Mesocletodes elmari, Menzel, Lena, 2011

Menzel, Lena, 2011, First descriptions of copepodid stages, sexual dimorphism and intraspecific variability of Mesocletodes Sars, 1909 (Copepoda, Harpacticoida, Argestidae), including the description of a new species with broad abyssal distribution, ZooKeys 96, pp. 39-80 : 42-46

Mesocletodes elmari sp. n. Figs 214

Etymology:

The name is dedicated to the author’s father, Elmar Menzel.

Locus typicus:

Guinea Basin, RV “Meteor“, Cruise M63/2 (DIVA-2), station 75/7 (0°50.0'N, 5°35.0'W, 5139m), March 19, 2005.

Type material:

7 individuals Holotype: 1 female, dissected, mounted on 17 slides, coll. no. SMF 37012/1-17, RV “Meteor“, Cruise M63/2 (DIVA-2) at station 75/7 (0°50.0'N, 05°35.0'W, 5139m), March 19, 2005.

Paratypes: Paratype 1 (Allotype): 1 male, dissected, mounted on 9 slides, coll. no. SMF 37013/1-9, RV “Meteor“, Cruise M63/2 (DIVA-2) at station 78/7 (0°50.1'N, 05°35.1'W, 5136m), March 19, 2005.

Paratype 2: 1 female, mounted on 1 slide, coll. no. SMF 37014, RV “Meteor“, Cruise M63/2 (DIVA-2) at station 35/7 (28°6.8'S, 7°20.7'E, 5033m), March 03, 2005.

Paratype 3: 1 CV female dissected, mounted on 6 slides, coll. no. SMF 37015/1-6, RV “Meteor“, Cruise M63/2 (DIVA-2) at station 79/4 (0°50.0'N, 05°35.1'W, 5140m), March 19, 2005.

Paratype 4: 1 CV male dissected, mounted on 2 slides, coll. no. SMF 37016/1-2, RV “Meteor“, Cruise M48/1 (DIVA-1) at station 346-7/10 (16°17.0'S, 05°27.0'E, 5389m), July 27, 2000.

Paratype 5: 1 CIV male dissected, mounted on 8 slides, coll. no. SMF 37017/1-8, RV “Meteor“, Cruise M63/2 (DIVA-2) at station 97/7 (0°37.2'N, 06°28.1'W, 5168m), March 23, 2005.

Paratype 6: 1 CIII dissected, mounted on 7 slides, coll. no. SMF 37018/1-7, RV “Polarstern“, Cruise PS61 (ANT-XIX/4 (ANDEEP II)) at station 138-11/4 (62°58.03'S, 27°54.08'W, 4541m) March 18, 2002.

Description of adult female holotype.

(Figs 2-8) Habitus (Figs 2 [paratype], 3 A - B) of cylindrical shape, no clear distinction between prosome and urosome. Body length including FR 0.78 mm. Distal margins of cphth, prosomites and urosomites with conspicuous coarsely ornate and denticulated hyaline frill with many setules (Fig. 3 E). Body with several remarkably long sensilla. Distal margins of prosomites with long spinules: only dorsally in prosomites and first urosomite, in urosomites also laterally and ventrally. Distal margin of last urosomite without sensilla. Rostrum not protruding, with 2 sensilla. Body of prickly appearance, caused by small protrusions bearing one setule each, protrusions in urosomites and telson coarser than in prosomites (Fig. 3 D, F). Notch-like pores ventrolaterally on P4 - P5 bearing somites. Genital double somite fused ventrally. Telson (Fig. 3 A–C) as long as 2 preceding urosomites together, almost square from lateral and dorsal view. Ventrally with 2 rows of 6 long spinules each and on the outer edges, close to hyaline frill of last urosomite. 1 ventral notch-like pore on each side at inner edge near insertion of FR. Operculum with several denticles (Fig. 3 A).

A1 (Fig. 4 A, A’) 7-segmented, reticulated as shown for proximal part of A2 enp1 (Fig. 4 B). Segments 4 and 7 with aes. Second segment of paratype 2 ( A’) large, with 1 protrusion bearing 1 bipinnate seta (seta lost during preparation of holotype). Spines with STEs. First and second segment bear inner and outer spinules, third segment with outer spinules. Setal formula: 1: 0; 2: 8; 3: 5; 4: 2+aes; 5: 1; 6: 2; 7: 9+acrothek (=11+aes).

A2 (Fig. 4 B) with basis, reticulate ornamentation as shown for part of enp1. Exp 1-segmented, with 1 terminal and 1 subterminal seta. Enp 2-segmented, both segments with strong outer spinules. Enp2 with 2 bipinnate spines subterminally. 3 geniculate and 2 pinnate spines, and 1 naked seta terminally. Naked terminal seta fused basally to 1 outer pinnate spine. The innermost element is a reduced seta. Spines with STEs.

Labrum (Fig. 5 A) with 1 medial and 2 lateral rows of spinules, setules at oral surface.

