Laophontodes armatus Lang, 1936

George, Kai Horst, 2017, Phylogeny of the taxon Paralaophontodes Lang (Copepoda, Harpacticoida, Laophontodinae), including species descriptions, chorological remarks, and a key to species, Zoosystematics and Evolution 93 (2), pp. 211-241 : 214-215

Laophontodes armatus Lang, 1936

Note.

The re-description is based on one female (habitus) and the fragments of the type series, in order to destroy as few complete individuals as possible, and because of the compact detritus coverage on most complete specimens. Types SMNH 2158(a) (female) and SMNH 2158(b) (female) were dissected and distributed over 7 and 4 slides, respectively. Both urosomes of Type SMNH 2158(c) (females) were put on 1 slide, 1 urosome in ventral view, the other one in dorsal view.

In addition, the female and the male of the Magellan material were included to complete the re-description (additional female habitus, male habitus, mouthparts, sexual dimorphic parts of male).

Re-description of female.

Habitus (Figs 6A , 7A ) cylindrical and slender, tapering, no clear distinction between pro- and urosoma. Body length (from rostral tip to end of FR) about 770µm (Fig. 6A ) (Magellan female (Fig. 7A ) about 730µm). Cphth laterally running out into two triangular processes, each carrying a sensillum at its tip. Cphth dorsally with several sensilla and with sclerotized ridge that is densely covered with fine hair-like elements and splits into 2 backwardly directed processes posteriorly. R protruding, fused to cphth, triangular, subapically with pair of sensilla. All body somites except telson dorsally with paired cuticular processes (labelled as DP [Dorsal Processes] I-IX in Figs 6 and 7 ). DP VII and/or DP VIII-IX basally with long tube-pores and small cuticular projections. DP I-VIII with sensilla at their tips. Comparison of different females revealed a variability regarding shape, ornamentation, size and number of those projections (Figs 6A-C , 7B, B '), as well as with respect to the number of apical sensilla (Fig. 7B ). Posterior margins of body somites generally naked but P2-P6-bearing somites apically with sensilla. Telson square, slightly broader than long; dorsally with anal operculum apically with fine spinules. FR (Figs 6A , 7A, C , 8D ) approximately 3.5x longer than broad, equipped with seven setae: I and II of almost same length, standing close together subapically on the outer margin; III, IV, V, and VI arising apically, II and VI of same length, V being the longest seta; VII tri-articulate, arising subapically on dorsal side.

A1 (Fig. 8A ) 4-segmented, aes on third segment. First to third segments of almost same length; first segment with 1 bipinnate seta, remaining antennular setae naked; second segment with long spinules on bump along outer margin, 2 of its setae arising from projection surrounded by small spinules at its base; third segment slightly protruded apically, with 2 setae accompanying aes; fourth segment carrying a second, small aes. Setal formula: 1/1; 2/7; 3/6 + aes; 4/10 + aes.

A2 (Fig. 8B ) with allobasis carrying 1 abexopodal seta on distal third. Exp absent. Enp with subapical row of spinules, and with 2 unipinnate and 1 bare seta distally on inner margin; apically with 6 setae, three of which geniculate, outermost seta very small.

Md, mxl, and mx described from male.

Mxp (Fig. 8C ) with syncoxa lacking a terminal seta, but with rounded row of spinules; basis with 2 rows of spinules; enp turned into claw as long as basis and accompanied by small seta.

P1 (Fig. 9A ) with longitudinally prolonged coxa and basis, the latter carrying 1 outer bipinnate and 1 inner bare seta, the latter being displaced on anterior surface. Exp 3-segmented, slightly surpassing half of length of enp-1. Exp-1 with 1 outer bipinnate spine; exp-2 with 1 outer bare geniculate seta; exp-3 smallest, bearing 4 bare geniculate setae.

P2-P4 (Figs 10A-C , 12A-C, E ) intercoxal sclerites (Fig. 12F, G ) very slender, bow-like; bases transversely elongate bearing 1 tube pore anteriorly, and with 1 outer seta. Exps 3-segmented, exp-1 and exp-2 with 1 outer bipinnate spine; exp-3 with 3 outer bipinnate spines; apically with 1 spine and 1 plumose seta; P3 exp-3 additionally with 1 tube pore apically. P2 without enp (Figs 9A , 12A-C, E ), former insertion still detectable (triangular arrows in Figs 9A , 12A-C, E ); P3 and P4 carrying 2-egmented enps, enp-1 very small, without armature, enp-2 with few spinules and carrying 2 apical setae, the inner one of which being shorter than the outer one. Setal formula of P2-P4 is given in Table 2 .

