Review and Catalog of the Ostracode Family Rutidermatidae (Crustacea: Myodocopa)

. Cohen and Kornicker (1987) presented a catalog of species of the Rutidermatidae that had been published prior to March 1986. The present contribution includes one additional subfamily, one additional genus, and twelve additional species (one new) and, also, keys to subfamilies, genera, and species, illustrations of carapaces, tables giving characteristics of appendages, and maps showing distribution of species.


Introduction
Family Rutidermatidae belongs to the subclass Myodocopa, order Myodocopida.Order Myodocopida can further be divided into the three suborders Cladocopina, Halocypridina, and Myodocopina.The Rutidermatidae is one of five extant families included in the ostracod suborder Myodocopina.It contains two subfamilies: the Rutidermatinae with three genera (Alternochelata with four species, Rutiderma with 37 species, and Scleraner with two species) and the Metaschismatinae with one genus (Metaschisma with two species).Cohen and Kornicker [1] published a catalog of species of the Rutidermatidae that had been reported prior to March 1986.Since then, an additional subfamily and genus as well as 12 new species have been included in the family, and taxa have been reported from additional localities.We have updated the catalog to August 2009 and have included keys and appendices to help compare and identify the species in this family.Keys are used with care; determination of species should always be verified by use of the descriptions and figures.A tabular key to families of Myodocopida was given in Cohen and Morin [2,Appendix 3]  Composition.The Rutidermatidae includes two subfamilies, the Rutidermatinae (with three genera, Alternochelata, Rutiderma, and Scleraner) and the Metaschismatinae (with one genus, Metaschisma).
Description.Carapace oval in lateral view with male more elongate than female; surface punctate or smooth; prominent ribbing absent in Scleraner, present in most species of Rutiderma; projecting caudal process in some species, absent in others; rostrum generally rounded anteriorly; incisur minute in some species and forming small indentation creating overhanging rostrum in others; rostrum of adult male more prominent than that of adult female and juveniles.
First antenna: The third and fourth segments fused in females of some species, separated by suture in adult male; fifth segment long in female and juveniles, small in adult male; sensory bristle of adult female either bare or with few short filaments, of adult male with broad proximal part with numerous long slender filaments; sixth segment of juveniles and adult female minute and fused with fifth segment, of male long and with suture separating it from fourth and fifth segments; a-bristle of seventh segment not claw-like; d-and e-bristles of eighth segment about same length, bare with blunt tips; c-bristle of seventh segment and f-bristle of eighth segment of female about same length as d-and ebristles, of adult male extremely long and with numerous short filaments.
Second antenna: Protopodite without distal medial bristle; endopodite of female small with 1 segment in Rutiderma and 2 in Scleraner, of male 3-segmented and reflexed in both genera; exopodite of female with natatory hairs on long bristles of segments 6-9, of male on long bristles of segments 3-9, of juveniles without natatory hairs on bristles.
Mandible with long narrow hirsute exopodite on male, rudimentary or absent on female; second endopodial segment of female broad with stout ventral claw forming pincer with stout claw of third endopodial segment, of adult male second endopodial segment narrow without stout claw, and with long narrow claw on third endopodial segment.
Maxilla of female stout with 3 endites; exopodial segments of male with bristles; female with stout teeth on first exopodial segment, and broad flat tooth on second exopodial segment.Second thoracic leg well-developed in both sexes but with fewer bristles on male; terminus with opposing combs.
Furca of Rutiderma with 3 or 4 stout claws followed by 2 or 3 secondary claws, of Scleraner with 4 stout claws followed by 5 secondary claws, of Alternochelata with secondary claws between main claws.
Bellonci organ elongate, 1 or 2 segmented, with rounded or pointed tip.Lateral eyes of female small with 4 or 5 ommatidia, of male larger with 14-30 ommatidia.
Medial eye large, pigmented, with dorsal filaments on some species of Rutiderma.
