Spinoncaea humesi, Böttger-Schnack, Ruth, 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 : 208-215

SPINONCAEA HUMESI SP. NOV.

Synonymy

None.

Type locality

Northernmost Red Sea, 27∞25.00¢N, 34∞04.98¢E: Stn. 156; R/V Meteor leg 44/2: collected 4 March 1999 with MSN 0.055 mm net (Haul 9/3); depth 300–350 m; total water depth 798 m

.

Material examined

See Table 3 (b).

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): 381 Mm [traditional method: 310–320 Mm, based on several specimens].

Exoskeleton well chitinized. Prosome 2.0 times length of urosome, excluding caudal rami, 1.7 times urosome length including caudal rami. P2-bearing somite without dorso-posterior projection in lateral aspect ( Fig. 8B ). Integumental pores on prosome as indicated in Fig. 8 (A,B). Pleural areas of P4-bearing somite with rounded posterolateral corners.

Proportional lengths (%) of urosomites are 8.3: 51.7: 10.3: 9.5: 20.2. Proportional lengths (%) of urosomites and caudal rami are 7.0: 43.5: 8.7: 8.0: 17.1: 15.7.

P5-bearing somite with 3 paired midventral spinous processes ( Fig. 8E ).

Genital double-somite elongate barrel-shaped, 1.9 times as long as maximum width (measured in dorsal aspect) and 1.3 times as long as postgenital somites combined. Pore pattern and ornamentation on dorsal surface as in Fig. 8 (C); ventral surface with numerous rows of minute spinules ( Fig. 8E ). Paired genital apertures located dorsally at about 2/5 distance from anterior margin of genital double-somite; armature represented by 1 diminutive spinule ( Fig. 8J ).

Anal somite1.2 times longer than wide; slightly shorter than CR (measured along outer margin), or about as long as CR (measured along inner margin) ( Fig. 8C ), variation in length to width ratio as shown in Table 7 . Two pairs of secretory pores present dorsally near posterior margin. Paired dorsal sensillae anterior to anal operculum not found, possibly absent. Anterior margin of anal opening (vestigial anal opening) with minute spinules. Posterior margin of somite finely serrate ventrally and laterally ( Fig. 8C,D ).

Caudal ramus ( Fig. 8F ) 2.6 times longer than wide measured along inner margin and about 3 times longer than wide measured along outer margin; variation in length to width ratio of CR observed for specimens from the eastern Mediterranean and Indo-Pacific region as indicated in Table 7 . 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. 8D,F ); seta IV 1.5 times longer than seta III, bipinnate; seta V longest, dilated, naked at anterior half, with long pinnules bilaterally at posterior half [this seta easily gets lost during handling]; seta VI distinctly shorter than seta III, naked; seta VII long, about 2/3 length of seta V, plumose at distal part and bi-articulate at base. Inner margin of CR unornamented, posterior margin finely serrate ventrally. Dorsal anterior surface ( Fig. 8F ) with secretory pore near insertion of seta II.

Antennule 6-segmented ( Fig. 8G ), weakly chitinized, relative lengths (%) of segments measured along posterior nonsetiferous margin 7.5: 13.4: 45.2: 12.4: 7.5: 14.0. Armature formula: 1-[3], 2-[8], 3-[5], 4-[2+ae], 5-[2 (ae not discernible)], 6-[5 + (1+ae)]. Aesthetasc on segment 4 small and slender, aesthetasc on segment 5 not discerned [but present in male, arrowed in Fig. 11 (G)]; apical aesthetasc well developed and fused basally to adjacent seta. Segments 2 and 3 without ornamentation along inner, nonsetiferous margin.

Antenna 3-segmented, distinctly reflexed ( Fig. 9A ). Coxobasis with row of long spinules along outer margin and few strong spinules along inner margin; with very long seta at inner distal corner, ornamented with spinules bilaterally and 1 long spinule at distal part. Endopod segments unequal in length; proximal endopod segment elongate-oval, slightly expanded outer margin bearing short spinular row and 1 strong spine; posterior surface with row of short, strong denticles along inner margin; ornamentation on anterior surface not discerned. Distal endopod segment slightly longer than proximal segment, about 4 times longer than wide, with narrow cylindrical base articulating with the proximal endopod segment; posterior surface with long row of short spinules along outer margin; lateral armature consisting of 2 bare setae, with seta II slightly longer than seta I [for numbering of elements cf. Fig. 3 (A)], 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 unilaterally along entire length (A) or at distal part (C,D), 2 naked setae (E,F) of similar length and 1 very small posterior seta (G).

