Cristacoxidae

Huys, Rony & Kihara, Terue Cristina, 2010, Systematics and phylogeny of Cristacoxidae (Copepoda, Harpacticoida): a review, Zootaxa 2568, pp. 1-38 : 28-32

Autapomorphies of Cristacoxidae

Previous phylogenetic analyses ( Huys 1990; Huys & Lee 1998 /99) of the relationships of the families within the Laophontoidea suggested a sistergroup relationship between the Cristacoxidae and the Laophontopsidae . An extensive suite of autapomorphies in support of the monophyly of the Cristacoxidae was recognized by Huys (1990) including:

(1) spermatophore extremely long and slender with curled neck, comprising up to one third of the body length (when observed in situ);

(2) first antennulary segment with a posterior spinous process in both sexes;

(3) antennary exopod and abexopodal seta on allobasis absent. According to Ferrari (1992; based on unpublished data from F. Fiers) the antenna in Noodtorthopsyllus (presumably psammophilus ) bears a small sclerotized segment with one seta at the position of the exopod in copepodid I. He further claimed that in all later copepodids (including the adult) this segment is absent but the seta is retained. The latter part of this statement is erroneous since no exopodal seta is expressed in any of the known adult cristacoxids (or in any of the later copepodids of N. tageae examined in this study). Ferrari (1992) suggested that the absence of an antennary exopod in copepodids II–VI resulted from gene repression rather than gene loss because it is still expressed in the naupliar stages;

(4) mandibular palp uniramous and 2-segmented, comprising an asetose basis and quadrisetose endopod ( Fig. 12 B);

F M (5) proximal coxal endite of the maxilla with a modified basally fused spine; Huys (1990) described the spine as having “… a specialized, swollen tip consisting of fine spinules arranged in a U-shaped excavation…” but SEM observations revealed that the distal part of the spine is spoon-shaped with asymmetrically arranged serrations ( Fig. 12 A, D);

(6) praecoxa (one) and coxa (two) of P1 with serrate cristae around the outer margin; serially homologous crests are also present on the coxae of P2 and P3, and a lobate outgrowth is sometimes discernible on the coxa of P4;

(7) inner basal spine/seta of P1 displaced onto anterior surface of basis;

(8) P1 exp-3 with four geniculate setae;

(9) P2–P4 exp-2 without inner seta;

(10) P2–P4 exp-3 with two outer elements instead of three; these elements are typically elongate and setiform instead of short and spiniform;

(11) P3–P4 endopods 1-segmented (ancestral enp- 1 and enp-2 failed to separate); and

(12) fifth legs paedomorphic (neotenic) forming a common plate in both sexes, bearing two endopodal and five exopodal elements in addition to the outer basal seta.

During the course of this study two additional autapomorphies were identified, i.e.

(13) sexual dimorphism of P3 endopod. Despite the documented variation observed in the origin of the apophysis and the secondary subdivision of the P3 endopod into two pseudosegments, all known members of the Cristacoxidae consistently display the strong reduction (and sometimes complete loss, cf. N. tageae ) of the distal inner seta and the outer distal seta in the male ( Fig. 18); and

(14) the caudal ramus provides a double apomorphy. In all cristacoxids the caudal setae have spinous processes at their bases, the largest ones typically located at the inner distal corner and around the posterior margin between setae III and IV, the smaller ones at the bases of setae I, III and VII. Secondly, examination of developmental stages of N. tageae revealed that the ontogenetic trajectories of the caudal setae IV–VI deviate from the generalized podoplean model for caudal ramus development proposed by Huys et al. (2007). In this model, setae are gradually added in a regular pattern during the naupliar phase, commencing with the expression of setae IV and VII in nauplius I ( Fig. 19 A) and resulting in a total of five setae (II, III, IV, VI, VII) in nauplius VI ( Fig. 19 B). The moult from nauplius VI to copepodid I (cf. intermoult stage shown in Fig. 19 C) is marked by the addition of two setae, the anterolateral seta (I) and the inner terminal seta (V), completing the full array of caudal setae ( Fig. 19 D). The timing and expression of individual setae in N. tageae follows the podoplean model during the naupliar phase but the subsequent modification of setae IV–V does not. In generalized podopleans seta V appears as a short element, which is fused at the base to the long terminal accessory seta VI, forming a bifid setal complex. At the moult to copepodid II the setal complex separates completely at the base, seta VI reduces dramatically in size and seta V becomes the principal seta. This pattern persists in all subsequent copepodid stages, including the adult. In N. tageae (and conceivably all other cristacoxids) a [V–VI] setal complex is never formed ( Fig. 19 D–F) and seta V is the principal seta from copepodid I onwards when it is first expressed as a composite element. The latter forms a different bifid setal complex with seta IV which, unlike in typical podopleans, does not alter its length during the copepodid phase.

Figures

FIGURE 12. Noodtorthopsyllus tageae sp. nov. (Ƥ), scanning electron micrographs: (A) oral region, showing mandibular palps, maxillules, maxillae and syncoxae of maxillipeds [note large semi-circular setulose raised area between maxillae]; (B) detail of mandibular endopod and maxillulary rami; (C) detail of maxillulary arthrite; (D) detail of maxilla, showing serrate spoon-shaped spine on proximal coxal endite and pinnate claw on allobasis. Scale bars: 5 μm (B, D), 10 μm (C), 20 μm (A).

FIGURE 19. Caudal ramus development in Noodtorthopsyllus tageae sp. nov.: (A) left part of caudal area of nauplius II, ventral; (B) left caudal ramus of nauplius VI intermoult stage showing developing copepodid I inside, ventral; (C) caudal ramus of copepodid I shown in (B), ventral; (D) right caudal ramus of fully developed copepodid I, dorsal; (E) right caudal ramus of copepodid II, dorsal; (F) right caudal ramus of adult, dorsal. Roman numerals refer to caudal ramus setae as coded by Huys (1988) and Huys and Boxshall (1991).