Copulatory organ of adult male elongate terminating in small lobes bearing minute processes and bristles (Kornicker [4,page 171]).
Biology.Juveniles and adult females are carnivores eating mostly crustaceans and worms; guts of adult males generally are empty or have little food.Members of the family have 4 juvenile instars; carapaces of instars of both sexes are similar and generally resemble that of the adult female.The adult male is a more efficient swimmer than the female and is occasionally collected in the water column without females; it is generally sparser than the female in collections from substrate; juveniles of both sexes, which are without natatory hairs on the exopodial bristles of the second antenna, are restricted to the bottom (Kornicker [4,page 171]).
Distribution.Members of the family are widespread between latitudes of 45 • N and 53 • S at mostly shelf depths (0-200 m), but they also have been collected on the upper slope (200-1100 m).Rutiderma and Scleraner have been collected in the Subantarctic and are absent in the Antarctic (Kornicker [4,page 171]).Tables 1-4 list Rutidermatidae distribution by hemisphere, ocean, locations and depths, and water temperatures and salinities, for those species for which data are available.(Rutiderma).The Rutidermatidae is the only family having mandibles of juveniles and adult females with a stout claw on the second endopodial segment forming a pincer with the stout claw of the third endopodial segment.A stout claw is absent on the second endopodial segment of the mandible of the adult male (Kornicker [4,page 171]).
Ecology.Some abiotic variables that influence the distribution of living marine ostracods are substrate, temperature and salinity, depth, abundance and seasonality.
Temperature and Salinity.Rutidermatidae has been collected in water temperatures ranging from 9.8 • to 32 • C, salinities from 30 to 42‰ [1], and dissolved oxygen levels from 2.5 to 9.2 mg/l [18].When collected from Tampa Bay, R. darbyi was more abundant at greater depth, in coarser sediment, and in more saline water than was average for the bay suggesting that R. darbyi enters the bay from the Gulf of Mexico [18].
Depth.The Rutidermatidae has been collected as deep as 560 m.Deeper records exist but they are questionable [1].Alternochelata nealei was purportedly collected from 1100 m but the sample contained species of Cyclasteropinae and Asteropteroninae that were confined to continental shelf depths in the area [19].Kornicker [13] reported a single R. ovata collected at 1834 m but the sample contained many cypris larvae and euphausiids which were inconsistent with the reported method of collection.Biology: Reproduction.Rutidermatids are usually confined to the continental shelf (0-200 m depth) but are occasionally collected on the upper continental slope (200-1100 m depth).Males and females may be collected at different depths.In some species, females become completely benthic after mating by breaking bristles off the second antenna [16], whereas males typically remain free-swimming.Deep water may pose a barrier to their distribution as they are generally not collected around isolated island systems or Antarctica which has a deep continental shelf.Cohen [20] found that rutidermatids were abundant at a shallow lagoon site but uncommon at a deeper fore-reef site.Grabe et al. [17], however, collected fewer R. darbyi from shallow subtidal stations than from deeper stations offshore [21, pages 184-185, 196, 199].
Abundance.Large concentrations of rutidermatids have been found in a specific area.For example, rutidermatids were the most abundant family of ostracods collected in Belize [20], where R. dinochelata was the most abundant species, accounting for 32.4% of the myodocopids collected from a lagoon.R. darbyi was the second most abundant ostracod collected in Tampa Bay, accounting for 19.8% of the ostracods sampled [18].R. darbyi and R. mollitum were the third and fourth most numerous ostracod species in samples taken off Florida [22].
Seasonality.In Florida, the abundance of R. darbyi was correlated with the seasons [17].Horsley [22] found the abundance of myodocopid ostracods, including rutidermatids, was greater in May and June (193 rutidermatids sampled) than in December (100 rutidermatids sampled).
Life History and Ontogeny.From 1 to 6 brooded eggs, broken swimming bristles on adult females of A. sikorai, A. nealei, and A. lizardensis.

