Description of Female.
Length 5 mm.; depth ½ mm; width 1 ½ mm. Ovigerous, about 33 eggs. Colour in spirit yellowish-orange; eyes small, eye-lobes rounded; small triangular rostrum produced much less than ⅓ along 1st segment of antenna 1 peduncle.
Antinnae. First: Length 1 ½ mm., not reaching end of antenna 2 fiagellum. Flagellum of 6 segments, about ⅓ peduncle length; segments except very small end segment longer than wide with long setae distally. Peduncle, 1st segment
Corophium sextonae Crawford. 1—Antenna 1, ♂. 2—Antenna 1, ♀ 3—Antenna 2, ♂, 4—Antenna 2, ♀. 5—Lower Lip. 6—Maxilla 1. 7—Mandible showing palp. 8—Gnathopod 1, ♂. 9—Gnathopod 1, ♀. 10—Gnathopod 2, dactylos, ♂. 11—Peraeopod 1, ♀. 12—Peraeopod 4, ♀. 13—Epimeral plate. 14—Pleopod. 15—Pleopod coupling spines.
constricted proximally, widening quickly, then narrowing distally; greatest width nearly ½ length; 2 strong spines, one hooked, on inner margin proximally; long setae on inner and outer margins; a median marginal flange with row of about 5 strong spines, the 1st 3 hooked, on proximal ½, then long setae and a distal stout spine; 2nd segment ⅔ length 1st, linear, width ¼ length, long setae on margins and surface; 3rd segment narrower, less than ½ length 2nd, a few long setae; segment more like flagellar segments. Second: Length 1 ½ mm Peduncle, 2nd segment wide, short, with prominent gland-cone bearing 5 stout hooked spines; 3rd slightly wider that long, a few long marginal setae; inferodistal angle a little produced with 2 strong spines; 4th, greatest width less than ½ length, 5 strong spines in a single row along inferior margin; long setae on margins and surface; 5th ¾ length 4th, width ⅖ length, setae on margins and surface, 1 strong spine ½ along inferior margin. Flagellum not ⅔ length 5th segment of peduncle; 1st segment ⅖ length 5th peduncle segment; setae in distal and medial broken circlets; 2nd segment less than ½ length 1st, setae distally; 3rd segment very small, distally setose, 2 apical spines.
Mouthparts. Lower Lip: Lobes distally rounded and bristled; inner almost as long as outer; inner margin of outer plate bilobed. Mandibles: Cutting edge of 2 long narrow plates; molar process large. Palp, 1st segment widening distally, inner distal angle a little produced with long plumose setae; 2nd segment arising from outer distal angle, about ⅓ longer than 1st, a few long bristles on inner margin, a sparsely bristled long end seta. First Maxillae: Palp not narrowing throughout; 1st segment subsquare; 2nd reaching a little past outer plate, about 9 sharp spines distally. Second Maxillae: Plates distally rounded; outer slightly the longer, with long setae distally; inner with long setae on distal and inner margins. Maxilliped: Inner plate just reaching past merus base; 2 long plumose spines distally, about 3 down inner margin, a small spine proximally. Outer plate arising just below end of inner plate, reaching ⅔ along carpus inner margin, not widening much, outer margin rounding distally to inner, short plumose setae along inner margin. Ischium as long as wide, slightly longer than merus outer margin; merus inner margin ⅔ length outer, slightly less than width; 3 or 4 long plumose setae on inner distal angle. Carpus inner margin ½ as long again as merus outer margin, with strong fringe of long slender plumose setae: several plumose setae on carpus outer distal angle; carpus not widening distally; on one surface a single row of long plumose setae runs from ½ down inner margin of basos obliquely across ischium to merus outer distal angle. Propod small, sub-rectangular, more than ½ length carpus inner margin, width ½ length, long plumose setae on distal angles. Dactylos ½ propod length and width, plumose setae distally, long slender terminal nail about ¾ propod length.