Labrum ( Fig. 9B,C ) distinctly bilobed. Distal (ventral) margin of each lobe with 4 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. 9B ) with 2 paired rows 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. 9C ). Posterior face with 3 secretory pores located distally on lobe.

Mandible ( Fig. 9D ) gnathobase with 4 elements: 2 setae and 2 blades (for numbers of elements cf. Fig. 3D ). 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; small dorsal seta D absent; dorsal element (E) setiform and bipinnate.

Maxillule ( Fig. 9E ) indistinctly bilobed, surface ornamentation not discernible. Inner lobe (praecoxal arthrite) with 3 elements: outermost element spiniform, swollen at base, ornamented with row of spinules along 1 side and several spinules on the other side, 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 1 (or 2?) spinules. Outer lobe with 3 setiform elements [innermost element absent], which are curved and bare, innermost seta longest.

Maxilla ( Fig. 9F ) 2-segmented, allobasis nearly as long as syncoxa. Syncoxa unarmed, surface ornamented with 1 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 than those on outer row; outer margin with strong seta almost 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. 9F ).

Maxilliped ( Fig. 9G ) 4-segmented, comprised of syncoxa, basis and 2-segmented endopod. Syncoxa unarmed, surface ornamentation not discerned. Basis elongate, palmar margin with 2 spiniform elements unequal in length; proximal element unornamented and about half the length of distal one, which is bipinnate; fringe of short spatulated spinules between proximal seta and articulation with endopod; anterior surface with row of broad spatulated pinnules and short row of spinules of varying length along palmar margin as illustrated in Fig. 9 (G). Proximal endopod segment unarmed. Distal endopod segment drawn out into long curved claw, with pinnules along almost entire concave margin; accessory armature consisting of small, naked seta on outer proximal margin and unipectinate spine fused basally to inner proximal corner of claw.

Swimming legs 1–4 biramous ( Fig. 10A–D ), with 3- segmented rami. Armature similar to S. ivlevi , except for spine count on distal exopod segment of P2, showing 2 outer spines ( Table 6). Intercoxal sclerites well developed, without ornamentation. Coxae and bases with sparse surface ornamentation as figured. Bases with plumose (P1 + P3) or naked (P2 + P4) outer seta, arising from posterior surface, seta very long in P4, extending almost to tip of distal endopod spine; inner portion of basis slightly produced adaxially into rounded (P1) or pointed (P2–P4) process, which decreases in size from P2–P4; inner margin of basis ornamented with short spinule(s) in P1–P2 ( Fig. 10A,B ). 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, not discerned in P4. 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, which are also reduced in length. Spine on second segment of P2 reduced in length. Terminal spine slightly longer (P1) or shorter (P2–P4) than distal exopod segment.

Endopods. Outer margin of endopod segments with fringe of long setules. Inner seta of proximal endopod segment short, slightly swollen and ornamented with strong spinules bilaterally, reduced in length and spiniform in P4. Inner setae of P4 reduced in length, in particular setae on second endopod segment, with proximal seta reaching little further than insertion of distal seta and distal seta reaching only half length of seta on distal segment. Inner margin of P1 enp-2 ornamented with 3 long spinules. Distal margin of P1 enp- 1-and -2 ornamented with row of denticles or spinules on anterior face (not figured); outer margin of enp-3 terminating in long process obscuring insertion of distalmost inner seta. Conical process at distal margin of P2–P3 absent, but apical pore still present, located laterally between subdistal and distal spine ( Figs 10B,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 P1–P4 with spinule comb along proximal inner margin; also present on distal inner seta of middle endopod segment in P2–P4.

P5 ( Fig. 8H,I ) comprised of long, naked seta arising from lateral surface of somite, extending to posterior margin of genital double-somite, and small free segment representing exopod. Exopod 1.7 times longer than wide, bearing single long, bare seta, extending beyond posterior margin of genital double-somite; posterior margin ornamented with small spinule dorsally ( Fig. 8I ) and small spinous process ventrally ( Fig. 8H ).

P6 ( Fig. 8J ) represented by operculum closing off each genital aperture; armed with a minute spinule, which is difficult to discern.

Egg-sacs not observed, presumably similar to S. ivlevi .