Md (Fig. 5 B, C) gnathobase formed by 5 tooth-like projections: 1 dentate, 1 broad tooth, 3 strong teeth partly fused to broad grinding face. Strong seta close to grinding face. Md palpus 3-segmented, exp and enp articulated. 1 strong basal seta terminally, exp with 2 terminal and 1 subterminal setae, enp with 3 terminal setae.

Paragnaths (Fig. 5 D) on each side with 2 rows of traverse arranged brush-like setae orally and 1 row of long spinules at the surface.

Mxl (Fig. 5 E) praecoxal arthrite terminally with 6 strong elements: 3 hooks with 1 strong spinule each, 1 brushlike seta fused to arthrite and 2 unipinnate setae. Subterminally with another pinnate spine and 2 bare setae aborally. Coxa with 4 elements terminally: 1 strong seta fused to coxa and 3 bare setae. Basis with 2 bare setae. Enp incorporated into basis, with 2 bare setae, exp 1-segmented with 2 pinnate setae.

Mx (Fig. 5 F) syncoxa with 2 endites, the proximal one bearing 1 seta. Distal endite with 3 setae, the biggest one fused to segment. 2 strong setae fused to basis, distal one shows a suture, proximal one with 1 conspicuous strong spinule-like pinna (indicated by arrow in Fig. 5 F). Basis additionally with 1 bare seta. Enp 1-segmented, with 2 bipinnate setae of equal length (dash-depicted seta supplemented from paratype 2).

Mxp (Fig. 5 G, G1-G3) prehensile, syncoxa (Fig. 5 G1) slightly shorter than basis (proximal part of Fig. 5 G2), with 2 setae and several spinules. Basis slender, with spinules of different sizes. Enp 2-segmented. Enp1 (distal part of Fig. 5 G2) small, bare of setae. Enp2 (Fig. 5 G3) terminally fused to strongly pinnate claw, suture visible.

P1 (Fig. 6 A) with 3-segmented exp and 2-segmented enp. Intercoxal sclerite long and bow-like. Coxa 1/3 broader than basis, with several spinules on ventral margin. Basis with outer spine, outer pore, long inner spine ventrally oriented and several rows of spinules. Exp1 and exp2 without inner seta. Exp3 with 4 elements. Enp1 short, with strong inner spine inserted medially. Enp2 extremely long, surpassing exp in length, with 1 outer, 1 terminal and 1 inner seta. Enp2 with 1 peculiar spinule subterminally. For setal formula see Table 2.

P2-P4 (Figs 6 B, 7 A, B) with 3-segmented exps and 2-segmented enps. Intercoxal sclerites long and bow-like. Coxae little larger than bases. Bases twice as broad as long. Bases with outer spines, at inner margin with setular tufts. Outer margins of coxa with strong spinules, inner margins of coxa and basis with setules. Exp1 as long as exp2 and exp3 together. Exp1 without inner seta. Exp3 terminally with cuticular hooks. Enp1 short. Enp2 extremely long, decreasing in length from P2-P4, measured in relation to exp1. Enp2 with 1 strong, short spinule subterminally. Outer terminal seta of enp2 decreasing in length from P2-P4. Inner terminal seta in P2 enp2 lost during preparation (indicated by arrow in Fig. 6 B). Setation of exp and enp as in Table 2.

P5 (Fig. 8 A) benp with setophore with 2 spinules and 1 long bipinnate seta. Endopodal lobe not protruding, with 3 setae. Exp about 2 times as long as broad at base, bearing 3 outer, 1 terminal and 1 inner seta (dash-depicted setae supplemented from paratype 2).

P6 integrated into GF (Fig. 8 B), reduced to a fused opercular plate, armed with 1 short spine on each side (see asterisk in Fig. 8 B). GF with single aperture, accompanied by 1 row of spinules on each side.

FR (Fig. 3 G) long and slender, ornate, ventral spinules between seta VII and III. Approximately 13 times as long as broad (measured at base). Close to base ventrolaterally with 1 notch-like pore at external side (Fig. 3 G, C). Extremely elongated between setae VII and III. Seta I close to seta II. Seta VII triarticulate. Seta III located on dorsal side subterminally. Setae IV–VI located terminally. FR laterally with subterminal tube pore (see arrow in Fig. 3 G).

Description of adult male paratype

(Allotype) (Figs 8-11) The adult male corresponds to the adult female in all morphological characters unless deviations are mentioned below.

Habitus (Fig. 9 A, B) much smaller than adult female, body length including FR 0.40 mm. Body not of prickly appearance (Fig. 9 A–C), hyaline frill (Fig. 9 D) not ornate. Distal margins of first and second urosomites with long spinules dorsally, of third urosomite dorsally, laterally and ventrally, of last 2 urosomites only laterally and ventrally. With 2 spermatophores: first one inside first urosomite, second one inside second and third prosomite. Gut empty. FR (Fig. 9 E) as described for female.

