Synidotea innatans, Poore, 2012

Poore, Gary C. B., 2012, Four new valviferan isopods from diverse tropical Australian habitats (Crustacea: Isopoda: Holognathidae and Idoteidae), Memoirs of Museum Victoria 69, pp. 327-340 : 332-335

Synidotea innatans sp. nov.

Figures 5–7

Material examined. Holotype, Australia, Timor Sea , (11°42.4'S, 125°06'E), discarded fragment of fishing net floating on sea surface, G.C.B. Poore et al. (with Consulting Environmental Engineers), 26 Oct 2001, NMV J62816 (male, 11.3 mm) . Paratypes, same locality NMV J62817 (ovigerous female, 7.1 mm), NMV J62818 (12 males, 6.6–10.8 mm, 17 ovigerous females, 6.6–7.3 mm, 15 juveniles, 4.4–7.5 mm). All specimens fixed in 70% alcohol .

Description. Male. Body 3.0 times as long as greatest width at pereonite 3, dorsal surface smooth, pale, ornamented with numerous, small distinct chromatophores, arranged in a dense median stripe, densely on head, pleotelson and laterally, in oblique wavy bands midlaterally on pereonites, and with even single rows along posterior margins of pereonites; without dorsal sculpture. Head 2.0 times as wide as long, 0.7 times width of pereonite 3, front straight, strongly tapering in front of eyes, with shallow transverse depression; eye bulging, 0.40 times as long as median head length. Pereonite 1 0.80 width of pereonite 3, margin with rounded obtuse angle one-quarter from anterior suture, posterior three-quarters with parallel margins. Pereonite 2 with rounded anterolateral margins, parallel-sided over posterior three-quarters. Pereonite 3 lateral margin broadly convex. Pereonite 4 lateral margin broadly convex. Pleotelson 1.33 times as long as greatest width; tapering beyond pleonite 1 suture to 0.85 of greatest width to an obtuse angle at 0.7 length, then more steeply to narrow, barely-excavate posterior margin.

Antenna 1 flagellum 0.9 length of peduncle, with 9 pairs of aesthetascs. Antenna 2 0.5 body length; article 4 2.5 times as long as wide; article 5 4.3 times as long as wide; flagellum with 12 articles, 0.8 length of peduncle.

Maxilla 2 outer lobe strongly produced laterally, with marginal row of 24 long plumose setae. Maxillipedal basal endite longer than wide, with 1 coupling hook, apex setose. Maxillipedal palp 1.6 times as long as greatest width; article 3 1.4 times as long as wide. Epipod 1.2 times as long as wide, with broad transverse apex.

Pereopods with dense mat of setation on flexor margins of merus–propodus. Pereopod 1 propodus 1.5 times as long as greatest depth, palm excavate, mesial face with about 90 plumose setae; dactylus almost linear except for curved unguis, reaching back to base of carpus. Pereopod 2 propodus 1.2 times as long as merus and carpus together, 3.0 times as wide as long. Pereopod 4 propodus 2.9 times as wide as long. Pereopod 7 propodus 3.2 times as wide as long.

Penial plate 1.6 times as long as wide, double-waisted, with excavate distal margin.

Pleopod 2 with appendix masculina 1.27 times as long as endopod, with rounded apex, distally with numerous superficial spines. Uropod 3.8 times as long as distal peduncle width; endopod about 0.25 length of peduncle, mesial length 0.7 proximal suture length, suture at 80° to long axis, distal margin convex-truncate, at 80° to long axis, lateral margin curved into distal margins; with 3 setae.

Ovigerous female. Body 2.5 times as long as greatest width at pereonite 3. Head 2.4 times as wide as long, 0.64 times width of pereonite 3; eye bulging, 0.55 times as long as median head length. Pereonite 1 0.80 width of pereonite 3, margin barely convex, oblique. Pereonite 2 margin barely convex, oblique. Pereonite 3 margin barely convex, parallel-sided. Pereonite 4 margin barely convex. Pleotelson 1.3 times as long as greatest width; tapering beyond pleonite 1 suture to 0.75 of greatest width to an obtuse angle at 0.7 length, then more steeply to narrow, barely-excavate posterior margin.

Antenna 2 0.5 body length; article 4 2.2 times as long as wide; article 4 3.6 times as long as wide; flagellum with 13 articles, 1.3 times length of peduncle. Maxilla 2 outer lobe not expanded. Pereopods with mat of setae on flexor margins, less dense on pereopods 4 and 5 and sparse on 6 and 7.

Etymology. From innatare, Latin, to float, alluding to the discovery of this species on flotsam.

Distribution. Australia, Timor Sea, c. 11°S; on flotsam.

Remarks. The colour pattern of small chromatophores arranged in regular rows persists and is characteristic of Synidotea innatans . The new species differs in several respects from all other species in the region including S. poorei collected from buoys near Singapore ( Cai and Teo, 2012) and from others as detailed above.

The discovery of numerous specimens of this species on flotsam (an abandoned fragment of a fishing net), in the company of numerous shrimps, crabs and fishes, 170 km from land (the island of Timor) raises questions about the distribution of this species. This is only the second record of a species of Synidotea from this habitat. Hobday (2000) reported the normally benthic Synidotea harfordi Benedict, 1897 from the kelp Macrocystis pyrifera off the Californian coast. The new species is less elongate than S. harfordi and differs from the only two others known from benthic habitats near to where it was taken, that from Singapore and S. karumba , as detailed above. Thiel and Gutow (2005) reviewed the distribution of 13 rafting species of Idotea worldwide. Only one, I. metallica ( Bosc, 1802) , would appear to be an obligate rafter and it is cosmopolitan in the world’s oceans ( Poore and Lew Ton, 1993 for numerous citations; Abelló and Frankland, 1997). There is no suggestion that the new species is similarly widespread. The ability of these species to raft can not be used to suggest that this is how S. laticauda became distributed between estuaries in San Francisco Bay, Delaware, France and Spain ( Mees and Fockedey, 1993; Cuesta et al., 1996; Buschek and Boyd, 2006). Transportation by shipping seems more probable.

Figures

Figure 5. Synidotea innatans sp. nov. Holotype male top, paratype female below.

Figure 6. Synidotea innatans sp. nov. Holotype male left, paratype female right. Scale bar = 1 mm (habitus only).

Figure 7. Synidotea innatans sp. nov. Limbs from holotype male.