Spinoncaea ivlevi Böttger-Schnack 2003
Creators: name: Böttger-Schnack, Ruth
Publisher: name: Zenodo
Year: 2003
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Copepoda
Poecilostomatoida
Oncaeidae
Spinoncaea
Spinoncaea ivlevi

description: SPINONCAEA IVLEVI (SHMELEVA, 1966) COMB. NOV.
Synonymy
Oncaea ivlevi Shmeleva, 1966 Original description
Shmeleva (1966): 932–933, Fig. 1.1–1.9 (♀), 1.10–1.11 (♂)
Other descriptions
Shmeleva (1969): 5–8, 27, Fig. 3a–i (♀), Fig. 4a–h (♂); Malt (1982): 186–187, 193, Fig. 3a–k (♀), 4a–d (♂)
Type locality
Southern Adriatic Sea, Stn. 46: 40∞40.8¢N, 18∞50¢E; Stn: 47: 40∞57.6¢N, 18∞48.3¢E; 0– 500 m.
Material examined
See Table 3 (a).
Preliminary note
In the following, the typical, ‘robust’ form of S. ivlevi from the Red Sea main basin is described in detail. Morphological differences of a more elongate female form variant occurring in the southern Red Sea will be given below under ‘ Variability ’. The taxonomic identity of the 2 forms will be discussed by detailed comparison with specimens of S. ivlevi (Shmeleva) from the type locality in the Adriatic Sea, comparing and discussing also the taxonomic status of specimens from various other geographical locations.
Description of female
Body length (measured in lateral aspect; from anterior margin of rostral area to posterior margin of caudal rami, calculated as sum of individual somites): 400 Mm [traditional method: 338 Mm, range: 330–340 Mm, based on 5 specimens from the Red Sea].
Exoskeleton well chitinized. Prosome 2.4 times length of urosome, excluding caudal rami, 2.0 times urosome length including caudal rami. P2-bearing somite without dorso-posterior projection in lateral aspect (Fig. 2B). Integumental pores on prosome as indicated in Fig. 2 (A,B). Pleural areas of P4-bearing somite with rounded posterolateral corners.
Proportional lengths (%) of urosomites are 8.8: 54.2: 8.8: 9.5: 18.7. Proportional lengths (%) of urosomites and caudal rami are 7.4: 46.0: 7.4: 8.1: 15.9: 15.2.
P5-bearing somite with 2 paired midventral spinous processes (Fig. 2E).
Posterior margin of genital double-somite and postgenital somites with lobate hyaline frill (Fig. 2C,D).
Genital double-somite 1.8 times as long as maximum width (measured in dorsal aspect) and 1.4 times as long as postgenital somites combined; variation in length to width ratio as shown in Table 4; lateral margins rounded, largest width measured at halfway the distance between anterior and posterior margin, posterior part tapering slightly. Pore pattern and ornamentation on dorsal surface as in Figure 2 (C); ventral surface with numerous rows of minute spinules (Fig. 2E). Paired genital apertures located dorsally at about 2/5 distance from anterior margin of genital double-somite; armature represented by 1 diminutive spinule (Fig. 2J).
1 Beside several females of the intermediate ivlevi -form this sample also contained 1 ♀ ivlevi - type, which was similar to the elongate form, but differed in the form of the genital double-somite, with lateral margins more rounded than in typical S. ivlevi; the specimen is regarded as ‘ ivlevi of uncertain taxonomic status’ here.
2 Morphological characters intermediate between S. tenuis and the elongate form of S. ivlevi (CR length to width ratio and size of spine III; see text).
3 For details of morphological characters see text.
Anal somite about as wide as long; slightly shorter than CR (measured along outer margin), or about as long as CR (measured along inner margin) (Fig. 2C), variation in length to width ratio as shown in Table 4. Paired dorsal sensillae anterior to anal operculum not found. Two pairs of secretory pores present dorsally near posterior margin. Anterior margin of anal opening (vestigial anal opening) with minute spinules. Posterior margin of somite finely serrate ventrally and laterally (Fig. 2C,D).
