Rutiderma irrostrata Kornicker & Caraion 1978

Rutiderma irrostratum

HOLOTYPE.—“Grigore Antipa” 291, female (A–1 stage), length 1.27 m, some appendages on slide, remaining appendages and carapace in alcohol.

TYPE-LOCALITY.—Station X053.

ETYMOLOGY.—The species name, derived from Latin, means “without rostrum.”

PARATYPES.—“Grigore Antipa” 292, 2 juveniles from same sample as holotype; USNM 150106, ovigerous female from same station as holotype; USNM 152826, 1 ovigerous female from station A8a; USNM 154198, 1 A–1 male from same sample as holotype; USNM 156595, 1 specimen from station A7b; USNM 156606, 1 specimen from station A10b; USNM 156629, 1 specimen from station X068.

DESCRIPTION OF ADULT FEMALE (Figure 49–51a–g; Plate 31).—Carapace oval in lateral view with evenly rounded anterior, and truncate posterior with protruding caudal process (Figure 49); rostrum almost absent, a short faint line indicates location of incisur (line visible in transmitted light); upper and lower horizontal ribs extend from just anterior to central adductor muscle attachment area to posterior part of shell; on some specimens upper rib tends to continue weakly to anterior shell margin; in dorsal view ribs of each valve parallel.

Ornamentation: Long bristles along anterior margin and on valve surface (Plate 31a,b,f). Surface with abundant shallow fossae (Plate 31a-d); surface between fossae and on bottom of fossae with minute pits and nodes (Plate 31c-e).

Infold: Broad along anterior, ventral, and posteroventral margins; anterior infold with a single bristle near or dorsal to line indicating incisur locality (Figure 50a); 8 bristles on striate anteroventral infold; middle part of ventral infold bare; posteroventral infold anterior to caudal process with 10 small bristles mostly along inner margin of infold; caudal process with 6 bristles along list (Figure 50b); posterior infold dorsal to caudal process with 1 bare bristle.

Selvage: Wide lamellar prolongation present along anterior, ventral, and dorsal margins; edge of prolongation along anterior margin with few marginal hairs, along anteroventral and ventral margin with abundant hairs.

Central Muscle Attachment Scars: Consisting of about 14 individual scars.

Size: USNM 152826, length 1.33 mm, height 0.94 mm; USNM 150106, length 1.50 mm, height 0.94 mm.

First Antenna (Figure 50c): 1st joint: bare or with few faint distal hairs on medial surface. 2nd joint: long hairs forming 3 clusters on dorsal margin, lateral spines forming row in distal dorsal corner, 1 distal dorsal bristle, and 1 short lateral bristle in distal ventral corner. 3rd joint: fused with 4th, with 2 bristles (1 ventral, 1 dorsal). 4th joint: elongate, with 3 bristles (1 dorsal, 2 ventral). 5th joint: elongate, sensory bristle bare; 6th joint: fused to 5th, with short medial bristle. 7th joint: a-bristle slightly longer than bristle of 6th joint; b-bristle represented by minute spine; c-bristle bare, slightly shorter than sensory bristle of 5th joint. 8th joint: d- and e-bristles bare with blunt tips, shorter than c-bristle; f- and g-bristles bare, slightly shorter than c-bristle; minute spine at tip of sensory, c-, f-, and g-bristles.

Second Antenna: Protopodite bare. Endopodite 1-jointed with 4 anterior proximal bristles and a minute subterminal spine with base on lateral surface (Figure 50d). Exopodite: 1st joint with short medial spine on distal margin; joints 2–8 with spines forming row along distal margin; bristle of 2nd joint reaching just past 9th joint, with minute ventral spines forming 4 or 5 groups; bristles of joints 3–8 unbroken, with natatory hairs; 9th joint with 6 bristles (3 long and 1 short with natatory hairs, 2 much shorter, bare or with short hairs).

