two water-mites from illinois

Two Water-Mites from IllinoisAuthor(s): Rodger MitchellSource: Transactions of the American Microscopical Society, Vol. 74, No. 4 (Oct., 1955), pp.333-342Published by: Wiley on behalf of American Microscopical SocietyStable URL: http://www.jstor.org/stable/3224166 .

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OSTRACODS FROM NORTH CAROLINA OSTRACODS FROM NORTH CAROLINA

West Virginia: Fayette County (3) 1, 2, 5, 12. Kanawha County (1) 3, 12. Mercer County (1) 4. Pocahontas County (1) 3, 9. Raleigh County (3) 1, 3, 5. Summers County (1) 4. Upshur County (1) [Tygart Drainage] 3.

Entocythere humesi is known to inhabit streams in the St. Lawrence, Ohio, and Tennessee drainage systems. Within these streams it has been found to be associated with all of the crayfishes listed in Table 1.

LITERATURE CITED

DOBBIN, CATHERINE N. 1941. Fresh-water Ostracods from Washington and Other Western Localities. Univ. Wash. Pub. Biol., 4: 175-246.

HOFF, C. CLAYTON. 1943. Two New Ostracods of the Genus Entocythere and Records of Previously Described Species. Jour. Wash. Acad. Sci., 33: 276-286.

1944. New American Species of the Ostracod Genus Entocythere. Amer. Midi. Nat., 32: 327-357.

KOZLOFF, EUGENE N. 1955. Two new Species of Entocythere (Ostracoda: Cyther- idae) Commensal on Pacifastacus gambelii (Girard). Amer. Midi. Nat., 53: 156-161.

KOZLOFF, EUGENE N., and DONALD C. WHITMAN. 1954. Entocythere occidentalis

sp. nov., a Cytherid Ostracod Commensal on Western Species of Pacifastacus. Amer. Midi. Nat., 52: 159-163.

ROIJA, ENRIQUE. 1943. Estudios Carcinol6gicos. XIV. Nuevos Datos Acerca de los Entocythere (Crus. Ostracodes) de M6xico. An. Inst. Biol. Mex., 14: 553-566.

TWO WATER-MITES FROM ILLINOIS

RODGER MITCHELL

Department of Zoology, University of Vermont, Burlington

Through the courtesy of Lewis J. Stannard of the Illinois State Natural History Survey, the writer has been able to study two remarkable new species of water-mites. The material was collected by R. W. Larimore who made the collections by tying cheesecloth bags over the ends of drainage tiles. There is no further information regarding the habitat of these mites. One is a divergent species of Piersigia, a genus containing four very similar species that are largely limited to vernal ponds. The second species represents a new genus, Horreolanus. This is a highly modified member of the Mideopsidae, a family usually limited to per- manent standing waters. Occasional specimens of a third undetermined mideopsid were also found in the collections. The two abtindant species are of particular systematic interest because of their modified structure; moreover, their occurrence together is quite unexpected on the basis of current ecological information.

Holotypes and the bulk of the paratypes of the two new species are in the collection of the Illinois State Natural History Survey at Urbana, Illinois. A set of paratypes will be deposited in the Marshall Collection at the Chicago Natural History Museum.

West Virginia: Fayette County (3) 1, 2, 5, 12. Kanawha County (1) 3, 12. Mercer County (1) 4. Pocahontas County (1) 3, 9. Raleigh County (3) 1, 3, 5. Summers County (1) 4. Upshur County (1) [Tygart Drainage] 3.

Entocythere humesi is known to inhabit streams in the St. Lawrence, Ohio, and Tennessee drainage systems. Within these streams it has been found to be associated with all of the crayfishes listed in Table 1.

LITERATURE CITED

DOBBIN, CATHERINE N. 1941. Fresh-water Ostracods from Washington and Other Western Localities. Univ. Wash. Pub. Biol., 4: 175-246.

HOFF, C. CLAYTON. 1943. Two New Ostracods of the Genus Entocythere and Records of Previously Described Species. Jour. Wash. Acad. Sci., 33: 276-286.

