Hydracarina from California. Part I

Hydracarina from California. Part IAuthor(s): Ruth MarshallSource: Transactions of the American Microscopical Society, Vol. 62, No. 3 (Jul., 1943), pp.306-324Published by: Wiley on behalf of American Microscopical SocietyStable URL: http://www.jstor.org/stable/3223036 .

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HYDRACARINA FROM CALIFORNIA. PART I

RUTH MARSHALL

Rockford College

Material for the present study was supplied by Dr. P. R. Needham who was kind enough to send the water mites, chiefly from alpine waters, from collections secured in the course of his extensive field investigations of the fish food of California waters. Very little is known of the hydracarina of the West Coast or of any alpine forms in the Americas; consequently many undescribed species were found.

Most of the specimens examined came from Waddell Creek, described by Needham (1934, p. 246) as follows: "This is a short coastal stream some 40 miles south of San Francisco. It averages about three feet in width at the end of the dry season in late October and early November and in the rainy season is subject to severe floods ... its average annual width is about 20 feet. The bottom is largely of gravel and small rubble with fine, deep pools at frequent intervals. The stream rises in the Santa Cruz Mountains and flows some 15 miles into the ocean. Before flowing into the ocean it flows through a lagoon for approximately one mile. Here brackish water prevails. The food samples were taken at a series of stations in the first 3 miles above the lagoon."

Two other streams contributed considerable numbers of individuals: Merced River, in the Yosemite Valley, at an elevation of 4,200 ft.; and Martis Creek north of Lake Tahoe at an elevation of about 5,600 ft., flowing into the Truckee River.

The paper will appear in two parts. Part I describes the species of two

genera (with one small related genus), without reference to systematic relations, which comprise nearly one-half of the total collections.

GENUS Atractides

Of the genera represented in these collections the Atractides claim the

largest number of individuals (over 200) and species (ten, all new). They fall into two groups according to the form of the palpus: the first four species have long palpi due to the great length of the 2nd segment, this and the 3rd having also a well developed process on the inner distal border, a type of palpus accompanied by a long rostrum on the maxillary organ. The species of this group are related to (but distinct from) the type species, A. anomalus Koch, widely distributed over Europe and reported also from Turkestan and Algeria. In the second group of six species the palpus is short and stout, the processes of the 2nd and 3rd segments are not well developed and the rostrum is short, as in A. stadleri Walt.

However, the recognized division of the genus into two subgenera is based

306




on the relation of the four small anterior dorsal plates to the large posterior plate; in the larger subgenus Atractides ("the true Atractides") these plates are distinct from each other as shown in all but the last of the new species to be described. In the subgenus Rosetria, represented here by A. obovatus, the lateral of the small plates are posteriorly more or less fused with the large plate.

Viets (1936, p. 233) says of this genus: "Die Atractides-Arten sind rheo- phil und zum Teil in massigem Grade kaltstenotherm. Sie bewohnen vor allem fliessende, auch langsam fliessende Gewasser, anscheinend mehr die Gebirgs- als die Tieflands-bache. Diese Milben sind langsame Tiere, die zum Teil am Boden der Gewasser in Schlamm kriechen, in Bachmoosen klettern oder an Unebenheiten von Steinen usw. leben; das Schwimmver- mogen fahlt ihnen."

Atractides sierrensis n. sp. (Plate I, Figs. 1-4)

The body is oblong, slightly shouldered, a little narrowed in the males which are 0.68-.70 mm. long, the females measuring 0.85-.88 mm. The anterior margin between the eyes has a slightly convex outline with two well developed small conical hair-bearing processes on either side. In most of these preserved specimens there is seen, especially in young individuals, a large irregularly Y-shaped light dorsal area and a similar roughly triangular ventral posterior spot. Of the four anterior dorsal plates, the two median are more elongated than is usual. Anterior ends of the 1st and 2nd epimera project well beyond the body margin and leave a wide bay for the maxillary organ. The 3rd epimera in the male unite medially for only a short space. The rostrum is long, projecting with the palpi beyond the bay of the epimera. The palpi are elongate (slightly shorter in the 2nd segment in the female), with a conspicuous process on the inner distal margin of the 2nd and 3rd segments, each with a long hair; the 4th segment is curved and has two hair-bearing papillae in the center of the concave side, while the 5th is very short. Legs short, only the last being as long as the body, weak, sparsely supplied with spines developed mostly at the distal ends of the segments; leg IV has a few short hairs and the 6th segment, which is

long, is expanded distally. The new species resembles A. occidentalis Mar. (1933, p. 40) known for

Wyoming; but it is broader with correspondingly broader epimera and

genital plates and the two median anterior dorsal plates are much broader. This species is the largest in numbers in the collection, a total of over

100 individuals of all ages, the females usually the more abundant; they came from Waddell Creek, the Merced River and its South Fork, and one from the Truckee River.