A1 (Fig. 10 A) 9-segmented, haplocer. Segments 5 and 9 with aes. Second segment large, with 1 protrusion bearing 1 bare seta. Segments 5, 6 and 7 with modified setae. Setae of most segments bare. Setal formula: 1: 0; 2: 8; 3: 4; 4: 2; 5: 4+aes; 6: 2; 7: 2; 8: 2; 9: 9+acrothek (=11+aes).

A2, Md, Mxl, Mx and Mxp as described for adult female.

P1-P4 (Fig. 11 A–D) intercoxal sclerites, coxae, bases and segmentation of enp and exp as described for adult female, but with fewer spinules. P1 exp3 with 1 spine and 3 setae, the 2 innermost of wreathed appearance. P2-P4 inner exopodal setae long. P2-P4 enp2 with 2 long inner setae. Basal seta of P3 and P4 broken (indicated by arrow in Fig. 11 C, D). For setal formula see Table 2.

P5 (Fig. 8 D) with setophore (seta lost during dissection, see arrow in Fig. 8 D) with few spinules and 1 notch-like pore laterally. Endopodal lobe barely protruding, with 2 setae, outermost very short. Exp about twice as long as broad (measured at base), bearing 3 outer, 1 terminal and 2 inner setae.

P6 (Fig. 8 D1) with 2 setae.

Description of copepodid stages

(paratypes 3-6) (Figs 8, 10, 12-14) CV female (Fig. 12 C, C1): body length including FR 0.58 mm. Body not of prickly appearance. Penultimate urosomite is not formed. Distal margins of body somites with smooth hyaline frill and, except penultimate one, with sensilla. Extremities A1-P4 (not depicted) as described for adult female but smaller. P5 (Fig. 8 C) exp not separated from benp, setation of exp and basendopodal lobe as in adult female but smaller. P6 (Fig. 8 C1) with 2 setae. GF not expressed.

CV male: body as in CV female. A1 (Fig. 10 B) 6-segmented. Segments 3 and 6 with aes. Second segment large, with a protrusion bearing 1 seta. Setal formula: 1: 0; 2: 8; 3: 9+aes; 4: 2; 5: 2; 6: 9+acrothek (=11+aes). A2-mxp as described for adult female. P1-P4 (not depicted) and P6 (Fig. 8 E1) as described for adult male but smaller. P5 (Fig. 8 E) exp not separated from benp, setation of exp as in adult male but smaller. Right basendopodal lobe with 2 setae and 1 cuticular protrusion, which is missing on the counterpart (see asterisk in Fig. 8 E).

CIV male (Fig. 12 B, B1): body length including FR 0.50 mm. Body not of prickly appearance. 2 penultimate urosomites not formed. Distal margins of body somites with smooth hyaline frill and, except the penultimate one, with sensilla. A1 (Fig. 14 A) 6-segmented. Segments 3 and 6 with aes. Setal formula: 1: 0; 2: 6; 3: 6+aes; 4: 1; 5: 2; 6: 9+acrothek (=11+aes). A2-mxp (not depicted) as described for adult female but smaller P1-P4 (Fig. 13 A–D) with 2-segmented enp and 2-segmented exp. P1-P4 enp2 with 1 inner seta and 1 subterminal, outer seta. For setal formula see Table 2. Setal elements developed as in adult male, P5 (Fig. 8 F) exp not separated from benp. Basendopodal lobe with 2 setae and 1 cuticular protrusion, P5 not fused in the middle. P6 (Fig. 8 F1) with 2 setae. GF not expressed. FR with setular tuft (Fig. 12 B1) close to insertion in telson.

CIII (Fig. 12 A, A1): body length including FR 0.42mm. Body not of prickly appearance. 3 penultimate urosomites not formed. Distal margins of body somites with smooth hyaline frill. A1 (Fig. 14 F) 5-segmented. Setal formula: 1: 0; 2: 8+aes; 3: 1; 4: 2; 5: 9+acrothek (=11+aes). A2-mxp (not depicted) as described for adult female but smaller.

P1-P3 (Fig. 14 B–D) with 2-segmented enp and 2-segmented exp. Exp1 longer than exp2. P4 (Fig. 14 E) exp and enp 1-segmented. For setal formula see Table 2. P5 lost during preparation, P6 not expressed.

Morphological variability

(cf. Table 1). The body length including FR is variable: for adult females between 0.57 and 1.06 mm (the majority measured 0.7 to 0.9 mm), for adult males between 0.4 and 0.7 mm, for CV females between 0.5 and 0.75 mm, for CV males between 0.5 and 0.59 mm, for CIV males between 0.4 and 0.64 mm.

The spinulation also seems to be highly variable: the row of spinules ventrally at the telson ranges from numerous, long and slender to few, short and stout. In total, 16 specimens show setular tufts in the FR: six adult females, one CV male and the five CIV males bear setular tufts close to the telson, four adult females close to seta VII. The amount of spinules in A1 segment 3 varies. Four out of 56 adult females, all adult males and copepodid stages possess a non-ornate hyaline frill. A very rare feature (in two adult females, all CIV males) is also the presence of outer setae in P2-P4 enp2 or just in P2 enp2 (one adult female). The number of eggs (2-20) is variable, too.