Megacepon disparatum, An & Boyko & Li, 2011

An, Jianmei, Boyko, Christopher B. & Li, Xinzheng, 2011, Two new species of the genus Megacepon George, 1947 (Crustacea: Isopoda: Bopyridae) infesting Varunidae (Crustacea: Brachyura: Grapsoidea) from China, Journal of Natural History 46 (3 - 4), pp. 131-143 : 135-142

Megacepon disparatum sp. nov.

( Figures 3 , 4 )

Material examined

Infesting Metaplax sp. ( Figure 3 ), Xinying coast, Hainan Province, 19 ◦ 53 ′ N, 109 ◦ 30 ′ E, 22 May 1955, coll. Yongliang Wang, holotype female ( CIEG550501 ), allotype male ( CIEG550502 ) .

Infesting Metaplax longipes Stimpson, 1858 , Zhejiang, Qingjiang , Stn. 2, 29 ◦ 28 ′ N, 119 ◦ 50 ′ E, 20 September 1979, coll. unknown, paratype immature female ( CIEG790901 ) and mature male ( CIEG790902 ) .

Description of holotype

Length (including uropods) 9.72 mm, maximal width across pereomere 4, 5.42 mm, head length 1.85 mm, head width 2.05 mm, pereon length 3.87 mm, pleon and uropodal length 4.00 mm, dextral distortion 35 ◦. Pereomeres distinct, but pleomeres incompletely fused. No pigmentation ( Figure 4A, B ).

Head broad anteriorly, somewhat tapered posteriorly, with narrow frontal lamina, extending around sides. Eyes lacking ( Figure 4A ). Antenna of three articles, antennule of four articles, terminal articles of each setose ( Figure 4C ). Maxilliped with straight, non-articulated, non-setose tapered palp and short plectron ( Figure 4D ). Barbula with two long falcate lateral projections on each side, outer projection slightly longer than inner one, short triangular lobe medial to lateral projections ( Figure 4E ).

Pereon distinctly segmented, broadest across pereomere 4, coxal plates absent. Dorsolateral bosses on pereomeres 1–6, last three bosses on left side fused. Small tergal projections only on first two pereomeres ( Figure 4A ). Pereomere 5 with very small indistinct mid-dorsal projection, pereomere 6 with bilobed anteriorly directed middorsal projection. Pereomere 7 recessed under pereomere 6 and lacking projection. Oostegites completely enclosing highly vaulted brood pouch ( Figure 4B ). First oostegite ( Figure 4F, G ) with ovate anterior segment and rectangular posterior segment; anterior segment smoothly rounded anteriorly with deeply angled indentation posterolaterally enclosing pereopod; digitate internal ridge with single long slender projection laterally and row of eight much smaller slender projections along margin, posterior segment with straight lateral and medial margins, posterolateral margin deeply notched and posteromedial region tapering to rounded tip. Last pair of oostegites with surface tubercles. Pereopods subequal ( Figure 4H, I ).

Pleomeres fused dorsally and segmented ventrally, segment 1 bearing prominent trifid mid-dorsal triangular projection, other pleomeres lacking projections. Five pairs of biramous pleopods and lateral plates. Digitate lateral plates shorter than exopodites, but longer than endopodites. ( Figure 4A, B ). Uniramous uropods similar to pleopods and lateral plates and longer than either pleopods or total pleon length.

Description of allotype male

Length 2.27 mm, maximal width across pereomere 3, 0.64 mm, head length 0.13 mm, head width 0.36 mm. All body segments distinct ( Figure 4J, K ).

Head rectangular, eyes lacking ( Figure 4J ). Antenna of three articles, without setae; antennule of six articles, extending beyond margins of head ( Figure 4L ).

Pereomere widths subequal, with truncate margins. Pereomeres 2–7 with prominent mid-ventral tubercles ( Figure 4K ). Pereopods subequal, smaller posterior ( Figure 4M, N ).

Pleon of six pleomeres, first four pleomeres with mid-ventral tubercles ( Figure 4K ), first five with tuberculiform pleopods, sixth pleomere produced into two symmetrical posterolateral projections, uropods lacking ( Figure 4K ).

Etymology

The Latin adjective disparatum is selected to reflect the holotype’s possession of bilobate and trifid mid-dorsal projections on pereomere 6 and pleomere 1, respectively.

Distribution and hosts

Hainan Province, China, on Metaplax sp .; Zhejiang Province on Metaplax longipes Stimpson, 1858 .

