Exosphaeroma waitemata, Bruce, 2005

Bruce, Niel L., 2005, New sphaeromatids (Crustacea: Isopoda: Sphaeromatidea) from coastal and freshwater habitats in New Zealand, Zootaxa 1002 (1002), pp. 1-20 : 2-9

Exosphaeroma waitemata sp. nov. ( Figs 1–4)

Material examined.— Holotype: ♂ (5.9 mm), Hobsonville , Waitemata Estuary, Auckland, North Island, New Zealand, 36 47.959’S, 174 40.643’E, June 2001, sand flats ( NIWA 4068 ).

Paratypes: 3 ♂ (imm. 3.0, 3.5 [dissected]; ~ 5 [crushed] mm), 2 juveniles (3.0, 1.9 mm), same data as holotype ( NIWA 4069 ) . ♀ (non­ovig. 3.8 mm), Shoal Bay, Waitemata Estuary , Auckland, 36°49.072’S, 174°45.131’E, stn 14­4 ( NIWA 4070 ) . ♂ (crushed, uropod dissected), 3 ♀ (non­ovig. 3.7 mm, remainder crushed), manca (1.7 mm), Little Shoal Bay, Waitemata Estuary , Auckland, stn 14­2 ( NIWA 4071 ) . Manca (crushed, 1.2 mm), Little Shoal Bay, Waitemata Estuary , Auckland, stn 14­3 ( NIWA 4072 ) .

Description of male. Body 1.8 times as long as greatest width, weakly ovate, widest at pereonite 6; dorsal surfaces smooth. Cephalon anterior margin without transverse ridges, rostral process weakly developed, visible in dorsal view. Head about 1.2 times as long as pereonite 1, pereonite 1 about 1.4 times as long as pereonite 2; pereonites 2–6 subequal in length, pereonite 7 slightly shorter than 6. Coxae 2–7 ventrally subtruncate, ventral margin with setae; coxae of pereonite 6 extending posterior to and overlapping coxae of pereonite 7, posteriorly acute. Pleon medially about 2.5 times as long as pereonite 7, posterior margin with sublateral ‘keys’. Pleotelson strongly vaulted, posterior margin produced to narrowly rounded apex; ventral margin broad, with shallow and wide excavation.

Antennule peduncle article 1 1.4 times as long as wide, about 1.9 times as long as article 2, anterior and posterior margins convex; article 3 about two­thirds as long as article 1, 2.3 times as long as wide, 1.3 times as long as article 2; flagellum 7­articled, extending to anterior of pereonite 1, about 2.5 times as long article 3. Antenna relatively robust, peduncle articles 1 and 2 short, article 2 posterior margin with scale­setae; article 3 about 0.6 times as long as article 4; articles 4 and 5 subequal in length; articles 3–5 collinear; flagellum about 0.8 times as long as peduncle, extending to middle of margin of pereonite 1, with 11 articles.

Epistome anteriorly sub­truncate, anterior lateral margins rounded, with prominent medial constriction. Left mandible incisor with 4 cusps, lacinia mobilis with 3 cusps, spine row of 6 curved, serrate spines; right mandible incisor with 3 indistinct cusps, spine row of 2 broad­based distally serrate spines and 5 curved serrate spines; molar process round, crushing surface strongly ridged; palp articles 1 and 2 subequal in length, article 2 distolateral margin with 3 biserrate setae; article 3 with 5 biserrate setae, terminal seta being longest. Maxillule mesial lobe with 4 long, strongly CP RS and two short simple RS, lateral lobe with 8 broad­based, truncate RS and 2 curved, slender RS on gnathal surface, twelfth prominently pectinate seta set between these; truncate RS weakly serrate (2–4 teeth) or simple. Maxilla lateral lobe and middle lobe each with 11 curved, pectinate RS respectively, mesial lobe with about 18 serrate and biserrate RS, proximal seta longest. Maxilliped endite lateral margin strongly convex, distal margin sub­truncate, with 7 sinuate CP RS, I blunt and 1 acute RS at sublateral angle, distomesial margin with 3 CP RS and single coupling hook; palp articles 2–4 moderately lobate articles 2–5 with about 26, 22, 20 and 164 setae respectively, these setae being set in 2 rows.

