Johnwellsia bipartita, sp. nov.

Johnwellsia bipartita sp. nov.

(Figs. 1–5)

urn:lsid:zoobank.org:act: 142A465D-1E30-404B-9962-CCC7A10D3FE4

Type locality. China, Taiwan Strait, Xiamen, Dadeji Beach (24°26’30” N, 118°4’12” E); intertidal zone, gravelly sand.

Type material. Holotype adult female dissected on fifteen slides (OUCBL reg. no 2019.001). Paratypes are one adult male dissected on twelve slides (OUCBL reg. no 2019.002), ten female and ten male specimens preserved in 4% formalin (OUCBL reg. nos 2019.003–022), one female dissected on one slide (OUCBL reg. no 2019.023) and one male dissected on one slide (OUCBL reg. no 2019.024). All type specimens collected from the type locality by Dr Er Hua on 24 July 2010.

Etymology. The specific epithet is derived from the Latin bi, meaning two, and the past participle of partire, meaning to part, and refers to the 2-segmented condition of the male P5 exopod.

Description of female. Body length 505–530 µm (mean = 515 µm, n = 10), semicylindrical, widest at posterior margin of cephalothorax, tapering posteriorly without clear distinction between prosome and urosome (Fig. 1A–B). All somites with sensillae as illustrated, except for penultimate one. Conspicuous pores present on all somites. Rostrum (Fig. 1A–B) defined at base, elongated, triangular and with pointed tip; reaching to middle of antennulary segment 2, with pair of subapical sensilla. Cephalothorax with plain hyaline frill; pedigerous somites bearing P2–P4 with distinctly incised hyaline frills dorsally; genital double-somite and abdominal somites 2–3 also with incised frills all around posterior margin; incised frills consisting of dentate lappets (Figs 1A–B, 2A). P4-bearing somite with transverse rows of minute spinules dorsally. P5-bearing somite with spinular row around dorsal and dorsolateral posterior margin. Genital and first abdominal somite forming elongate double-somite; original segmentation marked by dorsolateral and lateral, internal, transverse chitinous ribs; ornamentation consisting of two pairs of dorsolateral spinule rows in anterior half, and almost continuous spinular row posteriorly (interrupted dorsally, ventral spinules markedly shorter than lateral ones); with additional rows of minute spnules laterally and dorsally (Figs 1A–B, 2A). Second abdominal somite with ventral spinular row in anterior half and almost continuous row of spinules near posterior margin (interrupted middorsally) (Figs 1A–B, 2A); with additional transverse rows of minute spinules ventrally and dorsally. Third abdominal somite with ventral row of spinules and additional transverse rows of minute spinules laterally and dorsally (Figs 1A–B, 2A). Anal somite with spinules either side of anal operculum and around ventral and lateral posterior margin (Figs 1A–B, 2A). Anal operculum (Fig. 1B) semi-circular, withour ornamentation; anal frill with long hair-like extensions.

Caudal rami (Fig. 1C–E) slightly broader than long, with slightly oblique, transverse row of spinules on dorsal surface and wrapped around inner margin; with several spinules, laterally and ventrally, around bases of setae II–V; with seven setae; lateral and ventral surface with pore (Figs 1D–E, 2A). Seta I minute, positioned ventrally near outer margin (Fig. 1E); seta II naked, originating from outer margin; seta III long and naked, positioned at outer subdistal corner, slender; terminal setae IV–V long and bipinnate (Fig. 1A), with weakly developed fracture planes, seta IV about half as long as seta V; seta VI long and naked, originating from inner subdistal corner; seta VII triarticulated at base, arising from dorsal surface (Fig. 1C).

Antennule (Fig. 2B–C) 9-segmented; segments 1–6 slender with segment 1 more elongate than in other parastenheliid genera; segments 7–9 short, in particular segment 7; all segments without spinular ornamentation; all setae naked; with aesthetasc on segments 4 and 9; apical acrothek consisting of aesthetasc and two setae. Armature formula as follows: 1-[1], 2-[10], 3-[6], 4–[3 + (1 + ae)], 5–[2], 6-[3], 7-[3], 8-[0], 9-[5 + acrothek].

Antenna (Fig. 2D). Basis and proximal endopodal segment completely fused, forming allobasis; abexopodal margin with two spinular tufts but no armature elements. Exopod 2-segmented; proximal segment with two setae, lateral one slender and naked, distal one long and unipinnate; distal segment with four setae: proximal one tiny and naked, apical margin with one unipinnate, spiniform element and two small naked setae. Endopod with sparse spinules along both lateral margins; lateral armature consisting of small naked element proximally and large unipinnate spine distally; distal armature consisting of one strong, unipinnate spine, four geniculate setae (longest one with large spinules around geniculation and fused at base to unipinnate seta) and one naked seta.

