures ( Figs 6 B, 7B). Possibly broken ventrolateral acicular spine close to opposite ventrolateral subcuticular structure ( Fig. 7 B). Pairs of sensory spots in paradorsal, subdorsal, and midlateral positions ( Figs 6 A, 7A). Three pairs of sensory spots in ventromedial position ( Fig. 6 B). Glandular cell outlets in lateroventral (single pair) and ventromedial (two pairs) positions ( Figs 6 B, 7B). Primary pectinate fringe with short tips along whole posterior edge of segment.

Segment 2 with unpaired paradorsal, and paired lateral accessory and lateroventral subcuticular structures ( Figs 6 A, B, 7A, B). Lateral accessory tubules arise from corresponding subcuticular structures ( Figs 6 B, 7B). Paired sensory spots in paradorsal, laterodorsal (two pairs), lateroventral, and ventromedial positions ( Figs 6 A, B, 7A, B). Paired glandular cell outlets in ventromedial positions ( Figs 6 B, 7B). Primary pectinate fringe on both tergal and sternal posterior edges, with longer tips than those on anterior segment.

Segment 3 with unpaired paradorsal, and paired lateral accessory and lateroventral subcuticular structures ( Figs 6 A, B, 7B). Paradorsal subcuticular structure located opposite that of preceding segment ( Fig. 6 A). Paired sensory spots in paradorsal, laterodorsal, and sublateral (two pairs) positions ( Fig. 6 A, B). Paired glandular cell outlets in ventromedial position ( Figs 6 B, 7B). Primary pectinate fringe similar to that of preceding segment.

Segment 4 with unpaired paradorsal subcuticular structure, on opposite side of that of preceding segment ( Fig. 6 A). Paired subcuticular structures in lateral accessory and lateroventral positions ( Figs 6 B, 7B, E). Unpaired sensory spot in subdorsal position close to subcuticular structure ( Fig. 6 A). Paired sensory spots in paradorsal, laterodorsal, midlateral, sublateral, and ventromedial positions ( Figs 6 A, B, 7B, E). Although a subdorsal acicular spine could not be examined, an unpaired subdorsal and one of the usually paired paradorsal sensory spots seem to be located perispinally. Glandular cell outlets in ventromedial position ( Figs 6 B, 7B, E). Primary pectinate fringe at posterior edge of tergal and sternal plates with tips slightly longer than those on preceding segment ( Fig. 7 E).

Segment 5 with unpaired paradorsal acicular spine and paired lateroventral tubules ( Figs 6 A, B, 7B, C, E). Subcuticular structures at the base of each spine and tubule, and in lateral accessory positions ( Figs 6 A, B, 7B, C, E). Unpaired sensory spot in subdorsal position, and paired sensory spots in paradorsal, laterodorsal, sublateral (two pairs), and ventrolateral positions ( Figs 6 A, B, 7B, E). Unpaired subdorsal and one of the usually paired paradorsal sensory spots located perispinally. Glandular cell outlets in ventromedial position ( Figs 6 B, 7B, E). Primary pectinate fringe similar to that on preceding segment ( Fig. 7 E).

Segment 6 similar to segment 4, except for having unpaired sensory spot in middorsal and paired sensory spots in ventrolateral positions, and lacking paired sensory spots in laterodorsal position ( Figs 6 A, B, 7D). Unpaired subdorsal and one of the usually paired paradorsal sensory spots located perispinally. Tips of primary pectinate fringe slightly shorter than those of segments 4 and 5.

Segment 7 with unpaired paradorsal, and paired lateral accessory and lateroventral subcuticular structures ( Figs 6 A, B, 7C, D). Unpaired sensory spot in subdorsal position, and paired sensory spots in paradorsal, ventrolateral positions ( Figs 6 A, B, 7D). Unpaired subdorsal and one of the usually paired paradorsal sensory spots seem to be located perispinally. Glandular cell outlets in ventromedial position ( Figs 6 B, 7D). Primary pectinate fringe similar to that of preceding segment.

