Anthessius — Illg 
357 
Anthessius nortoni, new species 
Figs. 59-91 
types: Holotypic female, USNM 103304, 
allotypic male, USNM 103305, paratypes, 
USNM 103306; paratypes in author s collection. 
Type locality, San Juan Island, Washington, 
from Diadora aspera ( Eschscholtz ) . 
SPECIMENS EXAMINED: From D. aspera: Cul- 
ver’s Point, San Juan Island, Washington, inter- 
tidal, July 5 , 1952, many specimens, females, 
males, developmental stages, including holotype, 
allotype. Off Reed Rock, San Juan Channel, 
Washington, dredged, 92 m., July 2, 1953, many 
specimens, females, males, developmental stages. 
Salmon Beach, Tacoma Narrows, Washington, 
intertidal, May 14, 1953, many specimens, fe- 
males, males. 
The description below and the illustrations 
are based on a number of specimens, some un- 
mounted, some whole mounts, some temporarily 
mounted dissections, some permanently 
mounted dissections. Holotype and allotype are 
permanently mounted dissections. 
DESCRIPTION: Female (Figs. 59-75): Body 
length 1.28 mm., greatest width .63 mm., aver- 
ages from 10 specimens. Body (Fig. 59) broad, 
of rather generalized cyclopoid contours, with 
thoracic and abdominal regionalization fairly 
emphatic. Cephalosome a complex bearing ap- 
pendages through first swimming legs and com- 
prising .34 of total body length, measured from 
apex of cephalosome to end of a caudal ramus. 
Segment of first legs strongly indicated by in- 
dentations and grooves, but mass of segment 
firmly coalesced with more anterior mass of 
body. Cephalosome and metasome together com- 
prising a forebody of almost circular outline. 
On anterior margin, apex of head protruded as 
slight bulge between bases of widely separated 
antennules (Fig. 60). No rostrum, apical ven- 
tral region of head a wide flattened expanse 
between bases of antennules and antennae. 
Metasome including pedigerous segments of 
second through fourth legs, with general body 
articulation between segments of legs 4 and 5. 
Urosome a complex including segment of legs 
5, genital segment and 3 additional abdominal 
segments, considering element of anal opening 
and supporting caudal rami as terminal segment. 
Urosome comprising .4 of total body length. 
Genital segment expanded laterally, dorsally 
with distinctive structures marking apertures of 
oviducts and sites of attachment of egg sacks 
(Fig. 61). Last abdominal segment with double 
row of spinules at midline on anterior ventral 
surface and with spinule rows on margins sub- 
tending each caudal ramus ( Fig. 62 ) . Egg sack 
about .6 as long as body, much exceeding tip 
of caudal ramus. Many small eggs in each egg 
sack. 
Antennule (Fig. 71) essentially 7-segmented, 
but with a complicated articulation and integ- 
urnental modification between second and third 
segments, so as to suggest either coalescence or 
incipient separation of an additional minute 
segment. Proportional lengths of segments, 
basal to distal: Segment I, 1.5; II, 3; HI, 1; IV, 
3; V, 2; VI, 1; VII, 1. Setae varying in length; 
count per segment: Segment I, 4 setae; II, 7 
setae near base of segment, 8 around distal end; 
III, 5 setae, 1 belonging to section suggesting a 
free segment; IV, 3 setae; V, 4 setae, 1 aesthete; 
VI, 2 setae, 1 aesthete; VII, 7 setae and 1 aes- 
thete, 4 setae on basal prominence of segment, 
3 setae and aesthete apical. 
Antenna ( Fig. 63 ) short and stout, with seg- 
mental composition much obscured by flexures 
involving integumental folds and torsions of 
one region of appendage on adjoining regions, 
probably essentially 3 -segmented. Basal segment 
fairly clear-cut, apical articulation diagonal, 1 
short external seta apically. Second segment with 
very complicated distal articulation, this proceed- 
ing diagonally across appendage; 1 short seta 
externally inserted. Terminal segment with cu- 
ticularized ridges and folds and with very broad 
distal margin furnishing insertion for 4 elab- 
orately articulated clawlike elements, varying 
much in size, and 2 setae. Another seta near 
distal margin. A subapical group of 4 setae of 
diverse lengths. Total elements: 4 claws, 7 setae. 
Mouthparts compactly and intricately ar- 
ranged in oral area (Fig. 64). Labrum of 2 
conspicuous lobes, overlying entirely blades of 
mandibles, and much of distal parts of maxillae. 
Mandible (Fig. 65) a flat plate, with very 
cuticularized anterior and posterior margins. 
Appendage terminating in long lashlike blade 
with complicated marginal ornamentation: Two 
