Rutiderma chessi Kornicker & Myers 1981

Rutiderma chessi

ETYMOLOGY.—The species is named for James R. Chess, who has supplied the authors with many ostracodes from the west coast.

HOLOTYPE.—USNM 158280, ovigerous female on slide and in alcohol, unique specimen (BM number 18).

TYPE-LOCALITY.—San Clemente Island, sta D-3, collected Sep 1973 by Mr. Roney and Mr. Dorsey.

DESCRIPTION OF ADULT FEMALE (Figures 19, 20).—Carapace with well-defined incisur and overhanging rostrum; caudal process well developed, slender; anterodorsal and ventral margin of each valve with minute processes producing scalloped edge in lateral view (Figure 19).

Ornamentation (Figure 19): 2 well-developed longitudinal ribs present, 1 above and 1 below central adductor muscle attachments; these being connected by vertical ribs at posterior and anterior ends; the posterior vertical rib bears a large process near its dorsal end and a smaller protuberance near its ventral end; a 3rd fairly well-developed rib present just within the anterodorsal and dorsal margins of valve and connected to upper horizontal rib by at least one radial riblet in anterior part of valve; a 4th low rib present along ventral margin and connected to lower horizontal rib by 6 or 7 radial riblets (distal end of the anterior riblet projecting past anteroventral margin of valve, and riblet more strongly developed than remaining riblets; posterior riblet extending onto caudal process); small protuberance present at middle of linear posterodorsal margin of valve and on posterior margin near posterior end of upper horizontal rib.

Infold (Figure 20a–c): Rostral infold with 10 bristles parallel to anterior margin; 2 minute bristles at inner end of incisur; anteroventral infold with 12 bristles forming row and about 6 ridges paralleling inner edge of infold (only 4 ridges shown on illustration); posterior end of ventral infold including caudal process with 16 or 17 small bristles forming row along edge of list forming dorsal rim of “pocket” (the anterior part of this list is better defined on left valve of holotype than on right valve); 2 or 3 bristles present ventral to list of caudal process near dorsal edge of process; a small bristle present on infold dorsal to caudal process. Infold of caudal process of left and right valves essentially similar except for well-defined right angle on posterior edge of list of left valve that is not present on right valve, but this could be due to variability within the species.

Selvage: Broad lamellar prolongation with marginal fringe present along anterior and ventral margins of valves; narrow bare lamellar prolongation present along margin of caudal process; lamellar prolongation divided at inner end of incisur and at minute bristle at tip of caudal process (Figure 20b).

Size: USNM 158280, length 1.21 mm, height 0.82 mm.

First Antenna (Figure 20d): 1st joint with medial and lateral spines forming rows. 2nd joint: lateral side with spines forming few proximal rows and row along distal margin dorsal to spinous bristle; medial side with few proximal spines forming rows near dorsal margin; dorsal margin with proximal spines and spinous bristle near middle. 3rd and 4th joints fused; 3rd joint short with 3 spinous bristles, 1 ventral, 2 dorsal; long 4th joint with 3 spinous bristles, 2 ventral, 1 dorsal. Sensory bristle of long 5th joint with 3 short proximal filaments and spine at tip. Medial bristle of minute 6th joint spinous. 7th joint: a-bristle spinous, slightly longer than bristle of 6th joint; b-bristle slightly longer than a-bristle, bare except for a 2 spines at tip; c-bristle with small proximal filament and 2 spines at tip. 8th joint: d- and e-bristles bare with blunt tips not quite reaching tip of sensory bristle of 5th joint; f-bristle stout, shorter than c-bristle, with 2 small proximal filaments and 2 spines at tip; g-bristle about same length as c-bristle, with fairly long proximal filament and 2 spines at tip.

Second Antenna (Figure 20e): Protopodite bare. Endopodite 1-jointed, with 4 short anterior bristles. Exopodite: elongate 1st joint with small medial bristle terminally; bristles of joints 2–5 fairly short, with blunt closely spaced ventral spines but no natatory hairs; bristles of joints 6–8 long, with natatory hairs but no ventral spines; 9th joint with 6 bristles (3 long with natatory hairs, 1 medium with natatory hairs, 2 minute and bare).