Caudal ramus (Fig. 2F) 1.8 times longer than wide measured along inner margin and 2.3 times longer than wide measured along outer margin; variation in length to width ratio as shown in Table 4. Armature consisting of 6 elements (for numbering of elements cf. Fig. 12F): seta II small, spiniform, and unornamented; seta III very strong, spiniform and ornamented with few minute spinules along medial margin, base of seta laterally concealed by serrate margin of CR (Fig. 2D,F); seta IV less than 1.5 times as long as seta III, bipinnate; seta V longest, lanceolate, naked at anterior half, with short pinnules bilaterally at posterior half; this seta easily gets lost during handling; seta VI short, about as long as seta III, bipinnate; seta VII long, about 2/3 length of seta V, bipinnate and biarticulate at base. Inner margin of CR with row of setules. Dorsal anterior surface (Fig. 2F) with secretory pore near insertion of seta II.
Antennule 6-segmented (Fig. 2G), weakly chitinized, relative lengths (%) of segments measured along posterior nonsetiferous margin 13.2: 12.7: 40.4: 13.2: 6.6: 13.9. Armature formula: 1-[3], 2-[8], 3-[5], 4-[2+ae], 5-[2 (ae not discernible)], 6-[5 + (1+ae)]. Aesthetasc on segment 4 very slender, aesthetasc on segment 5 not discernible, possibly absent [but see male, Fig. 5 (G)]; apical aesthetasc well developed and fused basally to adjacent seta. Segments 2 and 3 ornamented with short pinnules along nonsetiferous margin.
Antenna 3-segmented, distinctly reflexed (Fig. 3A). Coxobasis with row of long spinules along outer margin and few spinules of varying length along inner margin; with very long seta at inner distal corner, ornamented with strong spinules of decreasing length bilaterally. Endopod segments about equal in length; proximal endopod segment elongate-oval, expanded outer margin bearing spinular row(s) and 1 strong spine; posterior surface with row of short, strong denticles along inner margin; 2 strong denticles on anterior surface. Distal endopod segment about 3 times longer than wide, with narrow cylindrical base articulating with the proximal endopod segment; posterior surface with row of short spinules along outer margin; lateral armature consisting of 2 bare setae, with seta II shorter than seta I, and 1 long spiniform seta (III), ornamented with strong spinules bilaterally at distal half and unilaterally at proximal part, seta IV absent; distal armature consisting of 4 long spiniform setae (A–D), ornamented with spinules bilaterally at distal part and sometimes unilaterally along entire length (A), 3 naked setae (E–G) of varying length, posterior seta (G) extremely small.
Labrum (Fig. 3B,C) distinctly bilobed. Distal (ventral) margin of each lobe with 3 marginal teeth medially, differing slightly in size, long row of small spinules at outer ventral margin and row of small spinules or denticles along inner margin. Median concavity covered anteriorly by overlapping rows of fine spinules. Anterior surface (Fig. 3B) with paired row of long setules; median swelling weakly developed, with large secretory pore proximally. Posterior wall of medial concavity with two chitinized spinous teeth, flanked by row of minute denticles or spinules (Fig. 3C). Posterior face with 4 secretory pores located distally on lobe.
Mandible (Fig. 3D) gnathobase with 5 elements: 3 setae and 2 blades. Ventral element (A) as long as ventral blade (B), with long, fine setules along dorsal side; ventral blade strong and spiniform, unornamented; dorsal blade (C) strong and broad, spinulose along entire dorsal margin; dorsal elements (D,E) setiform and bipinnate, element D very short and inserting near base of seta E, difficult to discern in some specimens.
Maxillule (Fig. 3E) indistinctly bilobed, surface ornamentation not discernible. Inner lobe (praecoxal arthrite) with 3 elements: outermost element spiniform, swollen at base, ornamented with row of spinules and 1 coarse spinule, tip with tubular extension; middle element setiform and bare; innermost element smallest located along concave inner margin close to other elements, swollen at base and ornamented with 2 spinules. Outer lobe with 3 elements [innermost element absent]; outermost element curved and bare, similar in length to the following; element next innermost with long spinules unilaterally; innermost seta longest and bare.
Maxilla (Fig. 3F) 2-segmented, allobasis nearly as long as syncoxa. Syncoxa unarmed, surface ornamented with1 large secretory pore. Allobasis produced distally into slightly curved claw bearing 2 small spinules on outer margin and 2 rows of strong spinules along medial margin; spinules of inner row shorter, proximal group of 3 spinules on outer row longer, small gap between proximal and distal group; outer margin with strong seta extending to tip of allobasal claw, ornamented with long spinules bilaterally at distal part; inner margin with slender naked seta and strong basally swollen spine with double row of long spinules along the medial margin and few spinules along outer margin (Fig. 3F).
