Apatemon

Hechinger, Ryan F., 2012, Faunal survey and identification key for the trematodes (Platyhelminthes: Digenea) infecting Potamopyrgus antipodarum (Gastropoda: Hydrobiidae) as first intermediate host, Zootaxa 3418, pp. 1-27 : 6-7

Apatemon sp. I

(1. Apa1; Figs. 1 , 2–3 )

Stages: sporocysts (daughter) and cercariae

Host: Potamopyrgus antipodarum

Site in host: Sporocysts primarily in mantle, but also in digestive gland and basal visceral mass

Voucher localities: Mohaka River, North Island, New Zealand (-39.0805o lat, 177.1403o long); Mataura River, South Island (-46.3894o lat, 168.7968o long)

Prevalence: 2% (n = 100) at Mohaka River; 1% (n = 100) at Mataura River

Specimens deposited: USNPC #s: 105672-105674.

Diagnosis: Sporocysts active, opaque, elongate (at least 10:1 length:width). Length ~2000. Developing cercariae appear to number over 100.

Cercaria non-oculate, longifurcate (tail fork length> 1/2 tail stem), pharyngeate, with anterior organ (modified oral sucker), and ventral sucker (a "Strigea cercaria"). Body length ~130. Tail stem and fork length about equal to each other and to body length.

Descriptive notes: Cercaria tail stem with transverse tegmental annulations, central excretory vessel surrounded by about 6–7 pairs of large “caudal bodies” (over ¼ tail width) [caudal bodies contain glycogen stores ( Ginetsinskaya 1968)]. Anterior organ length 1/4 to 1/3 body length. Ventral sucker just post-equatorial, smaller (~ 1/3 the area) than the anterior organ (the modified oral sucker). Excretory bladder, small, V-shaped.

Remarks: I believe that this trematode corresponds to Winterbourn’s “F1”, despite his reporting the cercarial tail stem to be relatively much shorter (half the body length instead of approximately equal length) and the sporocysts to have a length:width ratio of only about 4:1, versus 10:1. Winterbourn appears to have had very little material to examine and the specimen he measured may not represent the typical condition.

I had recognized this trematode as likely belonging to the Strigeidae or the Diplostomidae (both within the superfamily Diplostomoidea). Dr. Bronwen Presswell (University of Otago) recently informed me that it is, indeed, one or more species of the strigeid genus, Apatemon (personal communication). She has a manuscript in preparation documenting this, and that it uses small fishes as second intermediate hosts and ducks as final hosts.

Figures

FIGURE 1. General characteristics of the parthenitae and cercariae of the trematodes infecting Potamopyrgus antipodarum as first intermediate host. Microphallus sp. “ livelyi ” (sp. 13), whose embryos develop directly to metacercariae, is not figured. Species numbers and codes follow Table 1 and species accounts. Cercariae are all to scale, with additional magnified views of three small cercariae (indicated by dashed lines). Parthenitae are not to scale. Scale bars consistently indicate 100 µm.

FIGURES 2 – 3. Apatemon sp. I. 2, Sporocyst with developing cercariae. Scale bar = 100. Numerical scale division = 25. 3, Cercaria. Scale bar = 100. Numerical scale division = 5.