Mandible (Figure 50e,f): Coxale endite bifurcate with secondary teeth and long spines. Basale: ventral margin with 4 proximal bristles (1 long with short marginal spines, 2 short pectinate, and 1 minute, bare) and 2 bristles near middle (1 short with spine, 1 minute, bare); dorsal margin of basale with 3 bristles near middle forming 2 groups with 1 short bristle in proximal group and 2 in distal group. No exopodite present. Endopodite: 1st joint with 3 short ventral bristles and spines forming rows on medial surface; 2nd joint with spines forming rows on medial surface; dorsal margin with 2 proximal bristles; ventral margin with stout terminal claws with serrate inner margin and proximal tooth; 1 short ventral bristle and small medial process present near base of claw; end joint with stout dorsal claw and slender ventral claw, each with minute teeth along ventral margins, 3 short medial bristles present lateral to stout claw, and 2 short lateral bristles present ventral to base of slender claw.

Maxilla (Figure 50g,h): Coxale with long hairs on dorsal margin and short distoanterior bristle with short marginal spines. Endite I with 3 stout pectinate bristles and 2 or 3 slender spinous bristles; endite II with 2 stout pectinate bristles and 3 or 4 short spinous bristles; endite III with 4 stout pectinate bristles, 2 short spinous subterminal bristles, and 1 spinous proximal lateral bristle. Basale with 1 slender distoanterior bristle with short marginal spines, and 2 short distoposterior bristles. Exopodite with 2 bristles. Endopodite: 1st joint with 1 α-bristle with short marginal spines, 1 β-bristle with faint marginal teeth, and distal spines on medial surface; 2nd joint with 1 stout claw with large teeth along ventral margin, 1 shorter claw without marginal teeth, 2 spinous a-bristles, 1 ventral posterior terminal bristle with slender teeth along both margins, and 1 medial bristle with teeth along posterior margin.

Fifth Limb (Figures 50i,j, 51e,f): Endite I with 2 bristles; endite II with 3 bristles; endite III with 4 bristles. Exopodite: main tooth of 1st joint consisting of a large prong with 2 distal marginal teeth and smaller elongate proximal tooth near middle of inner margin; a short bristle present near proximal tooth; outer edge of main tooth with slender proximal bristle; 2nd joint with large triangular tooth with inner edge consisting of 3 large prongs; distal of these with 2 marginal teeth on inner margin; middle prong and proximal prong with a marginal tooth on each side; base of proximal prong on anterior side of 2nd joint; I bristle present on inner margin proximal to proximal tooth, and 1 bristle present on posterior side near proximal prong; outer distal corner of triangular tooth of 2nd joint rounded, 3rd joint with 2 bristles on inner and outer lobes; 4th and 5th joints fused, with total of 4 spinous bristles.

Sixth Limb (Figure 51a): 2 plumose bristles in place of epipodial appendage. Endite I minute with 1 long bristle; endite II with 2 short spinous bristles; endite III with 2 long bristles; endite IV with 3 spinous bristles; end joint with anterior 2 bristles with short marginal spines and posterior 5 bristles plumose. (The 1st and 2nd endites could be interpreted as being only a single endite, in which case the limb would have only 3 endites).

Seventh Limb (Figure 51b,c,g): Each limb with 4 short proximal bristles (2 on each side), and 3 long and 2 short terminal bristles (3 on one side, 2 on other); proximal bristles with 3 small bells; short terminal bristles with 3 small bells; long terminal bristles with 6 bells of which proximal bell is much larger than others; all bristles with marginal spines; terminus bare.

Furca (Figure 50k): Each lamella with 3 strong claws followed by 3 secondary claws; strong claws with subequal slender spinelike teeth along posterior margin; long hairs present on lamella posterior to claws.

Rod-shaped Organ (Figure 51d): Elongate, 2-jointed with 1st joint widening distally; 2nd joint with tapered end bearing minute spine.

