“C. (Cythereis) ephippiata new species
Plate II, fig. 7; Plate III, fig. 3; Plate V, fig. 2; text fig. XVI.
Cythereis sp … T. Skogsberg, 1920, p. 145.
Description: Male –
Shell: Length, about 0.77 to 0.81 mm.; length:height, about 1.85 to 1.90:1. Seen from the side: Left valve: Rather elongated, highes somewhat behind middle, dorsal and ventral margins sub-parallel to each other. Dorsal margin slightly convex to nearly straight. Anterior and posterior parts of ventral margin almost straight, or the anterior is slightly sinuated; they form together a broadly rounded, more or less distinct corner somewhat below middle in a distinct, sub-rectangular, rounded, beak-like projection; margin of this beak has no distinct serrulation or spines; dorsal part of posterior margin passes into ventral margin without forming any distinct corner. Right valve almost perfectly of same shape as left one. Seen from below, shell is about twice as long as wide, with subparallel sides in middle, its anterior extremity sub-acuminate, its posterior sub-mucronate. Sculpture of surface: Surface covered with closely-set, angular excavations of moderate size and depth (in a few specimens rather shallow), and of somewhat varying shapes; in posterior part of shell, excavations are arranged in more or less distinct rows, sub-parallel to longitudinal axis of shell (male = female). Bottom of each excavation has about two to six small pits, bordered by ridges somewhat narrower and lower than those surrounding the large excavations. At muscle-spots surface sometimes is slightly elevated and nearly smooth. Of the main ridges, only the ventral is developed; this is represented, along greater part of ventral margin or shell, by a low ridge (in a few specimens somewhat higher than in the figure of female shell), and ends near posterior end of shell in a short, but usually rather prominent, wing-like, and rounded projection. Pores of surface often rather difficult to detect. Among bristles along anterior margin and along anterior part of ventral margin of shell, about thirty to forty are of moderate length, simple, and slightly widened and flattened; at least some of these bristles have very short, fine marginal hairs. Remaining bristles along margin of shell rather short, simple, and narrow. When seen by transmitted light, shells of specimens preserved in alcohol have a brownish color. Just behind eye, there is a rather broad, dark, saddle-shaped band, a character which makes the species very easy to recognize and from which it has been named. By reflected light shell has a pink tint, and saddle is milky white, when body is within shell (preserved specimens). When dried and seen by reflected light, shell is milky white, without any visible saddle. Saddle evidently caused by heavy incrustation of lime.
First antenna: Fourth joint somewhat more elongated than in C. (C.) montereyensis, being about 9/8, according to scale used in description of subgenus. The long claws are in some cases somewhat, though very slightly, longer relatively; and the two distal ones of them are somewhat weaker distally than in text fig. VI, 5 of the mentioned species. On lateral side of first joint, there are a number of scattered, short hairs. On medial side a rather short, irregular row of short hairs (almost scattered) occurs. Long hairs and pectination on anterior side of second joint are somewhat reduced.
Second antenna: Slightly more slender than usual. Exopodite: Somewhat more elongated than usual and rather distinctly three-jointed. Endopodite: Bristle of first joint somewhat shorter than in C. (C.) montereyensis. Second joint: Positions of bristles about same as in Pl. XXXV, fig 18, G. W. Müller, 1894. OF the three bristles at about middle of posterior side, the postero-lateral is furnished with a moderately strong pectination; the antero-lateral characterized by unusually distinct shaft and head; the medial rather narrow, of subequal width throughout its entire length, naked or almost so, and about half as long as the postero-lateral bristle of this group. The strong postero-distal bristle of this joint relatively weak and almost naked. Distal joint: Claws relatively long, end claw being about four to five times longer than anterior side of joint. Pilosity: On medial side of protopodite, there is a relatively long longitudinal row of fine and rather short hairs, as well as a number of scattered hairs; on lateral side of this joint, there are rather numerous more or less scattered hairs of moderate length and some hairs arranged in an irregular longitudinal row. Spines on distal plates of second endopodite joint, perhaps, somewhat stronger than in C. (C.) montereyensis.
Mandible: Masticatory joint: The next to the anterior tooth of pars incisiva, which is single in text fig. VII, 9 of C. (C.) montereyensis, is paired. The next to posterior pair of teeth somewhat larger relatively than in the mentioned species. There is a round hump on anterior side of dorsal half of this joint. Second endopodite joint: The long, annulated dorso-distal bristle, i.e., the bristle which is not attached to verruciform process, somewhat weaker and shorter relatively than in text fig. VII, 9 of C. (C.) montereyensis, being about, or not quite, twice as long as end joint. Sometimes the annulated, dorsal, bristle of distal joints is also a little shorter relatively than in C. (C.) montereyensis. Row of hairs on medial side of second endopodite joint usually consists of hairs somewhat longer than in figure mentioned above.
Maxilla: The long one of the four dorso-distal bristles of first joint of palp has hairs of moderate length.