Description of male

Body length: 367 Mm [traditional method: 290 Mm (range: 280–300 Mm, based on 3 specimens]. Pore pattern difficult to discern, possibly as in Fig. 11 (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) 6.9: 64.5: 4.1: 4.1: 4.1: 16.3; proportional lengths (%) of urosomites (caudal rami included) 6.0: 55.7: 3.5: 3.5: 3.5: 14.1: 13.7. Posterior margin of leg 5-bearing somite with 2 paired midventral spinous processes ( Fig. 11E ), not 3 as in female; no variation in number of processes observed in either sex. Caudal rami 2.1 times longer than wide measured along inner margin and 2.7 times longer than wide measured along outer margin. Caudal setae with proportional lengths as in female, except for seta IV, which is slightly shorter. Dorsal surface of genital somite unornamented, pore(s) absent or not discernible. Surface of genital flaps ornamented with several rows of small spinules as figured, surface ornamentation and pore pattern on ventral surface of anal segment and CR absent or not discernible ( Fig. 11E,F ).

Antennule ( Fig. 11G ) 4-segmented; distal segment corresponding to fused segments 4–6 of female; relative lengths (%) of segments measured along posterior nonsetiferous margin 8.3: 18.0: 44.9: 28.8. Armature formula: 1-[3], 2-[8], 3-[4], 4-[9+2ae+(1+ae)], aesthetascs very small and slender, small middle aesthetasc, which was not discernible in the female, arrowed in Fig. 11 (G), apical aesthetasc fused basally to adjacent seta smaller than in female.

Antenna as in female.

Maxilliped ( Fig. 11B,C ) 3-segmented, comprising syncoxa, basis and 1-segmented endopod. Syncoxa unarmed and unornamented. 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. 11B ), short row of spinules proximally; posterior surface with 2–3 rows of short spatulated spinules of graduated length along palmar margin ( Fig. 11C ); with 1 long seta within the longitudinal cleft, ornamented with strong spinules bilaterally, corresponding to distal seta in female, proximal seta absent. Endopod drawn out into long curved claw, concave margin ornamented with pinnules along distal half of concave margin, not along entire length 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 and ornamentation as in female.

P5 ( Fig. 11D,F ) exopod with shape and armature as in female; exopodal seta and long seta arising from lateral surface of somite somewhat shorter than in female.

P6 ( Fig. 11E ) represented by posterolateral flap closing off genital aperture on either side; covered by pattern of denticles as figured; posterolateral corners protruding laterally so that they are well discernible in dorsal aspect ( Fig. 11A,D ).

Spermatophore not observed.

Etymology

The species is named in honor of the late Professor Arthur G. Humes ( Ho, 2001), in recognition of his outstanding contribution to the taxonomy of symbiontic and parasitic copepods ( Huys & Boxshall, 2001), which also included a study on oncaeids.

Remarks

Taxonomy. Spinoncaea humesi is closely related to S. ivlevi , with which it has been confounded during earlier ecological studies in the Red Sea (see below). The two species can be separated by the different spine count on the distal exopod segment of P2, showing 2 outer spines in S. humesi , whereas the typical number of 3 spines is found in S. ivlevi . Other morphological characters separating the females of the two species are (1) the length ratio of prosome: urosome, being smaller in S. humesi than in S. ivlevi ; (2) the form of the genital double-somite, being barrel-shaped in S. humesi , but oval-shaped in S. ivlevi ; (3) the length ratio of antennary endopod segments, with the distal one being longer than the proximal one in S. humesi , whereas it is about equal in length in S. ivlevi ; (4) the length to width ratio of the antennary distal endopod segment, being greater in S. humesi than in S. ivlevi ; (5) the armature of the mandible, showing only 4 elements in S. humesi , with seta D absent, whereas the full set of 5 elements is found in S. ivlevi ; (6) the basal seta on P4, being as long as the leg in S. humesi , whereas it is only about half its length in S. ivlevi ; (7) the outer basal seta on P5, which is longer than the genital double-somite in S. humesi , while being only half its length in S. ivlevi . Further minor differences between S. humesi and S. ivlevi are found in the ornamentation of appendages, such as the lack of spinules on the inner nonsetiferous margin of segments 2 and 3 in the antennule, the greater number of setules on the inner margin of P1 enp-2, and the different ornamentation of P5 exopod. From the robust form of S. ivlevi , the new species can also be separated by the length to width ratio of the caudal rami, being much longer in S. humesi (but see below under ‘Variability’).