Eyes: Lateral eyes absent; medial eye pigmented, bare (Figure 51d).

Upper Lip (Figure 51d): Small, rounded, bare. Posterior: Hirsute.

Genitalia (Figure 50k): Consisting of oval sclerotized ring on each side of body.

Y-Sclerite (Figure 50k): Linear with short upturned distal end, without ventral branch.

Eggs: USNM 152826 and 150106 with 4 eggs in marsupium. In 152826 3 eggs were larger than the 4th; in 150106 2 eggs were larger than the other 2 (Figure 50l).

Gut Content: USNM 152826 with almost complete harpacticoid copepod, a polychaete worm of Family Glyceridae (ident. M. H. Pettibone), a freeliving nematode of the order Desmoscolecida (ident. D. H. Hope), and spines possibly belonging to a polychaete.

DESCRIPTION OF A–1 FEMALE (Figure 51h–l).—Carapace similar to that of adult female except smaller (Figure 51h): holotype, “Grigore Antipa” 291, length 1.27 mm, height 0.83 mm.

First Antenna (Figure 51i): Same as 1st antenna of adult female.

Second Antenna: Protopodite and endopodite similar to that of adult female except endopodite with only 3 anterior bristles. Exopodite: bristles shorter than those on limb of adult female and without natatory hairs; bristles of joints 2–8 with minute teeth along ventral margin; 9th joint with 5 bristles, all with either minute marginal spines or teeth; 1st joint with medial terminal spine; joints 2–8 with minute spines forming row near terminal margin.

Mandible, Maxilla, 6th Limb: Not examined in detail, but same type as on adult female.

Fifth Limb (Figure 51j,k): Epipodial appendage with 34–35 bristles. Exopodite similar to that of adult female.

Seventh Limb (Figure 511l): Proximal and terminal groups each with 4 tapered bristles; proximal bristles short, with 2-3 equal terminal bells and marginal spines; terminal bristles longer than proximal bristles, with 4 terminal bells (proximal bell longer than others) and marginal spines; terminus with few spines.

Furca, Rod-shaped Organ, and Eyes: Similar to those of adult female.

DESCRIPTION OF A–1 MALE (Figure 51m,n).—Carapace similar to that of A–1 female but slightly larger (Figure 51m): USNM 154198, length 1.35 mm, height 0.89 mm.

First Antenna: Same as limb of A–1 female.

Second Antenna: Protopodite and exopodite similar to those of A–1 female. Endopodite 3-jointed: 1st joint short with 4 ventral bristles (3 proximal, 1 distal); 2nd joint elongate with 2 short distoventral bristles; 3rd joint elongate with 1 minute bristle near middle of dorsal margin and 2 short terminal bristles.

Mandible, Maxilla, 6th Limb: Not examined in detail but of same general type as on adult female.

Fifth Limb (Figure 51n): Epipodial appendage with 33 bristles. Exopodite similar to that of adult female.

Seventh Limb: Proximal bristles with 2 bells, limb otherwise same as that of A–1 female.

Furca: Similar to that of adult female.

Lateral eye: Not seen with certainty; faint globe with what could be minute ommatidia observed.

COMPARISONS.—The main tooth of the 1st exopodite joint of the 5th limb of females and advanced juveniles of previously described species consist of 3 or 4 large prongs and a proximal peg. The main tooth of the new species Rutiderma irrostratum bears only 1 large prong with 3 marginal teeth. The b-bristle of the 7th joint of the 1st antenna is minute, much smaller than that bristle on previously described species. The tip of the 7th limb of R. irrostratum is either bare or has a few minute spines, unlike the tip of the limb of other species which bears 2 opposing combs with well-developed teeth. In addition, the rostrum is totally lacking on R. irrostratum and in its place is a minute line. The degree of development of the rostrum of previously described species varies, but none is without a rostrum. The above differences may warrant future inclusion of this species in a new subgenus of Rutiderma.