307



RUTH MARSHALL

Atractides tahoei n. sp. (Plate I, Figs. 5-7)

In this species, the body is oval, not heavily chitinized, 0.62 mm. long in the mature female; male unknown. The anterior border is convex between the eyes, with papillae and slender hairs. The protruding eye capsules lie above the centers of the median dorsal plates, the latter relatively large. All four of the anterior plates are distinct but not heavily outlined. The epimera occupy a large part of the ventral surface; the broad anterior ends of the 1st pair extend well beyond the body margin and form a broad bay for the maxillary organ. The 3rd epimera meet medially for some distance, a condition more common in the males of the genus; these individuals are, however, females, as shown by the genital area and the presence of eggs in the body. Margins of the 4th epimera extend only a little beyond the genital plates. The greater part of the genital area lies posterior to the center of the body. The maxillary organ has a very long slim rostrum which extends beyond the epimeral bay. The palpi are also long and slim due to the considerable length of the 2nd and 4th segments. The 3rd palpal segment has a large papilla with a fine hair on the inner distal part; the 2nd, in place of the usual process, has a thin plate; the 4th is curved and bears a large papilla with fine hairs midway on the concave side, while the 5th is very small, ending in finger-like processes. The legs are typical.

This species resembles A. anomalus Koch, an Old World form. It differs from it in the greater length of the 3rd epimera so that the 4th epimera and the genital area in the female occupy a more posterior position; also, the 2nd palpal segment has distally a plate instead of a slim process.

One mature female was found in Waddell Creek (April) and one imma- ture female in Taylor's Creek, Tahoe (September).

Atractides ellipsoidalis n. sp. (Plate II, Figs. 11-13)

In form, the body is an ellipse; mature females are 0.75 mm. in length, the male unknown. The anterior end is convex, with four small papillae

EXPLANATION OF THE PLATES

PLATE I

FIG. 1. Atractides sierrensis, ventral view, male. FIG. 2. Atractides sierrensis, dorsal view, male. FIG. 3. Atractides sierrensis, genital area, female. FIG. 4. Atractides sierrensis, right palpus and maxillary organ. FIG. 5. Atractides tahoei, dorsal view. FIG. 6. Atractides tahoei, ventral view, female. FIG. 7. Atractides tah,ei, palpus. FIG. 8. Atractides mercedensis, left palpus and maxillary organ.

308



HYDRACARINA FROM CALIFORNIA. PART I 309

2

PLATE I

1



RUTH MARSHALL

bearing fine hairs, the eye capsules only slightly bulging. The body wall is well chitinized but the small anterior dorsal plates are not heavily outlined, although distinct, the two medial approaching the body edge and

extending laterally beyond the limits of the eye capsules. The epimera are

elongated, the anterior ends of the 1st projecting well beyond the body and

forming a deep bay; the fused 2nd and 3rd meet in the median line for a short distance; the 4th are much elongated but the partly obliterated

posterior margins extend only a little beyond the genital area. The genital plates are elongated, narrowed posteriorly, for the most part lying anterior to the center of the ventral surface. The maxillary organ is stout with a stout rostrum. The palpi are rather small and slim; the 2nd segment is the

longest, with a distal median process bearing a hair as does also the much shorter 3rd; the 4th is shorter and much slimmer than the 2nd and has a well developed process midway on the concave side. The legs are weak, all shorter than the body, well provided with stout bristles which are found

chiefly on the distal ends of the middle segments. Closely resembling the Old World species, A. ellipticus (Mag.), the new

species appears to be smaller; the body is even more elongated with shoul- ders less pronounced, the epimera correspondingly more elongated, and the rostrum is stouter.

Four females were found in Martis Creek; one more female is known from Gibbon River, Yellowstone Park (collection of J. W. Scott).