Mandible (Fig. 3A–B). Coxal gnathobase well developed, with complex cutting edge bearing several multicuspidate teeth, with strong tooth at ventral corner and short, unipinnate seta at dorsal corner. Basis elongate, with row of spinules on both anterior and posterior surfaces, with three setae near inner distal corner: one spiniform and unipinnate and two setiform and naked. Endopod elongate, 1-segmented; with two lateral and four terminal setae (two of which fused at base); exopod minute, represented by one tiny seta arising from small protuberance.

Maxillule (Fig. 3C). Praecoxal arthrite with seven spiniform elements around distal margin, with two long setae on anterior surface, and two short elements near inner margin. Coxal endite cylindrical, with four naked setae; coxal epipodite represented by one seta. Basis with three setae on single endite; rami fused to basis but clearly discernible. Endopod 1-segmented, with three naked, apical setae. Exopod 1-segmented, with one short, naked and one long, unipinnate seta apically.

Maxilla (Fig. 3D). Coxa with three endites, proximal endite bilobate with one naked seta on inner cusp and two naked setae on outer cusp; middle and outer endite each with two naked setae and one basally fused pinnate spine; allobasal endite drawn out into strong, unipinnate spine and three setae (one of which minute); endopod welldeveloped, 1-segmented, not completely discrete at base, with two naked setae.

Maxilliped (Fig. 3E). Armature of syncoxa as in male (see below; Fig. 5H). Basis with two short, naked setae along palmar margin and few spinules around outer margin. Endopod represented by well-developed, unipinnate claw and three accessory, naked setae near its base.

P1 (Fig. 3F). Intercoxal sclerite small, unadorned. Praecoxa (not illustrated) small, triangular, with spinule row on distal margin. Coxa with row of large spinules along outer margin and medial part of distal margin, and row of small spinules on anterior surface; with pore on anterior surface. Basis with unipinnate inner spine and bipinnate outer spine; with row of spinules near base of outer spine, along inner margin and around base of endopod. Exopod 3-segmented, segments subequal in length, proximal segment with row of spinules along outer margin and unipinnate spine at outer distal corner; middle segment with row of spinules along outer margin and two setules along inner margin, with unipinnate spine at outer distal corner and short, plumose seta at inner distal corner; distal segment with plumose, inner distal seta, unipinnate, geniculate outer distal seta, and two unipinnate outer spines. Endopod 2-segmented, prehensile; proximal segment much longer than exopod, with long, uniplumose seta arising from proximal fourth of segment; distal segment small, with few spinules, one minute inner seta and two slightly curved, naked spines apically.

P2–P4 (Fig. 3G, 4A–B). Praecoxa triangular, with spinule row along distal margin; coxa with 1–2 row(s) of spinules along outer margin and row of tiny spinules on anterior surface; basis with row of spinules near proximal inner corner, row of fine setules distally between insertions of rami, and few spinules around base of outer seta, inner distal corner forming small, pointed process. Rami 3-segmented, slender; endopods about as long as (P2) or slightly shorter than (P3–P4) exopods; P2–P4 enp-3 longest, enp-1 widest and with convex inner margin. All segments with rows of large spinules along outer margin; with few spinules/setules on inner margin of exp-2, and enp-2 and -3; with anterior pore on all segments except for enp-1; distal inner seta on P3–P4 exp-3 very small. Armature formulae of P1–P4 as follows:

P5 (Fig. 4C). Rami discrete and baseoendopods not fused medially. Endopodal lobe small, trapezoid; with five setae (four pinnate, one short and naked) and few spinules around base of outer basal seta; anterior surface with two pores. Exopod about two times longer than maximum width; basal portion articulating with baseoendopod very narrow; with row of setules along inner and outer margins; with six setae: one long, bipinnate, inner seta, two naked setae apically (one very long, other one short), and one short naked and two bipinnate setae along outer margin.

Genital field (Fig. 2A) with large midventral copulatory pore; paired genital apertures positioned anteriorly, each covered by vestigial P6 bearing three setae, inner two short, outer one long and plumose.

Description of male. Sexual dimorphism expressed in urosomal segmentation and ornamentation, antennule, endopods of P2–P4, P5 and P6. Body slightly smaller than female, length 415–460 µm (mean = 440 µm, n = 10).

Genital and first abdominal somites not fused. Urosomal ornamention very similar to female, except for absence of transverse spinule row on ventral and lateral surfaces of penultimate somite.

