ABSTRACT -- The present work reviews the hosts, distributions,
synonyms and taxonomic characters of North American hairworms
(Gordioidea: Nematomorpha) and presents a key based on adult
morphological characters that can be observed under the dissecting and
light microscopes. A total of 18 described species are recognized in the
present work. However the field is complicated by incomplete
descriptions, lack of knowledge of morphological variation within
species and sexual dimorphism.
Hairworms, or Gordioidea, are fresh water members of the Phylum
Nematomorpha. These enigmatic organisms, which stand apart from other
invertebrates, have been little studied due to their secretive habits,
difficulty in rearing, lack of economic importance and problems
regarding their identification. All known species develop in
invertebrates, especially insects, but the larvae are capable of
encysting (without development) in a wide range of animals, including
vertebrates (Poinar, 2001; Schmidt-Rhaesa, 1997; Smith, 2001).
The present work reviews the hosts, distributions, synonyms and
taxonomic characters used in the identification of North American
hairworms and presents a key based on adult morphological characters
that can be observed under the dissecting and light microscopes (Fig.
TAXONOMIC CHARACTERS USED TO IDENTIFY HAIRWORMS
First stage hairworm larvae are transparent and provided with an
array of hooks, stylets and assorted devices for penetrating into the
body cavity of potential hosts (Fig. 2-4). While these characters could
be used for generic and even specific placement, too few larvae have
been examined to make this method of identification practical. Thus only
adult characters are used in identifying hairworms. Moreover, since the
adults are normally opaque, only external characters are practical.
Diagnostic characters of adult hairworms include: 1) the presence
and nature of the areoles (raised areas on the cuticle), especially
their type, shape, size, arrangement, and association with pore canals,
bristles, warts and papillae, 2) body shape, size and color pattern,
especially that associated with the anterior (calotte) and posterior
ends and, 3) features of the male tail, including first, whether it is
simple or forked and then if it bears preor postcloacal ridges, folds,
hairlines, bristle fields or tubercles. Caution should be taken since
the adults frequently exhibit sexual and age dimorphism in relation to
body size, shape and coloration as well as areole arrangement. In
addition, fixation artifacts such as body ridges, folds, etc. may result
from specimens remaining in alcohol for extended periods (the majority
of hairworm species have been described from museum specimens that have
been in preservative for a number of years). Unfortunately, the
intraspecific variation of most diagnostic characters is unknown, since
many species have been described from a single specimen or only one or
two specimens have been examined in detail.
When available, scanning electron microscopy is a useful tool for
studying fine details on the surface of hairworms. However this
technique is not necessary for identification purposes if good light
microscopes are available. Methods for preserving and preparing
specimens for optical microscopic examination can be found elsewhere
(Poinar, 2001; Smith, 2001).
Basically, all hairworms develop inside invertebrates, with a
free-living stage in an aquatic habitat where mating and oviposition
occur. Most, if not all, hairworms have an indirect life cycle,
involving an aquatic paratenic host (Fig. 2-3) and a terrestrial (or
rarely aquatic) developmental host (Fig. 2-1). The paratenic host (one
that carries a parasite internally but does not support its growth or
reproduction) ingests hairworm eggs containing preparasitic larvae or
free-living preparasitic larvae in the water habitat. These preparasitic
larvae enter the body cavity of the paratenic host by burrowing through
the intestinal wall. Penetration is assisted by an extensible proboscis
bearing circlets of spines as well as three stylets. After passing
through the gut wall, the preparasitic stage then encysts, usually in
the fat body, intestinal wall, connective tissue or muscle tissue of the
paratenic host (Fig. 2-3). The range of paratenic hosts is more
extensive than that of developmental hosts and can include fish, frogs
and even humans. Presumably, chemical cues signal whether a host is
suitable for development or encystment.
Growth and development of the hairworm larva occurs after the
paratenic host is consumed and the hairworm larva enters the body cavity
of a developmental (or definitive) host, usually an insect predator or
omnivore. In some cases, instead of developing, the hairworm larva will
re-encyst inside the predator. In this case, the predator becomes a
secondary paratenic host (Fig. 2-3). When reporting hairworm hosts, it
is important to state whether it is a paratenic or developmental host,
which is not always clear from the literature (White, 1969).
A list of the 18 species of North American hairworms recognized in
this work, and their synonyms, is given in Table 1. Available
information on naturally occurring paratenic and developmental hosts of
North American hairworms, along with notes on their distribution, is
presented below, followed by a key to the adults. It should be noted
that collection data on North American hairworms is quite sparse. Thus
the geographic ranges presented below present a biased view of the
actual range of species. It is likely that most North American hairworms
occur throughout North America, but only in certain ecological habitats.
