NEW CALANOID COPEPODS OF THE FAMILIES AETIDEIDAE, 

 EUCHAETIDAE, AND STEPHIDAE FROM THE GULF OF MEXICO 



By Abraham Fleminger, Fishery Research Biologist 



The numerous and widespread zooplankton col- 

 lections made by the United States Fish and AVild- 

 life Service vessel Alaska in the Gulf of Mexico 

 between the years 1951-53 offer the first opportu- 

 nity for a comprehensive account of the epiplank- 

 tonic copepods inhabiting the region. Previous 

 studies on this fauna have been confined to limited 

 coastal areas off Florida, Mississippi, and Ijouisi- 

 ana (Schmitt 195-1). The present investigation 



of the Alaska collections has already revealed a 

 ricli and varied fauna occurring in the surface 

 waters of the Gulf. Approximately 100 calanoid 

 species have been identified thus far, including 

 nine previously undescribed populations. Three 

 of these new forms, belonging to the families Aeti- 

 deidae, Euchaetidae, and Stephidae, respectively, 

 are described in this report. 



Family AETIDEIDAE 



BRADYIDIVS Giesbrecht 

 Bradyidius arnoldi, new species 



Plate 1, figs. 1-13 



LocuUiics, J/aferin?.— Gulf of Mexico: lat. 22°20' N., 

 loiiR. 87°31' W. (Alaska, cruise 4, station 11, 13 January 

 19.52, surface plankton tow, four males) ; lat. 29°06' N., 

 long. !>:rOO' W. [Alaska, crui.se 8, .station 2. 12 February 

 1953, 6 in. depth of plankton tow, one female) ; lat. 25°30' 

 N., lonjr 97°06' W. (/l?<jsAo, cruise 10, .station 5, 16 April 

 19.5.3, 3 m. depth of plankton tow. three immature cope- 

 podites). 



Meamrementfi. — All measurements made from 

 dorsal view along midsagittal plane: cephalo- 

 thorax measured from anteriormost margin of 

 forehead to posterior margin of intersegmental 

 fold between thoracic fusion segment IV-V and 

 genital segment ; length of abdomen from anterior 

 margin of genital segment to porteriormost limit 

 of right furcal ramus. Measurements made at 

 100 X magnification with aid of ocular microm- 

 eter; sj)ecimen immersed in aqueous solution of 50 

 percent glycerine. Slender glass rods used to 

 support cephalothorax and abdomen in horizontal 

 position during measurements of each. Measure- 

 ments given are total length (TL) and cephalo- 

 thorax-abdomen length ratio (CAR). 



1. Adult female: TL 1.67 mm., CAR 4.0:1 



2. Adult .males: TL 1.23 mm., CAR 2.8:1 (holotype) ; 

 TL 1.19 mm., CAR 2.8:1 ; TL 1.23 ram., CAR 2.8:1 



NOTK. — Approved for puhlli-atloii NovenibtT 9. lO.'iH. Fishery 

 Bulletin 117. 



Diagnosis. — A species relatively small in size 

 with respect to the genus in which the female 

 closely resembles B. armatm Giesbrecht and B. 

 paei-ficus ( Brodski ) . whereas the male is somewhat 

 similar to pacificus as well as B. similis (Sars). 



Adult female: Appears to differ only slightly 

 from atmatus (vide Sars 1902: pis. 20, 21) and 

 padfcus (vide Brodski 1950 : text fig. 65) . 



Thorax (figs. 1, 2) with segments IV-V im- 

 perfectly fused, weak line of demarcation visible 

 in dorsal view. Posteriormost portion of thoracic 

 segments I-III flared both dorsad and laterad, 

 fused cephalon-segment I flared to greatest extent. 

 Fusion segment IV-V terminating on right and 

 left sides in robust spiniform process, similar to 

 armutus, but processes originating more dorsad, 

 tilted dorsad, and with irregular medial and ven- 

 tral outlines. Anal segment shorter than preced- 

 ing segment. 



First antennae each with 24 segments, as long as 

 cephalothorax less spiniform processes of last seg- 

 ment. Mandible with dentition of gnathal lobe 

 (fig. 6b) dirtering from that in uimatiix; teeth 

 more numerous, those on ventral half of lobe over- 

 lapping. Stage V male copepodite with mandi- 

 bular gnathal lobe (tig. »ia) apparently similar 

 to that in armatus. Second maxillae (fig. 13) 

 with short seta on lobes 2-4, each with closely 

 spaced row of spinules on proximal portion; fal- 

 cate spine on lobe 5 with closely spaced row of 



355 