1944. New American Species of the Ostracod Genus Entocythere. Amer. Midi. Nat., 32: 327-357.

KOZLOFF, EUGENE N. 1955. Two new Species of Entocythere (Ostracoda: Cyther- idae) Commensal on Pacifastacus gambelii (Girard). Amer. Midi. Nat., 53: 156-161.

KOZLOFF, EUGENE N., and DONALD C. WHITMAN. 1954. Entocythere occidentalis

sp. nov., a Cytherid Ostracod Commensal on Western Species of Pacifastacus. Amer. Midi. Nat., 52: 159-163.

ROIJA, ENRIQUE. 1943. Estudios Carcinol6gicos. XIV. Nuevos Datos Acerca de los Entocythere (Crus. Ostracodes) de M6xico. An. Inst. Biol. Mex., 14: 553-566.

TWO WATER-MITES FROM ILLINOIS

RODGER MITCHELL

Department of Zoology, University of Vermont, Burlington

Through the courtesy of Lewis J. Stannard of the Illinois State Natural History Survey, the writer has been able to study two remarkable new species of water-mites. The material was collected by R. W. Larimore who made the collections by tying cheesecloth bags over the ends of drainage tiles. There is no further information regarding the habitat of these mites. One is a divergent species of Piersigia, a genus containing four very similar species that are largely limited to vernal ponds. The second species represents a new genus, Horreolanus. This is a highly modified member of the Mideopsidae, a family usually limited to per- manent standing waters. Occasional specimens of a third undetermined mideopsid were also found in the collections. The two abtindant species are of particular systematic interest because of their modified structure; moreover, their occurrence together is quite unexpected on the basis of current ecological information.

Holotypes and the bulk of the paratypes of the two new species are in the collection of the Illinois State Natural History Survey at Urbana, Illinois. A set of paratypes will be deposited in the Marshall Collection at the Chicago Natural History Museum.

333 333



RODGER MITCHELL

Horreolanus nov. gen. (Figs. 1-4) Diagnosis. Dorsal and ventral body shields entire, with no secretory

pores or setae. Anterior pairs of coxae touching mesally, posterior two pairs separate. Genital field of typical mideopsid form, and distinctly posterior to coxae IV. Chelicerae fine, with the two segments fused. Palps massive, bulk-like and with only three segments.

Remarks. The assignment of Horreolanus to the family Mideopsidae is based on the conclusion that the general coxal configuration and structure of the mouthparts are divergent features of little phylogenetic significance. Form and structure of the genital field are thought to be especially significant and they clearly support the assignment of the genus to the Mideopsidae. The mouthparts do not resemble those of mideopsids; instead they are similar to the form seen in two divergent genera of the family Mamersopsidae, Mamersopsis and Platymamersopsis.

This odd new genus raises again the question of relationships between the Mamersopsidae and the families of the superfamily Mideopsae. As the water-mite families were subdivided during the 1930's these two groups, originally placed together and recognized as related (Viets 1914), became so widely separated that their relationships are now obscured. Viets (1936) mentioned this but until more is known of their phylogeny there is no way of solving this classification problem. The present classification of these groups is arbitrary, at least for certain genera.

Until relationships and phylogeny of the superfamily Mideopsae (sensu Lundblad, 1941b) are more clearly understood considerable con- servatism should be shown in proposing higher categories; hence, the assignment of Horreolanus to the nominate subfamily of the Mideopsidae.

Horreolanus orphanus n. sp. (Figs. 1-4) Description. Body enclosed by a dorsal and a ventral plate. Dorsal

plate entire, bearing neither setae nor secretory pores, separated from the venter by a narrow band of flexible integument free of sclerites or pores. Ventral plate consisting of the unexpanded coxae and genital field fused with the heavily sclerotized integument. Dorsal and ventral plates, exclusive of the coxae and genital field, coarsely ocellate. Coxae forming two widely separated pairs. Anterior coxal groups touching mesally but with a broad triangular bay for the mouthparts. Posterior coxal groups broad faterally and separated mesally. Legs rather long and slim, with setae not modified for either swimming or crawling. Tarsal claws simple and angular.

