Digenea, C. Agardh, 1822

McDermott, John J., 2011, Parasites of shore crabs in the genus Hemigrapsus (Decapoda: Brachyura: Varunidae) and their status in crabs geographically displaced: a review, Journal of Natural History 45 (39 - 40), pp. 2419-2441 : 2425-2426

Infraclass DIGENEA

Bridgman (1971) described a new trematode species Maritrema setoenensis (Microphallidae) based on metacercariae encysted in the hepatopancreas of intertidal specimens of H. penicillatus and H. sanguineus from the coast of Japan ( Table 2). Macrophthalmus dilitatus (de Haan, 1835) (Macrophthalmidae) from the same location was also infected. Both varunids were heavily parasitized, with prevalences from 73 to 92% ( Bridgman 1971; Bridgman et al. 1972). Intensities in H. sanguineus ranged from 1 to 50 cysts per crab. In some coastal areas, however, this species was devoid of infections. The first intermediate host was Littorina brevicula Philippi, 1844 , with parasite prevalences from 3 to 8%. Adult flukes were found in the small intestine of the Curlew, Numenius madagascariensis Linnaeus, 1766 .

Another intertidal microphallid, Maritrema novaezealandensis , uses H. crenulatus and H. sexdentatus as second intermediate hosts in New Zealand ( Table 2). Prevalences and mean intensities of metacercariae in each of these two crabs from Otago Harbour were 98% and ∼ 40 cysts per crab ( Koehler and Poulin 2010). Another varunid, Cyclograpsus levauxi H. Milne Edwards, 1853 , from the same locality had a prevalence of 27% and mean intensity of ∼ 1, whereas specimens of the varunid, Austrohelice crassa (Dana, 1851) were uninfected. Additionally, two other intertidal species from different families, Macrophthalmus hirtipes (Hombron and Jacquinot, 1846) and Halicarcinus varius (Dana, 1851; Hymenostomatidae), had prevalences of 100% and intensities of 154 and 199, respectively. Halicarcinus whitei (Miers, 1876) is also a host for Maritrema novaezealandensis , in Otago Harbour ( Martorelli et al. 2004).

Further evidence of the non-specificity of Maritrema novaezealandensis were infections of two amphipods, an isopod and a stomatopod at prevalences ranging from 43 to 82% with relatively low intensities in these small hosts (∼ 14–15) ( Koehler and Poulin 2010); some mortality occurred ( Leung et al. 2009). The first intermediate host of Maritrema novaezealandensis is the prosobranch Zeacumantus subcarinatus (Sowerby, 1855) , and its definitive host is the Red-billed gull Larus novaehollandiae scopulinus (Forster, 1844) .

Koehler and Poulin (2010) recovered an unidentified Microphallus sp. from H. crenulatus and H. sexdentatus (40 and 94% prevalence and 68 and 150 intensity, respectively) and two other varunids as well as Macrophthalmus hirtipes , but none from H. varius . Other non-brachyuran crustaceans were not infected. This metacercaria likely originated from the cercariae described by Martorelli et al. (2008) from Zeacumantus subcarinatus .

The seven other microphallid trematodes listed in Table 2 were all identified from H. penicillatus and/or H. sanguineus collected in Japan or Korea. Levinseniella conicostoma , Probolocoryphe acadai and Microphalloides japonicus also infected several other grapsid crabs ( Otagaki 1958a, b; Bridgman et al. 1972). Kifune and Takao (1972) recorded prevalences of 28.4, 19.6 and 59.8% in H. penicillatus for Levinseniella conicostoma , Maritrema longiforme and Spleotrema macrorchis , respectively. Maximum intensity for Maritrema longiforme infections was 20 and for Spleotrema macrorchis was 118.