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Description of Male.
Length 3 mm.; depth ¾ mm.; width ⅔ mm.
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Antennae. First: Length 1 mm. Flagellum as long as last 2 peduncle segments, of about 7 segments, segments longer than wide, a few very fine setae distally on each. Peduncle, 1st segment barely shorter than 2nd, twice as wide; 3rd ½ length 2nd, narrower; all with a few fine setae on margins and end. Second. length about 1 mm. Flagellum barely longer than 5th peduncle segment; segments slightly longer than wide, very fine setae distally, of 5 segments. Peduncle, 2nd segment very stout, small but prominent gland-cone; 3rd shorter and narrower, a few setae distally; 4th segment nearly 3 times as long as 3rd, proximal width about 1/1 length; inferodistally produced downwards and slightly forwards in small lobes; fine setae on margins and end; 5th segment ½ length 4th, width ⅓ length, a few fine setae on margins and end.
Mouthparts. Upper Lip: Distal margin slightly concave. Lower Lip: Ovate inner lobe well developed, smaller than outer, distally bristled; distal margin of outer lobes tending to straight, median and distal margins finely bristled. First Maxiallae: Inner plate very small, finely bristled distally. Outer plate wide, distal margin straight with 9 or so finely-toothed spines. Palp slightly longer than outer plate, of 2 segments. 1st about ⅓ length 2nd; 2nd widening slightly distally, straight end margin has about 9 very small teeth. Second Maxillae: Inner plates slightly the shorter, inner and distal margins of each fringed with long fine setae. Mandibles: Spine-row of about 4 spines (right); cutting edge and weak molar process present; palp large, 1st segment ½ length 2nd. 3 or 4 setae on inner margin of 2nd medially and distally; 3rd segment ¾ length 2nd; slightly oblique and truncate distal margin fringed with fine setae, longest outermost, row of 3 or 4 setae below these on outer margin. Maxilliped: Small narrow inner plate reaching carpus base, end margin and distal ½ of inner margin with several long plumose setae. Outer plate reaching ⅔ along carpus, outer margin convex, inner straight with 8 or 9 increasingly longer teeth on distal ½; single and paired fine setae inside these teeth. Merus and ischium of more or less equal length, merus narrower; stout seta on merus inner distal angle, fringe of very long finely-plumose setae running from basos inner margin across surface to ischium distal margin. Carpus more than twice merus length, width ½ length, inner and distal margin and surface with double row of several long finely-plumose setae, longest at outer distal angle. Propod width ½ length, length ½
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Text-Fig. 6.
Paracorophium excavatum (G. M. Thomson). 70—Maxilla 2. 71—Gnathopod 1, ♂. 72—Gnathopod 2, ♂. 73—Peraeopod 1, ♂. 74—Peraeopod 3, ♂. 75—Peraeopod 4, ♂. 76—Peraeopod 5, ♂. 77—Epimeral plate 1. 78—Epimeral plate 2. 79—Epimeral plate 3. 80—Uropod 1. 81—Uropod 2. 82—Uropod 3. 83—Telson.
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carpus, long finely-plumose setae distally. Dactylos unguiform, ⅔ propod length and narrower, long terminal nail and several accompanying setae.
Gnathopods. First: Sideplate large, heart-shaped if posterodistal angle is regarded as distal apex; anterior margin greatly constricted proximally, plate strongly convex anterodistally; ventral margin with numerous setae; posterior with 3 strong spines medially. Basos slender, proximally constricted, distal width ⅓ length, distal margin fringed with plumose setae anteriorly, 2 or 3 very long plumose setae distally on posterior surface, almost as long as basos itself; 4 or 5 shorter setae proximally. Ischium ¼ basos length, fringe of 3 or 4 extremely long and stout plumose setae at posterodistal angle. Merus ovate, slightly smaller than ischium, long plumose setae distally on posterior margin. Carpus as long and wide as basos, not narrowing noticeably, anterior margin slightly convex, row of several long single plumose setae on distal ½ and part of distal margin; posterior fringed with long plumose setae, a parallel similar row on posterior surface. Propod ¾ carpus length, widening somewhat distally, greatest width ½ length; oblique row of 4 or so long setae medially on anterior surface, a few fine short setae distally; palm oblique, not well defined, rounding to straight posterior margin; palm very minutely combed (like proximal ½ of dactylos posterior margin), guarded by row of short setae. Curved dactylos barely longer than palm, ½ propod length. Second: Sideplate subrectangular, width ⅔ depth, a few setae ventrally; 3 or 4 short strong spines on straight posterior margin. Basos width ⅓ length, constricted proximally, posteriorly convex; 2 or 3 long setae medially on posterior surface, 1 at distal angle. Ischium subsquare, ⅓ basos length. Merus lanceolate, extending downwards as continuation of ischium and basos and almost at right angles to carpus which arises proximally from merus anterior margin; merus as long as basos, medial width ⅖ length, distally acute, margins convex, strong fringe of very long plumose setae on anterior, most of them reaching end of gnathopod. Carpus basically subtri-angular, greatest width slightly more than ½ length, nearly as long as merus; posterior margin fringed with long plumose setae; a similar fringe running obliquely across surface from anterodistal angle almost to posteroproximal; 1 or 2 long setae anterodistally, anterior margin convex. Propod ovate, greatly expanded, margins somewhat convex, distal ½ of posterior straight; anterior with a few fine long setae and as long as basos; posterior as long as basos plus ischium, produced distally to strong but narrow defining tooth; strong median tooth on palm almost as long as defining tooth, a deep excavation between teeth, each tooth with slender setae across surface proximally, a few fine setae on inner tooth margins. Stout strongly curved dactylos slightly swollen basally, fine short setae on inner margin proximally; not reaching farther than outer tooth and seldom as far as tooth.