Capitulum small, broad, lying deep in the bay between coxae I. No well-defined constriction separates a rostral region on the capitulum. From a broad bulb-like base the capitulum tapers to a more or less pointed tip (Fig. 3). Chelicerae fine, elongate, with the tip fused to the shaft and resting on the flat dorsal surface of the capitulum. Palp three- segmented (Fig. 4); basal segment massive, ovoid in shape, second segment a simple ring, and the terminal segment broadly conical with the tip bent, bearing a long coarse seta on the flexor surface.

Male genital field (Fig. 1) ovoid, consisting of paired immovable lateral sclerites with a narrow median gap for the gonopore, and four (rarely five) pairs of nearly-rectangular genital acetabula. Female genital field (Fig. 2) a spherical ring surrounding the flexible lips of the

334



WATER-MITES FROM ILLINOIS

gonopore. Four pairs of genital acetabula (and rarely a supernumerary acetabula) just within the ring.

Discussion. The derivation of the three-segmented palp from the five-segmented palp characteristic of all water-mites can be understood through musculature and form of the segments. As shown in Figure 4 the basal segment has a distinct heavily sclerotized proximal ring. This appears to represent the true first segment. Segment 1 is separate in all other mideopsids but it is usually reduced to a narrow collar.

2

FIG. 1. Horreolanus orphanus, male venter with the left legs and the mouthparts removed.

FIG. 2. Horreolanus orphanus, female genital field. FIG. 3. Horreolanus orphanus, capitulum. lateral aspect with one palp removed. FIG. 4. Horreolanus orphanus, left palp, lateral aspect with the two muscles that

originate in the basal segment indicated by dotted lines. FIG. 5. Piersigia crusta, right palp, lateral aspect.

As shown in the unmodified water-mite palp (e. g. Unionicola; Mitchell, 1955) two muscles originate on segment 2, the first inserts on segment 3 and the second on segment 4. If this is taken to be the ancestral form and it is assumed that muscle attachments have not shifted from one segment to another, then the musculature of the Horreolanus palp is adequate to establish the identity of the true second, third, and fourth segments.

Two muscles originate on the basal segment in Horreolanus; one inserts on the penultimate segment, the other on the terminal segment (Fig. 4). At least the distal portion of the basal segment in Horreolanus

335



RODGER MITCHELL

represents the true second segment because of the two muscles originating there: the first of these muscles must insert on the true third segment, the penultimate segment in Horreolanus; the second muscle must insert on the true fourth segment, which is the terminal segment in Horreolanus. It seems unlikely that the fifth segment is lost entirely and the constriction that sets aside the bent tip of the terminal segment may mark the line of fusion between the true fourth and fifth segments.

Other systems of segmental homologies are possible but seem less desirable since all of them would require a muscle to shift from one segment to another or else the development of an entirely new muscle.

Measurements. A series of 20 of each sex was used. All figures are in millimeters; the mean is listed and the range is given in parentheses. Male: Venter 1.065 (1.114-0.967) long, 0.706 (0.790-0.654) wide. Dor- sum 0.927 (1.027-0.836) long, 0.642 (0.693-0.589) wide. Capitulum 0.231 (0.251-0.218) long, 0.098 (0.109-0.093) wide. Genital field 0.207 (0.237- 0.172) long, 0.179 (0.193-0.147) wide. Female: Venter 1.209 (1.272- 1.117) long, 0.857 (0.959-0.725) wide. Dorsum 1.101 (1.175-1.019) long, 0.755 (0.801-0.684) wide. Capitulum 0.232 (0.256-0.202) long, 0.102 (0.109-0.098) wide. Genital field 0.273 (0.321-0.240) long, 0.226 (0.262-0.191) wide.

Specimens. All specimens were collected from drainage tiles leading into Jordan Creek near Fairmount, Vermilion County, Illinois. R. W. Larimore Collector. Holotype; male collected V-26-1952. Paratypes; 32 males and 18 females, V-26-1952. 3 males and 3 females, V-2-1952.