Maxilliped (Fig. 3G) 4-segmented, comprised of syncoxa, basis and 2-segmented endopod. Syncoxa unarmed, surface ornamentation not discerned. Basis elongate, palmar margin with 2 spiniform bipinnate elements, proximal element about half the length of distal one; fringe of short spatulated spinules between proximal seta and articulation with endopod; anterior surface with row of broad spatulated pinnules and short spinules of varying length along palmar margin as illustrated in Fig. 3 (G). Proximal endopod segment unarmed. Distal endopod segment drawn out into long curved claw, with pinnules along entire concave margin; accessory armature consisting of minute, naked seta on outer proximal margin and unipectinate spine fused basally to inner proximal corner of claw.
Swimming legs 1–4 biramous (Fig. 4A–D), with 3- segmented rami. Spine and setae formula as shown in Table 5. Intercoxal sclerites well developed, without ornamentation. Coxae and bases with sparse surface ornamentation as figured. Bases with plumose (P1) or naked (P2–P4) outer seta, arising from posterior surface, longest in P4; inner portion of basis slightly produced adaxially into rounded (P1) or pointed (P2–P3) process, bearing short spinule(s) along inner margin in P1–P2 (Fig. 4A,B), pointed process smallest in P4. Inner basal seta on P1 spiniform and naked. Respective legs without distinct length differences between exopod and endopod. Bases of spines on exopodal and endopodal segments anteriorly surrounded by small spinules, hardly discernible in P2–P4. Surface ornamentation of all segments sparse.
Exopods. Outer margin of exopod segments with well developed serrated hyaline lamella; inner margin of proximal exopod segments with long setules. Secretory pore present on posterior surface of distal segments, also present on anterior surface of P2. Hyaline lamellae on outer spines well developed; outer and terminal spines of P1 with subapical tubular extension, except for spine on exp-2 and proximalmost spine on exp-3. Spine on middle segment and proximal spine on distal segment of P2 reduced in length. Terminal spine equal in length to (P1) or shorter than (P2–P4) distal exopod segment.
Endopods. Outer margin of endopod segments with fringe of long setules, except for first endopod segment of P4. Inner seta of proximal endopod segment short, slightly swollen and ornamented with spinules bilaterally (P1–P3) or spiniform with strong spinules bilaterally (P4). Inner setae of P4 reduced in length, in particular setae on middle segment, with proximal seta reaching little further than insertion of distal seta and distal seta reaching only half length of seta on distal segment. Distal endopod segments with large secretory pore in P1 and P4, located on anterior surface (P1) or on posterior surface (P4). Inner margin of P1 enp-2 ornamented with 2 long spinules (arrowed in Fig. 4A). Distal margin of P1 enp-1- and -2 ornamented with row of denticles or spinules on anterior face; outer margin of enpd-3 terminating in long process obscuring insertion of distalmost inner seta, process ornamented with short spinule. Distal margin of P2–P3 not produced into conical process, but apical pore of reduced process present, located laterally between subdistal and distal spine (Fig. 4B,C). Outer subdistal spine on P3 equal in length to outer distal spine, reaching as far as insertion of this spine. Inner setae of distal endopod segments in P2–4 with spinule comb along proximal inner margin; this comb less obvious in P1; also present on distal inner seta of middle endopod segment in P2–P4.
P5 (Fig. 2I,H) comprised of long, naked seta arising from lateral surface of somite, and small free segment representing exopod. Exopod 1.6 times longer than wide, bearing single long, bare seta; posterior margin ornamented with small spinule ventrally (Fig. 2I) and small spinous process dorsally (Fig. 2H).
P6 (Fig. 2J) represented by operculum closing off each genital aperture; armed with a short spinule, variable in conspicuousness (e.g. not discerned in specimen from Monterey Bay, cf. Fig. 7A).
Egg-sacs paired (Fig. 2K), each sac containing 2 large eggs (diameter 40–50 Mm).