Fifth limb: Exopodite slightly longer, when compared with protopodite, than in C. (C.) montereyensis; first exopodite joint slightly longer than second and third exopodite joints, which are subequal. Bristle on posterior side of protopodite about as long as, or somewhat longer than, distal joint and of about same type as in C. (C.) montereyensis, male; its hairs are, however, somewhat longer. Bristle on first exopodite joint somewhat weaker than in the mentioned species. End claw, which is almost naked, somewhat longer relatively, and perhaps slightly weaker than, in C. (C.) montereyensis.
Sixth limb: Joints of about same relative lengths, and with about same relative lengths and types of bristles as in C. (C.) glauca, female. Posterior bristle of protopodite has hairs somewhat longer than in most species of this subgenus. End claw somewhat longer than in C. (C.) montereyensis, with very fine pectination. On outside of protopodite, somewhat distally to posterior bristle, there is a group of fairly long hairs.
Seventh limb: Of about same shape as in C. (C.) montereyensis; exopodite, however, somewhat more elongated than in this species. Bristles of protopodite, too, approximately as in this species; the two distal of the three bristles on anterior side of this joint, however, usually slightly shorter relatively. Bristle on first exopodite joint narrow (it resembles corresponding bristle of sixth limb in male) and about as long as second exopodite joint, or somewhat shorter. End claw somewhat longer than in C. (C.) montereyensis. On outside of protopodite, somewhat distally to posterior bristle, there is a group of fairly long hairs.
Chitinous support of these three limbs, on sides of posterior part of body, usually somewhat stronger and of a somewhat simpler type than in C. (C.) montereyensis.
Brush-shaped organ: About intermediate between that of C. (C.) montereyensis and that of C. (C.) platycopa.
Penis: Right and left organs of same type. No spiral thickening detected in walls of vans deferens. Free tube of ductus ejaculatorius of moderate length; its point, which does not extend to point of copulatory appendage, furnished with a rather characteristic spine. Copulator appendage rather short and pointed.
Description: Female –
Shell: Length, about 0.76 to 0.80 mm.; length:height, about 1.75 to 1.80:1. Of about same type as in male but somewhat higher relatively; usually posterior part somewhat lower, when compared with anterior part, than in males.
Second antenna: Exopodite: Relatively short, being only about one and one-half times longer than anterior side of first endopodite joint, or slightly longer; its proximal joint, which is not much wider than distal joint, not widened distally; proximal joint shows slight signs of articulation at about middle. Endopodite: Of the three bristles at about middle of posterior side of second joint, the postero-lateral and the medial are furnished with moderately strong pectination. Just as in male, claws of distal joint are almost naked.
Fifth limb: Bristle on posterior side of protopodite swollen at base and has long hairs proximally and short hairs distally. Bristle on first exopodite joint, which is about half as long as second exopodite joint, or slightly longer, has about same strength as in C. (C.) montereyensis, female.
Sixth limb: Differs from that of male mainly in the following respects: Bristle on posterior side of protopodite has about same type as corresponding bristle on fifth limb in female. Bristle on posterior side of protopodite has about same type as corresponding bristle of fifth limg in female. Bristle on first exopodite joint of about same type and relative length as in C. (C.) montereyensis, female.
Seventh limb: Of about same type as in male; bristle of first exopodite joint, however, of about same type and relative length as in C. (C.) montereyensis.
As to genital verruca, furca, and posterior part of body, see text fig. XVI, 4. I have not been able to detect any rows of spines on posterior part of body. The verruca on which terminal bristle of body is situated is less developed than in most species of this genus.
Remarks: This species is identical with the form discussed on page 145 of my work of 1920 under the name of Cythereis sp. At this place the length of the male shell is erroneously stated to be 0.80 to 0.83 mm., instead of 0.77 to 0.81 mm. The lengths of the larval stages are, however, correct. This makes, of course, the agreement with Brooks’s law still more striking.
The outlines of the larval shells show the peculiarities noted by G. W. Müller, 1894, p.181. The surface of the shell in the two youngest stages is covered with closely-set, small, rounded pits which are not arranged in distinct groups or “excavations,” according to the terminology used in the description given above. In the first larval stage, the sculpture exhibits a type transitional between that of the second larval stage and that of the mature specimen; some of the walls between the pits are somewhat higher than others. (Is this an illustration of the phylogenetic development of the sculpture? Cf. G. W. Müller, 1894, p.88.) The saddle-shaped structure is to be found in the first, and usually also in the second, larval stage; not, however, in the third larval stage.
Two males and two females, as well as the shells of the remaining specimens, were examined.
Habitat: Falkland Islands – S.A.E., Station 41, Berkeley Straits, Port Louis, lat. 51°33’S., long. 58°9’W.; 23.VII.1902; depth, 2 to 4 m.; clay and sand: One female. S.A.E., Station 46, Carenage Creek, Port Louis, lat. 51°32’S., long.58°7’W.; 9.VIII.1902; depth, 1 m.; sand with great quantities of Codium: Fourteen mature specimens, males and females, and some larvae (two specimens and one valve of the first larval stage, four specimens and three valves of the second larval stage, and five specimens and two valves of the third larval stage).” (Skogsberg 1928, p.100-106)
