Phyllodurus undetermined

Phyllodurus sp. (Fig. 1) Phyllodurus sp. Itani et al., 2002: 70–76, fig. 1 (Amami-Oshima Island, Kagoshima Prefecture, Japan, infesting Upogebia carinicauda (Stimpson, 1860)); Itani, 2004a: 21 (mention); Itani, 2004b: 37–40 (Japan, infesting U. carinicauda); Markham, 2005: 93 (mention); Hong, 2013: 337 (mention); Itani et al., 2014: 111 (mention); Uyeno & Iseto, 2021: 28 (list). Material Examined: Japan: Mature male (7.7 mm) (SMF 62931), infesting branchial chamber of female Upogebia yokoyai Markarov, 1938 (ca. 58 mm TL, rostrum broken), Yoshino-gawa, Tokushima city, Tokushima, coll. K. Sakai, 7 Sep 1982 (SMF 30513). Hosts: Upogebia carinicauda (Stimpson, 1860) and U. yokoyai Makarov, 1938. Description: Mature male (SMF 62931): Body (Fig. 1A, B) elongate, unpigmented, distinctly segmented dorsally, ventrally and laterally, symmetrical, total length 7.7 mm, maximal width at third pereomere, 2.5 mm (Fig. 1A). Head ovate, distinct from first pereomere, approximately 2.8 times as wide as long; anterolateral margin depressed relative to posterior region of head, posterolateral corners rounded; eyes absent (Fig. 1A). Antennule and antenna of 3 and 5 articles, respectively (Fig. 1C); antenna approximately 3 times longer than antennule; antennule with tufts of setae at distal end of articles 2 and 3; antennae with setae on distal margin of article 2 and tuft of setae on distal margins of articles 3–5; antennae extending beyond distal margin of head (Fig. 1A, B). Maxillipeds present, composed of two ovate segments apparently lacking terminal setae (Fig. 1C). Pereomeres separated, directed and tapered laterally; 1–4 more or less rounded laterally, 5–7 with acute tips (Fig. 1A); midventral tubercles absent (Fig. 1B). Pereopods 1 with elongate dactylus (¾ as long as propodus), stout ischium (¾ as long as propodus) and stout basis (subequal in length to propodus) (Fig. 1D); pereopods 2–7 with short dactylus (ca. ½ as long as propodus), elongate ischium (subequal in length to propodus) and elongate basis (1.5x as long as propodus) (Fig. 1E); scales present on ventral border of propodus of pereopods 1–7; all pereopods with raised ridge at distoventral margin of propodus for insertion of dactylus tip (Fig. 1E); dactylus of pereopod 1 overreaching raised ridge (Fig. 1D). Pleon (Fig. 1F) of five segments plus pleotelson; shorter than pereon; pleomeres progressively narrower posteriorly, distinctly separated, lateral margins of pleomeres 1–3 with pointed tips; 4–6 with rounded tips; pleomeres 1–3 extended laterally, 4 and 5 extended posterolaterally; midventral tubercles absent; pleopods absent; pleotelson with setose posterolateral margins and second tuft of setae mediolaterally (Fig. 1F); uropods and anal cone absent. Remarks: Itani et al. (2002) first reported on “an undescribed species” of Phyllodurus and stated that “taxonomic work is in progress.” However, no description or images of these specimens or any other Japanese specimens assigned to this genus have since been published. The only other species in the genus, P. abdominalis Stimpson, 1857, has a wide range on the Pacific coast of North America from southern British Columbia, Canada, to Sinaloa, Mexico (Markham 1977, 2005) but has not been documented from Japan or surrounding waters. We concur with Markham (2005) that it cannot be assumed that the specimens from Japan represent a new species without full description and illustration of specimens and comparison with P. abdominalis. Given the situation with Orthione griffenis Markham, 2004 being introduced from Asia to North America, the reverse could be true of the Japanese Phyllodurus sp. Unfortunately, we only have a male to examine and, while P. abdominalis has been reasonably well described (e.g., Markham 1977), neither sex has ever been completely illustrated. A comparison of the present male from Japan with the descriptions of males from North America (e.g., Richardson 1905; Markham 1977) shows that the shape of the pereomeres and pleomeres does appear to differ but a comparison with fully illustrated female and male specimens is required to make any conclusions on the status of the Japanese Phyllodurus sp. Although female and male specimens of P. abdominalis and other specimens of the Japanese species are normally found attached to pleopods on the ventral surface of the host abdomen (Itani 2002), the present male was in the branchial chamber, as can be seen from the gill fragments still attached to some of the pereopods. If the parasites of U. carinicauda and U. yokoyai are conspecific, then U. yokoyai is a new host for Phyllodurus sp. Sakai (2006: 144) listed SMF 30513 as containing one male (9.8 mm CL, four ovigerous female (14–14.9 mm CL) and one female U. yokoyai (broken rostrum, ca. 58 mm TL), but made no mention of the male Phyllodurus sp.

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