Atractides mercedensis n. sp. (Plate I, Fig. 8; Plate II, Figs. 9, 10)

The body is broad and shouldered, 0.62 mm. long in the female; the male is unknown. The anterior margin is strongly convex, the eye capsules protruding with two papillae and hairs medial to each. An indistinct

Y-shaped area is seen on the dorsal surface. Body wall not heavily chitin-

ized, with pores small and rather sparse. Anterior dorsal plates relatively large, the medial almost as extensive as the lateral; their outlines faint but distinct from the posterior plate which projects slightly over the ventral surface. Epimeral plates occupy most of the ventral surface; the 1st pair

PLATE II

FIG. 9. Atractides mercedensis, ventral view, female. FIG. 10. Atractides mercedensis, dorsal view. FIG. 11. Atractides ellipsoidalis, right palpus and maxillary organ. FIG. 12. Atractides ellipsoidalis, dorsal view. FIG. 13. Atractides ellipsoidalis, ventral view, female. FIG. 14. Atractides californicus, right palpus and maxillary organ. FIG. 15. Atractides californicus, genital area, female. FIG. 16. Atractides californicus, anterior dorsal area.

310




9

13

16

PLATE II

311

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RUTH MARSHALL

have blunt anterior ends, moderately projecting, and form a large broad bay for the maxillary organ. The fused 2nd and 3rd epimera meet for a short distance in the medial line above the genital area; the posterior inner borders of the 4th show faintly near the end of the body. The large genital plates in the female lie for the most part posterior to the center of the body. The maxillary organ is broad with a large rostrum which extends a little beyond the epimeral bay. The palpi are long and the large 2nd segment is broad with a well developed process and hair on the inner distal margin; the 3rd has a similar process; the 4th is about as long as the 2nd and half as wide with a broad projection and hairs on the concave side; the 5th is very small, ending in finger-like processes. The legs are typical, sparsely supplied with short spines which are chiefly on the distal ends of the segments; the 5th segment of leg IV has a few pectinated spines.

A. mercedensis closely resembles A. maglioi Koen. found in western Europe; but in the former the 1st epimera and their anterior projections are shorter and stouter with a broader bay and the rostrum is also shorter and broader.

Four females were found in collections from the Merced River.

Atractides waddellicus n. sp. (Plate III, Figs. 17-20)

In this larger species the body is nearly circular, averaging 1.20 mm. in length in the female, 1.15 mm. in the male which is relatively a little nar- rower. Most preserved specimens are dark but some show a central red area and in nearly all there is seen more or less clearly a large Y-shaped light dorsal mark and a posterior ventral roughly triangular spot. The margin between the eyes is slightly indented and there are two small hair-bearing processes. The medial anterior dorsal plates extend laterally barely as far as the eyes. All epimera are relatively broad; the 1st project beyond the body margin leaving a moderately deep bay for the stout maxillary organ; in the male the united 2nd and 3rd join medially for only a short distance. The genital plates in the two sexes differ little but are smaller and more

PLATE III

FIG. 17. Atractides waddellicus, genital area, male. Fig. 18. Atractides waddellicus, anterior dorsal area. FIG. 19. Atractides waddellicus, left palpus. FIG. 20. Atractides waddellicus, ventral view, female. FIG. 21. Atractides geographicus, genital area, male. FIG. 22. A!ractides geographicus, palpus. FIG. 23. Atractides geographicus, ventral plates, female. FIG. 24. Atractides geographicus, anterior dorsal view. FIG. 25. Atractides compactus, anterior dorsal area. FIG. 26. Atractides compactus, left palpus and maxillary organ.

312




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21

24

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25

PLATE III

313

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RUTH MARSHALL

elongated in the male. The rostrum is short, lying well within the epimeral bay. The palpi are small and stout; the inner distal borders of the 2nd and 3rd bear each a coarse hair without a papilla but the 3rd has a projecting distal outer border; the 4th has a convex inner border on which is a long fine hair on a slight papilla. The legs are weak, all shorter than the body, with stout bristles, those at the distal ends of the segments flattened, and a few short hairs; leg I has few bristles except two long ones on the 1st segment, while the 6th is short with a rounded end; leg IV has its last three segments long, its distal bristles slightly serrated on the 4th and 5th, lacking in the 6th which is slightly enlarged at the end.

