Spinoncaea, Böttger-Schnack, 2003

Böttger-Schnack, Ruth, 2003, Taxonomy of Oncaeidae (Copepoda, Poecilostomatoida) from the Red Sea. V. Three species of Spinoncaea gen. nov. (ivlevi-group), with notes on zoogeographical distribution, Zoological Journal of the Linnean Society 137 (2), pp. 187-226 : 189-193

GENUS SPINONCAEA GEN. NOV.

Diagnosis

Oncaeidae . Body cyclopiform, prosome elongate. P2- bearing somite without dorsoposterior projection in female. Cephalosome without lateral lobate extensions. P5-bearing somite with 2 or 3 paired midventral spinous processes. Genital double-somite in female oval or oval-elongate, not swollen dorsally; with several transverse spinule rows ventrally. First and second postgenital somites shorter than anal somite. Posterior margins of urosomites with lobate or undulate hyaline frill. Anal somite with wide anal opening; vestigial operculum with minute spinules. Exoskeleton moderately chitinized.

Sexual dimorphism in antennule segmentation and armature, maxilliped, genital segmentation and ornamentation, and P6; slight modifications also in P5, sometimes in caudal rami and in number of midventral spinous processes on P5-bearing somite.

Antennule 6-segmented in female, with armature formula 1-[3], 2-[8], 3-[5], 4-[2+ae], 5-[2 (ae absent or not discernible)], 6-[5 + (1+ae)]; 4-segmented in male, with formula 1-[3], 2-[8], 3-[4], 4-[9 + 2ae + (1+ae)]. Distalmost seta of female segment 3 absent in male. Proximal aesthetascs short and delicate, aesthetasc on segment 5 not discernible in female, possibly absent. Spinular row along inner nonsetiferous margin of segment 2 and 3 (absent in S. humesi ).

Antenna prehensile. Enp-1 without projection on outer margin; inner margin with denticular row. Enp- 2 about as long as enp-1; posterior surface with single row of spinules; lateral armature consisting of 2 bare setae (seta IV absent) and 1 long spiniform seta with strong spinules (III); distal armature consisting of 4 strong setae (A–D), ornamented with spinules bilaterally at distal part and unilaterally in some cases along entire length, and 3 bare setae (E–G) of varying length, seta G very short, all elements shorter in length than setae A–D.

Labrum distinctly bilobate. Lobes with 3–4 marginal teeth apically flanked by row of small spinules. Median concavity membranous, with anterior patch of overlapping spinules. Posterior face with group of 3–4 large pores near apical margin of each lobe; with 2 sclerotized teeth medially. Anterior face without paired integumental pockets or slit-like pores; spinular row(s) present.

Mandible with 2 blades and 2 or 3 setae. Seta A as long as blade B. [Blades fused basally along posterior surface; dorsal concavity of B cupping ventral basal process of C.] Blade C spinulose along entire dorsal margin. Seta D spiniform and very short ( S. ivlevi ) or absent ( S. humesi sp. nov., S. tenuis sp. nov.). Seta E longest, spiniform and multipinnate.

Maxillule weakly bilobate, with 6 elements: inner lobe (= praecoxal arthrite) with 3 elements, innermost one not distinctly displaced, outermost element spiniform and bearing 2 rows of spinules; outer lobe with 3 elements, setiform and sparsely pinnate or naked, innermost element absent.

Maxilla with allobasis equal in length to syncoxa.

Maxilliped ♀ ovoid-elongate. Basis without ornamentation on posterior surface; anterior surface with double row of strong, spatulated setules along palmar margin and additional spinular row increasing in length distally; both palmar elements spiniform, proximal one about half the length of distal one, bipinnate ( ivlevi ) or bare, distal one bipinnate. Enp-1 completely separated. Enp-2 with long, pinnate claw, rudimentary outer setule, and fused unipinnate inner spine.