Peraeopods. First: Sideplate subrectangular, width nearly ⅔ depth, a few setae on ventral surface posteriorly; 3 short strong single spines medially along posterior margin. Basos length nearly three times width, a few fine short setae distally, 3 or so longer setae medially on anterior surface. Ischium subsquare. ¼ basos length, fine setae posterodistally. Merus ½ basos length, distal width ¾ length, narrowing proximally, anterior margin slightly convex, fine setae distally. Carpus ⅓ basos length, almost as long as wide; several fine setae distally and 4 or 5 along posterior margin. Propod narrowing distally to dactylos, proximal width ½ length, length ⅔ basos, a few fine setae distally, 4 or 5 along posterior
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margin. Slender dactylos ⅔ propod length. Third: (From slide B.2, Chilton Collection). Basos greatly expanded, ovately eccentric, greatest width (in oblique plane) more than length, anterior margin greatly convex medially with several long fine setae; posterior margin greatly convex proximally with 10 or so single short plumose setae. Ischium subsquare, about ¼ basos length, 3 or 4 setae on anterodistal angle. Merus ½ basos length, width ⅔ length, anterodistally produced downwards a little along carpus; strong spine or two on posterodistal angle, 5 or 6 long plumose setae on anterior margin. Carpus slightly more than ⅓ basos length, width ½ length, 2 curved spines medially on posterior margin, 3 at posterodistal angle; a few long setae on end margin. Propod width ⅕ length, length ½ basos; long fine setae, distally, about 4 single strong spines on anterior margin. Strong curved dactylos less than ½ propod length. Fourth: Basos ovate, margins convex, posterior more strongly so; 3 or so short setae proximally on anterior, 1 or 2 very short setae on distal ½, tuft of setae at distal angle; fringe of short plumose setae along posterior margin; greatest width about ¾ length; several long fine plumose setae on merus anterior margin; otherwise like Pr. 3 and 5. Fifth: Basos ovate, anterior margin slightly convex, several fine setae proximally and at distal angle, shorter setae distally; greatest width ⅔ length; distal ⅔ of posterior margin convex, proximal ⅓ more or less straight and forming obtuse angle with convex portion which is fringed with short plumose setae; posterodistal angle almost right-angled. Ischium ¼ basos length, longer than wide, setae at anterodistal angle. Merus width ⅖ length, length nearly ½ basos; a few fine setae on anterior margin, 2 large single spines on posterior margin, 2 at distal angle. Carpus as wide, slightly longer, setae and small spine medially on anterior margin, spine and several long setae distally; larger spines medially on posterior, setae and 2 spines distally. Propod ⅔ basos length, a few setae on anterior margin, 2 pairs of strong spines on posterior, tuft of long setae on end margin. Curved slender dactylos comparatively short.
Epimeral Plates. Third much larger than 2nd, 2nd larger than 1st. First: Subsquare, 2 plumose setae near anterior insertion; posterior margin crimped as in Gn.l. Second: As wide as deep, anterior margin rounding to slightly convex ventral, long plumose setae on ventral surface and distal portion of posterior margin, about 16 in all. Third: Very wide and shallow, ventral margin more or less straight, angles rounded to straight lateral margin; plate widest distally.
Pleopods. Normal, rami much longer than peduncle, of about 11 or 12 segments, paired plumose setae.
Uropods. First: Peduncle longer than rami, outer ramus slightly shorter than inner; about 6 short strong spines on peduncle outer dorsal margin, 2 distally on inner; 2 spines dorsally on outer ramus, 2 or 3 at end; 1 or 2 dorsally on inner, 4 or 5 at end; peduncle produced in ventral process under rami and ½ their length, process in side view narrow, somewhat spatulate from above. Second: Inner ramus as long as peduncle, outer slightly shorter; single spine on peduncle outer distal angle; 4 spines on end of inner ramus, 2 on inner margin; 4 spines on end of outer ramus, 1 on outer margin medially. Third: Peduncle longer than rami, outer ramus twice length inner; 2 small setae on inner margin of peduncle. 4 or 5 long setae on end of outer ramus, 3 on inner. Telson: Distally convex, with long single seta on each side arising from last pleon segment.