Piersigia crusta n. sp. (Figs. 5-9) Diagnosis. Dorsal shield broad and triangular with only one pair of

small hyaline areas. Two pairs of large three or four pointed dorsocentralia. Six pairs of broad lateroglandularia occupying nearly the entire body margin. No marginalia between lateroglandularia 3 and 4. Dis- tinguished from all other Piersigia by the expanded dorsal sclerites, especially the lateroglandularia.

Remarks. No attempt has been made to apply a reference system to the dorsal sclerites of Piersigia. The system proposed here is indicated in Figures 6 and 7. Although basically a geographic system, the numbered sequences do refer to skeletal elements of similar function. Anatomical evidence supporting the groupings and their nomenclature follows the description.

Description. Anterior shield (Fig. 6) broadly triangular, heavily sclerotized, and reticulate over most of its area; a pair of anteriorly- placed median hyaline areas. Two pairs of circular hyaline areas each with a seta; one at the lateral angle of the dorsal shield, the other just lateral to the large hyaline area. Variation in the shape and size of the hyaline areas is common.

Six pairs of lateroglandularia around the margin, each expanded and heavily sclerotized; these are lateroglandularia 2-7. The first pair fused with the dorsal shield. Dorsoglandularia 1 at the anterior margin of the dorsal shield; dorsoglandularia 2-4 typically crescent-shaped and centrally located on the dorsum. Dorsocentralia 1-2 expanded, with three or four drawn out points, and forming a square in the center of the dorsum. Dorsocentralia 3 a median, posteriorly-placed, three pointed sclerite. Lateralia 1 mesad of lateroglandularia 2, lateralia 2 mesad of latero-

336




glandularia 4, and lateralia 3 mesad of lateroglandularia 5. Marginalia similar to the lateralia in shape, one pair just lateral to the dorsal shield, a pair between lateroglandularia 6 and 7, and a median one posteriorly between lateroglandularia 7.

Plates of the venter (Fig. 7) similar to other Piersigia. Two pairs of coxal plates, the anterior group separated. Genital field between the second coxal group. Anal plate just posterior to the genital field. Three crescent-shaped ventroglandularia present: one just latero-posterior to the genital field, one mesad to lateroglandularia 6, and one anterior to lateroglandularia 7. A small ventralia between ventroglandularia 2 and 3.

Capitulum, chelicerae, and palp of typical Piersigia form (Figs. 5, 7). Differences lie only in the chaetotaxy of the palp. Palp segment 2 with two mesally-placed setae on the dorsal surface and two to four setae on dorso-distal tip. Seven pectinate setae mesally-placed on the tip of segment 3. Four to six setae on the tip of segment 5.

Genital field (Fig. 7) with two pairs of lightly sclerotized areas bearing numerous small knob-like acetabula, the anterior pair elongate, the posterior pair more circular. A marginal sclerite extends between the two acetabulate areas on each side and encloses the mesal and posterior margins. Mesal border of the male genital sclerite more concave and with a broader posterior extension, and a longer anterior extension of the sclerite.

Specimens. All specimens were collected from drainage tiles leading into Jordan Creek near Fairmount, Vermilion County, Illinois, by R. W. Larimore. Holotype; male, collected V-30-1952. Paratypes; 1 female, same data. 1 female, IV-14-1952. 1 female, IV-21-1952. 1 male and 3 females, IV-26-1952. 2 females, V-18-1952.

BODY SCLERITES AND MUSCULATURE

Relationships and phylogeny of water-mites will doubtless be clearer when adequate anatomical data have been gathered. At present few accounts exist and new contributions must stand as factual tabulations in anticipation of the time when the facts of anatomy can adequately support phylogenetic discussions. The following account is based on dissections of ten formalin-fixed specimens of P. crusta. Preservation was not ideal and some small muscles may have been overlooked. The major features and general outline of the musculature were entirely clear and serve as the basis for the proposed nomenclature of body sclerites. Many homologies suggested or implied by the use of common terms in acarine morphology are assumptions justified more by convenience than anatomy. This is especially true of the body sclerites and musculature, which was the reason for using a strictly functional classification in treating Unionicolidae anatomy (Mitchell, 1955). The three major functional muscle groupings used in descriptions of unionicolids are also applicable to Piersigia.

