Mediomastus hanedaensis, Tomioka, Shinri, Nishi, Eijiroh & Kajihara, Hiroshi, 2014

Tomioka, Shinri, Nishi, Eijiroh & Kajihara, Hiroshi, 2014, Two new species of Mediomastus (Annelida, Capitellidae) from Tokyo Bay, Japan, ZooKeys 422, pp. 115-126: 121-122

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Mediomastus hanedaensis

sp. n.

Taxon classification Animalia Scolecida Capitellidae

Mediomastus hanedaensis   sp. n. Figs 7-11

Material examined.

Holotype: CBM-ZW 1095, Haneda, Tokyo Bay, St. 07s-L4e-1-c, 35.52949905°N, 139.7836609°E, incomplete. Paratypes (two specimens): CBM-ZW 1096, same collection site as holotype, incomplete, mounted on SEM stub; CBM-ZW 1097, same collection site as holotype, incomplete, cut into 5 portions, all mounted on two slides. All specimens collected spring 2007.


Holotype incomplete, with 27 segments, sex uncertain; 16.2 mm in length; 1.33 mm in maximum width. Body color whitish yellow in ethanol. Epithelium smooth. Nephridiopores lacking. Branchiae absent. All segments cylindrical.

Prostomium (Fig. 7A) conical, with short palpode; eversible proboscis with numerous minute papillae. Peristomium 1.2 times as wide as long, slightly longer than chaetiger 1, without eyespot, achaetigerous.

Thoracic chaetigers biannulate. Thin, unilimbate, capillary chaetae with narrow wing (Figs 8A, 9A) present on chaetigers 1-4; noto- and neurochaetae each 8-13 in number per fascicle (Fig. 8A). Chaetigers 5-10 with hooded hooks, but without paddle-like chaetae. Notopodial hooded hooks (Figs 8B, 9B) with short, blunt fang and 6 teeth (Fig. 9B); hood with small opening (Fig. 8B); shaft not constricted (Fig. 9B); shoulder indistinct (Fig. 9B); 6-8 hooks per fascicle (Fig. 8B). Neuropodial hooded hooks (Figs 8C, 9C) with short, stout fang and 7 teeth (Fig. 9C); hood with small opening (Fig. 8C); shaft without constriction (Fig. 9C); shoulder indistinct (Fig. 9C); 4-7 hooks per fascicle (Fig. 8C).

Abdominal segments 2.5 times as wide as long (Fig. 7B), with hooded hooks only. Hooded hooks with long fang and 3 teeth (Figs 8D, 9D); fangs in abdominal hooks longer and sharper than those in thoracic hooks; opening of hood wider than that of thoracic hooks; shaft with distinct constriction (Fig. 9D); 2-5 hooks per fascicle (Fig. 8D).

Transition from thorax to abdomen marked by alteration in shape of segments (longer in abdomen), shape of shaft of hooded hooks (with constriction in abdominal hooks), and length of fang of hooded hooks (longer in abdominal hooks).

Methyl-green staining.

Among the three specimens observed, methyl-green staining resulted in three patterns (Fig. 10). Numerous minute spots sparsely and uniformly covered segments 5-9, 7-10, or 8-10; segment 10 (Fig. 10A) or 11 (Fig. 10B, C) with denser spots. Figure 11 shows the stained worm diagrammed in Fig. 10A.


The specific name is an adjective, referring to the type locality.


Mediomastus hanedaensis   is similar to Mediomastus warrenae   in the shape of the thoracic hooded hooks, but differs from the latter in the staining pattern with methyl green (segments 8 and 9 uniformly spotted in Mediomastus hanedaensis   vs. post-chaetally spotted in Mediomastus warrenae   ) and in the shape of the thoracic capillary chaetae (unilimbate in Mediomastus hanedaensis   vs. bilimbate in Mediomastus warrenae   ).