Description of male
Body length: 369 Mm [traditional method: 313 Mm, range: 310–320 Mm, based on 3 specimens from the Red Sea]. Pore pattern as in Fig. 5 (A). Sexual dimorphism in antennule, maxilliped, P6, and in genital segmentation, slight modification in setal length of P5. Proportional lengths (%) of urosomites (excluding caudal rami) 9.2: 61.3: 4.0: 4.0: 4.8: 16.7; proportional lengths (%) of urosomites (caudal rami included) 7.9: 52.6: 3.4: 3.4: 4.1: 14.3: 14.3. Posterior margin of leg 5-bearing somite with paired row of 2 or 3 midventral spinous processes (Fig. 5E). Caudal rami 1.9 times longer than wide measured along inner margin and 2.5 times longer than wide measured along outer margin, similar to female. Caudal setae with proportional lengths as in female. Dorsal surface of genital somite covered with minute denticles or spinules, arranged in a specific pattern (Fig. 5D) and a paired posterolateral pore. Surface of genital flaps and ventral surface of anal segment ornamented with several rows of strong denticles or spinules and a paired posterolateral pore (Fig. 5E,F). Ventral surface of caudal ramus with secretory pore near posterior margin (Fig. 5E).
Antennule (Fig. 5G) 4-segmented; distal segment corresponding to fused segments 4–6 of female; relative lengths (%) of segments measured along posterior nonsetiferous margin 9.0: 19.3: 40.7: 31.0. Armature formula: 1-[3], 2-[8], 3-[4], 4-[9 + 2ae + (1+ae)], aesthetascs very small and slender, small middle aesthetasc close to seta, which is not discernible in the female, shown separately in Fig. 5 (G), apical aesthetasc fused basally to adjacent seta.
Antenna as in female.
Maxilliped (Fig. 5B,C) 3-segmented, comprising syncoxa, basis and 1-segmented endopod. Syncoxa with single secretory pore at inner distal margin, unarmed. Basis elongate, moderately inflated in proximal half, forming small bulbous swelling; anterior surface with row of short spinules along palmar margin, developed into small distal flap (Fig. 5B), short row of spinules proximally; posterior surface with 2–3 rows of short spatulated spinules of graduated length along palmar margin (Fig. 5B,C); with 1 long setae within the longitudinal cleft, ornamented with strong spinules bilaterally, corresponding to distal seta in female, proximal seta absent (Fig. 5B). Endopod drawn out into long curved claw, concave margin ornamented with pinnules along entire concave margin as in female; accessory armature consisting of short, unipectinate spine basally fused to inner proximal corner of claw; tip of claw without hyaline apex.
P1–P4 with armature as in female; length of inner setae on middle segment of P4 as in robust form of female.
P5 (Fig. 5E,F) exopod with general shape and armature as in female; exopodal seta and long seta arising from lateral surface of somite somewhat shorter than in female.
P6 (Fig. 5E) represented by posterolateral flap closing off genital aperture on either side; covered by pattern of strong denticles as shown in Fig. 5 (E); posterolateral corners protruding laterally so that they are well discernible in dorsal aspect (Fig. 5D).
Spermatophore oval (Fig. 5E), of variable size according to state of maturity; swelling of spermatophore during development not affecting shape and relative size of genital somite.
Remarks
Taxonomy. Shmeleva (1966) described both sexes of Oncaea ivlevi from the southern Adriatic Sea and figured the female habitus, antennule, antenna, maxilliped and swimming legs, as well as the dorsal aspect of the male. Later, she published a French version of the original Russian description by including material from the equatorial Atlantic and provided figures of the habitus, antenna, maxilliped and swimming legs for both sexes as well as the female antennule (Shmeleva, 1969). The setal count of female P3 differed between the 2 publications: the correct number of 2 setae is figured in the original description (1966: fig. 1.8), whereas only 1 seta was figured in the subsequent account (1969: fig. 3h). In both descriptions the inner seta on the distal endopod segment of P4 is lacking in the female (1966: fig. 1.9; 1969: fig. 3i), whereas in the male P4, the presence of this seta might be deduced from the insertion figured (fig. 4h). The inner seta on P4 can easily be overlooked, because it is located on the posterior surface of the segment (cf. Figs 3D and 5C,G). Shmeleva figured the basis of P2 with a long spine at the adaxially produced inner margin (1966: fig. 1.7; 1969: fig. 3g), which was not confirmed during the present study and is not found in any other oncaeid species known to date.