First the coxal muscles (Fig. 9) which are associated, as the name indicates, with the basal plates of the legs. These muscles originate on the coxae and insert on the first leg segment. The next group, supportive muscles (Fig. 9), insert on the transverse coxal ligament from which an elevator of the first leg originates. The third group consists of muscles with both attachments on the body wall. They run in a dorso-ventral plane and are called dorso-ventral muscles (Figs. 8-9, Table

337



RODGER MITCHELL

1). A few small muscles have both attachments on one surface, either the dorsum or the venter. They are named dorsal or ventral muscles according to the surface to which they are attached. It is probably best to distinguish these from the dorso-ventral muscles even though they may function similarly.

Three other groups of small obscure muscles which originate on the body wall have special functions in moving mouthparts, genitalia, or the anal pore. The capitulum muscles insert on the capitulum, the genital muscles on the external genital plates, and the anal muscles on the anal pore or its plate. Only the origins of these muscles are considered in this study.

dgl. /-4 6 l t./-3 7 -L^------- marg./ a

- 7

t,, ,

^^^c^ ^

/ vgj.

, y'cr I ',

Igl./- 7 marg. 2-3

FIG6.6. Piersigia crusta, dorsal body surface. FIG. 7. Piersigia crusta, ventral body surface.

ABBREVIATIONS: a., anal muscles; cap., capitulum muscles; ctr., dorsocentralia; d., dorsal muscles; dep., depressors of leg segment 1; dgl., dorsoglandularia; dv., dorso-ventral muscles; elev., elevators of leg segment 1; g., genital muscles; lat., lateralia; lgl., lateroglandularia; marg., marginalia; s., supportive muscles; v., ventral muscles; vgl., ventroglandularia; vtr., ventralia.

The coxal and supportive muscles act directly to produce leg move- ments. Function of the dorso-ventral muscles remains largely a matter of supposition (Mitchell, 1955). It seems reasonable to assume that the muscles contribute to the tonus and rigidity of the body essential for efficient locomotion, especially in leg extension, which is hydrostatic rather than muscular. In addition, periodic contractions may contribute to the circulation of body fluids.

Nineteen dorsal sclerites are present in Piersigia crusta. Although differing greatly in form, there are, in fact, only two functional types. The sclerites are either simple sclerotized muscle attachments or else setigerous sclerites that partially surround, and may protect, gland

338




openings. Muscle attachments are suffixed by -alia placed on a prefix indicating location; hence, dorsalia, marginalia, etc. The sclerites associated with the gland pores have similar location prefixes on the suffix -glandularia; hence, dorsoglandularia, lateroglandularia, etc.

These geographic terms were introduced by Lundblad (1927) for the Thyasinae and later applied to the Sperchonidae (Lundblad, 1930), and several other families (Lundblad, 1941a). The adaptability of such a geographic system makes it easy to use in a great many groups. Only location and function are implied by the names; hence, similar terms in several families need not, and, in fact, do not indicate homologies between sclerites. Morphological significance is attached to names only in com- parisons of closely related forms in the same family.

8 -cop. 9 d" 2cap. 2 dv. I

dv. 6-12

elev. I

FIG. 8. Piersigia crusta, inner surface of the dorsum.

s. 2

d* 7 dep. nr

FIG. 9. Piersigia crusta, inner surface of the venter.

Glandularia of Piersigia are normally crescent-shaped sclerites located just anterior to a gland pore. Each sclerite has a small circular hyaline area from which a single seta arises. No muscles are attached to the glandularia (with the exception of the anterior ventroglandularia which is the origin for anal muscle 1). Four rows of glandularia are present on the dorsum. The median rows consist of three pairs of unmodified crescent-shaped glandularia plus the anterior pair which is fused with the anterior margin of the anterior dorsal shield. These are the dorsoglandularia (Fig. 6; dgl. 1-4). Seven heavily-sclerotized expanded lateroglandularia lie in a row along the margin of the dorsum (Fig. 6; lgl. 1-7). The anterior lateroglandularia is fused with the lateral angle of the dorsal shield. Three fairly typical ventroglandularia are present on the ventral surface posterior to the coxae (Fig. 7; vgl.).