Certain species, e.g. Gordius robustus and Paragordius varius, appear to
be more widespread than others. Distribution depends on climatic and
ecological conditions and available hosts. Environmental disruption by
humans has a direct impact on hairworms and limits their occurrence to
more remote habitats with natural water sources.
SYNOPSIS OF NORTH AMERICAN HAIRWORM SPECIES WITH GEOGRAPHIC
LOCATION AND HOST RECORDS (IN ALPHABETICAL ORDER)
Chordodes morgani Montgomery, 1898a. This is essentially an eastern
North American species with reports from as far south as Florida and as
far west as Nebraska (Chandler, 1985). Montgomery (1898a) mentions that
a blattid served as host to this species and Schmidt Rhaesa et al.
(2003) reported Periplaneta fulginosa and Parcoblatta sp. as hosts.
Studier et al. (1991) reported parasitism by this hairworm in the camel
cricket, Ceuthophilus stygius and cave cricket, Hadenoecus subterraneus.
Gordionus densareolatus (Montgomery 1898a) nov. comb. has been
reported from Western North America (Montgomery, 1907).
Gordionus lineatus (Leidy 1851) has been reported from eastern
North America (Montgomery, 1898a, 1907; Leidy, 1851), including a cave
in the Great Smoky Mountains National Park (Reeves, 2000).
Gordionus longareolatus (Montgomery 1898b) has only been reported
from California (Montgomery, 1898b).
Gordionus platycephalus (Montgomery 1898a) has been reported from
the Ungava Region of Eastern Canada, Montana, Penn-sylvania, Wyoming,
Guatemala (Montgomery, 1898a, 1907) California and Utah (Poinar and
Weissman, 2004) suggesting that it occurs throughout North America.
Hosts include the orthopteran, Stenopelmatus spp. (Poinar and Weissman,
Gordionus sinepilosus Schmidt-Rhaesa et al., 2003 has been reported
only from one locality in British Columbia.
Gordionus violaceus (Baird 1853) occurs throughout North America
(Smith, 1991; Schmidt-Rhaesa et al., 2003).
Gordius alascensis Montgomery 1907, which was assigned to the genus
Gordionus by Schmidt-Rhaesa et al. (2003), has been reported only from
Alaska (Montgomery, 1907).
Gordius attoni Redlich 1980 has been reported from northern North
America (Redlich, 1980; Schmidt-Rhaesa et al., 2003).
Gordius difficilis Montgomery 1898a (Smith 1994) has been reported
from eastern North America (Smith, 1994). The ground beetles, Chlaenius
prasinus (Coleoptera: Carabidae) and Pterostichus melanarius have been
reported as developmental hosts for this species (Hanelt and Janovy,
2000; Bolek and Coggins, 2001).
Gordius robustus Leidy 1851 occurs throughout North America,
including Mexico (Chandler, 1985; Camerano, 1915) and Hawaii
(Montgomery, 1898a; Heinze, 1934). The North American developmental
hosts for this species include various Acrididae (Ward and Whipple,
1918), Odonata (Cappucci, 1977), the orthopterans, Stenopelmatus fuscus
Brunner (Cappucci, 1977), Stenopelmatus spp. (Poinar and Weissman,
2004), Anabrus simplex Haldeman (Thorne, 1940), Orchelimum nigripes
Scudder (May, 1919), Orchelimum vulgare Harris (May, 1919), Scudderia
furcata Brunner (May, 1919), Phaneroptera furcata (Brunner), (Thorne,
1940), Steiroxys sp. (Poinar and Weissman, 2004), Conocephalus nemoralis
(Scudder), C. fasciatus (May, 1919), Gryllus sp. (Poinar and Weissman,
2004) and the carabid, Gastrellarius honestus Say (Leidy, 1856).
Neochordodes californensis de Miralles and de Villalobos 1995 has
been reported only from California.
Neochordodes occidentalis (Montgomery 1898a) has been reported from
western North America (Chandler, 1985), including Mexico (Poinar and
Weissman, 2004). Developmental hosts include the orthopterans
Stenopelmatus spp. and Pediodectes sp. (Poinar and Weissman, 2004). Ward
and Whipple (1918) state that an acridid is also a developmental host,
while mosquito larvae served as experimental paratenic hosts in studies
by Poinar and Doelman (1974).
Parachordodes tegonotus Poinar, Rykken and Labonte (2004) has only
been reported from Oregon. Developmental hosts are the ground beetles
Pterostichus inopinus Casey, Pterostichus castaneus Dej. and
Pterostichus amethystinus Mann. (Carabidae: Coleoptera) (Fig. 2-1).