Remarks

This species is most similar to Megacepon aff. goetici sensu Bourdon and Stock (1979 , not M. goetici sensu stricto, see below) as well as to M. sheni sp. nov., described above (see Remarks for M. sheni for similarities and difference between M. disparatum and M. sheni ). Megacepon disparatum sp. nov. can be distinguished from M. aff. goetici by lack of a medial boss on pereomere 5 of the female (present in M. aff. goetici ), differently shaped oostegite 1 (lateral margins nearly parallel in M. disparatum , not parallel in M. aff. goetici , nearly right-angled notch near distal end of posterior segment in M. disparatum , lacking in M. aff. goetici ), and male with only four midventral pleonal tubercles ( M. aff. goetici with five tubercles). An immature female ( Figure 4O ) was also collected with a mature male that matches the allotype in all aspects. This female shows segmentation on the pleon that is lacking in the adult, and has only slightly developed medial projections on pereomeres 5, 6 and pleomere 2 ( Figure 4P ).

List of species and records of Megacepon George, 1947

Megacepon choprai George, 1947 sensu stricto

Sex known. Female only.

Host. Muradium tetragonum (Fabricius, 1798) (Sesarmidae) .

Locality. Madras, India.

Remarks. This description is incomplete, with most characters provided being sufficient only to identify as a bopyrid. The illustrations are very stylized and hard to interpret as indicated by Markham (2010). However, Shiino (1958) provided a clearer description of the species (see immediately below). Although George’s paper is often cited as “1946,” it was published in 1947 (as per printed notice in bound volumes of the journal).

Megacepon choprai sensu Shiino, 1958 (= M. choprai )

Sex known. Female only.

Host. Chiromantes dehaani (H. Milne Edwards, 1853) (Sesarmidae) .

Locality. Okayama, Japan.

Remarks. Shiino’s (1958) record for this species may well represent Megacepon choprai sensu stricto based on the shape of the mediodorsal bosses and the raised nature

of the dorsal ridges (lacking produced median bosses) on the female’s pereomeres. Unfortunately, neither Shiino nor George had a male specimen.

Megacepon choprai sensu Markham, 1980 (= sp. nov. A?)

Sex known. Female and male.

Host. Episesarma mederi (H. Milne Edwards, 1853) (Sesarmidae) .

Locality. Thailand.

Remarks. The females reported by Markham (1980) do not appear to be conspecific with M. choprai , because they have strong mediodorsal bosses on pleomeres 1–6 (in contrast to the more generally raised dorsal pereomeres without medial bosses on M. choprai ). Additionally, the male reported by Markham (1980) has a differently shaped head (more rectangular in shape with pointed mediolateral extensions) than otherwise reported for species of Megacepon and also a differently shaped pleotelson with moderately projected and stout posterolateral lobes. It may be that Markham’s (1980) record represents an undescribed species of Megacepon , but in the absence of males and topotypic material of M. choprai sensu stricto, it would be inadvisable to describe it at this time.

Megacepon choprai sensu Markham, 1990 (= sp. nov. A?)

Sex known. Female and male.

Host. Perisesarma maipoense (Soh, 1978) (Sesarmidae) .

Locality. Hong Kong.

Remarks. Markham (1990) did not illustrate these specimens and mentioned only some small differences between them and his earlier material ( Markham, 1980). We have no reason to think that this record is of a different taxon than that of Markham (1980), but it is very likely both records represent something other than M. choprai sensu stricto.

Megacepon choprai sensu Markham, 2010 (= sp. nov. B?)

Sex known. Female only.

Host. Perasesarma erythodactyla (Hess, 1865) ( Sesarmidae ).

Locality. Queensland, Australia.

Remarks. This record may also not represent M. choprai sensu stricto, although there are, as noted by Markham (2010), similarities between the shapes of the first oostegites, they are not identical. The general body shape of this female is different from that of either M. choprai sensu stricto or sensu Markham (1980, 1990) and there are fewer mediodorsal bosses than in the material of Markham (1980, 1990) but more than on M. choprai sensu stricto. Unfortunately, once again, no male was present. In the absence of a male, and with only a single female, it is not possible to determine if this record is representative of an undescribed species.

Megacepon goetici ( Shiino, 1934)

Sex known. Female and male.

Host. Gaetice depressus (De Haan, 1835) (Varunidae) .

Locality. Seto, Japan.

Remarks. Shiino (1958) emended the species name to “ goeticii ” but the original spelling must be maintained. While Shiino (1934) provided excellent illustrations and descriptions of many of the salient features of both males and females, he did not illustrate or described the female’s oostegite I or barbula.

Megacepon goetici sensu Shiino, 1939 (= M. goetici ?)

Sex known. Female and male.

Host. Gaetice depressus (De Haan, 1835) (Varunidae) .

Locality. Ryûkyû, Japan.

Remarks. The two records from Shiino (1939, see also immediately following) are especially problematic. If we accept the level of variability in the males reported by Shiino (1934, long distolateral pleotelson lobes, no medioventral tubercles) and Shiino (1939, nearly absent distolateral pleotelson lobes, first two pleomeres only with medioventral tubercles), then we encompass nearly all the range of variation seen in males in the genus Megacepon . Either there is more than one species parasitizing Gaetice depressus in Japan, or the males are highly polymorphic, which would make all purported species-specific characters of Megacepon males suspect. At present the females of M. goetici sensu lato do not show any corresponding degree of variation.