Several other elements are incomplete or missing in Shmeleva’s figures, such as the number of elements on the caudal ramus in both sexes, the lateral and distal armature of the antenna and the armature of the antennule. Also, the level of detail required for taxonomic descriptions of oncaeids is not met by her figures (e.g. the ornamentation of the proximal basal seta and the distal endopod segment (claw) on the maxilliped are missing). Shmeleva erroneously described the exopod of P5 as having 2 setae (1966: p. 933), not just one, and did not mention the seta on the P5- bearing somite near the leg; it might be possible that she mixed up the two elements by mistake. In the male, the sexually dimorphic antennule and the lack of the proximal basal element on the maxilliped was not noted by Shmeleva (1966, 1969). Her description of sexually dimorphic distal endopod spines in P3 and P4, being shorter in the male (1969: fig. 4g,h), was not confirmed upon re-examination of specimens from the Adriatic and/or the Red Sea.
Despite the differences between Shmeleva’s description and the present account, specimens from the Red Sea were regarded as conspecific with O. ivlevi on the basis of (1) the leg armature and (2) the possession of a very strong spinous seta III on the caudal ramus. The second character is also found in the closely related Spinoncaea humesi sp. nov., but differences in the leg armature clearly separate the two species (see below). The identification of Red Sea S. ivlevi was furthermore supported by comparison with specimens from the Adriatic Sea, which appeared to be conspecific. Differences between specimens from the two areas are summarized and discussed below under ‘Variability’.
Spinoncaea ivlevi is closely related to S. tenuis sp. nov. and S. humesi sp. nov., which are described in the present account. It differs from its congeners by the number of elements on the mandible, showing the full complement of 5 elements (with seta D small in size), whereas a reduced number of 4 elements (seta D absent) is found in S. tenuis and S. humesi. From S. tenuis it can be furthermore separated by (1) the proportional lengths of the urosomites, (2) the much stronger spine (III) on the CR, (3) the different form of seta IV, which is setiform and not dilated as in S. tenuis and (4) the length of seta V, which is much shorter than in S. tenuis. Another difference was found in the ornamentation of the inner margin of P4 enp-2, showing the typical fringe of long setules in S. ivlevi, as compared to only one long spinule in S. tenuis. However, the consistency of this character needs to be confirmed by further studies. S. ivlevi and S. humesi can be separated most easily by the different spine count on the distal endopod segment of P2, showing 3 spines in S. ivlevi, but only 2 spines in S. humesi. The two species also differ in (1) the form of the genital doublesomite, which is barrel-shaped in S. humesi, (2) the proportions of the distal endopod segment of the antenna, (3) the length of basal seta on P4 and (4) the length of the seta near P5, representing the outer basal seta of the incorporated protopod of leg 5. Further differences between the two species, including details of ornamentation, are described below under ‘ Remarks’ of S. humesi.
Variability. Two form variants of female Spinoncaea ivlevi were found in the Red Sea, a robust form as described above and an elongate form, which differed in the length to width ratio of the genital doublesomite, the anal somite and the caudal ramus: generally, the elongate form showed higher ratios than the robust form (Table 4). The elongate form differed from the robust form in the following characters: (1) total body length smaller than robust form, measuring 388 Mm [traditional method: 310 Mm, based on 2 specimens from southern Red Sea]; (2) exoskeleton less chitinized than robust form; (3) prosome 2.2 times length of urosome, excluding caudal rami, 1.8 times urosome length including caudal rami (Fig. 6A); (4) proportional lengths (%) of urosomites and caudal rami are 7.3: 46.1: 7.0: 7.3: 15.7: 16.4 (Fig. 6B); (5) P5-bearing somite with number of midventral spinous processes differing between left (2 processes) and right (3 processes) side of specimen examined (Fig. 6B); (6) genital double-somite more elongate than in robust form, 1.9 times as long as maximum width (measured in dorsal aspect) and 1.5 times as long as postgenital somites combined, lateral margins rounded in anterior half, largest width measured at 4/5 the distance between anterior and posterior margin, posterior part tapering gradually (Fig. 6B); (7) anal somite 1.3 times longer than wide; about as long as CR (measured along outer margin) or distinctly longer than CR (measured along inner margin) (Fig. 6B); (8) caudal ramus about twice as long as wide measured along inner margin and 2.5 times longer than wide measured along outer margin; armature and ornamentation as in robust form, except for seta II ornamented with a single long spinule (Fig. 6B) – seta V lacking in all Red Sea specimens examined; and (9) reduced inner setae on P4 enp-2 shorter than in robust form, with proximal seta hardly reaching insertion of distal seta and distal seta reaching little further than insertion of inner seta on distal segment (Fig. 6C). Antennule, antenna, and mouthparts of the Red Sea elongate form were not examined in detail. Males of S. ivlevi in the Red Sea could not be separated into the 2 forms during the present study, because they did not exhibit morphological differences in general habitus corresponding to the two female forms, and microscopical examination of undissected specimens gave no clear evidence of differences in the setal length on P4 enp-2 (see above under no. 9). Thus, the observed morphological differences of the females were not regarded sufficient to warrant a separation of the two forms into different species and they are regarded as conspecific in the present paper.
