PHYLOGENY OF ARIETELLID COPEPODS 



109 



those of female or slightly different in armature elements of 

 antennary second endopod segment and mandibular first 

 exopod segment. 



Leg 5 variable, but not natatory, almost symmetrical to 

 strongly asymmetrical; coxae and intercoxal sclerite fused to 

 form common base or separate; right basis sometimes fused 

 with coxa; right endopod 1-segmented, bulbous or absent; 

 right exopod distinctly or indistinctly 3-segmented, first and 

 second segments each with seta on outer margin (rarely first 

 segment unarmed), second segment with tuft of setules on 

 inner distal angle of second segment, third segment with 0-3 

 elements terminally; left endopod 1- or 2-segmented, 

 unarmed or completely absent; left exopod distinctly or 

 indistinctly 3-segmented, first and second segments each with 

 seta on outer margin, third segment with 1-3 elements 

 terminally. 



Type genus. Arietellus Giesbrecht, 1892. 



Remarks. The above diagnosis excludes Rhapidophorus 

 Edwards, 1891, which was inadequately described and has 

 never been redescribed. Although the family was briefly 

 defined by Sars (1902), Rose (1933), Brodsky (1950) and 

 Campaner (1977), the present amended definition includes 

 new information on the genital systems of females and the 

 armature elements on the appendages. 



Genus Crassarietellus gen. nov. 



Diagnosis. Female. Body compact, prosome ovoid in dorsal 

 view; cephalosome separate from first pedigerous somite; 

 posterior corner of prosome produced posteriorly to form 

 rounded lobe. Urosome short, at most one-third as long as 

 prosome; genital double somite wider than long, with pair of 

 gonopores ventrolaterally and paired copulatory pores each 

 located beneath ventral projection; anal operculum not 

 developed; caudal rami symmetrical, longer than wide, with 

 vestigial seta I and normally developed seta II. 



Antennule symmetrical reaching to posterior end of second 

 pedigerous somite, 22-segmented; segments I — III fused, with 

 7 setae and 2 aesthetascs; segments IV, VI, XII and XIII each 

 with 2 setae and 1 aesthetasc; segments XXIII and XXIV 

 separate; compound segment XXVI-XXVIII with 8 setae 

 and 1 aesthetasc; posterior margin of ancestral segments I to 

 XIII fringed with long setules; segments IV-VIII with trans- 

 verse row of long setules along distal end of segment. 

 Antenna: first endopod segment with medial inner seta; 

 second segment bearing 3 midlength and 5 terminal setae; 

 exopod indistinctly 10-segmented exopod. Mandibular gna- 

 thobase with tuft of setules at midlength and 3 teeth on 

 cutting edge. Mandibular palp: endopod rudimentary, 

 1-segmented, with 2 setae; seta on first exopod segment not 

 reduced; outer seta on fifth exopod segment relatively long. 



Maxillule: praecoxal arthrite with 5 stout, serrate spines 

 and 1 process; coxal epipodite having 6 setae; coxal endite 

 bearing long seta; second basal endite with vestigial seta; 

 endopod rudimentary, 1-segmented with 2 setae. Maxilla: 

 first syncoxal endite with 2 setae and vestigial element; 

 second syncoxal endite with 2 setae; basal endite carrying 

 stout spine with row of spinules medially. Maxilliped with 

 second to sixth endopod segments bearing 4, 4, 3, 3 and 4 

 setae, respectively; innermost seta on fourth and fifth endo- 

 pod segments not reduced; setae a and b on sixth endopod 

 segment not reduced. 



Leg 1 bearing 2 outer lateral spines on third exopod 



segment. Leg 5 having distinctly 1-segmented, rudimentary 

 endopod with 2 setae and indistinctly 3-segmented exopod 

 with 3 outer lateral and 2 terminal spines. 



Male. Left antennule geniculate, 19-segmented; segments 

 I-IV fused, with 9 setae and 4 aesthetascs; segments XXI and 

 XXII fused; segments I to X fringed with setules along 

 posterior margin; segments IV to VIII with transverse row of 

 setules as in female. Mouthparts and legs similar to those of 

 female. 



Leg 5 with coxae and intercoxal sclerite incompletely fused 

 to form common base; coxa separate from basis. Right leg 

 lacking endopod; exopod, at least 2-segmented, first segment 

 with outer spine on distal corner. Left leg: endopod incom- 

 pletely 2-segmented, first segment expanded, second segment 

 small, semispherical; exopod distinctly 3-segmented, first 

 segment with spine on outer corner, second segment 

 expanded, bearing outer spine at midlength, third segment 

 small, having 2 small outer setules and chitinized, long 

 terminal seta. 



TYPE SPECIES. Crassarietellus huysi, gen. et sp. nov. 



Other species. Crassarietellus sp. based on a male which 

 was erroneously assigned to Scottula abyssalis Sars, 1905 by 

 Sars (1924, 1925). 



Remarks. Sars (1924, 1925) assigned one male collected 

 from off Lisbon to Scottula abyssalis Sars, 1905, the female of 

 which was captured off the Azores. However, this male 

 should be included in the new genus Crassarietellus based on 

 the similarities of the mouthparts: the indistinctly 

 10-segmented antennary exopod (compare Fig. IF with Fig. 

 7D); 5 serrate spines and a process on the praecoxal arthrite 

 and 6 setae on the coxal epipodite of the maxillule (Figs 5A, 

 8A); 2 non-reduced setae on the sixth endopod segment of 

 the maxilliped (Figs 5C, 8E). Additionally, a transverse row 

 of setules is present, on each of the antennulary segments IV 

 to VIII in the male (Fig. 7A), that is found only in the genus 

 Crassarietellus. The ornamentation of the appendages of the 

 male, such as the many tiny spinules along the outer margin 

 of the mandibular palp and the stout, outer processes on the 

 exopod segments of legs 1 to 4, also supports the proposal to 

 place the male in Crassarietellus. The right leg 5 of the male 

 lacks distal exopod segment(s), a condition which Sars (1924, 

 1925) misinterpreted as '1-segmented left' exopod. 



Etymology. The new generic name Crassarietellus (Latin 

 crassus meaning thick) refers to the ovoid, compact body 

 form of the new genus. The specific name is named in honour 

 of Mr. Rony Huys. 



Ecological note. The type species of the new genus was 

 found in near-bottom samples taken at depths of 3974-4060 

 m. The plump body and the relatively short antennules 

 indicates that the new genus is hyperbenthic. 



Crassarietellus huysi gen. et sp. nov. (Figs 1-6) 



Material examined. 3 99- 



Types. Holotype: 9, 18 IV 1977, North Atlantic (off western 

 Africa), 20°8.5'N, 21°1.2'W-20°20.8'N, 21°53.0'W, 

 3974-4036 m in depth, dissected and mounted on slides, 

 prosome and urosome preserved in 70% ethanol, BM(NH) 

 1993. 424. Paratype 1: $, 18 IV 1977, 20°19.7'N, 

 21°51.3'N-20°18.4'N, 21°40.5'W, 4008-1060 m in depth, dis- 

 sected and mounted on slides, prosome preserved in 70% 