Segment 8 similar to segment 6 except for having paired laterodorsal sensory spots, and lacking middorsal and sublateral sensory spots ( Figs 6 A, B, 7D).

Segment 9 with unpaired paradorsal and paired lateroventral subcuticular structures ( Figs 6 A, B, 7C, D). Unpaired sensory spot in dorsal and paired sensory spots in subdorsal, laterodorsal, midlateral, ventrolateral, and ventromedial positions ( Figs 6 A, B, 7D). Glandular cell outlets in ventromedial position ( Figs 6 B, 7D). Primary pectinate fringe similar to that of preceding segment.

Segment 10 with lateroventral subcuticular structures ( Figs 6 B, 7D). Sensory spots in subdorsal and ventrolateral positions ( Figs 6 A, B, 7D). Primary pectinate fringe with shorter tips than that of preceding segment.

Segment 11 with lateral terminal spines ( Figs 6 A–C, 7D). Lateral terminal accessory spines lacking. Gonopores not observed. One pair of subdorsal sensory spots in center of tergal plate, and two pairs of subdorsal sensory spots close to posterior ends of tergal extension ( Fig. 6 A). One pair of ventromedial sensory spots ( Fig. 6 B). Dorsal posterior end with triangular tergal extension.

Remarks. Dracoderes toyoshioae sp. nov. belongs to the genus Dracoderes because the species has the appropriate combination of characters, including: a neck of nine placids; segment 1 comprising a closed cuticular ring; segments 2–11 with one tergal and two sternal plates; some dorsal spines laterally displaced alternately left or right; lack of a midterminal spine; and lack of lateral terminal accessory spines. However, it differs markedly from other Dracoderes species, especially in having a dorsal spine (subcuticular structure) on segment 1, ventromedial spine on segment 1 and lateral accessory and lateroventral spines/tubules/subcuticular structures on segments 2–8. Molecular phylogenetic analyses also supported a close relationship between the new species and other Dracoderes species (see below).

Although only one specimen of Dracoderes toyoshioae was available for study, and some spines and tubules were broken or lost, this species can be easily distinguished from congeners. The most conspicuous difference is the position of subcuticular structures, and the spines and/or tubules possibly arisen from these subcuticular structures. Dracoderes toyoshioae shows middorsal and ventromedial spines on segment 1, whereas its congeners lack both. Furthermore, D. toyoshioae sp. nov. possesses two pairs of lateral (lateral accessory and lateroventral) spines, tubules and subcuticular structures on segments 2–8, whereas its congeners lack such pairs at least segments 2–4, 6 and 7 ( Higgins & Shirayama 1990; Adrianov & Malakhov 1999; Sørensen et al. 2012; Thomsen et al. 2013). Dracoderes toyoshioae also differs from its congeners in the formula of dorsal perispinal sensory spots; the other species all have perispinal sensory spots on all segments bearing a middorsal or a paradorsal spine ( Higgins & Shirayama 1990; Adrianov & Malakhov 1999; Sørensen et al. 2012; Thomsen et al. 2013), whereas D. toyoshioae bears perispinal sensory spots on segment 1 and 4–8 and the sensory spots on segments 2, 3 and 9 are not located perispinally.

Additional specimens of Dracoderes toyoshioae sp. nov. will be necessary for a more detailed examination of morphology, especially for the exact composition of spines and tubules, and sexually dimorphic characters. I searched for this species without success at stations close to the type locality and at similar depths (ca. 500–700 m). This perhaps suggests that the species occurs at very low density, is patchily distributed or occupies a microhabitat at the type locality that is not present at the other localities.

Figures

FIGURE 1. Map of Japan, with enlargements indicating the sampling sites. A, Main island of Okinawa; B, Iriomote and Ishigaki Islands.