Three rows of paired dorsal sclerites are present. Each row has a Three rows of paired dorsal sclerites are present. Each row has a

339



RODGER MITCHELL

different structure, but all serve as muscle attachments (Fig. 8). The five centralia, two pairs and a median sclerite (Fig. 6; ctr.) are expanded sclerites with heavy margins. Each one has three or four points and a fairly light central zone. All of them have three to five muscle attachments. A row of three lateralia (Fig. 6; lat.) lies just mesad to the lateroglandularia. The lateralia are small elongate sclerites with heavily sclerotized margins and a tiny clear central zone. These have only one or two muscle attachments.

Two paired and a median posterior marginalia (Fig. 6; marg.) are present. They resemble the lateralia in form but their orientation is transverse and they lie between lateroglandularia. The anterior pair lies between the first and second lateroglandularia, the second between the sixth and seventh lateroglandularia, and the terminal marginalia lies between the last pair of lateroglandularia.

The composition of the large dorsal shield is not understood. The lateral angles are lateroglandularia 1 and the median anterior margin is, in part, formed from dorsoglandularia 1. In addition, the several muscle insertions seem indicative of the fusion of several sclerites. Three well- separated muscle origins are present on the shield (Fig. 8), but these do not correspond to any structural lines of the dorsal shield, or with any of the series of sclerites posterior to the shield.

Musculature of Piersigia Coxal muscles (Fig. 9; elev., dep.). Elevators of leg 1 insert on the

antero-dorsal margin of segment 1 and come from three origins, the coxal ligament and two origins on the mesal margin of coxa I. There is one depressor which inserts on the ventral margin of segment 1 and arises from a broad origin on the mesal margin of coxa I.

The single broad elevator of leg II inserts dorsally on segment 1 and originates mesally on coxa II. Two depressors insert together ventrally on segment 1 and diverge to their origins, one to the anterior margin of coxa II, the other to the posterior margin of coxa II.

Leg III has two elevators which originate on the anterior margin of coxa III, one near the center, the other mesal. These insert on the dorsal margin of segment 1. The two depressors insert ventrally on segment 1 and diverge to origins on the anterior and the posterior margin of the coxa.

The insertions of the two elevators of leg IV are together on the dorsal margin of segment 1 and their origins are on the anterior margin of coxa IV and the mesal angle of coxa IV. The depressor of leg IV inserts ventrally on segment 1 and originates on the mesal margin of coxa IV.

As noted in previous work on Unionicolidae (Mitchell, 1955) and unpublished studies on the Hydryphantidae, active swimming forms have large and elongate elevators for the first three legs and these are opposed by very short depressors. In both of the above families the opposing coxal muscles of crawling forms are nearly balanced as to length and size. The fact that only one elevator (leg I) originates on the transverse ligament, rather than three which is typical in swimming forms, as well as the balanced size and length of the opposing coxal muscles indicates Piersigia crusta to be a form well adapted for crawling. Other species of Piersigia have a similar musculature. They are found crawling about in the debris of pond bottoms and are ineffectual swimmers. The crawl-

340




ing adaptation of Piersigia is in marked contrast to the swimming habit of the most closely related genus, Eylais. Unfortunately the musculature of Eylais is unknown.

Dorso-ventral Muscles (Figs. 8-9; dv.: Table 1). The attachments of the dorso-ventral muscles cannot be considered origins and insertions since both attachments are to the body wall. All dorso-ventral muscles are attached to either centralia or marginalia dorsally. There are three to five muscle attachments on the larger centralia while the small lateralia have one muscle attachment (with the exception of lateralia 3 which has two muscle attachments). Most ventral attachments are on the coxal plates. Precise attachments of the dorso-ventral muscles are listed in Table 1.

TABLE 1

Piersigia crusta. The dorso-ventral muscles and their attachments are listed according to the numbering used in Figures 8 and 9.