P5 (Fig. 9B ) with outer seta arising from long spinulose setophore; benp completely reduced, represented by 2 setae, one of which of fishbone pattern, the other seta bare. Additionally with 3 tube pores. Exp fused with baseoendopodal part, long and slender, laterally with 2 bare setae; subapically with 2 bipinnate setae and 1 tube pore; apically with 1 long bipinnate seta.

P6/GF (Fig. 8E ). P6 small, forming bilobate sclerotized structure in front of gonopore, each leg carrying 1 small bipinnate seta.

Redescription of male.

The male differs from the female in the following features: body size, shape of A1, shape of P3 and P4 endopods, ornamentation of P5, complete loss of P6.

Habitus (Fig. 7C ) slender, slightly smaller than female with a body length of about 560µm. Ornamentation of cphth and body somites very similar to that in female, with slight variation regarding DP I-DP IX.

A1 (Fig. 11A ) 5-segmented, chirocer, aes at fourth and fifth segment. First segment apically with 1 bipinnate seta at anterior margin, accompanied by several long spinules; second segment as long as first, with 7 bare setae; third segment small, with 7 bare setae; fourth segment swollen, almost circular in shape, with 6 bare setae, and with strong, tooth-like spine at anterior margin; in addition with pedestal carrying at least 1 bare seta and aes (broken in Fig. 11A ); fifth segment as small as third, tapering distally and bearing 8 bare setae, two of which arising subapically together with small aes forming a trithek. Setal formula: 1/1; 2/7; 3/7; 4/7(-8-9?) + aes; 5/8 + aes.

Md (Fig. 11B ) gnathobase broken in Fig. 10B , only 1 massive tooth and basal part of seta discernible; palp 1-segmented, equipped with 6 setae, two of which biplumose, the others bare; lateral seta (broken in Fig. 11B ) arising from small protrusion.

Mxl (Fig. 11C ) praecoxal arthrite bearing 6 apical spines and 1 bare seta; additionally with 2 bare surfaces setae and 2 rows of spinules laterally; coxa with 2 bare setae apically; basis carrying 4 setae (2 broken in Fig. 11C ).

Mx (Fig. 11D ) syncoxa with 3 rows of spinules and with 2 slender endites, carrying each 1 uniplumose and 2 bare apical setae. Basis elongate, produced into strong claw accompanied by 1 bare seta anteriorly and posteriorly at its base. Enp small, with 2 bare setae.

P3 (Fig. 10D ) exopod resembling that of female. Endopod 3-segmented, first segment very small and unarmed; enp-2 long and slender, with row of long spinules at inner margin, and apically produced into outwardly curved apophysis; enp-3 not reaching length of apophysis, bearing 2 apical biplumose setae, the innermost half as long as the outer one.

P4 (Fig. 10E ) exopod resembling that of female. Endopod 2-segmented, first segment very small and unarmed; enp-2 slender, not reaching length of exp-1, with row of long spinules at inner margin. At distal half with 1 bare inner seta, additionally with 2 biplumose apical setae.

P5 (Fig. 9C ) with outer seta arising from long spinulose setophore; benp completely reduced and being represented by 1 seta of fishbone pattern. Additionally with 2 tube pores. Exp fused with baseoendopodal part, long and slender, laterally with 1 bare seta; subapically with 1 bare seta and 1 tube pore; apically with 2 setae, the innermost fishbone-like, the outermost biplumose.

Remarks.