FIGURE 6. Dracoderes toyoshioae sp. nov., camera lucida drawings of holotype, female (ZIHU- 04990). A, B, segments 1 – 11, except for lateral terminal spine, dorsal and ventral views, respectively; C, whole animal, dorsal view. Asterisks and circles indicate sensory spots and glandular cell outlets, respectively. Possible missing spines / tubules are illustrated with dotted lines. Abbreviations: cf, cuticular folding; gc, glandular cell outlet; lasus, lateral accessory subcuticular structure; lat, lateral accessory tubule; lts, lateral terminal spine; lvsus, lateroventral subcuticular structure; lvt, lateroventral tubule; mdsus, middorsal subcuticular structure; pds, paradorsal acicular spine; pdsus, paradorsal subcuticular structure; pl, placid; ss, sensory spot; te, tergal extension; vls, ventrolateral acicular spine; vlsus, ventrolateral subcuticular structure.

FIGURE 7. Dracoderes toyoshioae sp. nov., Nomarski photomicrographs of holotype female (ZIHU- 04990). A, segments 1 and 2, dorsal view; B, segments 1 – 5, ventral view; C, segments 5 – 11, dorsal view; D, segments 6 – 11, ventral view; E, segments 4 – 6, ventral view. Dashed circles indicate sensory spots. Abbreviations: gc, glandular cell outlet; lasus, lateral accessory subcuticular structure; lat, lateral accessory tubule; lts, lateral terminal spine; lvsus, lateroventral subcuticular structure; lvt, lateroventral tubule; mdsus, middorsal subcuticular structure; pds, paradorsal acicular spine; pdsus, paradorsal subcuticular structure; pf, primary pectinate fringe; vls, ventrolateral acicular spine.

Tables

TABLE 5. Measurements for the holotype of Dracoderes toyoshioae sp. nov. (in micrometers). Abbreviations: (ac), acicular spine; LA, length of lateral accessory tubule; LTS, length of lateral terminal spine; LV, length of lateroventral tubule; MSW, maximum sternal width; S, segment length; SD, length of subdorsal acicular spine; SW, standard width; TL, trunk length; VL, length of ventrolateral acicular spine.

Character Measurement	Character	Measurement
TL 331	S7	36
MSW-6 83	S8	38
MSW-6/TL 25.1%	S9	35
SW-10 64	S10	36
SW-10/TL 19.3%	S11	44
S1 57	SD5 (ac)	80
S2 31	VL1 (ac)	53
S3 31	LA2 (tu)	10
S4 32	LV5 (tu)	14
S5 33	LTS	341
S6 34	LTS/TL	103%

TABLE 6. Summary of the locations of cuticular structures, tubules, and spines in Dracoderes toyoshioae sp. nov. Abbreviations: ac, acicular spine; gc, glandular cell outlet; (l) unpaired and present on left side; LA, lateral accessory; LD, laterodorsal; lts, lateral terminal spine; LV, lateroventral; MD, middorsal; ML, midlateral; PD, paradorsal; (r), unpaired and present on right side; SD, subdorsal; SL, sublateral; ss, sensory spot; tu, tubule; VL, ventrolateral; VM, ventromedial.

Position MD	PD	SD	LD	ML	SL	LA	LV	VL	VM
segment 1 ac? 2 3	ss ac? (l), ss ac? (r), ss	ss	ss, ss ss	ss	ss, ss	tu ac/tu?	gc ss, ac/tu? ac/tu?	ac	ss, ss, gc, gc, ss ss, gc gc
4 5 6 ss	ac? (l), ss ac (r), ss ac? (l), ss	ss (l) ss (r) ss (l)	ss ss	ss ss	ss ss, ss ss	ac/tu? ac/tu? ac/tu?	ac/tu? tu ac/tu?	ss ss	ss, gc gc ss, gc
7 8 9 ss	ac? (r), ss ac? (l), ss ac? (r)	ss (r) ss (l) ss	ss ss ss	ss ss		ac/tu? ac/tu?	ac/tu? ac/tu? ac/tu?	ss ss ss	gc ss, gc ss, gc
10 11		ss ss, ss, ss					ac/tu? lts	ss	ss