The reference material of female S. ivlevi from the type locality in the Adriatic Sea corresponded to the elongate form from the Red Sea in all morphological characters described above (Fig. 6D–G, Table 4). Antennule, antenna, and mouthparts of the Adriatic specimens were examined in detail and proved to be similar in morphology to the typical ‘robust’ form from the Red Sea. The single male specimen available from the Adriatic Sea was similar in dorsal aspect (Fig. 7B) and size [310 Mm, traditional method] to specimens from the Red Sea, with minor differences in the length of exopodal seta on P5, being somewhat shorter, and the proportional lengths of caudal setae, with seta IV being slightly longer than in Red Sea specimens. The proportional lengths of endopodal seta on P4 could not be clearly investigated on the single specimen available, which was undissected. At present, it cannot be decided, which one of the 2 forms of S. ivlevi is conspecific with O. ivlevi sensu Shmeleva, because it is not known whether the robust form of S. ivlevi occurs in the Adriatic Sea as well. If subsequent investigations confirm that only the elongate form occurs in the Adriatic Sea, this form should be identified as the original S. ivlevi and one of the female specimens examined during the present study might then be designated as the neotype (Fig. 6A, Table 3 (a), ZMH reg. no. K-40095). If subsequent investigations prove both forms to be found in the type locality, however, it has to be decided by the next reviewer which one of the two forms will be designated as the neotype, as Shmeleva’s original description does not give sufficient information to solve this question. Pending the solution of this problem both forms are regarded as O. ivlevi sensu lato.
In the Red Sea, the two forms of S. ivlevi differed in regional distribution. The robust form was distributed in the entire Red Sea main basin, extending to the northernmost parts and the Gulf of Aqaba (Böttger-Schnack et al., 2001), whereas the elongate form has thus far been found only in the southernmost Red Sea and in the Gulf of Aden. Outside the Red Sea, specimens similar to the ‘robust’ form of S. ivlevi were recorded from the eastern Mediterranean, the NE Indian Ocean (oceanic and off NW Cape of Australia) as well as in the NW Pacific (Kuroshio extension) and the NE Pacific (Monterey Bay) during the present study (Tables 3 and 4). Specimens close to the ‘elongate’ form of S. ivlevi were recorded from the Adriatic Sea (see above), from the eastern Mediterranean and from the NE Indian Ocean and the NW Pacific (Tables 3 and 4). The morphological characteristics of the form variants differed somewhat between geographical regions, thus making unequivocal designation to either form difficult. The ‘robust’ form of S. ivlevi in the eastern Mediterranean, for instance, showed a combination of characters of the two Red Sea forms: the length to width ratio of the anal somite was intermediate between the robust and the elongate form of Red Sea S. ivlevi, whereas the caudal rami of the Mediterranean robust type were more similar to the Red Sea elongate form (Table 4). Despite these morphological differences, the Mediterranean form was called ‘robust’, in order to differentiate it from a more ‘elongate’ form of S. ivlevi found in this area, whose main characteristic, i.e. the elongate genital double-somite, was even more pronounced than that of the elongate form in the Red Sea. The length to width ratio of the anal somite of the ‘elongate’ form from the eastern Mediterranean was intermediate between the two Red Sea forms (Table 4); however, the specimens were assigned to the elongate form based on the shape of the genital double-somite and the reduced setal length on the second endopod segment in P4. The specimen from Monterey showed a length to width ratio of the anal somite intermediate between the two forms of S. ivlevi from the Red Sea (Table 4). It was classified as a ‘robust’ form primarily on the basis of the setal length on the second endopod segment of P4 [which can be examined without dissecting the specimen].
The classification of form variants of S. ivlevi from geographical localities other than the Red Sea and the type locality (Adriatic Sea) during the present study was based on a limited number of morphological characters which can be examined without dissecting the specimens. More detailed taxonomic examinations of S. ivlevi from the world ocean, including the mouthparts and more details of the swimming legs, are needed to clarify the taxonomic status of the various form variants. Future taxonomic investigations should a priori focus on Spinoncaea species from the Adriatic Sea, in order to elucidate the remaining uncertainties in the identification of the species from the type locality of S. ivlevi.