Key to the Species of
Alternochelata Kornicker [6] (See also Tables 5 and 6).
1. Carapace with rounded posteroventral corner; each lamella of furca with main 1, 2, 3, 5 Carapace with angular posteroventral corner; each lamella of furca with main claws  Life History and Ontogeny.Adult male and female, A-1 male, 4 to 6 eggs, broken swimming bristles on females.

Alternochelata nealei Kornicker and Caraion
Life History and Ontogeny.Adult male and female, from two to three eggs, female with broken natatory bristles.

Alternochelata polychelata (Kornicker
Comparisons.Alternochelata polychelata differs from A. nealei in having a distinct caudal process on the carapace, and while, on A. nealei, the main claws of the furca are 1-3, and 5, on A. polychelata, the main claws are 1, 2, 4, and   6.Furcal claw distribution also distinguishes A. polychelata from A. lizardensis in that A. polychelata has secondary claws between two sets of primary claws.Alternochelata polychelata also has a more rounded posteroventral corner of the shell than A. sikorai.
Life History and Ontogeny.Adult male and female, 1 to 3 eggs; broken swimming bristles on female.
Comparisons.The species A. sikorai is closely related to A. nealei, having the claws of the furca similarly distributed and the carapace having a similar shape.It differs from that species in having the reticulations of the carapace being formed by rows of minute but distinct pustules.The distribution of furcal claws differs from that of A. polychelata, and the posteroventral corner of the shell is more rounded (Kornicker [16, pages 24-25]).[37].Metaschismatinae Kornicker [37,  Life History and Ontogeny.From 3 to 6 brooded eggs, broken swimming bristles on adult females of M. nex.Instar A-1 male with short bristles without natatory hairs on exopod of second antenna.Kornicker [37] (Figure 2(a)).Metaschisma nex Kornicker [37, pages 123-128, 192 Distribution.This genus is cosmopolitan between the latitudes of 45 • N and 53 • S, at depths from intertidal to 317 m (questionably to 1834 m), and contains about 37 species (Cohen and Kornicker [1, page 2], Kornicker [49, page 123], Kornicker [50, page 22]).

Key to Species of Rutiderma (Females)
See also Tables 3, 4 Habitat.Clayey silt and sand.
Life History and Ontogeny.Adult male, A-1 male, and female, from 3 to 4 eggs.
Comparisons.The surface ornamentation of R. apex resembles that of R. judayi McKenzie [9], except that the female is without a small process near the middle of posterior margin that projects past the posterior end of the valve.The length of the female carapace of R. judayi is from 0.95 no. of fil. on sens.br.no. of br. on the 4 endites       no. of br. on the 4 endites  no. of br. on the 4 endites no. of fil. on sens.br.no. of br. on the 4 endites   Comparisons.R. arcuatilis is closely related to R. dinochelata.On R. arcuatilis the curvature of the list of the caudal process has a low angle with the ventral margin.On both R. dinochelata and R. mortenseni (only male known), the curvature of the list forms about a 45 • angle with the ventral margin.Also, on both of these species, bristles are present on each end of the curved list, whereas R. arcuatilis bears several bristles along the list (Kornicker [16, page 70]).Habitat.Benthic (infauna).Gravelly sand, sedimentary pocket with nodules of melobesians in large ripples, coarse sediment among coral patches.
Gut content.One specimen with two harpacticoid copepods, and fragment of (?) nematode.
Comparisons.Rutiderma arx differs from both R. leloeuffi and R. tridens in the female carapace having a smaller rostrum and in the terminal claw of the second endopodial segment of the female mandible not having a pronounced tip.The infold of the caudal process of R. tridens has 3 "teeth" along the dorsal margin of the "pocket" that are absent on R. arx, and the carapace of R. tridens bears lateral ribs absent of R. arx.Rutiderma irrostrata differs from R. arx in having a carapace with lateral ribs, and in having marginal teeth on the 3 lobes of the large flat tooth forming the second exopodial segment of the fifth limb.The carapace of R. arx differs from that of R. compressa and R. normani in lacking lateral ribs.Only the male is known of R. fusca; the posterior edge of the alar process on the carapace of that species bears a backward pointing triangular process at the ventral and dorsal ends that is not present on the male of R. arx.The male R. arx (length 1.30-1.34mm) is longer than the male R. fusca (length 1.10 mm) (Kornicker [49, page 136]).[14] (Figure 3(a)).Rutiderma  Comparisons.The rib structures on the carapace of R. chessi differ from those of other species of Rutiderma in southern California.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 second and third endopodial segments of the female mandible are longer and more slender than those on other species of Rutiderma in the area (Kornicker and Myers [14, page 34]).[16] (Figure 3  Distribution.Carrie Bow Cay, Belize; Fleming Key, Key West, Florida; Virgin Islands.
Life History and Ontogeny.Adult female, 4 eggs.
Comparisons.The elongate finger-like extension of the tip of the stout terminal claw of the second endopodial segment of the mandible and the small, slender, unringed, posterior bristle on the endopodite of the second antenna of the adult female distinguishe R. cohenae from the previously described species.A few species have one of the above characters but not both.The new species differs from R. mortenseni Poulsen [10, page 38], of which only the male is known, in the morphology of the infold of the caudal process and in having fewer bristles on the rostral infold (Kornicker[16, page 67]).[55] (Figure 3(c)).Rutiderma  Life History and Ontogeny.Female, A-1 female, juvenile.