Males of S. humesi and S. ivlevi differ in the armature of swimming legs and mouthparts as well as in the length of the outer basal seta on P5 as stated above. Also, the surface ornamentation in S. humesi males seems to be reduced (P6) or even absent (genital somite).

Morphological differences separating S. humesi from S. tenuis are summarized below under ‘ Remarks’ of S. tenuis .

Variability. The length to width ratio of the caudal rami of female Spinoncaea humesi varied between different geographical regions ( Table 7 ). In specimens from the SE Indian Ocean (off Australia) and NW Pacific (Kuroshio Extension) this ratio was similar to that of the elongate form of S. ivlevi co-occurring in both areas (cf. Table 3 ). Thus, differentiation of the two species in Australian waters and the Kuroshio extension requires (microscopical) examination of the leg armature.

Ecological notes. Spinoncaea humesi is distributed throughout the Red Sea main basin, where it co-occurs with S. ivlevi in the epipelagic zone ( Böttger-Schnack, 1988, 1990b, 1995; as Oncaea ivlevi ). In the Gulf of Aqaba, the northernmost extension of the Red Sea, it was found to be very rare or even absent, thereby emphasizing the isolated position of this area (Böttger-Schnack et al., 2001).

The species was also recorded from the eastern Mediterranean in the present account, but has not yet been found in the Adriatic Sea. In samples from the Indo-Pacific region it occurred in the NE Indian Ocean, off Australia, and in the NW Pacific (Kuroshio Extension), but was not recorded from the NE Pacific (Monterey Bay). The absence of the species in the northern Arabian Sea may be due to some seasonal variation in abundance (see under S. ivlevi ). More detailed taxonomical investigations of this new Spinoncaea species in the world ocean are necessary to fully elucidate its zoogeographical distribution.

Data on the vertical distribution and vertical migration of S. humesi in the Red Sea are not yet available, as the species was not separated from its sibling species, S. ivlevi , during the earlier ecological studies. Generally, the two species exhibited an unimodal distribution in the lower epipelagic zone, at 50–100 (200) m ( Böttger-Schnack, 1988, 1990b, 1995). A detailed investigation of the distribution patterns of both species in the northernmost Red Sea is in progress.

Figures

Figure 3. Spinoncaea ivlevi (Shmeleva, 1966) comb. nov., female, robust form (Red Sea). (A) Antenna, lateral elements are numbered using Roman numerals, distal elements are identified by capital letters; (B) labrum, anterior; (C) same, posterior; (D) mandible, showing individual elements, which are identified by capital letters; (E) maxillule; (F) maxilla; (G) maxilliped, anterior.

Figure 8. Spinoncaea humesi sp. nov., female (Red Sea). (A) Habitus, dorsal; (B) same, lateral (appendages omitted); (C) urosome, dorsal; (D) urosome, lateral; (E) P5-bearing somite (setae on left side omitted) and genital double-somite, ventral; (F) caudal ramus, dorsal; (G) antennule; (H) leg 5, lateral; (I) same, dorsal; (J) genital aperture.

Figure 9. Spinoncaea humesi sp. nov., female (Red Sea). (A) Antenna; (B) labrum, anterior; (C) same, posterior; (D) mandible, showing individual elements; (E) maxillule; (F) maxilla; (G) maxilliped, anterior.

Figure 10. Spinoncaea humesi sp. nov., female (Red Sea). (A) P1, posterior; (B) P2, posterior, intercoxal sclerite not shown; (C) P3, posterior; (D) P4, posterior, reduced proximal seta on second endopod segment arrowed.

Figure 11. Spinoncaea humesi sp. nov., male (Red Sea) (A) Habitus, dorsal; (B) maxilliped, anterior; (C) maxilliped, medial view; (D) urosome, dorsal, seta V on left side missing; (E) urosome, ventral; (F) same, lateral; (G) antennule, middle aesthetasc on segment 4 arrowed.

Figure 12. Spinoncaea tenuis sp. nov., female (Red Sea). (A) Habitus, dorsal; (B) same, lateral (appendages omitted); (C) urosome, dorsal, setae V and VII on left side and setae IV–V on right side omitted; (D) urosome, lateral; (E) antennule; (F) caudal ramus, dorsal, setae are numbered using Roman numerals; (G) genital aperture; (H) leg 5, exopod, dorsal; (I) same, lateral.