Australian Amphipoda: Melitae

J.K. Lowry, P.B Berents & R.T. Springthorpe

Parelasmopus sowpigensis Lowry & Springthorpe

Type material. HOLOTYPE: male, 8.9 mm, AM P60496. PARATYPES: female, 7.1 mm, AM P60497; 3 males, 13 females, AM P60498; 13 males, 8 females, AM P60499.

Type locality. Sow and Pigs Reef, Port Jackson, New South Wales (33º 30'S 151º 16'E), shelley sand, 5 m depth.

Description. Based on holotype male, AM P60496 and paratype female, AM P60497. Head lateral cephalic lobes broad, rounded, with anteroventral notch or slit, anteroventral corner with acute/subacute tooth. Antenna 1 longer than antenna 2; peduncular article 1 not geniculate with article 2, subequal in length to article 2, with 4 or more robust setae along posterior margin; flagellum with 22 articles; accessory flagellum with 4 articles. Antenna 2 peduncular article 2 cone gland reaching at least to end of peduncular article 3; article 4 longer than article 5, or article 4 subequal to article 5; flagellum with 6 articles. Mandible palp present, well developed, article 3 rectolinear, setose on distomedial margin, subequal to article 1 or shorter than article 1, article 2 shorter than article 3, article 1 curved, swollen distally, longer than article 2, at least 3 x as long as broad. Maxilla 1 inner plate with setae mainly terminal.

Pereon. Gnathopod 1 not sexually dimorphic; coxa anteroventral corner not produced, coxa posteroventral corner notch absent; merus without posterodistal tooth; carpus about 2 x as long as broad; propodus without anterodistal projection, posterodistal margin not swollen, palm acute, convex, without posterodistal corner, defined by posterodistal robust setae. Gnathopod 2 sexually dimorphic; subchelate; left and right gnathopods subequal in size; coxa posteroventral corner notch absent; merus with sharp posteroventral tooth; carpus short; propodus without medial depression, without strong concentration of setae, palm nearly transverse, straight, smooth, with group of anterodistal robust setae, defined by posterodistal robust setae, without posteroventral corner; dactylus closing along palm, reaching end of palm, apically blunt. Peraeopod 5 basis posterior margin straight. Peraeopod 5 basis posteroventral corner narrowly rounded or subquadrate. Peraeopod 6 coxa anterior lobe ventral margin slightly produced, rounded. Peraeopod 6 basis posterior margin concave (slighlty). Peraeopod 6 basis posteroventral corner broadly rounded, or narrowly rounded or subquadrate. Peraeopod 6 propodus not expanded posterodistally. Peraeopod 7 basis posterior margin straight. Peraeopod 7 basis with posterior margin smooth or minutely castelloserrate, posteroventral corner narrowly rounded or subquadrate. Peraeopod 7 propodus not expanded posterodistally.

Pleon. Pleonite 1 without dorsal serrations, without dorsodistal spines, not dorsally bicarinate. Pleonite 2 without dorsal serrations, without dorsodistal spines, not dorsally bicarinate. Pleonite 3 without dorsal serrations, without dorsodistal spines, dorsally smooth. Epimeron 1 anteroventral corner without curved spine. Epimera 1-2 posteroventral margin without spines above posteroventral corner. Epimeron 3 posterior margin smooth, posteroventral corner with small acute spine, posteroventral margin smooth. Urosomite 1 without dorsal carina, without a small dorsal hump, without dorsal serrations, without spines or gape, dorsally bicarinate. Urosomite 1 without posterodorsal spine. Urosomite 2 posterior margin smooth, without dorsolateral robust setae. Urosomite 3 without dorsal robust setae. Uropod 1 peduncle with basofacial robust seta, without distoventral spur. Uropod 3 subequal or slightly exceeding length of uropods 1 and 2; inner ramus subequal in length to outer ramus; outer ramus medium length (1.1 to about 1.5 x longer than peducle), 1-articulate. Telson cleft. Telson without robust setae on inner margins. Telson each lobe with 3 or more apical/subapical robust setae, apical conical extension reaching scarcely one third along longest seta.

Habitat. Marine.

Depth zone. Littoral (5 m).

Remarks. This species fits Parelasmopus because of the highly distinctive mandibular palp with its very long first article and very short second article, but it differs in not have a serrate posteroventral margin on epimeron 3, nor does it have dorsally bicarinate first and second pleonites. J.L. Barnard (1972a) established Ifalukia for one species of Parelasmopus which lacked dorsal carinae on the pleonites and urosomites, and lacked posteroventral serrations on epimeron 3. Parelasmopus sowpigensis is most similar to Ifalukia, but differs in having a dorsally bicarinate first urosomite. It therefore strictly fits neither genus. If the mandibular palp is a synapomorphy defining Parelasmopus, then it appears that some species in the complex have either lost or never had dorsal carinae or serrate ventral margins. Until the phylognetic implications of these questions can be analysed it is best to maintain a broad concept of the genus.

Parelasmopus sowpignensis is therefore a distinctive species differing from other Australian species in having dorsally smooth first and second pleonites and smooth ventral margins on epimeron 3.

Distribution. New South Wales: Sow and Pigs Reef, Port Jackson (AM).

Australian geographic areas. South-eastern Australia.

Type material. HOLOTYPE: male, AM P60496. PARATYPES: female, AM P60497; 3 males, 13 females, AM P60498; 13 males, 8 females, AM P60499.

Pereon. Gnathopod 2 carpus long; palm acute, convex, lined with robust setae, defined by posteroventral corner; apically acute/subacute.

Pleon. Habitat. shelley sand.

Remarks. This species fits Parelasmopus because of the highly distinctive mandibular palp with its very long first article and very short second article, but it differs in not have a serrate posteroventral margin on epimeron 3, nor does it have dorsally bicarinate first and second pleonites. J.L. Barnard (1972a) established Ifalukia for one species of Parelasmopus which lacked dorsal carinae on the pleonites and urosomites, and lacked posteroventral serrations on epimeron 3. Parelasmopus sp. is most similar to Ifalukia, but differs in having a dorsally bicarinate first urosomite. It therefore strictly fits neither genus. If the mandibular palp is a synapomorphy defining Parelasmopus, then it appears that some species in the complex have either lost or never had dorsal carinae or serrate ventral margins. Until the phylognetic implications of these questions can be analysed it is best to maintain a broad concept of the genus.

Parelasmopus sp. is therefore a distinctive species differing from other Australian species in having dorsally smooth first and second pleonites and smooth ventral margins on epimeron 3.

Cite this publication as: 'J.K. Lowry, P.B Berents & R.T. Springthorpe (2000 onwards). Australian Amphipoda: Melitae Descriptions, Illustrations, Identification and Information Retrieval. Version: 2 October 2000. https://crustacea.net'.