A near relative is A. simulans Mar. (1933, p. 40) known for the female only in Wyoming and Yellowstone Park; but the new species is larger and broader, the 1st epimera are longer, reaching nearly to the genital organ in the female, with a broader bay for the stouter rostrum.

In Waddell Creek 16 specimens were found (five collections, April, May, June, August, September, the latter young); two females were found in the Merced River.

Atractides geographicus n. sp. (Plate III, Figs. 21-24)

The body is oblong, slightly angular, the length in the female 0.90-1.00 mm., in the male, 0.75-0.60 mm. The original colors are probably dark; in preservation there is usually seen a large irregularly Y-shaped dorsal and a triangular ventral light area. At the anterior end there is a slight con- cavity; between this and the eye capsule of each side there are two small but well defined elevations, one sharp, the other rounded, each bearing a fine hair. The two medial of the anterior dorsal plates are relatively short. The epimera are somewhat elongated, the anterior ends of the 1st projecting well beyond the body edge to form a deep and narrow bay; the posterior inner borders of the 4th are faintly outlined, dipping most posteriorly in the female, while in the male the median edges of the 3rd meet for but a short distance. The genital areas are much alike, larger and anteriorly broader in the female. The rostrum is of medium length, the palpi small and stout, not protruding beyond the epimeral bay. The 2nd palpal segment is stout and bears a long hair on the inner distal border as does also the 3rd, but there are no processes; the 4th has a pronounced bulge on the inner margin, with a fine hair on a slight papilla near the distal end.

Like the preceding species, A. waddellicus, this new species resembles A. simulans Mar. in the palpi and the anterior dorsal structures; it differs from both in being shouldered and more elongated, with the ventral plates correspondingly longer.

Forty-four individuals were found, chiefly in Waddell Creek (nine collections, April to September), with five from the Merced and its South Fork.

314




Atractides compactus n. sp. (Plate III, Figs. 25, 26; Plate IV, Fig. 27)

The body of this species is moderately chitinized, broadly oval, females averaging 0.76 mm. in length; male unknown. The area between the eyes is slightly concave, with very small papillae and slender hairs; Ithe eye capsules are only slightly bulging. The dorsal plates are not heavily outlined, the median being wide, extending as far as the outer margins of the eye capsules; the lateral plates are broad, the outlines indistinct at the posterior ends. The large posterior plate extends slightly over the ventral plate at the end of the body. The epimera occupy most of the ventral surface; the tips of the 1st are blunt, only slightly projecting over the anterior end of the body but leaving a deep bay; the fused 2nd and 3rd meet for a short distance in the mid-region; the posterior median borders of the 4th are faintly outlined well toward the end of the body. The genital plates of the female are somewhat elongated, situated mostly posterior to the center of the body. The maxillary organ is stout with a short rostrum and is well within the epimeral bay. The palpi are small and stout; the 2nd and 3rd segments have each a stout hair on the slightly developed process distally on the concave side; the 4th has but a slight papilla with hairs on the middle of the concave side. The legs are relatively stout; IV is about as long as the body, leg I has slender bristles, while the others have stouter and longer bristles, chiefly on the distal ends of the middle segments.

In dorsal aspect the new species resembles A. sandalensis Sok. (1926, p. 72) of eastern Europe; A. compactus, however, is smaller, the epimera occupy more of the ventral surface, the 1st not reaching to the genital area, while the palpi are stouter.

The six females known were found in Waddell Creek.

Atractides californicus n. sp. (Plate II, Figs. 14-16)

The female body is oval, 0.92 mm. long; male unknown. The anterior border is slightly indented between the eyes, with two slender hairs on either side, the inner on a small but distinct papilla. The eye capsule of either side, under projections of the body margin, lies directly over the outer angle of the medial plate. The four anterior small plates are well defined, well removed from the body margin and relatively wide. The anterior ends of the 1st epimera project well beyond the body wall and form a broad bay for the maxillary organ and palpi. Genital organ of the female is broad and situated anterior to the center of the ventral surface. The maxillary organ is broad, with a short rostrum which does not reach to the tips of the 1st epimera. The palpi are small, of moderate width, slightly projecting beyond the epimeral bay; each bears several hairs and is without

conspicuous papillae on the 2nd and 4th segments.

315



RUTH MARSHALL

The new species resembles A. luteus Viets (1935, p. 580) described for Java; but A. californicus is larger, the anterior margin is concave rather than convex, the epimera project farther forward and the central pair of anterior dorsal plates are shorter and wider.

