Mappates plataxus Rangnekar 1958

Mappates plataxus Rangnekar, 1958

(Fig. 72)

Material examined. 15♀♀ from Platax teira (Forsskål, 1775) (TC16981) 11 January 2016, 8 ♀♀ QM Reg. No. W53127, 7♀♀ NHMUK Reg. Nos 2017.346–352.

Site on host. Attached at mid-length of gill filaments on lateral faces between adjacent filaments.

Differential diagnosis. Cephalothorax elongate (about 1.5 times longer than maximum width), covered by dorsoventrally flattened cephalothoracic shield with marked lateral sutures in anterior third (Fig. 72A); thoracic zone of shield enlarged, completely concealing fourth pedigerous somite and anterior half of genital complex in dorsal view: frontal plates and lateral margins with well-developed marginal membranes; frontal plates without lunules. Genital complex broad, more than twice as wide as long; bearing well defined fifth legs at posterolateral corners (Fig. 72B); leg comprising outer protopodal seta plus exopodal segment bearing 3 plumose setae. Abdomen vestigial, largely incorporated into posterior surface of genital complex. Caudal rami located either side of anal slit on posterior margin. Antenna with posterior process on proximal segment (Fig. 72C). Post-antennal process lacking tine; associated papillae unisensillate. Maxillule with posterior process enlarged to form flattened lobe with rounded apex (Fig. 72C). Maxilliped with smooth myxal margin and large subchela. Sternal furca absent. Leg 1 with vestigial endopod; distal exopodal segment of leg 1 with 3 plumose setae on posterior margin; distal margin spine 1 longer than spine 2; spines 2 and 3 each with accessory process; seta 4 originating on surface of segment, about as long as spine 3. Leg 2 with 3-segmented rami; outer margin spines on exopodal segments 1 and 2 aligned with long axis of ramus. Leg 3 with 2-segmented rami; first exopodal segment bearing large recurved spine, lacking inner seta (Fig. 72D): compound distal segment bearing 3 spines and 4 setae in total: first endopodal segment unarmed, expanded to form small velum, compound distal segment bearing 3 plumose setae (Fig. 72E). Leg 4 uniramous, 2-segmented (Fig. 72F); exopodal segment compound, bearing 5 subequal spines distally. Mean body length of female 3.34 mm, range 3.18 to 3.49 mm (based on 10 specimens).

Remarks. The female of M. plataxus was redescribed in detail by Dojiri & Ho (2013) but the male is still unknown. It is a distinctive species with its elongate dorsal cephalothoracic shield marked with a characteristic pattern of sutures, the lack of a sternal furca, and the flattened lobate form of the posterior process of the maxillule. A second species of Mappates, M. alter Kabata, 1964, was established by Kabata (1964b) based on material from an ephippid fish host, Zabidius novenaculeatus (McCulloch, 1916) (as Platax novenaculeatus) caught off Heron Island, Queensland. The two species can be readily distinguished by the size of the posterior zone of the dorsal cephalothoracic shield which completely conceals the genital complex and abdomen in dorsal view in M. alter whereas in M. plataxus the genital complex extends well beyond the posterior margin of the cephalothoracic shield.

Although M. plataxus is known from India (Rangnekar, 1958; Pillai, 1985) and Sri Lanka (Kirtisinghe, 1964) across to Taiwan (Ho & Lin, 2004), this is the first record from Australia. In Moreton Bay it occurred on the type host Platax teira, but elsewhere it has been reported from Platax orbicularis (Forsskål, 1775) (Ephippidae) (Ho & Lin, 2004) and Drepane punctata (Linnaeus, 1758) (Drepaneidae) (Prabha & Pillai, 1983).