''Aonchotheca forresteri'' is a

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...

nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-Parasitism, parasitic nematodes also known as eelworms. They are a diverse animal phylum inhab ...

that infects the

marsh rice rat The marsh rice rat (''Oryzomys palustris'') is a semiaquatic North American rodent in the family Cricetidae. It usually occurs in wetland habitats, such as swamps and salt marshes. It is found mostly in the eastern and southern United States, fr ...

(''Oryzomys palustris'') in

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...

. Occurring mainly in adults, it inhabits the stomach. It is much more common during the wet season, perhaps because its unknown

intermediate host In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' (symbiont). The guest is typically provided with nourishment and shelter. Examples include a ...

is an

earthworm An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. Th ...

that only emerges when it rains. The worm was discovered in 1970 and formally described in 1987. Originally classified in the genus ''

Capillaria ''Capillaria'' ( hu, Capillária, 1921) is a fantasy novel by Hungarian author Frigyes Karinthy, which depicts an undersea world inhabited exclusively by women, recounts, in a satirical vein reminiscent of the style of Jonathan Swift, the firs ...

'', it was reclassified in '' Aonchotheca'' in 1999. ''A. forresteri'' is small and narrow-bodied, with a length of 13.8 to 19.4 mm in females and 6.8 to 9.2 mm in males. Similar species such as '' A. putorii'' differ in features of the alae and

spicule Spicules are any of various small needle-like anatomical structures occurring in organisms Spicule may also refer to: *Spicule (sponge), small skeletal elements of sea sponges *Spicule (nematode), reproductive structures found in male nematodes ( ...

(organs in the male), the size of the female, and the texture of the eggs.

Taxonomy

''Aonchotheca forresteri'' was discovered during a survey of the endoparasites of Florida

s (''Oryzomys palustris'') by John Kinsella from 1970 to 1972,Forrester, 1992, p. 100 and is one of several new parasite species in this study, which was done because there were no previous comprehensive studies of the endoparasites of the species. Together with Danny Pence, Kinsella described the worm in a 1987 paper as ''Capillaria forresteri''; the

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

honors Donald J. Forrester of the College of Veterinary Medicine,

University of Florida The University of Florida (Florida or UF) is a public land-grant research university in Gainesville, Florida. It is a senior member of the State University System of Florida, traces its origins to 1853, and has operated continuously on its ...

. Kinsella and Pence described it as one of many species of ''

'', a large and

taxonomically In biology, taxonomy () is the scientific study of naming, defining ( circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxa (singular: taxon) and these groups are given ...

difficult genus. They suggested that it may be closest to some other small species that live in the digestive systems of mammals, such as the very similar '' C. putorii'', which is found in a variety of

carnivora Carnivora is a Clade, monophyletic order of Placentalia, placental mammals consisting of the most recent common ancestor of all felidae, cat-like and canidae, dog-like animals, and all descendants of that ancestor. Members of this group are f ...

ns in North America and Europe.Kinsella and Pence, 1987, p. 1295 In 1982, Moravec had placed ''Capillaria putorii'' and a number of related species in a separate genus, '' Aonchotheca'', and in 1999 Pisanu and Bain transferred ''Capillaria forresteri'' and various other species to that genus from ''Capillaria''. Thus, the species is now known as ''Aonchotheca forresteri''.

Description

''Aonchotheca forresteri'' is a small, narrow-bodied worm. It is narrowest at the front and increases in width to about three fourths of its length. The

cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...

, the surface layer, is smooth. Females are 13.8 to 19.4 mm long, averaging 16.9 mm, which makes them substantially longer than female ''A. putorii'', and 55 to 70 (average 62) μm wide. The eggs are smooth, lacking the elaborate pattern on the surface seen in ''A. putorii'', and are 53 to 58 (54) μm long and 21 to 24 (21) μm broad. The

esophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...

, the frontmost part of the digestive system, is 2.9 to 3.9 (3.6) mm long and is lined by 36 to 45 (40) cells known as

stichocyte Stichocytes are glandular unicellular cells arranged in a row along the posterior portion of the oesophagus, each of which communicates by a single pore with the lumen of the oesophagus. They contain mitochondria, rough endoplasmic reticulum, abund ...

s. The

vulva The vulva (plural: vulvas or vulvae; derived from Latin for wrapper or covering) consists of the external sex organ, female sex organs. The vulva includes the mons pubis (or mons veneris), labia majora, labia minora, clitoris, bulb of vestibu ...

is located 66 to 105 (83) μm behind the end of the esophagus and the

anus The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, d ...

is near the end of the worm, which is rounded. At 6.8 to 9.2 (7.7) mm, males are only about half as long as females. Their maximum width is 34 to 42 (37) μm. The length of the esophagus is 2.3 to 3.0 (2.6) mm, of which the muscular pharynx makes up 260 to 315 (273) μm, and is lined by 35 to 42 (37) stichocytes. The back region of the worm is 4.5 to 6.2 (5.1) mm long. The back, or rectal, opening of the digestive tube is located near the end of the worm, and the length of the

cloaca In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, a ...

is 530 to 576 (550) μm. Near the back end, there are two alae (ridges) at the sides (laterally), which are 40 to 55 (46) μm long; these are located at 10 to 15 μm from another, small ala at the tip. In ''A. putorii'', the lateral alae are much longer and reach the ala at the tip. The spicule, a spikelike structure that functions in reproduction, is curved at the tip and hardened and has a length of 380 to 426 (406) μm. It is smaller than that of the similar '' A. tamiasstriati'' from North American

chipmunk Chipmunks are small, striped rodents of the family Sciuridae. Chipmunks are found in North America, with the exception of the Siberian chipmunk which is found primarily in Asia. Taxonomy and systematics Chipmunks may be classified either as ...