NUMBER DORSAL ATTACHMENT VENTRAL ATTACHMENT

1 Posterior angle, dorsal shield. Antero-mesal angle, coxa I. 2 Posterior angle, dorsal shield. Antero-lateral angle, coxa I. 3 Lateral angle, dorsal shield. Body wall lateral to coxa I. 4 Lateralia 1. Postero-mesal angle, coxa II. 5 Centralia 1. Antero-mesal angle, coxa III. 6 Centralia 1. Body wall lateral to coxa III. 7 Centralia 1. Postero-dorsal projection, coxa III. 8 Centralia 2. Postero-dorsal projection, coxa IV. 9 Centralia 2. Body wall posterior to coxa IV.

10 Centralia 3. Ventral body wall. 11 Centralia 3. Ventral body wall. 12 Centralia 3. Ventral body wall.

Supportive Muscles (Figs. 8-9; s.). All six supportive muscles insert on the transverse coxal ligament, a narrow median ligament lying just over the genital field and between coxae III. The origin of the first supportive muscle is on the anterior margin of coxa III, the second on centralia 2, the third on the body wall just dorsal to coxa III, the fourth on the lateral margin of coxa IV, the fifth on lateralia 2, and the sixth on the anterior projection of the genital sclerite. Function of the fifth supportive muscle is doubtful; its main action could be either the support of the transverse coxal ligament or activation of the genital sclerite.

Dorsal Muscles (Fig. 8; d.). Dorsal muscles 1 and 2 attach to the dorsal shield anteriorly. Posteriorly dorsal muscle 1 attaches to centralia 1, dorsal muscle 2 attaches to centralia 2. Dorsal muscle 3 attaches anteriorly to an undifferentiated region of the body wall between lateroglandularia 3 and 4. It is attached posteriorly to marginalia 2.

Ventral Muscles (Fig. 9; v.). These muscles have at least one attachment to a coxa. Ventral muscle 1 extends from the dorso-lateral projection of the anterior margin of coxa III. The second ventral muscle extends from the postero-lateral angle of coxa IV to ventralia 1.

Capitulum Muscles (Figs. 8-9; cap.). Three capitulum muscles are present, the first two originating on the dorsal shield and the third on the transverse coxal ligament. Since the capitulum was not studied, insertions of these muscles cannot be given with any precision. The first inserts on the medial dorsal part of the capitulum, the second inserts

341



RODGER MITCHELL RODGER MITCHELL

laterally at the base of the capitulum, and the third on the lateral wall of the capitulum.

Genital Muscles (Figs. 8-9; g.). Genital muscle 1 originates on the ventro-lateral projection of coxa IV and inserts on the lateral margin of the genital sclerite. The second genital muscle originates on lateralia 3 and inserts on the posterior extension of the genital sclerite.

Anal Muscles (Fig. 9; a.). Anal muscle 1 is the only muscle attached to a glandularia; it originates on the anterior ventroglandularia and inserts on the margin of the membranous anal pore. Anal muscle 2 attaches dorsally to lateralia 3 and ventrally to the antro-lateral margins of the anal plate.

REFERENCES CITED

LUNDBLAD, 0. 1927. Die Hydracarinen Schwedens I. Zool. bidrag Uppsala, 11: 185-540.

1930. Die Hydracarinen der Insel Borholm. K. Danske Vidensk. Sels., Biol. Medd., 7: (7) 96 pp.

1941a. Die Hydracarinenfauna Sudbrasiliens und Paraguays. K. Svenska veten-

skap. Handl., (3) 19: (7) 183 pp. 1941b. Eine Ubersicht des Hydrachnellensystems und der bis jetzt bekannten

Verbreitung der Gattungen dieser Gruppe. Zool. bidrag Uppsala, 20: 359-379. MITCHELL, RODGER D. 1955. Anatomy, Life History, and Evolution of the Mites

Parasitizing Fresh-Water Mussels. Mus. of Zoology, Univ. of Mich., Misc. Publ. No. 89, v+ 28 pp.

VIETS, KARL. 1914. Hydracarinen-Fauna von Kamerun. Arch. f. Hydrob., 9.342- 388.

1936. Die Tierwelt Deutschlands und der angrenzenden Meersteile. Wasser- milben oder Hydracarina. Teil 31-32, 7: x+ 574 pp., Jena.