Rutiderma compressa Brady and Norman
Comparisons.The incisur on R. compressa is less distinct and the rostrum and caudal process is less prominent than on R. leloeuffi.The incisur forms a right angle, unlike R. licina, which has a deep incisur with overhanging rostrum.It is distinguished from R. ovata in that the carapace does have a projecting posteroventral caudal process.Rutiderma compressa differs from R. gerdhartmanni in the morphology of the first antenna.While R. gerdhartmanni has a bristle on the second segment and 2 bristles on the third segment, R. compressa lacks a bristle on the second segment and has just 1 on the third segment.Rutiderma compressa can also be differentiated from R. gerdhartmanni in that R. compressa has numerous riblets between the anterodorsal rib and anterodorsal shell margin, while R. gerdhartmanni lacks these riblets.
Comparisons.The carapace of R. darbyi differs from known species in the study area in having several flat spinelike processes along the ventral edge of "pocket" in the caudal process of the left valve.They are absent on the right valve.The spine-like processes are generally visible when the whole specimen is viewed using transmitted light and an objective lens having a magnification of 10x or 20x.The spine-like processes are present on juveniles and adults of both sexes (Kornicker [16,page 47]).[6] (Figure 3(d)).Rutiderma (Rutiderma)  Comparisons.The carapace of the male R. dinochelata differs from that of R. flex in that the upper lateral rib does extend anteriorly to intersect the anterior edge of the rostrum and the lower lateral rib does extend anteriorly to midlength of the carapace.The species R. dinochelata differs from R. sterreri in that the tip of the Bellonci organ is pointed, not rounded.The list of the caudal process of the female R. vox is longer and more oblique than that of the female R. dinochelata.Rutiderma dinochelata is very similar to R. arcuatilis, but they differ in that the list of the caudal process on R. arcuatilis has a low angle with the ventral margin, but, in R. dinochelata, the curvature of the list forms about a 45 • angle with the ventral margin.Habitat.Mud.Life History and Ontogeny.Adult male, A-1 male, female, ovigerous female (3 to 4 eggs), juvenile.

Rutiderma dux Kornicker [50] (Figures 3(g)-3(h), 4(a)). Rutiderma dux
Comparisons.Rutiderma dux is close to R. normani Poulsen [10, page 22], and they could be conspecific.The female sixth limbs of the two species differ in that the ventral margin of the end segment of R. normani is straight (Poulsen [10, Figure 4j]), whereas the anterior 3 bristles on the end segment of R. dux are on a long projection.Also, Poulsen [10, pages 26, 28] described both the female and male furcae of R. normani as having 3 main claws and 3 secondary claws, whereas the female and male furcae of R. dux have 4 main claws and 2 secondary claws (Kornicker [50, page 28]).[52] (Figure 4(b)).Rutiderma  Life History and Ontogeny.Adult female.