Only three individuals were found; they came from Waddell Creek.

Atractides oblongatus n. sp. (Plate IV, Figs. 28, 29; Plate V, Fig. 40)

The pronounced oblong form of the body suggests the specific name. The female is 0.70 mm. long, 0.50 mm. wide for the greater part of its length; male unknown. The anterior rounded outline is only slightly broken by two very small hair papillae between the eyes. The anterior median plates are relatively broad. The 1st epimera are elongated, with blunt anterior ends and form a wide deep bay for the maxillary organ; the 4th are much elongated, their posterior outlines almost obliterated. The genital plates are also elongated, much narrowed posteriorly. The rostrum is stout and broad, hardly extending out as far as the tips of the 1st epimera. The palpi are small and stout; the 2nd and 3rd segments are of about the same size and each bears a stout hair on the inner side but no papilla; the 4th has a slight papilla with two fine hairs and ends in a broad point, while the 5th is very small and curved. The legs are very short and weak with a few small bristles; the distal ends of segments are expanded.

The elongated form is found in several species of Atractides but it seems to be associated usually with a long palpus and rostrum. But in A. angulatus Walt. (1928, p. 78), from India, there is a close resemblance to A. oblongatus; in the latter, however, the body is a little longer with the 4th epimera correspondingly elongated, while the palpi and maxillary organ, although of the same general form, are a little stouter.

Only two specimens are known; they came from Waddell Creek.

Atractides obovatus n. sp. (Plate V, Figs. 35-39)

The form is broadly obovate, the body wall only moderately chitinized. Males are 0.65 to 0.68 mm. long, with the greatest width, in the anterior

PLATE IV

FIG. 27. Atractides compactus, ventral view, female. FIG. 28. Atractides oblongatus, dorsal view. FIG. 29. Atractides oblongatus, ventral view, female. FIG. 30. Calonyx constans, right palpus and maxillary organ. FIG. 31. Calonyx constans, left leg IV. FIG. 32. Calonyx constans, genital area, nymph. FIG. 33. Calonyx constans, genital area, female. FIG. 34. Calonyx constans, genital area and left epimera, male.

316




27

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PLATE IV

34

317



RUTH MARSHALL

third of the body, 0.55 to 0.60 mm.; the largest female measured 1.00 by 0.90 mm. In preservation a large Y-shaped dorsal area is seen and a smaller roughly triangular posterior ventral area. The anterior border is but slightly indented, the hair-bearing papillae are slight, the eye capsules slightly protruding. The anterior medial dorsal plates are broad, very close to the body edge and faintly outlined, as are also the two lateral plates on the posterior borders where they are partly fused with the large dorsal plate, the latter extending posteriorly over the ventral plate. The epimera occupy a great part of the ventral surface; the 1st pair extends well beyond the body edge and leaves a deep wide bay for the maxillary organ. The genital areas in both sexes lie almost entirely posterior to the center of the body, the plates scarcely differing except in the greater size in the female; above them the united 2nd and 3rd pairs of epimera have a somewhat longer line of union in the male. The maxillary organ is large and stout, with a short rostrum, and lies with the small palpi within the epimeral bay. The palpi are short and stout; the 2nd and 3rd segments are large and each bears a long coarse hair without papillae near the inner distal end; the 4th is slim with fine hairs on a slight papilla on the inner side; the small 5th has several stout blades. The legs are slim, moderately provided with bristles; leg IV is about as long as the body.

The relationships of A. obovatus are uncertain. It belongs to the subgenus Rusetria Thor, the type species designated being A. spinirostris Thor (1923: 8, Fig. 5) now considered in part a synonym for A. connexus Koen., a European species. The new species closely resembles the figure given by Thor in form and dorsal aspect (less like published figures of A. connexus); but the epimera occupy more of the ventral surface while the palpi are stouter and lack the well developed distal processes on the 2nd and 3rd segments.

Seven individuals were found in Waddell Creek.

Genus Testudacarus

This genus was erected by Walter (1928; p. 75); the material consisted of one individual only, a female, from India, described as T. tripeltatus. It is the only report of this rare genus before the present paper. In collections

PLATE V FIG. 35. Atractides obovatus, dorsal view. FIG. 36. Atractides obovatus, ventral view, male. FIG. 37. Atractides obovatus, right leg IV. FIG. 38. Atractides obovatus, genital area, female. FIG. 39. Atractides obovatus, palpus. FIG. 40. Atractides oblongatus, right palpus and maxillary organ. FIG. 41. Calonyx ovata, genital area, young male. FIG. 42. Calonyx ovata, genital area, female.

