Ph. (Philomedes) rotunda n. sp.
Description: — Female:
Shell: — Length, 1.9-2.1 mm.; length : height about 1.3 : 1; length : breadth about 1.6 : 1. Seen from the side it has a broad oval shape, with its posterior part somewhat larger than the anterior part, the greatest height being at about the middle. The dorsal, posterior and ventral margins are uniformly rounded, passing into each other without any corners; the ventral margin is weakly pouting just behind the incisur. The rostrum has a broadly rounded anterior corner, its ventral corner is rather pointed, but is without any spine (such as we find, for instance, in Ph. (Ph.) globosa, Lilljeborgi and other species of this sub-genus). The incisur is moderately deep and narrow, and is not marked off from the ventral margin of the shell by any protuberance (cf., for instance, Ph. (Ph.) globosa and Lilljeborgi). Seen from beneath it is oval, with its greatest breadth at about the middle, the anterior and the posterior ends rather broadly (more so than in Ph. (Ph.) globosa, for instance; cf. the figure for this species) and almost symmetrically rounded; its side contours are uniformly arched. Surface of the shell: This has no marked sculpture; in transmitted light it appears to be rather finely and irregularly reticulate; in reflected light each mesh seems to correspond to a rather shallow cavity. It is sparsely furnished with moderately long, scattered bristles, which are characterized by suddenly becoming narrower from a rather broad basal part (their type is about the same as the long bristle of Ph. ( Ph.) globosa). The pores of the surface are rather small and numerous and very difficult to observe with certainty. Seen from inside: Medial bristles: The bristles on the rostrum are about as numerous as on Ph. (Ph.) Lilljeborgi; most of them seem not to have any long hairs distally. Posteriorly on the list there are a moderate number of bristles, partly arranged in small groups. Between the posterior part of the list and the margin of the shell there are a few short bristles. On the other hand there is at thisplace no such pocket as has been given as characteristic of Ph. (Ph.) Lilljeborgi. The rostral selvage has rather short marginal hairs.
First antenna: — This agrees in its details with this antenna of Ph. (Ph.) globosa. No variation was observed in the number of sensorial filaments on the end bristles. There are rather abundant hairs on the second joint, and short, stiff hairs were also observed on the first joint, especially ventrally.
Second antenna: — Exopodite: This is very like that of Ph. ( Ph.) globosa. The bristles on the second to the fourth joints are about as long as the first joint. In females with large eggs in the brood chamber the long natatory bristles were broken off as in the species just mentioned. The endopodite is also very like that of Ph. ( Ph.) globosa. Sometimes a rather short bristle, with short hairs, may be found somewhat distally of the long ventral bristle on the second joint. The distal bristle on this joint is perhaps somewhat more pointed than in Ph. ( Ph.) globosa.
Mandible: — Protopodite: Basale: This has from seven to nine bristles ventrally, some of which are rather long and some of moderate length. Apart from the two distal bristles there is only one bristle dorsally, situated just in front of the middle of the joint; this bristle is about as long as this joint. The two distal bristles are somewhat different in length, somewhat longer or shorter than this joint. All three are of about the same type, with one or a few wreaths of long, stiff secondary bristles at the middle and short, fine hairs distally. The two bristles of the exopodite are somewhat shorter than the distal bristles on the second protopodite joint, but of about the same type as these. Endopodite: Of the four ventral bristles on the first joint the shortest one is about half as long as the second endopodite joint, the three others are about as long as this joint; they are all furnished at the middle with one or a few wreaths of long, stiff secondary bristles and with short hairs distally. Second endopodite joint: The anterior proximal group of bristles comprises three bristles, of which the medial ones are somewhat shorter than the lateral one, the latter being about half as long as this joint; all of them are usually furnished with short, fine hairs. End joint: The longest middle claw is about as long as the second endopodite joint. The anterior claw is only about a third of this length. The weak anterior bristle in this species is somewhat longer than the anterior claw. Pilosity: The second protopodite joint and the second endopodite joint have groups of short, fine, stiff hairs on the outside similar hairs are also found distally-anteriorly on the first endopodite joint.
Maxilla: — This is very like this limb in Ph. (Ph.) globosa. Protopodite: The bristle on the anterior side of the palp on the boundary between the protopodite and the endopodite is long, being about as long as the endopodite, and has no long secondary bristles. Endopodite: This has four or five bristles on the first joint distally-posteriorly. The end joint has three or four c-bristles; the powerful bristles among the b- and d-bristles have a very weak equipment, almost smooth.
Fifth limb: — This is very like the corresponding appendage in Ph. (Ph.) globosa. In one specimen three bristles were observed on the outer lobe of the third exopodite joint on this limb of one side.
Sixth limb: — Very like that of Ph. (Ph.) globosa. The second exopodite joint has, on the average, somewhat more numerous bristles.
Seventh limb: — This has about the same relative length as in Ph. (Ph.) globosa. Cleaning bristles: These are rather numerous, 23-26 being observed; in most eases
as in Ph. (Ph.) Lillieborgi, three dorsal ones and two ventral ones are situated close together, distally, sometimes three dorsal ones and three ventral ones were observed; the rest are scattered irregularly proximally of the former ones, being in most cases somewhat more numerous on the dorsal side of the limb. They are of moderate and somewhat varying length, and are furnished with from two to five bells, cut off transversally distally; the tongue of the distal bell is also cut off transversally. Proximally of the bells the cleaning bristles are furnished with from one to five wreaths of short, stiff hairs, placed obliquely. The end comb consists of about twelve to sixteen teeth of moderate strength and length, decreasing somewhat in length the more proximally they are situated. These teeth are furnished proximally on each side with a rather strong secondary tooth and are rounded distally; there are no wing-shaped processes at the sides (such as are found, for instance, in Ph. (Ph.) globosa and Lillieborgi), or if they do exist,
they are very weak and have no freepoints. The cavity situated dorsally of the end comb
is rather deep and is furnished dorsally with three moderately long, claviform, smooth, chitinous pegs.