s and larger than that of '' A. murissylvatici'' from various North American and European small rodents, but about as long as that of ''A. putorii'', which however lacks the curved tip.Kinsella and Pence, 1987, p. 1295; Pisanu and Bain, 1999, pp. 21, 23

Distribution and ecology

Marsh rice rats from

Paynes Prairie Paynes Prairie Preserve State Park is a Florida State Park, encompassing a savanna in Alachua County, Florida lying between Micanopy and Gainesville. It is also a U.S. National Natural Landmark. It is crossed by both I-75 and U.S. 441 (which ha ...

Alachua County Alachua County ( ) is a county in the north central portion of the U.S. state of Florida. As of the 2020 census, the population was 278,468. The county seat is Gainesville, the home of the University of Florida since 1906, when the campus ope ...

;

Cedar Key Cedar Key is a city in Levy County, Florida, United States. The population was 702 at the 2010 census. The Cedar Keys are a cluster of islands near the mainland. Most of the developed area of the city has been on Way Key since the end of the 19th ...

Levy County Levy County is a county located on the Gulf coast and in the northern part of the U.S. state of Florida. As of the 2020 census, the population was 42,915. Its county seat is Bronson. History Levy County was created in 1845, after the Seminol ...

; and

Lake Istokpoga Lake Istokpoga is a freshwater lake in Highlands County, Florida. It is fed by two creeks, Arbuckle Creek and Josephine Creek. The oblong-shaped lake is approximately wide by long. It is considered the fifth largest lake in the state of Fl ...

Highlands County Highlands County is a county located in the Florida Heartland region of the U.S. state of Florida. As of the 2020 census, the population was 101,235. Its county seat is Sebring. Highlands County comprises the Sebring-Avon Park, FL Metropolita ...

, all in Florida, have yielded ''A. forresteri''. In Paynes Prairie, the type locality, 82 of 178 animals examined were infected with 1 to 50 (average 10) worms, but in Cedar Key only a single rat contained one worm. The worms were found in the front part, or fundus, of the stomach, with their front ends in the fundal tissue and their back ends projecting into the inside. In Paynes Prairie, there was no significant difference in rate of infection between males and females, but only 4% of juveniles were infected, compared to 52% of adults. Most species of ''Capillaria'' occur in multiple hosts, but ''A. forresteri'' has been found only in the marsh rice rat, even though several other small mammals (the round-tailed muskrat, ''Neofiber alleni'';

cotton mouse The cotton mouse (''Peromyscus gossypinus'') is a species of rodent in the family Cricetidae found in the woodlands of the US South. Description Adults are about long, with a tail around , and weigh 34-51 g. Its general appearance is very si ...

, ''Peromyscus gossypinus'';

hispid cotton rat The hispid cotton rat (''Sigmodon hispidus'') is a rodent species long thought to occur in parts of South America, Central America, and southern North America. However, recent taxonomic revisions, based on mitochondrial DNA sequence data, have ...

, ''Sigmodon hispidus''; and

marsh rabbit The marsh rabbit (''Sylvilagus palustris'') is a small cottontail rabbit found in marshes and swamps of coastal regions of the Eastern and Southern United States. It is a strong swimmer and found only near regions of water. It is similar in app ...

, ''Sylvilagus palustris'') occur in Paynes Prairie. The rice rat eats more animal food than any of those, and perhaps ''A. forresteri'' has an

that is not eaten by the other species.Kinsella and Pence, 1987, p. 1297 ''A. forresteri'' is markedly more prevalent in the wet season (spring) than the dry season (autumn), perhaps because rainfall patterns influence the habits of the rice rat in some way. One possibility is that the intermediate host is an

or other

oligochaete Oligochaeta () is a subclass of animals in the phylum Annelida, which is made up of many types of aquatic and terrestrial worms, including all of the various earthworms. Specifically, oligochaetes comprise the terrestrial megadrile earthworms ...

worm that moves to the surface when it rains.

References

Literature cited

*Forrester, D.J. 1992
Parasites and diseases of wild mammals in Florida
University of Press of Florida, 459 pp. *Kinsella, J.M. 1988. Comparison of helminths of rice rats, ''Oryzomys palustris'', from freshwater and saltwater marshes in Florida. Proceedings of the Helminthological Society of Washington 55(2):275–280. *Kinsella, J.M. and Pence, D.B. 1987
Description of ''Capillaria forresteri'' sp. n. (Nematoda: Trichuridae) from the rice rat ''Oryzomys palustris'' in Florida, with notes on its ecology and seasonal variation
(subscription required). Canadian Journal of Zoology 65(5):1294–1297. *Pisanu, B. and Bain, O. 1999
''Aonchotheca musimon'' n. sp. (Nematoda: Capillariinae) from the mouflon ''Ovis musimon'' in the sub-Antarctic Kerguelen archipelago, with comments on the relationships with ''A. bilobata'' (Bhalerao, 1933) Moravec, 1982 and other species of the genus
(subscription required). Systematic Parasitology 43(1):17–27. {{Taxonbar, from=Q4778685 Nematodes described in 1987 Enoplea Parasitic nematodes of mammals Parasites of rodents