318



IIYDRACARINA FROM CALIFORNIA. PART I

38

39

1i2

PLATE V

319



RUTH MARSHALL

from Waddell Creek two more specimens were found, a male and a female, representing two new species. The genus is closely related to the Atractides from which it differs most conspicuously in having but three small anterior dorsal plates rather than four, these being followed by a row of smaller plates on either side so that the large dorsal plate is surrounded by them. Also there are but six genital acetabula.

Testudacarus americanus n. sp. (Plate VI, Figs. 46-48)

The body of the female is 0.80 mm. long, broadly oval; male unknown. The anterior margin is convex, the eye capsules slightly bulging with a small papilla and two fine hairs medial to each. Pores are conspicuous on all plates; the cuticula is coarsely striated. The central of the three small anterior dorsal plates is broad and extends out to the region of the eyes; the lateral plate on each side narrows posteriorly with outlines clear but not heavy. The seven succeeding smaller plates of either side which complete the encirclement of the large central plate are but faintly outlined; three of these are elongated and four, alternating with them, are small and each bears a gland opening plate with a hair, in these details closely resembling the type species. The epimera are even more completely fused than in the Atractides and form a smaller area: the anterior ends of the 1st pair project well beyond the body margin and leave a large bay for the maxillary organ; the 4th which are smaller than the united 2nd and 3rd have very indistinct posterior outlines and bear the sockets for leg IV on the lateral borders. The genital plates are almost entirely anterior to the center of the body and are broadest at the anterior end, with but six acetabula. The maxillary organ is small and broad with a short rostrum and lies well within the epimeral bay. The palpi are small and stout with many long hairs on the extensor side; the 2nd and 3rd segments bear fine bristles on the inner distal margins. The legs are short and weak, the IV, the longest, shorter than the body; bristles are small and numerous but there are no swimming hairs.

The new species is closely related to T. tripeltatus Walt. but somewhat smaller; the median of the three anterior dorsal plates is much broader, the lateral plate on either side of it shorter; the united 2nd and 3rd epimera are larger, the 4th smaller in T. americanus.

PLATE VI

FIG. 43. Testudacarus minimus, dorsal view. FIG. 44. Testudacarus minimus, right palpus. FIG. 45. Testudacarus minimus, ventral view, male. FIG. 46. Testudacarus americanus, dorsal view. FIG. 47. Testudacarus americanus, ventral view, female. FIG. 48. Testudacarus americanus, palpus.

320




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47

PLATE VI

321



RUTH MARSHALL

Testudacarus minimus n. sp. (P1. VI, Figs. 43-45)

This new species is based upon the study of one young male. It is only 0.475 mm. long, slightly ovate in form. The anterior end, including the eye region, is projecting with a slight point in the center. The eye capsules are slightly bulging and there are two papillae with hairs medial to each. Body pores are fine, the cuticula coarsely striate. The large central dorsal plate is well developed as are also the three anterior plates. Of those which follow the latter, seven on each side as in the other two species, the four small ones can be made out fairly well, chiefly because each bears a large gland opening plate and long hair; the three elongated alternating plates are very faintly outlined. The fused epimera occupy a large part of the ventral surface; the 1st pair have projecting anterior ends and form a large bay for the maxillary organ. The boundary between the 2nd and 3rd pairs is not quite obliterated and medially they approach each other for some distance; the 4th epimera are small, roughly triangular, with attachments for the leg on the middle of the outer side. The genital plates are similar in form and position to those of Atractides males; together they form an elliptical area posterior to the center of the body, the faintly attenuated posterior borders of the 4th epimera dipping down to enclose them. The maxillary organ is broad and stout with a short rostrum which with the palpi are well within the epimeral bay. The palpi are stout, the three middle segments of about the same length; there are several long hairs on the extensor side of the 2nd and 3rd which bear also a stout hair on the inner distal projections of each. The legs are stout; leg IV is longest but shorter than the body; bristles are sparse and there are no swimming hairs.