Rutiderma exrex Kornicker in Kornicker and Thomassin
Comparisons.Rutiderma exrex is quite similar to R. rex and they could be conspecific.The carapace of R. exrex differs from that of R. rex in three characters: (1) the ribs and riblets of R. rex have high relief, whereas, those of R. exrex are barely visible, (2) the ridge forming the anterodorsal edge of the pocket of the infold of the caudal process is slightly convex posteriorly on R. rex and slightly concave on R. exrex, but there is some variability in this character; and (3) the posterior edge of the alar process on the outer surface of each valve as well as the posterodorsal edge of the valves of R. rex bears small tubercles that are either absent or much smaller in R. exrex.Also, the length of the female carapace of R. rex is from 0.90 to 0.92 mm (3 specimens), whereas the length of the female R. exrex is from 0.99 to 1.19 mm (3 specimens), but the difference could be the result of intraspecific variability.The carapace of R. exrex differs from those of R. arx and R. ferax in having a caudal process with less posterior projection, and the ridge forming the anterodorsal edge of the pocket of the infold of the caudal process forms a 45 • angle in R. exrex but forms a shallow arc at a much lower angle with the ventral edge of the caudal process in R. arx and R. ferax.Also, the ribs and riblets on the outer surface of the carapace of R. ferax have much greater relief than those of R. exrex.The tip of the dorsal margin  Life History and Ontogeny.Adult female.
Comparisons.Rutiderma ferax is very similar to R. rex.The main difference noted is in the infold of the caudal process of the carapace: the ridge dorsal to the pocket is straight of slightly convex and forms a 45 • angle in R. rex (see Kornicker [49,Figure s 82b,c]) and is a shallow concave arc more-or-less parallel to the ventral edge of the caudal process in R. ferax.The length of the carapace of the female R. ferax is 1.16 mm, compared to from 0.90 to 0.92 mm (three specimens) for R. rex (Kornicker [49,page 142]).The caudal process has greater posterior projection in R. ferax.The anterodorsal and anteroventral infolds of R. rex each bears 4 or 5 bristles compared to 8 on R. ferax.The endopodite of the second antenna of R. ferax bears a small posterior spine absent on R. rex.The proximal and middle lobes of the second exopodial segment of the fifth limb of R. ferax bear 1 or 2 marginal cusps absent on R. rex.The Y-sclerite of R. rex bears a ventral branch absent on R. ferax (Kornicker and Thomassin [52, page 87]).5.12.Rutiderma flex Kornicker in Kornicker et al. [56] (Figure 4(d)).Rutiderma flex Kornicker in Kornicker et al.
Distribution.Type locality only.
Habitat.Sediment at 25 m depth about 365 m inside cave.
Life History and Ontogeny.Adult male.
Comparisons.The carapace of the male R. flex differs from that of R. dinochelata in that the upper lateral rib does not extend anteriorly to intersect the anterior edge of the rostrum, and the lower lateral rib does not extend anteriorly to midlength of the carapace.The structure of the posterior edge of the shelf in the anterior part of the pocket of the infold of the caudal process of R. flex differs from those of R. darbyi (Kornicker [16,Figure 23b]) and R. schroederi (Kornicker and Iliffe [77, Figure 53c,d (female)]).The infold of the rostrum of R. flex bears a row of 7 bristles compared to 12 on R. mortenseni (Poulsen [10,Figure 11b]).The adult male of R. flex is larger than that of R. licina Kornicker [16], the furca bears 1 or 2 instead of 3 secondary claws, and the basis of the mandible bears 4 instead of 6 bristles near the ventral margin (Kornicker et al. [56, page 95]).[10] (Figure 4(e)).Rutiderma fusca Poulsen [10, pages 7, 8, 11, 14, 17, 38, 41-44, 8, 9].
Distribution.Type locality only.
Life History and Ontogeny.Male.
Comparisons.The Bellonci organ of R. fusca is pointed, whereas the Bellonci organ of R. rex is broadly rounded.Rutiderma fusca differs from the male R. arx in that the posterior edge of the alar process on the carapace of R. fusca species bears a backward pointing triangular process at the ventral and dorsal ends not present on the male R. arx.Comparisons.The specimens identified by Hartmann as R. compressa have been assigned to a new species primarily because of the sixth limb on which the anterior part of the end segment forms a projecting process bearing 3 bristles.The sixth limb of R. compressa was not described in the original description by Brady and Norman [55] but was illustrated by Müller [59] from a specimen collected near South Africa.His figure shows the anterior part of the end segment of the sixth limb to be only very slightly separated from the posterior part.I have not examined either the specimens described by Brady and Norman or that described by Müller, and it is possible that they do not belong to the same species; however, both Brady and Norman and Müller illustrated the first antenna of a female.These illustrations show the lack a lateral bristle on the second segment and only 1 dorsal bristle on the third segment.The first antenna of R. gerdhartmanni bears a lateral bristle on the second segment and 2 dorsal bristles on the third segment.I do not, however, rely strongly on those differences in the first antennae, because bristles may have been overlooked by Brady and Norman and Müller, or they may have described and illustrated second antennae from juveniles.The carapace illustrated by Brady and Norman bears numerous riblets between the anterodorsal rib and the anterodorsal shell margin.These are not present on R. gerdhartmanni.The length of the carapace of the female R. gerdhartmanni is in the order of from 1.35 mm to 1.39 mm; the length of R. compressa given by Brady and Norman [55, page 674] was 1.5 mm; the length of the specimen identified as R. compressa by Müller was given by him as 1.6 mm [59, page 92] (Kornicker [13, page 657]).[16]  Comparisons.The infold of the caudal process of the left valve of R. gyre does not have the flat spines present on the left valve of R. darbyi.Rutiderma mortenseni Poulsen [10], is known only from a single adult male.The male of R. gyre differs from the male of R. mortenseni in having from 6 to 8 rather than from 10 to 12 bristles forming a row on the rostral infold (Kornicker [16, 62a]).
Holotype.Female without eggs or embryos, Zoological Museum, University of Copenhagen.Comparisons.Rutiderma hartmanni differs from R. vox in that it has an upturned tip on the c-bristle (claw) of the second endopodial segment of the female mandible.Rutiderma hartmanni can be distinguished from R. kalkei by the c-bristle on the first antenna; it lacks filaments on R. hartmanni but has 1 on R. kalkei.5.17.Rutiderma irrostrata Kornicker and Caraion [47] (Figure 5(d)).Rutiderma  Life History and Ontogeny.Ovigerous female, A-1 female and male, juvenile.
Stomach Contents.Harpacticoid copepod, polychaete, and a nematode in the gut.
Comparisons.The main tooth of the first exopodite segment of the fifth 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 R. irrostrata bears only 1 large prong with 3 marginal teeth.The b-bristle of the seventh segment of the first antenna is minute, much smaller than that bristle on previously described species.The tip of the seventh limb of R. irrostrata 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. irrostrata 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 (Kornicker and Caraion [47, page 60]).Life History and Ontogeny.Female, male.

