Argestes angolaensis sp. nov. (Copepoda: Harpacticoida: Argestidae) from the Angola Basin (Southeast Atlantic), and the phylogenetic characterization of the taxon Argestes Sars, including the redescription of A. mollis Sars, 1910, and A. reductus (Itô, 1983) *
Author
George, Kai Horst
text
Zootaxa
2008
1866
223
262
journal article
49035
10.5281/zenodo.183720
03ab62fe-6d00-4c63-8d3a-6f2ea72025f1
11755326
183720
Argestes angolaensis
sp. nov.
Figures 2–14
Locus
typicus
. Northern
Angola
Basin, #346 (
16°17.0’S
,
05°27.0’E
, depth:
5389m
).
Holotype
(#346/512) (i.e. station 346, replicate no. 5, MUC core no. 12): female, placed on 11 slides, coll. nos. SMF 32027/111. Seven
paratypes
(PT) were put on slides and used for species description: PT1 (#346/81): female, coll. no. SMF 32028, PT2 (#346/82): female, coll. no. SMF 32029, PT3 (#346/87): female, fixed on 10 slides, coll. nos. SMF 32030/110, PT 4 (#346/85): female, put on 10 slides, coll. nos. SMF 32031/110, PT5 (#346/81): female, coll. no. SMF 32032, PT6 (#346/61): male, placed on 3 slides, coll. nos. SMF 32033/13, PT7 (#346/ 710): male, fixed on 8 slides, coll. no. SMF 32034/18. The remaining
90 specimens
are preserved in alcohol and distributed in eight vials with respect to the corresponding MUC cores, coll. nos. SMF 32035–SMF 32042.
Female
.
Habitus (
Fig. 2
A, B) slender, body length including FR of approximately 545µm. Cphth less than 1/3 of total body length. Whole body densely covered with small spinules, except the P5bearing thoracic somite, the second and the third abdominal somite, and the telson, which show fewer but bigger spinules. Body with several remarkably long sensilla arising from tubercles. In particular, the sensilla of the P5bearing thoracic somite and abdominal somites are very long.
FIGURE 2:
Argestes angolaensis
sp. nov.
, female. A. Habitus, lateral view, B. Habitus, dorsal view. Scales: 100µm.
Telson (
Fig. 3
) as large as 2 preceding abdominal somites together, almost square from lateral view, but tapering slightly from dorsal/ventral view. Ventrally with a pair of small tube pores at inner margin close to FR, and with some strong spinules near the proximal margin. Anal operculum small, with row of spinules at its distal margin and accompanied by 2 sensillate tubercles.
FR (
Fig. 3
) long and slender, varying remarkably in length (cf.
Figs 2
B, 3), and covered with many spinules of different sizes. All 7 setae concentrated at terminal part: I and II subterminally on outer margin, I smaller than II. III ventrally at terminal margin. IV and V largest setae, inserting terminally. VI as long as III, arising at the inner terminal margin. VII dorsally, arising from knoblike projection. Setae I–III and VI in many specimens of “rattail” appearance.
FIGURE 3:
Argestes angolaensis
sp. nov.
, female. Telson and FR, ventral view. Scale: 50µm.
FIGURE 4:
Argestes angolaensis
sp. nov.
, female. A. A1, general shape, B. A1, setation of single segments. Scale: 50µm.
A1 (
Fig. 4
) 7segmented, fifth segment smallest, all segments with several bare and bipinnate setae. Second segment at its posterior margin with few long spinules. Aes on fourth segment, arising together with 2 setae from protrusion. Sixth segment terminally with 1 very long bipinnate seta. Seventh segment terminally with small aes, and at posterior terminal margin with remarkable long seta. All segments covered with small spinules.
Setal formula: 1/1; 2/9; 3/7; 4/4 + aes; 5/2; 6/3; 7/11 + aes.
