74 



L. BOUCK, D. THISTLE AND R. HUYS 



INTRODUCTION 



Species of Zausodes C.B. Wilson are typical inhabitants of sandy 

 substrata in shallow subtidal localities, however, some records 

 indicate that their horizontal zonation extends into the infralittoral of 

 sandy beaches (Wilson, 1932; Mielke, 1990, 1997). Although the 

 genus was originally proposed for the type species Z arenicolus 

 from the Woods Hole area (Wilson, 1932), most species that have 

 been added since are subtropical in distribution. The genus currently 

 comprises nine species but only two of them, Z arenicolus and Z 

 septimus Lang, 1965, have been recorded again since their original 

 description (Bell & Woodin, 1984; Coull, 1971a-b; Foy & Thistle, 

 1991; Mielke, 1990, 1997). The taxonomy and phylogenetic posi- 

 tion of the genus within the family Harpacticidae are not well 

 understood for a variety of reasons. First, species of Zausodes are 

 amongst the smallest Harpacticidae and males often do not exceed 

 0.4 mm in size. Second, Wilson's (1932) generic diagnosis contains 

 a number of significant inconsistencies which originate from his 

 imperfect description of Z arenicolus. Lang (1965) clarified some 

 of the erroneous statements but did not present a complete 

 redescription. Third, several subsequent descriptions are grossly 

 inadequate and severely hamper both species identification and 

 phylogenetic reconstruction of relationships. This is particularly the 

 case for the species described by Jakobi (1954) and Krishnaswamy 

 (1954). Finally, the current subfamilial classification of the 

 Harpacticidae introduced by Lang (1948) is inadequate. The genus 

 Zausodes was placed in the Zausodiinae together with Zaus Goodsir 

 and Zausopsis Lang, however recent discoveries of new taxa (Ito, 

 1979; Watkins, 1987) have provided strong indications for a close 

 relationship between Zausodes and Perissocope Brady, a genus 

 currently assigned to the Harpacticinae. 



While examining a collection of harpacticoids from the northern 

 Gulf of Mexico, previously identified by D.Thistle and co-workers 

 as Z arenicolus (Foy & Thistle, 1991; Ravenel & Thistle, 1981; 

 Thistle, 1980; Thistle etal, 1995), we found several other species of 

 Zausodes which could not be assigned to the type species. Although 

 Z arenicolus was present among the specimens, as confirmed by 

 comparison with Wilson's type material, three species new to sci- 

 ence were found. Since one of these was very similar to Z areolatus 

 Geddes, the type locality of which is in the relatively nearby 

 Caribbean (Geddes, 1968a), the type material of the latter was 

 obtained for comparison. 



This paper describes the three new species from the Gulf of 

 Mexico, provides complete redescriptions for both Z arenicolus and 

 Z areolatus and analyses the phylogenetic relationships between 

 the species. The genus Zausodes is redefined in the light of these 

 findings. 



MATERIALS AND METHODS 



Samples were taken by SCUBA divers with a 15.5 cm 2 corer. The 

 top 3 cm of each core were preserved in sodium-borate-buffered 

 formalin. In the laboratory, harpacticoids were concentrated from 

 each sample with a modified Barnett (1968) extraction technique 

 combined with a 0.062-mm mesh sieve. After rose bengal staining, 

 harpacticoids were sorted under a dissecting microscope and mounted 

 in glycerol on slides. 



Specimens were dissected in lactic acid, and the dissected parts 

 were placed in Hoyer's mounting medium (Pfannkuche & Thiel, 

 1988) on H-S mounts (Shirayamae/a/., 1993) or Cobb slide frames 



(Westheide & Purschke, 1988). Drawings were prepared with a 

 camera lucida on a Zeiss Standard 16 compound microscope equipped 

 with differential interference contrast. Habitus views were drawn at 

 800x; other illustrations were drawn at 2000x. Body size was 

 measured along a line halfway between the dorsal and ventral 

 margins in lateral view at 256x with the aid of a camera lucida. 

 Terminology follows Huys & Boxshall (1991). Abbreviations used 

 in the text and figures are: ae = aesthetasc; P1-P6 = first to sixth 

 thoracopods; exp(enp)-l(2,3) to denote the proximal (middle, distal) 

 segment of a ramus. 



Phylogenetic relationships between taxa were analyzed using the 

 phylogenetic computer package PAUP 3.1 prepared by David L. 

 Swofford of the Laboratory of Molecular Systematics, Smithsonian 

 Institution (Swofford, 1993; Swofford & Begle, 1993). Since evolu- 

 tion within the Copepoda is assumed to proceed typically by 

 oligomerization (Huys & Boxshall, 1991), all characters were set 

 irreversible using the CAMIN-SOKAL option. This option sup- 

 presses character reversals at the expense of introducing extra 

 convergences and thereby increasing the tree-length. The options 

 employed in the analysis were BRANCH AND BOUND, which 

 guaranteed to find all most parsimonious trees, and the MINF 

 optimization, which assigns character states so that the f-value is 

 minimized. 



SYSTEMATICS 



For practical reasons the systematics section of this paper is ar- 

 ranged according to the conclusions arrived at in the phylogeny 

 section below. Species are allocated to genera following the topol- 

 ogy of the most parsimonious cladogram obtained by the phylogenetic 

 analysis (Fig. 33A). 



Family Harpacticidae Dana, 1846 



Genus Zausodes C.B. Wilson, 1932 



In its revised concept (see below) the genus is restricted here to the 

 type species and Z septimus. Lang (1965) had already recognized 

 the close relationship between these species, pointing out their 

 similarity in the9P5. Z arenicolus displays two characters which 

 are not found in any of the species of the former Zausodes complex: 

 (1) the 3-segmented P4 endopod, and (2) the presence of a 

 mucroniform process on enp-2 of the male P2. The former is an 

 evolutionary labile character, frequently showing intermediate states 

 in other species (Lang, 1965), whilst the latter is regarded here as a 

 plesiomorphy retained within the former Zausodes complex only in 

 Z arenicolus, but being present in many other harpacticid genera 

 such as Perissocope, Harpacticus Milne-Edwards and Tigriopus 

 Norman (Huys et al. , 1 996). It is assumed that in all other species of 

 the former Zausodes complex this process was secondarily lost. 



Diagnosis. Harpacticidae. Antennule 9 8-segmented, with pin- 

 nate or plumose setae on segments 1-6; without strong, modified 

 spines on segments 3-5 or enlarged pectinate or pinnate spines on 

 segment 6. Antennule cf without modified spines on segment 3. 

 Antennary exopod 1-segmented, with 2 apical setae. Maxilla with 4 

 spines/setae on praecoxal endite. P2-P3 endopods 3-segmented, P4 

 endopod 2- or 3-segmented. P2 9 enp-3 with 2 inner setae. P3 9 enp- 

 2 without inner seta. P4 exp-3 with 3 outer spines in both sexes. P4 

 enp-3 (or enp-2 when 2-segmented) with 1 inner seta in both sexes. 



