CALANOID COPEPODS FROM GULF OF MEXICO 



359 



Diagnosis.— A western Atlantic-Gulf of Mexico 

 population closely resembling an Indo-Pacific 

 congenitor, E. cancinna Dana, as described by 

 Giesbrecht (1892) and Scott (1909). 



Adult female: Differs from concinna chiefly 

 in details of thoracic fusion segment IV-V and 

 genital segment. 



Posterior terminal margins of thoracic fusion 

 segment IV-V in lateral view symmetrical, 

 rounded, neither side produced posteriad (figs. 

 •2,4). 



Right side of genital segment with unique 

 acuminate process and smaller, more postero- 

 ventrah digitiform process, both extending 

 laterad (figs. 4, 5, 8). Genital boss prominent, 

 asymmetrical, extending posteroventrad from 

 right side as conspicuous lobiform process (figs. 

 4. 7, 8) ; in dorsal view process barely visible (fig. 

 5). Posterior ridge of genital orifice with short 

 lateroventral processes (fig. 7). Anteroventral 

 portion of genital segment with small rounded 

 swelling anterior and left of genital boss (figs. 2, 

 7,8). 



Adult male : Differs from concinnn with respect 

 to minute details of left fifth leg. 



Iveft fifth leg with Re. slightly expanded at dis- 

 tal portion; distal portion bearing short thick 

 haii-s on lateral as well as medial margins, about 

 five serrations on anterior portion of apex, and 

 small cteniform row of hairs on remainder of 

 apex (figs. 9, 10, 13). Base of terminal segment 

 with two processes, somewhat as in concinna (vide 

 Giesbrecht 1892: pi. 16, fig. 19), but proximal 

 process smaller and ensiform, larger distal proc- 

 ess with expanded basal portion and digitiform 

 apex (figs. 9, 10, 13). 



Types.— X\\ deposited in United States National 

 Museum. Female holotype, Xo. 99197, selected 

 from material of Alaska, cruise 8, station 5; lat. 

 28°.54' N., long. 90°11' W.: 13 February 1953; 

 3 m. depth of plankton tow. Paratypes: Xos. 

 99198-99202. 



Further description. — Relation of rostrum and 

 frontal organ similar in male and female, forming 

 angle of approximately 90° ; distal portion of ros- 

 trum curving moderately posteriad (fig. 1) . CAR 

 as well as length relations of both abdominal seg- 

 ments and six terminal segments of first antennae 

 similar to those of concinna. calculated from Gies- 

 brechfs (1892) description and figures. 



Cephalic appendages as in K. marina (Prestan- 

 drea), except for first maxillae. First external 

 lobe of first maxillae witli four elongated setae, one 

 short seta. Endopodite of second maxillae with 

 one spinulated seta as in Sewell's (1947) pro- 

 visional SiJecies Group II. 



First legs (figs. 15, 16) apparently as in con- 

 cinna. Female second leg with proximal two ex- 

 ternal spines of Rej equal in size, larger than distal 

 spine (fig. 11). I^gs 3-4 with external spines of 

 Re3 of equal length. Left fifth leg of male with 

 rudimentary endopodite. 



Egg cluster in spawning females with five-eight 

 eggs extending posteroventrad from genital boss 

 in single layer, two eggs wide. Individuals of 

 both sexes often with stalked ciliates fixed to pos- 

 terior thoracic segments and abdomen as in marina 

 but smaller in size. 



Remarks. — In the new species, the female is 

 readily separated from cancinna by the following : 

 (1) the acuminate process extending laterad from 

 the right side of the genital segment, (2) the form 

 of the genital boss, especially the right lobiform 

 process, which in doi-sal view barely protrudes 

 lieyond the lateral limit of the genital segment, 

 and (3) the rounded terminal portions of thoracic 

 fusion segment IV-V. 



The new species also resembles E. consimilis 

 Farran (Indo-Pacific region) and E. murrayi 

 Sewell (Arabian Sea), the latter two known only 

 from the female sex. It differs from can.fi milis in 

 the same manner that distinguishes it from con- 

 cinna. In contrast, murrayi could be confusing 

 since its genital segment beare a weak protuber- 

 ance at the midpoint of the right side and the ter- 

 minal portions of thoracic fusion segment IV-V 

 are rounded (Sewell 1947: text fig. 26A-D). 

 However, in SewelFs species the protuberance is 

 not acuminate, the genital boss is on the posterior 

 half of the segment, and the right lobe adjacent 

 to tlie genital orifice extends posteriad (ibid.). 

 The genital segment, in particular the acuminate 

 process extending laterad from its right side, ap- 

 pears to distinguish paraconcinna from all other 

 species of the genus. 



In the male, the new species is distinquished 

 from cancinna only with difficulty. Apparently, 

 the two are best separated by the distal portion 

 of Re, of the left fifth leg. According to both 

 Giesbrecht (1892: pi. 16, fig. 19) and Scott (1909: 

 pi. 19, fig. 27), this segment in coTi^/ma terminates 