A2 (
Figs 5
A, A’) with allobasis and 1segmented exp bearing 1 bare seta and 3 long spinules. Enp and allobasis covered with small spinules. Enp laterally with 2 bipinnate setae, the second subterminal with tube pore. Terminally, enp carries 5 geniculate setae and 1 unipinnate seta. Subterminally with long tube pore, fused with longest seta.
Md (
Fig. 6
) with gnathobase (
Fig. 6
A, A’) formed by several toothlike projections. Subterminal seta not discernible. Md palp (
Fig. 6
B) strong, covered with spinules, basis with 2 bipinnate setae. Enp 1segmented, with 1 outer bipinnate seta, additionally with 3 subterminal and 2 terminal bipinnate setae. Exp smaller than enp, with 1 outer and 2 terminal bipinnate setae.
Mxl (
Fig. 5
B, B’) with distinct exp. Precoxal arthrite terminally with 6 spines, subterminally with another spine. At its proximal margin with 1 unipinnate seta, and on its surface with 2 bare setae. Coxa terminally with 3 setae. Basis terminally with 2 setae. Enp represented by 1 bare seta. Exp long and spinulose, terminally with 2 multipinnate setae.
Mx (
Fig. 5
C) unfortunately broken at its distal part that is therefore not described. Syncoxa with 2 endites, the proximal one bearing 1 bare seta. Distal endite with 3 setae, the biggest one fused to segment, bipinnate. Basis fused to syncoxa, with 3 setae. Enp distinct, with 2 bare setae.
Mxp (
Fig. 5
D) prehensile, syncoxa slightly shorter than basis, with many spinules of different sizes, distally with 2 long multipinnate setae. Basis covered with small spinules, additionally with 2 rows of long spinules. Enp produced into long unipinnate claw, with 1 bare seta at its base.
P1 (
Fig. 7
) with 3segmented exp and enp. Coxa considerably bigger than basis, with several spinules and 1 row of setules at its outer margin. Intercoxal sclerite transversely long and bowlike. Basis with inner and outer spine, covered with small spinules and long setules at its inner margin. Both exp and enp covered with small spinules on anterior side. Exp1 without, exp2 with inner seta. Exp3 with 5 setae/spines, three of which are subterminal with tube pores. Enp1 and 2 with 1 inner seta each, enp3 with 2 terminal setae, the longer one subterminally with tube pore, and 1 outer spine. For setal formula see table 1.
P2–P4 (
Figs. 8–10
) with 3segmented exps and enps. Coxae approximately 2.5 times bigger than bases, showing decreasing covering with small spinules from P2 to P4. Each coxa on outer side with 3 strong spinules. Bases much broader than long, exps and enps turned outwardly. Bases with outer spines, at inner margin with long setules, covered with small spinules as in coxae. Appendages covered with small spinules, in most specimens showing a decrease from P2 to P4 (but cf.
Fig. 10
B: female P4!). Setation of exp and enp as in table 1. Exp3 as long as exp1 and exp2 together. Enps showing increasing length of segments, enp1 being the shortest, and enp3 the longest segment. As shown in
Fig. 10
B, few females show a variability in the setation of P4 exp3 (as also in the covering with spinules). Instead of only 1, it bears 2 inner setae, the first being considerably smaller than the second.
TABLE 1:
Argestes angolaensis
sp. nov.
, female, setation of P1–P4 (no. outer spines in roman numbers).
Natatory leg
|
Exp1
|
Exp2
|
Exp3
|
Enp1
|
Enp2
|
Enp3
|
P1
|
I0 |
I1 |
III20 |
01 |
01 |
I20 |
P2
|
I1 |
I1 |
III22 |
01 |
01 |
I22 |
P3
|
I1 |
I1 |
III23 |
01 |
01 |
I22 |
P4
|
I1 |
I1 |
III21(2) |
01 |
01 |
I22 |
FIGURE 5:
Argestes angolaensis
sp. nov.
, female. A. A2, A’. A2 of counterpart, showing exp, B. Mxl without praecoxal arthrite, B’. precoxal arthrite, C. Mx, D. Mxp. Scales: 50µm.