Laophontodes armatus causes remarkable confusion. Comparison of Lang’s (1936) original description (material from the Falklands) with that of Pallares (1968a) (material from Argentina) reveals some considerable differences; for instance, in the dorsal body processes (DP) of the Argentinian specimens ( Pallares 1968a) the DP I seems to consist of 2 separated pairs of processes, an anterior pair antrorse and a posterior pair backward ( Pallares 1968a, Fig. XXXIII/1). In contrast, the DP I in Lang’s (1936, 1965) Falkland descriptions corresponds to that documented in the present contribution (Figs 6A , 7A, C ), showing 1 pair of backwardly-directed processes and a median antrorse sclerotized ridge carrying hair-like setules which splits into 2 sclerotized clips. Furthermore, in the Argentinian specimens the dorsal processes of the remaining body somites are very small and set widely apart, while in the Falklands’ specimens they have the characteristic, typical shape. A third discrepancy is found in the female P5: the endopod bears 1 seta according to Pallares (1968a) but 2 setae according to Lang (1936). Two setae are also recorded here in the re-description (Fig. 9B ). Unfortunately, due to the unavailability of the Argentinian material it has not been possible to re-examinate it and confirm these discrepancies. However, the Chilean material is almost identical to that of the Falklands (Fig. 7 ), therefore supporting the assumption that the Chilean and the Falklands’ material represent the same species. The examination of new records of L. armatus from Argentina is pending.

A further discrepancy concerns the descriptions of both Lang (1936) and Pallares (1968a) when compared to the present re-description of L. armatus . Both Lang (1936) and Pallares (1968a) described the endopod of the second swimming leg bearing 2 segments with 2 apical setae. However, in the present re-description of L. armatus , the author noted that the P2 lacks an endopod (Figs 10A , 12A-E ). This re-description is based on Lang’s own Falkland material and four different females were examined revealing a consistent lack of a P2 enp (Figs 10A , 12A-C ).

The remaining swimming legs, P3 and P4, of the Falkland females do present endopods. Both the single male and the female specimens from the new Chilean material also lack a P2 endopod (Fig. 12D, E ). Thus, although damage only to the P2 might be plausible for one specimen, it is less so for all individuals, suggesting that Lang (1936) erred, probably by confusing another swimming leg for the P2. The loss of a P2 endopod in L. armatus presents a derived state. Regarding the description of the P2 provided by Pallares (1968a), the apparent presence of a P2 endopod in the Argentinian specimens might represent another discrepancy between the two original records, but this needs to be confirmed with new material.

Figures

Figure 6. Paralaophontodes armatus (Lang, 1936) comb. n., female from the type series. (A) habitus, dorsal view, dorsal processes labelled DP I-DP IX; (B) urosome of second female; (C) dorsal processes DP V-DP IX, detail, of third female. Arrow points to cuticular overlap of sensillum-bearing tip. Scale bars: (A, B) 100 µm; (C) 50 µm.

Figure 7. Paralaophontodes armatus (Lang, 1936) comb. n., (A) female from the Magellan material (Punta Arenas), habitus dorsal; (B, B ') dorsal Processes DP VIII and DP IX of A.; (C) male from the Magellan Material (Punta Yartou), habitus dorsal. Scale bars: (A, C) 100 µm; (B, B ') 50 µm.

Figure 8. Paralaophontodes armatus (Lang, 1936) comb. n., female from the type series. (A) A 1; (B) A 2; (C) mxp; (D) FR, dorsal view; (E) genital field. Scale bar: 50 µm.

Figure 9. Paralaophontodes armatus (Lang, 1936) comb. n., (A, B) female from the type series; (A) P 1; (B) P 5; (C) male from the Magellan material (Punta Yartou), P 5. Scale bar: 50 µm.

Figure 10. Paralaophontodes armatus (Lang, 1936) comb. n., (A-C) female from the type series; (A) P 2, triangular arrow indicates insertion of the ancestral endopod; (B) P 3; (C) P 4 endopod; (D, E) male from the Magellan material (Punta Yartou); (D) P 3 endopod; (D ') P 3 apophysis of counterpart; (E) P 4 endopod. Scale bar: 50 µm.

Figure 11. Paralaophontodes armatus (Lang, 1936) comb. n., male from the Magellan material (Punta Yartou); (A) A 1, setation of segments 3 - 5 shown separately; (B) md; (C) mxl; (D) mx. Scale bars: (A) 50 µm; (B-D) 20 µm.

Figure 12. Paralaophontodes armatus (Lang, 1936) comb. n., (A-C) P 2 (bases) of different females of the type series; (D) P 2 of male from the Magellan material (Punta Yartou); (E) P 2 of female from the Magellan material (Punta Arenas); triangular arrows pointing to insertion of the ancestral endopod; (F) intercoxal sclerite of A; (G) intercoxal sclerite of C. Scale bar: 50 µm.