Maxilliped ♂. Palmar margin forming shallow longitudinal cleft bordered by anterior fringe of short blunt setules, developed into small distal flap, and posterior 2 or 3 rows of coarse, blunt spinules. Anterior surface of basis with short spinular row near distal seta ( ivlevi ) or unornamented. Distal palmar seta long and bipinnate, proximal seta absent. Endopodal claw curved, pinnate, without hyaline apex.

(a) S. ivlevi , S. tenuis sp. nov. (b) S. humesi sp. nov.

Swimming leg armature formula given in Table 2 (interspecific differences in exopodal spine count marked in bold).

Intercoxal sclerite of P1 sometimes ornamented with paired row of long, fine spinules.

Outer basal seta very long in P4, sometimes exceeding length of exopod.

P1 exopod. Outer and terminal spines with subapical tubular extension, which is lacking on exp-2 and on proximalmost spine of exp-3; lateral spines on exp-3 slightly increasing in size distally.

P1 endopod. Enp-1 with inner seta sometimes spiniform and reduced in length. Enp-2 with few, long spinules along inner margin. Enp-3 outer spine stout, with narrow serrate hyaline flanges; base of distal inner seta concealed beneath long anterior spinous outgrowth of segment.

P2-P4 exopods. Outer spines stout, with broad serrate hyaline flanges; lateral spines on P2 exp-3 (not on P3–P4) slightly increasing in size distally.

P2-P4 endopods 3-segmented. Enp-1 with inner seta short and spiniform, with strong spinules, particularly in P4. Enp-2 of P4 with both inner setae reduced in length, proximal one much shorter than distal one. Enp-3 longer than enp-1 and -2 combined; without conical processes. Enp-3 inner distal spine slightly increasing in length from P2–P4, with moderately narrow serrate hyaline flanges; outer distal and outer spines small, serrate hyaline flanges very narrow or sometimes even absent (P4).

P5 represented by very long outer basal seta and small exopod delimited from somite; exopodal seta long and setiform, naked or sparsely plumose. Sexual dimorphism in length of exopodal seta.

Genital apertures of ♀ large, located at about midregion of dorsal surface of genital double-somite; each operculum with small spinule, which is hardly discernible.

Male P6 membranous flaps produced posterolaterally into spinous process; without armature.

Caudal ramus about two to three times as long as wide; variation in length to width ratio within and between geographical regions; without conspicuous dorsal expansion surrounding base of seta VII. Seta I absent; setae II small, spiniform and naked or with 2 spinules; element III a modified strong spine, sometimes ornamented with few spinules along medial margin, base of spine concealed by extended posterolateral margin of CR; setae IV less than 3 times longer than seta III, indistinctly dilated; seta V with anterior half distinctly dilated and naked, posterior part with short pinnules, seta VI short, sometimes bipinnate, not fused basally to seta V; seta VII long and naked or sparsely plumose. No seta displaced.

Etymology

The generic name is derived from the Latin spina, meaning spine, and refers to the spiniform posterolateral seta (III) on the caudal ramus. Gender: feminine.

Type species: Oncaea ivlevi Shmeleva, 1966 = Spinoncaea ivlevi ( Shmeleva, 1966) comb. nov.

Other species: Spinoncaea humesi sp. nov. Spinoncaea tenuis sp. nov.