FIGURE 6:
Argestes angolaensis
sp. nov.
, female. A. Md gnathobase, shown from different positions, B. Md palpus. Scale: 50µm.
FIGURE 7:
Argestes angolaensis
sp. nov.
, female P1 with corresponding intercoxal sclerite. Scale: 50µm.
FIGURE 8:
Argestes angolaensis
sp. nov.
, female P2 with intercoxal sclerite. Scale: 50µm.
FIGURE 9:
Argestes angolaensis
sp. nov.
, female P3. Scale: 50µm.
FIGURE 10:
Argestes angolaensis
sp. nov.
, A. female P4, note exp3 with only 1 inner seta, B. P4 exp of another female, showing small first inner seta (triangular arrow). Scales: 50µm.
P5 (
Fig. 11
A) benps fused together, forming a single plate. Outer basal seta arising from moderately produced setophore. Endopodal lobe strongly reduced, represented by 1 longer biplumose and 1 shorter bare seta. Exp distinct, long and slender, with 2 outer, 2 terminal, and 1 inner seta. Additionally, outer distal margin with extremely long tube pore.
FIGURE 11:
Argestes angolaensis
sp. nov.
, A. female P5, B. female genital field, C. male P5. Scale: 50µm.
FIGURE 12:
Argestes angolaensis
sp. nov.
, male. A. Habitus, dorsal view, B. P4 exp, triangular arrow pointing to normally developed first inner seta. Scales: A. 100µm, B. 50µm.
FIGURE 13:
Argestes angolaensis
sp. nov.
, male. Habitus, lateral view. Scale: 100µm.
FIGURE 14:
Argestes angolaensis
sp. nov.
, male A1. A. general shape, B. Setation of single segments. One seta broken at both segments 4 and 6. Scale: 50µm.
GF (
Fig. 11
B) strongly cuticularized, with several small and long spinules surrounding the gonoporus. P6 reduced, detectable as paired small processes without setae, flanking the GF.
Male
.
Habitus (
Fig. 12
A, 13) smaller than female, body length including FR approximately 480µm. Coverage of body with small cuticular spinules not reaching density as in female. Tubercles bearing sensilla longer than in female.
A1 (
Fig. 14
A, B) haplocer, 10segmented. All segments except fifth and tenth with small spinules. Sixth segment with strong aes. Eighth segment additionally with toothlike spinule. Ninth segment terminally with strong seta (broken in
Fig. 14
B).
Setal formula: 1/1; 2/1; 3/6; 4/5; 5/2; 6/6+aes; 7/2; 8/3; 9/1; 10/11+aes.
P4 (
Fig. 12
B) sexually dimorphic. General shape as in female, but exp3 always bears 2 welldeveloped inner setae.
P5 (
Fig 11
C) exp distinct, shorter than in female, with 6 setae and 1 long tube pore. Benps fused, with 1 small seta.
Remarks
. With
98 adult
individuals,
Argestes angolaensis
sp. nov.
was by far the most abundant argestid taxon collected in the
Angola
Basin during DIVA 1 expedition in 2000. The high number of collected specimens, usually a highly uncommon occurrence for deepsea sampling, provides a good insight into the intraspecific morphological variability, which certainly exists, but whose study is not the object of the present contribution. However, comparison of the specimens revealed remarkable variability in body and furcal length (male bodies varying between 380 and 480µm length), in body ornamentation (density and size of spinules covering body and appendages), and even in setation (cf. P4 exp,
Fig. 10
B). Nevertheless, an assignment of the corresponding specimens to different new species seems rather implausible, because the mentioned variability shows a quite heterogeneous distribution over the individuals, preventing the recognition of any morphological pattern. Moreover, all specimens share a series of apomorphic characteristics (cf. discussion), justifying their allocation into one single species. Taking into account similar conditions in other taxa e.g.
Ancorabolidae
(
George 2006; George, personal observation
), it has to be stated, that intraspecific variability in deepsea
Harpacticoida
is greatly underestimated.