Onychostenhelia bispinosa, Huys, Rony & Mu, Fang-Hong, 2008

Huys, Rony & Mu, Fang-Hong, 2008, Description of a new species of Onychostenhelia Itô (Copepoda, Harpacticoida, Miraciidae) from the Bohai Sea, China, Zootaxa 1706, pp. 51-68 : 53-63

Onychostenhelia bispinosa sp. nov.

( Figs 1–8 )

Material examined. Holotype: adult Ψ dissected on 20 slides (NHM reg. no 2002.662). Paratypes: 1 ɗ dissected on 20 slides (NHM reg. no 2002.663), 10 ΨΨ and 2 ɗɗ preserved in alcohol (NHM reg. no 2002.664– 674). One Ψ and 1 ɗ prepared for SEM, mounted on stub but not registered.

Description. The present species is very similar to O. falcifera , which Itô (1979) described in great detail. Therefore, the following description is confined to those features which are different to, or which were not described for, O. falcifera . Unfortunately the type material of the latter is no longer available for re-examination.

FEMALE. Body ( Fig. 1 A–B). Length 500–610 µm (mean 557 µm, n = 11), shape and general body facies as in O. falcifera .

Rostrum ( Figs 1 A, 6A, 8C–D) clearly defined at base and extending beyond second antennulary segment; triangular, with concave lateral margins and distinctly bifid tip; furnished with numerous integumental pits and a central tube-pore on dorsal surface and with a pair of lateral sensilla just below apex.

Caudal ramus ( Fig. 6 B) elongate, cylindrical, 8 times longer than basal width with a row of spinules on distal ventral margin; seta I and seta II well-developed, inserted at 90% of ramus length on dorsolateral outer margin; seta III slender, about as long as caudal rami, inserted subapically on outer distal margin; distal seta IV somewhat longer than caudal ramus, seta V thickened proximally, about 3 times as long as caudal ramus and seta VI minute, closely set to seta V; seta VII triarticulate at base, inserted on inner margin opposite setae I and II.

Antennule ( Fig. 2 A–B) 7-segmented with aesthetasc on fourth and distal segments. Segments 1-4 with pitted region on dorsal surface. Segment 1 longest, with three rows of spinules on anterior margin, segments 1 and 2 with a strong, chitinous spur on distal posterior margin. All setae naked except for 1 plumose seta on each of segments 2, 3 and 7. Apical acrothek consisting of aesthetasc and 2 setae. Setal formula as follows: 1- [1], 2-[9], 3-[9], 4-[4 + (1 + ae)], 5-[2], 6-[4], 7-[7 + (2 + acrothek].

Antenna ( Fig. 3 A) as in O. falcifera except for subdistal inner corner of endopod with 2 spines and 2 setae. It is conceivable, however, that Itô (1979) overlooked one of the setae.

Mandible ( Fig. 3 B–C) as in O. falcifera .

Maxillule ( Fig. 3 D) as in O. falcifera except for 11 elements present on arthrite (7 spines and 2 setae on distal edge, 2 parallel setae on anterior surface); exopod and endopod fused basally, forming a bilobate structure ( Figs 8 A–B).

Maxilla ( Fig. 3 E) as in O. falcifera except for basis armed with 2 claws (one of them fused with segment) and 4 setae.

Maxilliped ( Fig. 3 F) as in O. falcifera except for outer and distal edge of basis with a row of long spinules.

P1 ( Fig. 4 A). As in O. falcifera

P2–P4 ( Figs 4 B, 5A–B). Segment shapes as in O. falcifera , except for P2 coxa which is not laterally expanded. Distribution of ornamentation elements slightly different; P2 with long setules along inner margins of basis and enp-1; presence of pores on anterior face of distal segment of rami not mentioned by Itô (1979). P3–P4 exp-3 with only 2 outer spines (3 outer spines in O. falcifera ) and ornamentation of terminal setae on distal segments of rami slightly different (biserrate instead of with unilateral membranous flange). Setal formula as follows:

[formulae in brackets denote male condition]

P5 ( Fig. 6 C). Baseoendopods fused medially. Exopod not fused to baseoendopod; longer than in O. falcifera ; basal fusion of largest laterodorsal seta (on outer margin) was not mentioned by Itô (1979) but from his figure 15-3, it seems as if this seta is not fused to the ramus. Outer basal seta plumose. Armature of baseoendopod distinctly different: outer two elements well developed, second outer minutely pinnate (both small, slender and naked in O. falcifera ); middle element a well developed seta with hyaline border on one side and minute pinnules on other (same length but naked in O. falcifera ); second inner as long as middle seta but innermost seta less than one third length of middle seta (in O. falcifera second inner element is a short pectinate spine and inner element a long serrate spine).

MALE. Sexual dimorphism in antennule, P3 endopod, P4 rami, P5, P6, and in urosomal segmentation and ornamentation.

Body. Length 440–560 µm (mean = 500 µm, n = 3).

Rostrum ( Fig. 7 G) bifid. Note that the female of O. falcifera , as described by Itô (1979), possesses a rostrum with rounded tip, while the male of that species possesses a rostrum with bifid tip similar to that found in O. bispinosa . Re-examination of topotypes of O. falcifera is desirable to verify whether the bifid condition of the female rostrum of O. falcifera was overlooked by Itô (1979).