BEHAVIOR OF THE MIRACIDIUM OF FASCIOLOIDES MAGNA (BASSI, 1875) WARD, 1917 IN THE

PRESENCE OF A SNAIL HOST1

W. C. CAMPBELL AND A. C. TODD

University of Wisconsin, Madison, Wisconsin

The manner in which miracidia establish contact with their molluscan hosts has long been a subject of interest to trematologists. It might perhaps be assumed that the relationship between a miracidium and its snail host is peculiar to the particular species of trematode involved. Nevertheless the early investigations in trematode biology gave rise to an impression that some force, such as a chemotactic attraction, might generally be involved in bringing the miracidium into contact with its particular snail host. From time to time this impression has been both

'From the Department of Veterinary Science, University of Wisconsin, Paper N.S. 174. Published with the approval of the director of the Wisconsin Agricultural Experiment Station and supported in part by the Research Committee of the Graduate School with funds from the Wisconsin Alumni Research Foundation, in part by Pitt- man-Rboterson Project (W-15-R) of the Wisconsin Conservation Department.

laterally at the base of the capitulum, and the third on the lateral wall of the capitulum.

Genital Muscles (Figs. 8-9; g.). Genital muscle 1 originates on the ventro-lateral projection of coxa IV and inserts on the lateral margin of the genital sclerite. The second genital muscle originates on lateralia 3 and inserts on the posterior extension of the genital sclerite.

Anal Muscles (Fig. 9; a.). Anal muscle 1 is the only muscle attached to a glandularia; it originates on the anterior ventroglandularia and inserts on the margin of the membranous anal pore. Anal muscle 2 attaches dorsally to lateralia 3 and ventrally to the antro-lateral margins of the anal plate.

REFERENCES CITED

LUNDBLAD, 0. 1927. Die Hydracarinen Schwedens I. Zool. bidrag Uppsala, 11: 185-540.

1930. Die Hydracarinen der Insel Borholm. K. Danske Vidensk. Sels., Biol. Medd., 7: (7) 96 pp.

1941a. Die Hydracarinenfauna Sudbrasiliens und Paraguays. K. Svenska veten-

skap. Handl., (3) 19: (7) 183 pp. 1941b. Eine Ubersicht des Hydrachnellensystems und der bis jetzt bekannten

Verbreitung der Gattungen dieser Gruppe. Zool. bidrag Uppsala, 20: 359-379. MITCHELL, RODGER D. 1955. Anatomy, Life History, and Evolution of the Mites

Parasitizing Fresh-Water Mussels. Mus. of Zoology, Univ. of Mich., Misc. Publ. No. 89, v+ 28 pp.

VIETS, KARL. 1914. Hydracarinen-Fauna von Kamerun. Arch. f. Hydrob., 9.342- 388.

1936. Die Tierwelt Deutschlands und der angrenzenden Meersteile. Wasser- milben oder Hydracarina. Teil 31-32, 7: x+ 574 pp., Jena.

BEHAVIOR OF THE MIRACIDIUM OF FASCIOLOIDES MAGNA (BASSI, 1875) WARD, 1917 IN THE

PRESENCE OF A SNAIL HOST1

W. C. CAMPBELL AND A. C. TODD

University of Wisconsin, Madison, Wisconsin

The manner in which miracidia establish contact with their molluscan hosts has long been a subject of interest to trematologists. It might perhaps be assumed that the relationship between a miracidium and its snail host is peculiar to the particular species of trematode involved. Nevertheless the early investigations in trematode biology gave rise to an impression that some force, such as a chemotactic attraction, might generally be involved in bringing the miracidium into contact with its particular snail host. From time to time this impression has been both

'From the Department of Veterinary Science, University of Wisconsin, Paper N.S. 174. Published with the approval of the director of the Wisconsin Agricultural Experiment Station and supported in part by the Research Committee of the Graduate School with funds from the Wisconsin Alumni Research Foundation, in part by Pitt- man-Rboterson Project (W-15-R) of the Wisconsin Conservation Department.

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two water-mites from illinois

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