Antennule (Fig. 5A–B) indistinctly 11-segmented, haplocer; segment 1 elongate; segment 4 largely incorporated into moderately swollen segment 5; geniculation located between segments 7–8 with four segments distal to it; segment 11 with surface suture along dorsal surface; aesthetasc on segments 5 and 11; all setae naked except for bipinnate seta on segment 1; armature formula as follows: 1-[1], 2-[10], 3-[8], 4-[2], 5-[4 + (1 + ae)], 6-[2], 7-[4 + 3 modified spines], 8-[1 + 2 modified spines], 9-[1], 10-[2], 11-[6 + (1 + ae)].

Maxilliped (Fig. 5H). As in female, syncoxa with two setae near inner distal corner.

P2 (Fig. 5C). Exopod as in female. Endopod 2-segmented; compound enp-2 with only one plumose inner seta, arising from proximal third of segment (homologue of inner seta of ♀ enp-2).

P3 (Fig. 5D). Exopod as in female. Enp-3 shorter than in female, without inner setae.

P4 (Fig. 5E). As in female except enp-3 slightly shorter.

Armature formulae of P1–P4 as follows:

P5 (Fig. 5F). Baseoendopods fused medially, forming deeply incised transverse plate. Endopodal lobe with row of spinules along outer margin; with two short elements (inner one unipennate and spiniform, outer one naked and shorter than inner one); anterior surface with two pores; outer basal seta bipinnate and arising from short setophore. Exopod 2-segmented; exp-1 with row of spinules along outer margin and naked seta at outer distal corner; exp-2 with short naked seta at outer subdistal corner, long bipinnate seta apically and unipinnate spine at inner subdistal corner; anterior surface of exp-2 with pore.

P6 (Fig. 5G) represented on each side by small plate closing off genital aperture; with three setae, middle seta about twice longer than other two, innermost one unipinnate.

Variability. In one dissected male the P2 enp-2 displayed two inner setae on one side.

Remarks. The new species cannot be placed in Parastenhelia, Microthalestris, Karaytugia gen. nov. or Penicillicaris gen. nov. since it does not display the sexual dimorphism on the P3 endopod (enp-3 with spinous apophysis; see Fig. 7A–F) that characterizes these four genera. The absence of sexual dimorphism in the male antenna also excludes the species from assignment to Thalestrella and the lack of a transformed inner base spine in the male P1 prevents it from being accommodated in Foweya, Paraleptomesochra or Psammoleptomesochra. Johnwellsia bipartita sp. nov. appears to be morphologically closest to two species that were previously assigned to Parastenhelia, P. megarostrum and P. pyriformis, but which will be transferred to a new genus Porirualia gen. nov. below. Both species and J. bipartita sp. nov. share the same sexual dimorphism on P3, involving the loss of setation elements on male enp-3. In members of Porirualia gen. nov. the proximal inner seta of enp-3 is lost in the male while the further derived state (involving the additional loss of the distal inner seta) is observed in Johnwellsia gen. nov. (Fig. 7G–I). Two additional synapomorphies supporting a sistergroup relationships between these genera are the modification of the distal seta on the mandibular basis into a short spine, and the reduction of the outermost endopodal element of the P 5 in both sexes, being represented by a minute seta. Johnwellsia gen. nov. differs from Porirualia gen. nov. in the following characters: (a) rostrum reaching to middle of antennulary segment 2 (vs very large, reaching to at least halfway the fourth antennulary segment in the female); (b) antennule ♀ very slender with elongate segment 1 (vs more compact and segment 1 short); (c) antennary allobasis without abexopodal seta; (d) mandibular exopod rudimentary, represented by single seta on minute protuberance (vs 1-segmented with three setae); (e) maxillipedal basis with two setae (vs one seta); (f) P1 enp-1 inner seta long but not extending beyond distal margin of segment; (g) P2 endopod ♂ sexually dimorphic (2-segmented and distal inner seta of ♀ enp-3 lost in ♂; Fig. 6C); (h) P 5 ♀ without series of transverse striae along inner margin of endopodal lobe; and (i) P5 exopod ♂ 2-segmented, with four elements in total (vs 1-segmented, with 5–6 elements). Species of both genera also differ in the shape of the female P5 exopod which is moderately elongate and shares a very narrow articulation with the baseoendopod in Johnwellsia gen. nov. (Fig. 4C). The 2-segmented P5 exopod in the male is an unusual condition in the family, being found only in Parastenhelia willemvervoorti sp. nov. and Karaytugia aydini (Kuru & Karaytuğ, 2015) comb. nov. (Vervoort 1964; Kuru & Karaytuğ 2015; Table 1 herein).