Other records of S. ivlevi. A taxonomic record of Spinoncaea ivlevi was given by Malt (1982; as Oncaea ivlevi), who redescribed the species from the NE Atlantic. She noted some morphological differences between her specimens and Shmeleva’s original description, such as the armature of the caudal rami, the ornamentation of maxillipedal elements and the length of the terminal spine on the exopods of swimming legs, all of which were similar to those described for Red Sea specimens in the present paper. The apparent sexual difference in endopodal spine lengths as described by Shmeleva (1969) was not commented upon by Malt (1982). Malt’s redescription of S. ivlevi includes an incomplete figure of the maxilla, but the remaining mouthparts are lacking. In her redescription, the number of elements on the antennule (fig. 3d) is incomplete and one element is missing on the lateral armature of the antenna (fig. 3e). In the swimming legs (fig. 3I–k) she erroneously figured the seta on the first endopod segment in P1–P4 as being long and slender, not swollen and reduced in length as typical for Spinoncaea (in particular in P4); also, the proximal seta on the second endopod segment in P4 is as long as the distal seta (fig. 3k), not short and spiniform. In the male maxilliped, she erroneously reported two short palmar setae (p. 187, fig. 4d), not one long seta as typically found in the ivlevi-group. The lack of detail of her figures makes it difficult to assign her specimens to one of the two form variants of S. ivlevi. Malt’s statement (p.187) that the second endopod segments of P2–P4 have ‘relatively small conical projections’ seems to be erroneous, because it does not match with her figures. Instead, she figured the distal exopod segment of P4 having a conical projection (fig. 3k), which is not found in Spinoncaea species.
In a comprehensive study on the seasonal and vertical distribution of microcopepods in the Adriatic Sea, Kršinić (1998) reported S. ivlevi as a dominant species in the 50–300 m layer. In the zone of its maximum abundance, at 100–200 m, the species contributed about 30% to the total number of oncaeids (F. Kršinić, unpubl. data). Kršinić was not aware of the closely related S. tenuis sp. nov., which was found to co-occur with S. ivlevi in the epipelagic zone of the Adriatic during the present study. Thus, he might have included both species under the name O. ivlevi.
Ecological notes
Geographical distribution. Spinoncaea ivlevi is distributed in the entire Red Sea, including its northernmost extension, the Gulf of Aqaba (Böttger-Schnack et al., 2001). In the Strait of Bab al Mandab, at the southern entrance of the Red Sea, a great number of unidentified copepods of the ivlevi -group had been reported by Böttger-Schnack (1995; as Oncaea ivlevi / K). Re-examination of parts of this material during the present study showed that the samples contained a mixture of S. ivlevi elongate form, S. tenuis and S. humesi. In the adjacent Arabian Sea, living S. ivlevi have not yet been recorded, but a number of empty exoskeletons (carcasses) were found in the central region indicating less favourable environmental conditions for the species during the sampling period (Böttger-Schnack, 1996). Unidentified specimens of the ivlevi -group from the northern Arabian Sea (Böttger-Schnack, 1996; as Oncaea sp. D) were found to consist of S. tenuis and tregoubovi - type specimens upon recent re-examination.
Vertical distribution and vertical migration. The vertical distribution of S. ivlevi in the Red Sea needs to be re-evaluated, because the species was not separated from the closely related S. humesi during the earlier quantitative studies (Böttger-Schnack, 1988, 1990a,b, 1995; as Oncaea ivlevi typical form). Generally, the two species combined exhibited an unimodal distribution in the lower epipelagic zone, with maximum abundances at 50–100 (200) m and no diurnal vertical migration became apparent (Böttger-Schnack, 1990a). Females usually were vertically more extended than males. Seasonal and/or regional differences from this distribution pattern during various seasons and in different regions of the Red Sea appeared to be minor (Böttger-Schnack, 1990b, 1995 and unpubl. data). An evaluation of the species specific distribution pattern of S. ivlevi and S. humesi in the northernmost Red Sea and the Gulf of Aqaba is in progress (R. Böttger-Schnack & W. Hagen, in prep.).
description: Published as part of 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, pp. 187-226 in Zoological Journal of the Linnean Society 137 (2) on pages 193-207, DOI: 10.1046/j.1096-3642.2003.00056.x, http://zenodo.org/record/4634423