Mandible (Figure 20f,g): Coxale endite bifurcate, pectinate. Basale: ventral margin with 4 proximal bristles (2 pectinate unringed, 2 ringed), and 2 bristles proximal to middle; dorsal margin with 1 bristle near middle and 2 distal to middle. 1st endopodial joint with 2 short ventral bristles and medial spines forming rows. 2nd endopodial joint: dorsal margin with 3 short proximal bristles; medial surface with abundant spines; ventral margin with 1 or 2 minute distal bristles, and small sclerotized process with minute bristle medial to base of stout terminal claw (Figure 20g); dorsal margin of terminal claw with proximal tooth, serrate margin; claw with short curved tip. 3rd endopodial joint with stout terminal claw with short curved tip and serrate ventral margin, 3 slender medial bristles near ventral end of base of stout claw, 1 unringed flat bristle (with serrate ventral margin) ventral to stout claw, and 2 short bristles located lateral to stout terminal claw of 2nd joint.

Maxilla (Figure 20h): Endites I to III with 2 or 3 stout pectinate claws and several ringed bristles. Dorsal margin of precoxale with fringed margin. Dorsal margin of coxale with 1 bristle with slender marginal spines. Basale with dorsal bristle similar to bristle of coxale (not present on illustrated left limb but on right limb), and short bristle near middle of medial margin (on right limb this bristle appears to be placed on 1st endopodial joint near middle of ventral margin of basale). 1st endopodial joint with 1 spinous alpha-bristle and 1 spinous beta-bristle, and hairs forming rows near dorsal margin. 2nd endopodial joint with 2 stout pectinate claws and 5 slender, spinous, ringed bristles. Exopodite small with 2 bristles (not visible on illustrated limb, and obscure on both mounted limbs of specimen).

Fifth Limb (Figure 20i–m): Endite I with 3 bristles; endite II with 5 bristles; endite III with 7 bristles (Figure 20i). Exopodite: 1st joint with 3 stout teeth with secondary teeth distal to 1 smooth smaller tooth and 1 short bristle; outer edge with 1 bristle (Figure 20j). 2nd joint with large 3-lobed tooth (none of the lobes with secondary teeth); posterior side of joint with minute bristle near outer corner; inner margin of joint with 3 proximal bristles (distal of these small) (Figure 20m). 3rd joint with 2 bristles on outer lobe and 3 on inner lobe. 4th and 5th joints fused, with total of 4 spinous bristles.

Sixth Limb (Figure 20n): Endite I with 3 bristles; endites II, III, IV with 2 bristles; end joint with 3 spinous anterior bristles on projection followed by 4 stouter hirsute bristles (the anterior of the hirsute bristles with short spines replacing hairs near tip); posterior edge of stem with 1 or 2 epipodial bristles with marginal hairs.

Seventh Limb (Figure 20o): Each limb with 4 proximal bristles, 2 on each side, and 6 terminal bristles, 3 on each side; each bristle with up to 5 bells and distal fairly strong marginal spines; terminus with comb of 5 alate teeth opposing 3 teeth (outer 2 of these with long marginal spines).

Furca (Figure 20p): Each lamella with 4 stout primary claws followed by 2 small secondary claws; claw 1 with anterior distal hairs and both long and short posterior teeth; anterior margin of right lamella with slender spines; long hairs on lamellae following claws and medially at bases of claws.

Bellonci Organ (Figure 20d,q): Elongate with short broad faintly striated section proximal to middle (whether short striated section is separated by sutures or merely folds from remaining part of organ cannot be ascertained with mounted specimen; longitudinal striations not shown in illustration); tip of organ tapering to point.

Eyes (Figure 20d,q): Medial eye tapering distally, with brown pigment. Lateral eye small, with 4 light amber colored ommatidia (Figure 20q).

Posterior of Body: Hirsute.

Eggs: USNM 158280 with 4 eggs in marsupium.

Comparisons: The rib structures on the carapace of the new species R. chessi differ from those of other species of Rutiderma in the vicinity. The species whose carapace resembles it most closely is R. judayi, which is smaller, has 3 instead of 2 main horizontal ribs on each valve, has more processes along the posterodorsal margin, and has a less acute caudal process. The main claws on the 2nd and 3rd endopodial joints of the female mandible (Figure 20f) are longer and more slender than those on other species of Rutiderma described herein (see Figures 2e, 6f, 12f, 18g).

REMARKS CONCERNING MALE OF R. chessi.—It is possible that the 2 males we have referred to R. lomae herein are in reality males of R. chessi. The latter conclusion would be supported by the shape of the tip of the bellonci organ, which is rounded in the female of R. lomae and pointed on both the female of R. chessi and the male of R. lomae. Also the vertical rib near the posterior end of the carapace of the female R. lomae is discontinuous, but it is continuous in both the female R. chessi and male R. lomae. We identified the males as R. lomae rather than R. chessi mainly because the caudal processes of the specimens more closely resemble those of the female R. lomae. The collecting of the males in the same locality as where females of R. lomae were collected was also a factor in our consideration. Additional collections are required to resolve the problem.