Rutiderma judayi McKenzie [9] (Figures 5(e)-5(f)). Rutiderma judayi
Comparisons.Rutiderma judayi differs from R. vox in having a deep indentation at midheight of the posterior edge of the alar process on each valve.The carapace of R. judayi is similar to R. apex but differs in that the female has a small process near the middle of the posterior margin that projects past the posterior end of the valve.The carapace is also similar to R. chessi but differs from it in that R. judayi has 3 instead of 2 main horizontal ribs, has more processes on the posterodorsal margin, and has a less acute caudal process.Northwest Atlantic: shelf off South Carolina to Florida; Gulf of Mexico: Tampa Bay, shelf off Florida, Alabama.
Life History and Ontogeny.Female, male, 3 to 4 eggs.
Remarks.The species differs from other species in the genus in having the lamellar prolongation of the selvage continuing along the anterior ridge of the caudal process.In other species the selvage and lamellar prolongation are present along the outer edge of the caudal process (Kornicker [16,page 36]).[10] (Figure 6 Comparisons.Rutiderma mortenseni has 10-12 bristles in the rostral infold, whereas R. gyre has just 6-8.On R. arcuatilis, the curvature of the list of the caudal process has a low angle with the ventral margin, but, on R. mortenseni, it forms a 45 • angle.The two species also differ in that R. arcuatilis has bristles all-on the ends.
Remarks.Poulsen [25, Figure 7] identified two juveniles of Rutiderma normani as "females?",but on page 30 he stated for the same two specimens: "As the copulatory limbs and the secondary sexual characters of the first and second antennae were not developed, the sex of these two young larvae could not be ascertained."The endopod of the second antenna of the adult female of the species has only one short segment (Poulsen [10, page 23, Figures 4f.f ]), whereas, the endopodes of the second antennae of the two juveniles (Figures 7b, 7i) are elongate.Therefore, it is the opinion of Kornicker (herein) that the two juveniles are males.7(c
Life History and Ontogeny.Female, male, 2 eggs.Comparisons.R. rostrata is similar to R. pax in having carapaces with poorly defined lateral ribs and in not having a prominent backward projecting caudal process.Rutiderma hartmanni differs from R. rostrata in that the shell of R. rostrata lacks riblets or ridges and is ovular, whereas, in R. hartmanni, the shell is ridged and has a posterior pointing process (Poulsen [10]).[10] (Figures 8(c 1, Figure 1 Fifth row].
Life History and Ontogeny.Females, male, juvenile females, from 2 to 4 eggs.
Comparisons.The carapace of R. rotunda is similar to R. ovata because of the absence of a projecting posteroventral caudal process.It differs from R. ovata in that it has a less well-developed incisur and a more ornate carapace.Rutiderma rotunda also differs from R. compressa in the incisur.Rutiderma compressa has a right angle between the incisur and the margin, whereas R. rotunda has an obtuse angle.[50] (Figure 8 Comparisons.This species differs from the previously described species of the genus in having 7 furcal claws (3 primary and 4 secondary).The carapace of R. sagax is readily separated from that of R. dux because of the absence of flat pointed spines on the infold of the caudal process of the left valve.In addition to having fewer claws, the furca of R. dux differs from that of R. sagax in having 4 rather than 3 primary claws (Kornicker [50, page 31]).[77]  Habitat.Sandy sediments on ledges of upper slope and submarine escarpment.
Comparisons.The carapace of R. schroederi outwardly resembles that of R. darbyi Kornicker [16,page 36].The infold of the caudal process of the left valve of R. schroederi is without the pleated ruffle present on R. darbyi (the ruffle is easily visible through the outside of the left valve).The carapace of R. schroederi also outwardly resembles R. gyre Kornicker [16,page 54], but the infold of the caudal process of R. schroederi is without the vertical crescent list present on R. gyre.The endopodites of the second antennae of R. darbyi and R. gyre are without the ringed posterior bristle present on R. schroederi.The carapace of R. schroederi also outwardly resembles that of R. cohenae Kornicker [16,page 62], which was collected near San Salvador, Bahamas, and Key West, Florida, from subtidal to 4 m depth (Kornicker [16,page 62]).The morphology of the infolds of the caudal processes of the two species is also similar.The rostral infold of R. schroederi bears 17 bristles compared to 7 or 8 for R. cohenae.The length of the carapace of the unique female of R. schroederi is 1.73 mm, compared to a range of 1.24 to 1.29 mm for two females of R. cohenae (Kornicker [16,page 63]).A major difference between the two species occurs in the mandible: the c-bristle of the second endopodial segment of R. cohenae has a prolonged finger-like tip that is absent on R. schroederi.Slides of three type-specimens of R. cohenae were reexamined during the present study, and all 6 limbs have the long finger-like tip on the c-bristle.The two specimens of R. schroederi examined do not have the long finger-like tip, but the tip of one limb of the holotype is obviously broken.The endopodites of the second antennae of R. schroederi and R. cohenae both share the unusual character of having a fairly long posterior bristle; the bristle is ringed in R. schroederi and unringed R. cohenae, but specimens should be examined to determine whether this character might be variable (Kornicker and Iliffe [77,page 61]).