Gnathopods. First: Sideplate ovately subtriangular, anterodistally rounded, about 4 short setae anteriorly, 3 very long plumose setae ventrally. Basos proximally constricted, posterior margin convex, distal width ⅓ length, a single very long seta at posterodistal angle. Ischium subrectangular, posterior margin about ¾ width, length more than ¼ basos; row of long plumose setae posteriorly on distal margin. Merus small, subtriangular, posterior margin as long as ischium, 3 or 4 long plumose setae on posterodistal angle, 1 or 2 on surface. Carpus about ¾ basos length, greatest width ⅖ length; anterior margin slightly convex, single seta about ⅔ along, 3 or 4 short setae distally; straight posterior margin has double fringe of long plumose setae, some as long as propod. Propod as long as carpus, width
¼ length, not widening much; about 4 rows of 2 to 6 long plumose setae proximally on surface, several more setae at anterodistal angle, several midway along posterior margin; long seta-tipped spine at about ¾ marks beginning of obliquely convex and poorly defined palm, several shorter seta-tipped spines along palm. Stout curved dactylos shorter than palm, only as long as propod is wide; inner margin has single tooth medially, a few small setae on surface and margins. Second: Sideplate small, subrectangular, single long plumose seta anterodistally. Basos width ½ length, a few fine setae distally. Ischium very small, wedge-shaped, posterior margin ¼ basos length, a fine seta posterodistally. Merus as long as basos and ischium combined, anterior margin slightly concave, contiguous with carpus posterior margin so merus and carpus appear as single plate; row of very long plumose setae on strongly convex posterior margin, a similar row running in more or less parallel arc along surface. Carpus subtriangular; anterior margin straight, barely shorter than merus, a few very fine setae distally. Propod slender, narrowing slightly distally; ½ as long again as basos, width about ⅕ length; slightly convex anterior margin has a few very small fine setae; oblique row of long plumose setae runs almost right across surface from posteroproximal angle; several short and long setae on posterior margin; tufts of moderately long setae on distal angles. Stout dactylos about ¼ propod length, tridentate with 2 or 3 very short setae.
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Peraeopods. First: Sideplate small, wider than deep. Basos margins slightly convex, width nearly ½ length; 3 very long single setae on posterior surface, a few very small fine setae on margins. Ischium subsquare, ¼ basos length, 2 or 3 fine setae posterodistally. Merus slightly more than ½ basos length, width ⅔ length, anterior margin constricted a little proximally, a few marginal setae posteriorly, single seta midway along anterior margin, tuft at anterodistal angle. Carpus subtriangular, wedged between merus and propod, posterior margin less than ⅓ merus length, with several long setae. Propod width less than ½ length, anterior margin ⅖ basos length, margins slightly convex, posterior margin setose, setae on anterodistal angle; distally narrowed to slender dactylos; dactylos as long as propod, width about 1/7 length Second: Similar. Third: Like Pr. 4, but stouter; basos posteriorly lacks plumose setae. Fourth: Basos ovate, greatest width ⅔ length, margins convex, anterior with a few fine marginal setae, tuft at distal angle; posterior with 1 or 2 fine setae proximally, 4 or 5 longer plumose setae distally. Ischium subsquare, ⅓ basos length, tuft of setae anterodistally. Merus, posterior margin a little constricted proximally, length ⅔ basos, distal width ½ length, several setae on anterior margin, fringe of fine bristles distally, tuft of long setae posterodistally. Carpus subrectangular, width ¾ length, length ½ merus, oblique row of 5 stout spines across surface postero-proximally; similar are of 7 spines across distal surface, the last and very stout spine on posterodistal angle. Propod slender, ⅖ basos length, narrowing slightly to stout short dactylos. Fifth: Basos ovate, narrowing distally, margins equally convex, greatest width ⅖ length. Ischium subrectangular, width ⅔ length. Merus ⅔ basos length, width ⅓ length, a few setae on each margin. Carpus similar, tuft of long setae on each distal angle, as long as merus, narrower. Propod still narrower, almost as long as basos, several groups of 1 or more long setae on margins, strong tuft posterodistally Curved simple dactylos ⅕ propod length.
Epimeral Plates. Wider than deep, subrectangular, distal angles rounded, 4 or 5 long plumose setae ventrally.
Pleopods. Biramous, rami arising from outer half of distal margin, outer ramus barely longer than peduncle; rami of about 9 segments, each with pair of long plumose setae; peduncle wider than long, inner distal angle produced downwards a little.
Urosome. Segments coalesced, uropods arising from marginal notches.
Uropods. First: Reaching a little past ends of 2nd uropods which are barely longer than 3rd; peduncle width little more than ¼ length; rami subequal, ½ peduncle length, outer dorsal margin of peduncle has about 11 short stout seta-tipped spines, inner has about 5 sharp spines distally; distal margin medially produced to small lobe between rami; outer ramus distally acute; both rami slightly convex, outer margin has about 8 seta-tipped spines right along, 3 spines distally on inner; inner ramus similar. Second: Peduncle as long as inner ramus, outer slightly shorter; peduncle width ¾ length, single spine on inner distal angle; rami for most part distally rounded but with stout acute tooth terminally; outer ramus with 2 spines ½ along outer margin, 3 at end; inner ramus with 2 or 3 along outer margin, 2 at end of inner. Third: Peduncle reaching end of telson. 1 or 2 setae at outer distal angle, peduncle ¾ length of rounded terminal segment which has about 12 long setae on convex end margin. Telson: Narrowing to straight distal margin, wider than long, 2 parallel rows each of 4 small teeth along surface; 3 or 4 setae on proximal angles.