BASAL LAOPHONTID EVOLUTION 



101 



along the posterior margin of the first segment (character 10) is a 

 unique feature displayed by the species related to E. longicauda. 

 There are no equivalent structures known from other Laophontidae 

 and consequently this feature should be regarded an evolutionary 

 novelty for this species-group. In males of the same group the 

 enlarged fifth segment has produced an anterior sub-cylindrical 

 outgrowth bearing a stout modified spine (character 12). Minute 

 outgrowths are found on the first segment of C. bulligera but these 

 are not considered important enough to warrant a separate score. 



Maxillulary endopod armature (character 14) 

 The maxillulary endopod typically bears 2 setae along the outer 

 margin of the basis, representing the incorporated endopod. This 

 condition is found in all esolinids while in several other laophontid 

 genera the endopod is represented by a cluster of 3 setae (e.g. 

 Langia, Quinquelaophonte: Mielke (1997)). A notable exception is 

 Archilaophonte in which the outermost third seta is secondarily 

 displaced to a more proximal position, i.e. at the base of the exopod. 

 Consequently, character 14 is scored for A. maxima despite the 

 clearly derived positional pattern. 



Male P3 endopod segmentation (character 20) 

 The P3 endopod in the males of A. typhlops and Esola sp. sensu 

 Chislenko (1967) is 2-segmented as in the female. The outer spine 

 forming the apophysis in the males of other esolinids has remained 

 largely unmodified except for reduction in size and basal fusion. 

 This virtual absence of sexual dimorphism is considered the 

 apomorphic state on the basis of ontogenetic evidence. Huys ( 1 990o ) 

 demonstrated that the typical 3-segmented condition is accom- 

 plished at the final moult by secondary subdivision of the distal 

 segment and allometric growth of the spinous apophysis. The 

 atypical pattern in A. typhlops, resembling the condition of a 

 copepodid V stage, is interpreted here as the result of neoteny, i.e. 

 the decrease in developmental rate has delayed the segmentation 

 beyond the final moult. 



Male P3 endopod armature (character 21) 



The modification of the male P3 endopod in esolinids has no effect on 

 the number of armature elements. In particular, the homologue of the 

 outer spine in the female is transformed into a spinous process or 

 apophysis arising from the middle segment in the male (but see 

 character 20), and the proximal inner seta on enp-2 of the 2-segmented 

 endopod in the female is retained on enp-2 of the 3-segmented 

 endopod in the male [typically 1.1.220 pattern]. The presence of the 

 latter seta in males is a particularly conservative character in primitive 

 laophontids, however, outside the esolinid grouping it is found only 

 in Onychocamptus and one species group of the genus Laophonte. The 

 fate of this seta during male development can only be traced in 

 Laophontidae displaying the full complement of 3 inner setae in the 

 female enp-2. In these species (Table 2) the endopodal armature 

 pattern is most commonly [0-1.321] but can also be [0.311] in 

 Laophonte nordgaardi Sars or [0.320] in some species of 

 Paralaophonte Lang. Except for 6 species of Laophonte and all 

 species of Onychocamptus, the proximal inner seta is consistently lost 

 in the male, resulting in a 0.0.220 pattern. The only exceptions with 

 3 inner setae in the male are those that have lost sexual dimorphism 

 altogether (Folioquinpes, Paralaophonte innae Chislenko, P. 

 aenigmaticum Wells. Hicks & Coull ) . Vervoort ( 1 964) reported a very 

 long inner seta on the middle segment of Paralaophonte pilosoma but 

 re-examination of the holotype (USNM reg. no. 109763) has proven 

 this to be erroneous (Fig. 28E). 



The loss of the proximal inner seta in the male is an apomorphy of 

 pivotal importance in laophontid evolution since it unifies nearly 



95% of all species. Since many genera have only 0, 1 or 2 inner setae 

 in the female we have assumed that they are descendants from an 

 ancestral stock which displayed the 3-setae condition in the female 

 but lost the proximal one in the male. 



Female P5 exopod armature (character 25) 

 Female esolinids can be readily identified by the setal arrangement 

 around the outer margin of the P5 exopod. The two proximal setae 

 are displaced so that their respective insertion sites have become 

 superimposed on one another. Lang (1948) and Willen (1995) 

 pointed out that a similar displacement also occurs in Laophonte 

 parvula Sars (arrowed in Fig. 25G), however, we concur with the 

 latter author that this is the product of convergence. 



Results 



Analysis was performed with PAUP 3.1.1 (Swofford, 1993) using 

 the exact Branch and Bound algorithm (Hendy & Penny, 1982) 

 that is guaranteed to find all most parsimonious trees (MPTs), 

 with all characters set irreversible up and arbitrary solutions (zero- 

 length branches) suppressed. Analysis of the complete data (Table 

 4) produced 84 MPTs with tree length 40 and consistency index 

 0.675. The strict component consensus tree is illustrated in Fig. 

 32 and has a slightly longer length (42) and lower consistency 

 index (0.643). Relationships within the crown-group Esola are 

 poorly resolved, however construction of the majority-rule com- 

 ponent consensus tree revealed an additional group 

 {bulbifera-canalis-profunda). This boreo-mediterranean majority 

 component appears in 48 (57%) of the trees. A. longiremis, A. 

 hamondi and Esola sp. sensu Chislenko (1967) all have different 

 combinations of missing entries, however each is also a potential 

 taxonomic equivalent of A. typhlops (Table 4) and can therefore 

 be safely deleted (Wilkinson, 1995). Safe taxonomic reduction of 

 these taxa reduces the number of MPTs to 14 but does not alter 

 tree length or consistency index. 



The strict component consensus (Fig. 32) reveals a strongly 

 supported basal dichotomy which divides the Laophontidae into two 

 major clades. In order to reflect the robustness of this dichotomy, 

 subfamilial rank is attributed to the two corresponding lineages. The 

 Esolinae subfam. nov. includes Archilaophonte, Mourephonte and 

 all species previously assigned to Esola. It is supported by male 

 antennulary segmentation (character 8) and the female P5 exopodal 

 setation pattern (character 25). 



The primitive position of Archilaophonte conjectured by Willen 

 (1995) is confirmed. The genus represents the first offshoot in the 

 evolution of the Esolinae and is tentatively defined by the following 

 suite of autapomorphies: (a) 6-segmented 9 antennule (segment 6 

 compound), (b) 2-segmented PI exopod (fusion exp-2 and -3), (c) 

 PI enp-2 secondarily elongated P2, (d) P2 enp-2 with only 1 inner 

 seta, (e) P3 enp-2 6 with very long sigmoid apophysis, (f) P5 exopod 

 8 with 4 setae (loss of proximal inner seta), and (g) extremely 

 elongation of caudal rami. In addition, the maxillulary palp shows a 

 peculiar setal arrangement along the outer margin with 1 seta 

 positioned at the base of the bisetose exopod. Outgroup comparison 

 with the Normanellidae indicates that this seta is of endopodal origin 

 and must therefore have been secondarily displaced to a more 

 proximal position. The basal position of Archilaophonte is sup- 

 ported by the presence of (a) a spinous process on the posterior 

 margin of the 2nd antennulary segment, (b) maxillulary endopod 

 represented by 3 setae, (c) 3 setae on the maxillipedal syncoxa. and 

 (d) the well developed 6 P5 endopodal lobe bearing 2 long setae. 

 The apomorphic alternatives of these characters (Table 3) in con- 

 junction with the formation of a trifid compound element on 