Internal muscles are of limited use in identifying segments of R. schroederi.The interpretation of segmentation of the female fifth limb of this species is based mainly on that derived from the study of the fifth limb of Isocypridina (Kornicker [41, 42, pages 800, 806, 808]).[30,31]  Comparisons.The species R. sterreri differs from R. dinochelata in that the tip of the Bellonci organ is rounded, not pointed.The lengths of the three specimens of R. dinochelata listed by Kornicker [6, page 237] ranged from 1.14 to 1.22 mm (average 1.18 mm).The lengths of seven ovigerous females of R. sterreri measured herein ranged from 0.94 to 1.10 mm (average 1.00 mm).A closer comparison of the two species will require a better description of R. dinochelata (Kornicker [31,page 8]).[47]  Comparisons.The species R. tridens differs from R. compressa Brady and Norman [55], in not having anterodorsal and ventral ribs and riblets on the surfaces o the valves.The carapace of R. tridens resembles that of the female of R. compressa from South Africa illustrated by Müller [59, Plate 7:1].Müller's specimen has been put into the synonymy of R. tridens with a question because the first antenna illustrated by Müller [59,Plate 7:2] does not show a lateral bristle on the second segment, but this could be because the illustration is a medial view of the limb.The first, third, and fourth endites of the sixth limb illustrated by Müller [59,Plate 7:12] have a different number of bristles than do the same endites of the two specimens of R. tridens described herein, but this could be the result of intraspecific variability.Rutiderma tridens is easily separated from R. leloeuffi by the absence of ribs on the anterior half of the valves and by having a smaller caudal process.Klie ([5, page 406]) did not describe the specimens from Lüderitz Bay, South-West Africa, that he identified as R. compressa Brady and Norman; their identification should be verified.The carapace of R. tridens differs from that of R. mollita Darby [74], in having the caudal process projecting past the posterior end of the shell (Kornicker and Caraion [47, pages 65-66]).[50] (Figure 9 Comparisons.The carapace of R. tryx differs from that of R. sagax (only male known) in having an alar process with a convex rather than a concave posterior edge.The furca of R. tryx bears 6 claws on each lamella compared to 7 on R. sagax.The anterior ridge of the infold of the left valve caudal process of R. dux bears numerous flat pointed spines that are absent on R. tryx (spines usually are visible through shell).The furca of R. dux bears 4 primary and 2 secondary claws on each lamella compared to 3 primary and 3 secondary claws on the furca of R. tryx (Kornicker [50,page 36]).[48] (Figures 9(e    Distribution.Enewetak Atoll.
Comparisons.R. vox differs from R. normani in not having a serrate list on the infold of the caudal process of the right valve and from R. darbyi Kornicker [16,19] in not having a serrate list on the infold of the caudal process of the left valve.The female R. vox differs from the female R. lomae in having a longer caudal process, fewer bristles on the list of the caudal process, a shorter b-bristle on the seventh segment of the first antenna, an endopodite of the second antenna without a minute bristle near the middle of its margin, and a slightly stouter fourth claw on the furca.Rutiderma vox differs from R. judayi in not having a deep indentation at midheight of the posterior edge of the alate process on each valve.Rutiderma vox differs from R. gerdhartmanni, R. chessi, R. sterreri, R. arcuatilis, R. cohenae, and R. kalkei, in having marginal teeth on the 3 lobes of the second segment of the female fifth limb.The female R. vox differs from the female R. compressa, R. rostrata, R. leloeuffi, and R. tridens in not having a prolonged tip on the c-bristle of the second endopodial segment of the female mandible.Rutiderma vox differs from R. hartmanni, R. pax, and R. licina in not having an upturned tip on the c-bristle (claw) of the second endopodial segment of the female mandible.The list of the caudal process of the female R. vox is longer and more oblique than that of the female R. dinochelata.[20].Cohen [20,pages 322,324,327,330,331,332,334,325,Figure 4].
e n d .s e g ., n o .o f v .b r .e x c l .c l .e n d .s e g ., n o .o f b r .e x c l .c l .e x .s e g ., n o .o f p r i m a r y t