Phylogenetic relationships

The new genus Spinoncaea is closely related to O. tregoubovi Shmeleva, 1968 , Monothula subtilis ( Giesbrecht, 1892) , and Oncaea curvata Giesbrecht, 1902 , which together were found to form a robust clade within the family Oncaeidae ( Böttger-Schnack & Huys, 2001: figure 6). Oncaea prendeli Shmeleva, 1966 , which had not been available for the earlier phylogenetic studies, was assigned to this clade upon recent examination of specimens from the type locality in the Adriatic Sea. The Red Sea species Oncaea sp. K , which was erroneously named ‘ prendeli ’ in the earlier phylogenetic study by Böttger-Schnack & Huys (1998), will be described as a new species, Spinoncaea tenuis , in the present account. In the discussion, Böttger-Schnack & Huys (2001) pointed to the discrepancies in topology of the clade as compared to the preliminary consensus tree presented by Böttger-Schnack & Huys (1998), which were attributed to refinement of the data set by recent examination of the small species and the addition of characters which had previously been ignored or neglected. The monophyly of the revised clade was supported by the following characters: (1) the prehensile antenna in which the distal endopodal segment is elongate and slender, typically articulating with the proximal endopodal segment by means of a narrow base, and being distinctly longer than this segment; (2) the reduction of element IV on the antenna; (3) the secondarily enlarged proximal palmar seta on the male maxilliped, being much longer than the distal seta, whereas in all other oncaeids both setae are about equally long or the distal seta is markedly longer than the proximal seta; (4) the presence of a spinular row along the inner margin of P1 enp-2; this row is somewhat reduced in S. ivlevi and S. tenuis sp. nov., but still represented by a few long spinules, whereas in other Oncaeidae the margin of this segment is naked. The first character, a prehensile antenna, has evolved independently in other oncaeid lineages such as Conaea and Epicalymma , but this was regarded as the product of convergence by Böttger-Schnack & Huys (2001). The last two characters appear to be unique for the clade. All species of the clade show a close resemblance in labral structure, particularly the presence of 2 medial teeth on the posterior face of the concavity. The ornamentation of the labrum has proven to be of great importance in unravelling phylogenetic relationships within the Oncaeidae ( Böttger-Schnack & Huys, 1998) .

Two lineages were defined within the clade by Böttger-Schnack & Huys (2001): the tregoubovi – ivlevi - group lineage and the subtilis – curvata lineage. O. tregoubovi and the ivlevi -group cluster together on the basis of the following synapomorphies: (1) the presence of midventral spinous processes on the P5- bearing somite; (2) the reduction of the P5 exopod, being represented by a small free segment but retaining only 1 seta (and 1 spinule); and (3) the dilated caudal rami setae IV and (particularly) V. Within this clade, O. tregoubovi occupies the most primitive position. The monophyly of the ivlevi -group was substantiated by two synapomorphies: (1) hyaline frill of urosomites undulate or lobate; and (2) modification of caudal ramus seta III into a very strong spiniform element. Further differences between O. tregoubovi and the ivlevi -group found during the present study include (1) antennary seta IV being absent in ivlevi - group (small in tregoubovi ), (2) maxillule with 6 elements (7 in tregoubovi ), (3) distal palmar seta on male maxilliped absent (small in tregoubovi ) and (4) the relatively short caudal seta IV (long in tregoubovi ). Based on these morphological findings and supported by strong indications from our faunistic studies that the two taxa represent species complexes, both O. tregoubovi and the ivlevi -group are now attributed to generic rank. Oncaea prendeli , which had not been available for study during the earlier phylogenetic analyses, was recently re-examined based on material from the Adriatic Sea and is tentatively assigned to the tregoubovi -lineage of oncaeids. A detailed redescription of O. tregoubovi and O. prendeli is in progress, which will also include a summary of morphological characters separating the two species from Spinoncaea (R. Böttger-Schnack & R. Huys, in prep.).

The sister-group of O. tregoubovi and the ivlevi - group, the subtilis – curvata clade, is supported by: (1) the fusion of the P5 exopod to the supporting somite (but retaining its full complement of setae), and (2) the secondarily enlarged postgenital somites in the female, which are as long as or even longer than the anal somite. A further synapomorphy of this clade mentioned by Böttger-Schnack & Huys (2001) is the presence of marginal teeth apically on each lobe of the labrum, however, this character was found to be shared by the ivlevi -group upon recent reexamination.

Spinoncaea species differ in exopodal spine count on swimming leg 2, showing 2 spines ( S. humesi ) or the typical number of 3 spines ( S. ivlevi and S. tenuis ) on the distal segment. In other oncaeid genera, usually the swimming leg armature is uniform for all species (e.g. Triconia , Oncaea s.str.); however, differences in the exopodal spine count on leg 2 were also observed in a recently described new Red Sea species belonging to the zernovi -group ( Böttger-Schnack, 2002), indicating that this phenomenon might be more widespread in oncaeids than previously known.