Paratenic hosts include mayfly larvae and larvae of the caddis fly,
Rhyacophila sp. (Fig. 2-3). The latter is a predator and probably
represents a secondary paratenic host, having ingested mayfly primary
Paragordius varius (Leidy 1851) occurs throughout North America
(Chandler, 1985) including Hawaii (Camerano, 1901). Developmental hosts
include the orthopterans, Gryllus sp., Gryllus assimilis (Fab.), Gryllus
pennsylvanicus and Nemobius fasciatus (DeGreer) (Montgomery, 1903;
Poinar and Weissman, 2004; Schmidt-Rhaesa et al., 2003; Ward and
Whipple, 1918). White (1969) mentions larval mayflies (Baetes spp.,
Leptophlebia sp., Ephemerella spp.), caddis flies (Brachycentrus sp.),
black flies (Simulium spp.) and corixids (Sigara sp.) as hosts for the
larvae of P. varius. Unfortunately, it is not clear whether the hairworm
larvae were developing or just encysted in these hosts. However, the
like-lihood of hairworms developing in such small hosts as blackflies is
negligible. It is possible that some of the infections, especially those
in the blackflies, were caused by mermithid nematodes. Until further
evidence to the contrary, these records are considered as representing
Pseudochordodes gordioides (Montgomery 1898a) has been reported
from Western United States (Schmidt-Rhaesa et al., 2003).
Pseudochordodes manteri Carvalho 1942 has been reported only from
Pseduochordodes taxanus Schmidt-Rhaesa et al., 2003 was described
from a cave in Texas, which is the only known locality.
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
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GEORGE POINAR JR. AND CLAY M. CHANDLER
Department of Zoology, Oregon State University, Corvallis, OR 97331
Professor Emeritus, Biology, Middle Tennessee State University,
1016 W. Cunningham St., Milan, TN 38358
TABLE 1. Species of hairworms (with synonyms) reported from North
Chordodes morgani Montgomery 1898a C. puerilis Montgomery 1898a
Gordionus densareolatus (Montgomery Parachordodes densareolatus
1898a) nov. comb (Montgomery 1898a) (Camerano,
1915) (Schmidt-Rhaesa et al.,
G. leidyi Montgomery 1898a
Gordionus lineatus (Leidy 1851) Parachordodes lineatus (Leidy
(Schmidt-Rhaesa et al., 2003) 1851) (Camerano, 1915)
Gordius lineatus Leidy 1851
Gordionus longareolatus (Montgomery Parachordodes longareolatus
1898b) (Schmidt-Rhaesa et al., 2003) (Montgomery 1898b) (Camerano,
Gordionus platycephalus (Montgomery Parachordodes platycephalus
1898a) (Schmidt-Rhaesa et al., 2003) (Montgomery 1898a) (Camerano,
Gordionus sinepilosus Schmidt-Rhaesa et
Gordionus violaceus (Baird 1853) Parachordodes violaceus (Baird
(Heinze, 1935) 1853) (Camerano, 1897)
Gordius violaceus Baird 1853
Gordius alascensis Montgomery 1907 Gordionus alascensis
(Montgomery 1907) (Schmidt-
Rhaesa et al., 2003)
(Montgomery 1907) (Chandler,
Gordius attoni Redlich 1980
Gordius difficilis Montgomery 1898a, Gordius aquaticus difficilis
(Smith, 1994) Montgomery 1898a
Gordius robustus Leidy 1851 Gordius aquaticus robustus
G. agassizi Montgomery 1898a
G. lacustris Leidy 1871
G. subspiralis Diesing 1861
G. californicus Camerano 1915
G. villoti Rosa 1881
G. fasciatus Baird 1853
G. hawaiiensis Heinze 1934
Neochordodes californensis de Miralles
& de Villalobos 1995
Neochordodes occidentalis (Montgomery Chordodes occidentalis
1898a) Montgomery 1898a
Parachordodes tegonotus Poinar et al.
Paragordius varius (Leidy 1851) Gordius varius Leidy 1851
(Camerano, 1897) G. longilobatus Leidy 1870
Chordodes varius Romer 1897
Pseudochordodes gordioides (Mongomery Chordodes gordioides Montgomery
1898a) (de Miralles et al., 1997) 1898a
(Camerano 1896) (Schmidt-
Rhaesa et al., 2003)
Pseudochordodes manteri Carvalho 1942
Pseudochordodes texanus Schmidt-Rhaesa
et al. 2003.
KEY TO THE NORTH AMERICAN HAIRWORM SPECIES
A Cuticle smooth, lacking areoles or B
with flat, smooth areoles; male
tail bilobed (as in Figs. 1-1, 2,
3), with a postcloacal or
precloacal ridge or crescent;
female tail entire--Gordiidae
May 1919--Gordius L.
A Cuticle with distinct areoles usually E
ornamented with bristles or
tubercles; male tail entire (Fig.