Table 9
Atlantic: Great Bahama Bank; northern Gulf of Mexico; off Mauritania and Western Sahara.Pacific: Great Barrier Reef, Australia; coast of Chile.

Table 5 :
Summary of characteristics of mature females in Alternochelata.

Table 6 :
Summary of characteristics of Alternochelata male.

Table 7 :
Summary of characteristics of mature females in Rutiderma.

Table 8 :
Summary of characteristics of mature males in Rutiderma.

Table 9 :
Summary of characteristics of genera Metaschisma and Scleraner.

Table 10 :
Summary of characteristics of males and females of Alternochelata, Rutiderma, and Scleraner.

Table 1 ,
ISRN Zoology female mandible of rostrata has a long produced tip that is absent on R. apex.The ribs of the carapace of R. apex resemble those of R. hartmanni from the Gulf of Panama, but the carapace of R. apex is slightly larger and the caudal process has less posterior projection; the anterior ridge of the infold of the caudal process is more concave posteriorly on R. hartmanni, and the c-bristle of the second endopodial segment of the female mandible of R. hartmanni bears a small terminal extension that is absent on R. apex.The lateral ribs of R. rotunda are evenly rounded posteriorly, not indented like the vertical rib of R. apex, and each lamella of the furca of R. rotunda bears 3 primary claws compared to 4 on R. apex page 43]).Figures39, 40], Kornicker[33,Table 3], Rutiderma arcuatilis Kempf [68, page 668], Kornicker [48, page 84 (compares to R. vox)], Kornicker and Harrison-Nelson [43, Tables 8, 9].Holotype.USNM 158212, adult female.Type Locality.East side of Bolongo Bay, St. Thomas Island, U.S. Virgin Islands.18 • 18 59 N, 64 • 53 4 W, intertidal.
Distribution.Glorioso Islands, depth 24 to 26 m.Madagascar, depth: on reef flat to 31 m.
Zoology 29 of the claw-like c-bristle of the third endopodial segment of the mandible of R. arx has a small projecting tooth that is absent on R. exrex.The proximal and middle lobes of the large flat second exopodial segment of the fifth limb have 1 or 2 marginal cusps in R. ferax, but they are without cusps in R. exrex.The Y-sclerites of R. ferax and many specimens of R. arx are without a ventral branch, which is present in R. exrex.The female carapace of R. exrex is smaller than that of R. arc(Kornicker and Thomassin [52, page 92]).