Furca: — This has ten claws, diminishing in length posteriorly, without any clear division into main claws and secondary claws. Claws nos. 2 to 4 are rather decidedly bent; this bending varies, however, to some extent. The five anterior claws have a proximal- medial group of long, stiff bristles, the posterior ones have no such bristles. Medially close to the claws there are on the lamellae sparsely-scattered stiff bristles varying in length and number. In front of the first claw and behind the posterior one the lamellae are furnished with short, fine hairs; apart from these they are most frequently quite smooth.
Rod-shaped organ: — This organ is about 0.5 mm. long. It is finely pointed distally. Somewhat proximally of the middle of the organ a rather considerable portion of it is thin-walled; at this part the organ is flexible. There is no division into joints at all. It is smooth.
The male is unknown.
Relation to Ph. ( Ph.) laevipes Daday.
Remarks: — It is impossible to decide for certain whether this species is identical with
Ph. (Ph.) laevipes, though it does not seem impossible. As a preliminary I considered it best to describe it as a new species. The description of Ph. laevipes that is found in E. von DADAY, 1908, is exceedingly deficient, clearly drawn up without the author having the necessary knowledge of the forms belonging to this sub-genus.
Ph. laevipes = Ph. Charcoti Daday?
In passing I may point out that Ph. laevipes is probably a larva of the species Ph. Charcoti, which is described by E. von DADAY in the same treatise. DADAY himself indicates the possibility of these two forms being identical. Thus we read on p. 15 of this treatise: “En général, les particularités de l'organism rappellent beaucoup la Philomedes Charcoti, et, si la structure des pattes vermiformes ne différait pas autant, on pourra réunir les deux espéces, vu que touter deux sont du même endroit “(la côte de l'île Booth-Wandel, Terre de Graham, Antarctic), encore que capturees à des dates différentes.” According to this author the seventh limb of Ph. laevipes is, unlike that of Ph. Charcoti, quite bare. This character to which DADAY attached such great importance that he derived the name of the species from it, can, of course, not be regarded as any reason for not identifying these species. It is known that this absence of armature on the seventh limb is a character of the larva; all species of this genus seem to have a seventh limb of this type during the third larval stage. Other characters as well, such as the length of the shell, the number of furcal claws, etc. support the idea that- Ph. laevipes is a larva of Ph. Charcoti in the third stage.
The form dealt with by me here seems to differ from Ph. Charcoti, of which only the male is described, in at least one character, namely the number of bristles on the seventh limb. Ph. Charcoti is said to have only thirteen bristles, six on one side and seven on the other, while Ph. ( Ph.) rotunda is characterized, as we have seen above, by having a somewhat larger number (23-26).
Relation to Ph. (Ph.) orbicularis Brady.
Another species to which Ph. rotunda is certainly very closely related is Ph. (Ph.) orbicularis —which, curiously enough and certainly incorrectly, is regarded by its author, G. S. BRADY, as a southern variety of Ph. ( Ph.) globosa — “It is in all respects very similar to the well-known European species P. Brenda “(globosa)” and may perhaps be fairly looked upon as a southern variation of that form”. G. S. BRADY's description is unfortunately too incomplete to permit of a certain identification. The relatively great length of the shell (2.5 mm.) and the fact that “the surface of the shell is smooth and densely clothed with a villous coating of very short hairs” (G. S. BRADY, 1907, p. 4) seem, however, to argue against the identity of these forms. It is, however, not impossible that they are identical, nor can it be considered impossible that G. W. MÜLLER was right when in 1912 he identified Ph. orbicularis with Ph. laevipes.
Habitat: —South Georgia: S.A.E., Station 18, mouth of the West Fiord, Cumber- land Bay, lat. 54° 15' S., long. 36° 25' W.; 22. IV. 1902; depth, 250 m.; loose clay; temperature at the bottom + 1.2° C: 1 mature female; R. M. S. 136. S.A.E. Station 22, off May Bay lat. 54° 17' S., long. 36° 28' W. (type locality); 14. V. 1902; depth, 75 m.; clay with scattered algae; temperature at the bottom + 1,5° C: 1 mature female; R. M. S., on slides. S. A. E., Station 23, off the mouth of Moran Fiord, lat. 540 23' S., long. 36° 26' W.; 16. V. 1902; depth, 64-74 m.; grey clay with gravel and stones; temperature at the bottom + 1,65° C. 4 mature females and 14 larvae; R. M. S. 137. S. A. E. Station 24, off Grytviken, lat. 54°22' S., long. 36° 27' W.; 20.V.1902; depth, 95 m.; clay: 2 juvenes; R.M.S. 138. S.A.E., Station 30, Moran Fiord, lat. 54° 24' S. long. 36° 26' W.; 26. V. 1902; depth, 125 m.; clay with scattered stones; temperature at the bottom — 0.25° C: 1 mature female; R. M. S. on slides.
Type-specimen, on slides, R. M. S.” (Skogsberg 1920, p. 414-419)