The small size of the new species distinguishes it conspicuously from T. tripeltatus; it differs also in the projecting anterior end and broader epimeral bay. Of the dorsal plates, the large central one is more elongated and narrowed anteriorly, the central anterior plate is broader, the encircling plates fainter in outline in T. minimus. As this is the only male known for the genus, comparisons of the ventral plates cannot be made.

Genus Calonyx The genus Calonyx, Family Protziidae, is represented in this collection

by large numbers of individuals; two species are present, one being new. They are simple, soft-bodied, typically alpine forms.

Calonyx ovata (Mar.) (Plate V, Figs. 41, 42)

Originally described as a Protzia (Marshall, 1931; p. 312), female only, this species should be placed in the closely related genus Calonyx because of

322




the position of the genital area near the 3rd epimera and the development of delicate partly chitinized valves. The male is now known; the genital area is shorter than in the female and in the small aperture there is a cluster of very fine hairs. The stalked genital acetabula, characteristic of the two related genera, number here about thirty, very irregular in position, the posterior more crowded and longer stalked than the anterior; they are more or less enclosed by soft flaps from the body wall which bear long coarse hairs.

Collections were made in Martis Creek and the Merced River, a total of 24 individuals. The species is known elsewhere only from Green Lake, Wisconsin.

Calonyx constans n. sp. (Plate IV, Figs. 30-34)

The exact shape and measurements are difficult to determine in preserved material of these soft bodied mites. Largest females are 1.50 to 2.00 mm. long. The body is an elongated oval and shouldered; dorsally there is no "Frontale" but four rows of short hairs on small plates on each side. The epimera are typical. The genital areas, placed between the posterior groups of epimera, bear each 12 conspicuous stalked acetabula; the latter are in two groups on each side, two anterior and four longer stalked posterior ones. This constancy in numbers suggested the specific name. In the small male aperture is a bunch of fine blunt hairs; in both sexes there are very delicate slightly chitinized and sparsely papillose valves and soft hair-bearing folds partly enclosing the acetabula. In the nymph the epimeral groups are farther separated from each other than in the adults; the anterior genital acetabula are well developed, the posterior small, unformed, the adjacent body folds showing faintly. The maxillary organ of the adult has a long slim rostrum and the palpi are also slim. The legs with their scoop-shaped toothed claws are typical; leg IV is the longest, slightly slimmer than the others, the bristles in middle segments blade-like.

The new species differs conspicuously from C. ovata, the only other previ- ously described species from North America, in the smaller number of genital acetabula, uniformly 12; the palpi are slimmer, the maxillary organ is also slimmer and it has a longer rostrum.

Over 100 individuals were found, most of them in Waddell Creek; in smaller numbers they are found in Truckee River and Martis Creek, in the Merced and at the Blackstone Hatchery in Yosemite Valley. Additional collections came from alpine waters of the Medicine Bow area, southern Wyoming: they were found by Dr. I. H. Blake in swift streams at an alti- tude of 9,700 ft., with egg masses, under stones; and a few were specimens recovered from trout stomachs by Dr. J. W. Scott.

323



324 RUTH MARSHALL

BIBLIOGRAPHY

Marshall, R. 1931. Preliminary list of the Hydracarina of Wisconsin, I. Wis.Acad. Sci., Arts, Letters, Trans. 26: 311-319.

1933. Water mites from Wyoming as fish food. Trans. Amer. Micros. Soc. 52(1): 34-41. Needham, P. R 1934. Quantitative studies of stream bottom foods. Amer. Fisheries Soc.

Trans. 64: 238-247. Sokolow, I. 1926. Zwei neue Hydracarinenarten aus der Gattung Atractides C. L. Koch. Zool.

Anz 68(1, 2): 72-76. Thor, S. 1923. Neue Acarinasammlung vom Volgadistrikt. Arb. Biol. Wolga-Sta., 7(1, 2): 1-15. Viets, K. 1935. Die Wassermilben von Sumatra, Java & Bali, etc., Ergeb. der Deut. Limnolog.

Sunda-Expedition. Arch. Hydrobiol. 1:484-594. 1936. Die Tierweldt Deutschlands. VII, 31, 32 Teil, 574 pp. Jena.

Walter, C. 1928. Zur Kenntnis der Mikrofauna von Biitischen Indien. Records of the Indian Museum. 30(1): 57-108. Calcutta.



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Hydracarina from California. Part I

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