Antennule ( Fig. 2 C–D). Indistinctly 8-segmented, haplocer, segment 5 moderately swollen, geniculation between segments 6 and 7; proximal 2 segments with chitinous hook, segment 1 with 2 anterior rows of spinules; modified elements on segments 5, 6 and 7, aesthetascs on segments 3, 5 and as part of acrothek on segment 8. Setal formula as follows: 1-[1], 2-[9], 3-[7 + ae], 4-[2], 5-[8 + (1 + ae)], 6-[4 + 3 spinules], 7-[3], 8- [7 + acrothek]. Itô (1979) did not figure the small fourth segment nor the aesthetasc on the terminal segment, and illustrated 3 segments distal to the geniculation (instead of 2 in O. bispinosa ). Re-examination of the topotype material of O. falcifera is required to confirm these discrepancies.

P3 ( Fig. 5 C). Endopod as in Ψ except enp-1 without inner element and enp-2 proportionally longer with shorter outer spinous process. Exp-3 as in Ψ (shape sexually dimorphic in O. falcifera ).

P4 ( Fig. 7 A–B). Exopod modified. Exp-1 as in female. Exp-2 much longer and more slender than in female; outer margin straight (with pointed process in O. falcifera ), outer spine distinctly recurved and relatively slender (a thick straight spine in O. falcifera ). Exp-3 less curved than in O. falcifera and proximal outer element larger; on proximal outer margin, with a chitinous, recurved projection, being concave (cup-shaped) and filled with semi-hyaline granular material; arrangement of setae on distal margin as in female. Endopod as in female except proportionally shorter and enp-1 without inner element.

P5 ( Fig. 7 C). Baseoendopods forming single plate without setular ornamentation around free margin (present in O. falcifera ), exopods discrete. Exopods as in O. falcifera but distal half more strongly curved outwardly. Endopodal armature distinctly different; outer element a small seta (well developed in O. falcifera ); inner element a virtually straight, short, very stout spine with dentate margin near tip (much more elongate, distally curved and more slender in O. falcifera ).

P6 ( Fig. 7 D–E) asymmetrical, with right side fused to somite and left side represented by articulating operculum closing off functional gonopore, with a row of long setules around inner distal corner; each side with 3 elements, outermost plumose, others short and smooth. Itô’s (1979: Fig. 18-2) drawing gives a distorted view of the sixth pair of legs and it is not clear whether each leg has one or two spinular rows.

Urosome ( Fig. 7 E–F). Urosomites 2 and 3 with a distinct process on each laterodorsal corner (weak ones present in O. falcifera ). Penultimate somite with paired spinule rows on ventral surface (absent in O. falcifera ).

Etymology. The specific name refers to the presence of only two outer spines on P3 and P4 exp-3.

Figures

FIGURE 1. Onychostenhelia bispinosa sp. nov. (holotype Ψ; NHM reg. no 2002.662): (A) habitus, dorsal; (B) habitus, lateral.

FIGURE 2. Onychostenhelia bispinosa sp. nov.: (A) antennule Ψ, ventral (armature omitted); (B) antennule Ψ, ventral (disarticulated); (C) antennule ♂, ventral (armature omitted); (D) antennule ♂ ventral (disarticulated). [(A) – (B): holotype Ψ, NHM reg. no 2002.662; (C) – (D): paratype ♂, NHM reg. no 2002.663].

FIGURE 3. Onychostenhelia bispinosa sp. nov. (holotype Ψ; NHM reg. no 2002.662): (A) antenna; (B) mandible; (C) mandibular gnathobase; (D) maxillule, anterior [inset showing proximal endite of syncoxa]; (E) maxilla, anterior; (F) maxilliped, anterior.

FIGURE 4. Onychostenhelia bispinosa sp. nov. (holotype Ψ; NHM reg. no 2002.662): (A) P 1, anterior; (B) P 2, anterior.

FIGURE 5. Onychostenhelia bispinosa sp. nov.: (A) P 3 Ψ, anterior; (B) P 4 Ψ, anterior; (C) P 3 endopod ♂, anterior. [(A) – (B): holotype Ψ, NHM reg. no 2002.662; (C): paratype ♂; NHM reg. no 2002.663].

FIGURE 6. Onychostenhelia bispinosa sp. nov. (holotype Ψ; NHM reg. no 2002.662): (A) rostrum, dorsal; (B) distal

FIGURE 7. Onychostenhelia bispinosa sp. nov. (paratype ♂; NHM reg. no 2002.663): (A) P 4, anterior; (B) P 4 endopod viewed from another angle (setae not drawn at full length); (C) P 5, anterior; (D) armature elements of P 6; (E) urosome, ventral; (F) urosome, dorsal; (G) rostrum, dorsal.

FIGURE 8. Onychostenhelia bispinosa sp. nov. (Ψ): (A) maxillulary palp, showing basally fused exopod and endopod; (B) same, different angle; (C) rostrum, ventral; (D) rostrum, dorsal. Scale bars: 2 m (A – B), 10 μm (C – D).