1-5) or if bilobed, then without a
postcloacal (Fig. 1-1) or precloacal
ridge or crescent (as in Fig. 1-3);
female tail entire or trilobed (Fig.
B Male cuticle with large white spots; Gordius attoni Redlich 1980
broad semicircular postcloacal
crescent present (Fig. 1-1); elongate
white triangular streak from neck to
anterior fourth of body in both
sexes; head tapers (spindle-shape)
B Male cuticle with or without white C
spots, lacking an elongate white
triangular streak; head variable
C Male with both a precloacal Gordius difficilis Montgomery
semicircular hairline and a 1898a, (Smith 1994)
postcloacal ridge (Fig. 1-2); areoles
present or absent on females
C Male with either a postcloacal or a D
precloacal ridge, but not both
D Male with a precloacal ridge (Fig. Gordius alascensis Montgomery
1-3) areoles confluent, 1907
D Male with a postcloacal ridge (Fig. Gordius robustus Leidy 1851
1-1); areoles absent
E Female tail trilobed (Fig. 2-2); male Paragordius varius (Leidy 1851)
tail bilobed with length of lobes
greater than twice their width (Fig.
1-4); head end obliquely truncated
E Female tail entire; male tail bilobed F
with length of lobes equal to or less
than twice their width (as in Fig.
1-1, 2, 3), or male tail entire (Fig.
F Male tail bilobed M
F Male tail entire, lobes absent or G
G Cuticle with normally one kind of H
areole--Neochordodes Carvalho 1942
G Cuticle with two or more types of J
H Areoles containing short bristles and Neochordodes occidentalis
tubercles (some specimens possess a (Montgomery 1898a,b)
smaller type of areole) (Poinar and Doelman 1974)
H Areoles lacking bristles or tubercles Neochordodes californensis
de Miralles and de Villalobos
J Areoles with prominent tubercles, Chordodes morgani (Montgomery
crowns or papillae; female cloacal 1898a)
J Areoles without prominent tubercles, K
crowns or papillae; female cloacal
K Smaller areoles with knobs on Pseudochordodes gordioides
surface; arranged randomly (Montgomery 1898a)
K Smaller areoles without knobs on L
surface, arranged in uneven rows
L Large elevated areoles in clusters of Pseudochordodes manteri
usually two Carvalho 1942
L Large elevated areoles in clusters of Pseudochordodes taxanus
three and four Schmidt-Rhaesa et al. 2003
M Areoles of two types, large Parachordodes tegonotus Poinar,
megareoles with a central pore or Rykken and LaBonte 2004
tubercle and small microareoles
lacking a pore or tubercle; broad
hair line of short simple and
branched hairs beginning anterior to
cloacal aperture but not reaching to
point of bifurcation of tail lobes
M Areoles of one (microareolar) type, N
lacking a central pore or tubercle--
N Oblique rows of single and/or O
branched hairs flanking cloacal
aperture (Fig. 1-6, 7); areoles
closely opposed, may produce
N No such hairs on lateral body surface P
flanking cloacal aperture
O Body dark brown; areoles irregularly Gordionus violaceus (Baird
polygonal, not arranged in rows, well 1853)
separated from one another by
distinct interareolar region;
interareolar spaces with small
spinules or papillate processes;
areoles not showing sexual
dimorphism; hairline on male tail not
reaching point of bifurcation of tail
lobes (Fig. 1-6); calotte white
O Body light yellow to deep buff; Gordionus lineatus (Leidy 1851)
areoles closely opposed without
intervening spaces, having a tendency
to group themselves in longitudinal
rows in males (sexual dimorphism);
hairline extending beyond point of
bifureation of tail lobes (Fig. 1-7);
calotte dark or absent
P Tubercles located behind male cloacal Q
aperture (Fig. 1-7, 8); tale lobes of
male shorter than, equal to or longer
than wide; female tail not swollen;
P No tubercles behind male cloacal Gordionus platycephalus
aperture (Fig. 1-9); tail lobes of (Montgomery 1898a)
male longer than wide; female tail
swollen; head flattened
Q Tail lobes of males short (Fig. Gordionus densareolatus
1-10), length equal to or shorter (Montgomery 1898a)
than width; black ring surrounds
cloacal aperture; postcloacal
integumentary ridge; tubercles extend
anterior to cloacal aperture; areoles
more or less confluent, tending to
merge with one another and produce
transverse rows, head usually
Q Tail lobes of males longer than wide R
(Fig. 1-11); no black ring around
cloacal aperture, postcloacal
integumentary ridge absent; tubercles
not extending anterior to cloacal
R Areoles elongated, well separated Gordionus longareolatus
from one another: few interareolar (Montgomery 1898b)
R Areoles rounded to polygonal, Gordionus sinepilosus Schmidt-
numerous bristles in interareolar Rhaesa et al. 2003