Megacepon goetici sensu Shiino, 1939 (= M. goetici ?)

Sex known. Female only.

Host. Macrophthalmus japonicus (De Haan, 1835) (Ocypodoidea: Macrophthalamidae).

Locality. Kyûsyû, Japan.

Remarks. The record from a Macrophthalmus host is perhaps an aberrant occurrence of the parasite on this host because of settling of the larva on the wrong host species, which may happen in bopyrids (see Boyko, 2006). No other records of Megacepon species are known to infest hosts not in the Grapsoidea.

Megacepon goetici sensu Shiino, 1958 (= M. goetici ?)

Sex known. Female and male.

Host. Gaetice depressus (De Haan, 1835) (Varunidae) .

Locality. Mie Prefecture, Japan.

Remarks. Shiino (1958) figured and discussed only the two male pleotelsons, which are much like that reported from Gaetice hosts by Shiino (1939), bearing short mediolateral projections, but with even more variability in the number of medioventral tubercles.

Megacepon goetici sensu Markham, 1982 (= M. pleopodatopus Bourdon, 1981 )

Sex known. Immature female only.

Host. Gaetice depressus (De Haan, 1835) (Varunidae) .

Locality. Hong Kong.

Remarks. This immature female presents strong mediodorsal bosses on pereomeres 5 and 6, which is unlike that seen on M. goetici sensu stricto. Comparison of Markham’s (1982) record with the description of M. pleopodatopus shows clearly that they are conspecific (identical body shape, shape of oostegite 1, barbula shape).

Megacepon aff. goetici sensu Bourdon and Stock, 1979 (= sp. nov. C?)

Sex known. Female and male.

Host. Metopograpsus oceanicus (Hombron and Jacquinot, 1846) (Grapsidae) .

Locality. 55 m, Sumbawa, Indonesia.

Remarks. This taxon is probably not conspecific with M. goetici Shiino (1934) . The female body shape, presence of mediodorsal bosses on pereomeres 5 and 6, and shape of male pleotelson are all quite different. Based on the shape of the barbula and oostegite 1, it is not conspecific with M. pleopodatopus (or any of the other species, including the two new ones described herein). However, the oostegite 1 and barbula of M. goetici sensu stricto have never been described or illustrated, so this probable new species from Indonesia should not be described until M. goetici is fully described for comparative purposes.

Megacepon sesarmae ( Pearse, 1930)

Sex known. Male only.

Host. Chiromantes dehaani (H. Milne Edwards, 1853) (Sesarmidae) .

Locality. Kuei-Chi, China.

Remarks. At best, this is a species inquirendum described by Pearse (1930) from only a male specimen. It appears most similar to M. goetici and M. pleopodatopus and could represent either species. Collection of Megacepon material from topotypic hosts is needed to resolve the question of its identity.

Megacepon pleopodatopus Bourdon, 1981

Sex known. Female and male.

Host. Varuna litterata (Fabricius, 1798) (Varunidae) .

Locality. Sumba, Indonesia.

Remarks. Although Bourdon (1981) questionably placed this species in the genus, it is either a good species of Megacepon or a junior synonym of M. goetici . It is not conspecific with any of the other species in the genus, and not with M. aff. goetici sensu Bourdon and Stock (1979) . A full description of M. goetici , including oostegite 1 and barbula shape is required to decide the status of M. pleopodatopus .

Megacepon sheni sp. nov.

Sex known. Female and male.

Host. Metaplax sheni Gordon, 1931 (Varunidae) .

Locality. Hainan Province, China.

Remarks. See above under the species description.

Megacepon disparatum sp. nov.

Sex known. Female and male.

Host. Metaplax longipes Stimpson, 1858 (Varunidae) .

Locality. Hainan Province, China.

Remarks. See above under the species description.

Figures

Figure 3. Metaplax longipes Stimpson, 1858 showing bulge produced by Megacepon disparatum sp. nov., in right branchial chamber (arrow pointing to infesting chamber). Scale bar 1 cm.

Figure 4. Megacepon disparatum sp. nov. Holotype female (A–I): (A) dorsal view; (B) ventral view; (C) left antenna and antennule; (D) right maxilliped, external view; (E) right side of barbula; (F) right oostegite 1, external view; (G) right oostegite 1, internal view; (H) right pereopod 1; (I) right pereopod 7. Allotype male (J–N): (J) dorsal view; (K) ventral view; (L) left antennae; (M) left pereopod 2; (N) left pereopod 6. Immature paratype female (O, P): (O) dorsal view; (P) lateral view of peron and pleon (showing medial projections on pereomeres 5, 6 and pleomere 2). Scale bars: 1 mm (A, B); 0.13 mm (C, L, M, N); 0.40 mm (D, E); 0.57 mm (F–I); 0.26 mm (J, K); 0.67 mm (O), 0.44 mm (P).