Pereopod 1 without setulose fringe on inferior margins; basis about 3.7 times as long as greatest width, approximately twice as long as propodus; ischium 0.7 times as long as basis, 2.3 times as long as greatest width, superior margin with proximal, sinuate, acute RS, distal two­thirds with 5 long prominent simple setae; merus about 0.7 times as long as ischium, about 1.6 times as long as greatest width, superior distal angle with 8 acute long simple setae, inferior margin with 9 long simple setae distal­most being longest; carpus 1.38 times as long as wide, inferior margin with 6 long stiff simple setae; propodus 2.50 times as long as greatest width, 1.1 times as long as ischium, inferior margin with 4 simple setae, 3 small RS and distally with 1 blunt RS; mesial surface with 5 submarginal biserrate RS; dactylus 0.8 times as long as propodus, unguis inferior margin smooth, secondary unguis curved, pectinate. Pereopod 2 inferior proximal margin and submarginal surface of ischium–carpus with setulose fringe; basis 3.2 times as long as greatest width, inferodistal angle with single long simple seta, superior margin with widely spaced small penicilate setae; ischium 0.8 times as long as basis, 3.0 times as long as greatest width, distal half of superior margin with 8 evenly spaced long simple setae, distal inferior margin with 4 long simple setae; merus about half as long as ischium, superior distal angle about 12 long simple seta, inferior margin about 10 moderate and long simple seta; carpus slightly (1.1) times longer than merus, 1.5 times as long as greatest width, anterodistal angle with about 8 long simple seta, inferior margin with 8 long, stiff simple setae; propodus 0.7 times as long as ischium, 2.4 times as long as proximal width, superior distal angle with 1 long simple seta, inferior margin with weak setulose fringe and distal serrated scales, distal half with 5 stiff simple setae; dactylus 0.7 as long as propodus, inferior margin distally with scales, secondary unguis simple. Pereopod 3 similar to pereopod 2. Pereopods 3–4 with moderately developed setulose fringe on inferior margins of merus and carpus of pereopods 2–4. Pereopods 5–7 similar, ischium–carpus broad, bilaterally compressed; with more and far longer RS than pereopods 1–3. Pereopod 7 basis 4.0 times as long as greatest width, inferodistal angle with 2 long simple setae, proximal superior margin with patch of scale setae; ischium 0.7 times as long as basis, 1.2 times as long as greatest width, proximal superior margin scale setae, distal superior margin about 12 long simple setae, inferior distal angle with 8 long simple setae; merus 0.6 times as long as ischium, superior distal angle with 7 long simple setae (extending to distal margin of carpus), inferior margin with setulose fringe, distal margin with 9 long distally biserrate setae; carpus 1.6 times as long as merus, anterodistal margin with 8 short, acute biserrate and 4 long setae, inferior margin with setulose fringe, inferior distal angle with 8 long distally biserrate setae; propodus 0.9 times as long as ischium, 3.1 times as long as wide, inferior margin setulose, distally with 5 long setae, superior distal angle with 1 short palmate seta; dactylus 0.5 as long as propodus.

Penes slender, mutually adjacent, distally rounded; approximately 5 times as long as basal width (examined in situ).

Pleopod 1 exopod and endopod with c. 45 and 26 PMS respectively, exopod proximolateral RS present; endopod and exopod subequal in length, endopod 1.5 times as long as greatest width, distal margin truncate. Pleopod 2 exopod and endopod with c. 42 and 32 PMS respectively; appendix masculin a 13 times as long as basal width, distally folded, apically narrowly rounded. Pleopod 3 exopod and endopod with c. 38 and 14 PMS respectively; exopod transverse suture entire. Pleopod 4 rami without thick ridges, lateral, exopod transverse suture entire, lateral margin with continuous evenly spaced fine simple setae. Pleopod 5 rami without thick ridges; exopod transverse suture entire, with 2 scale patches, lateral margin with numerous evenly spaced simple setae. Uropod exopod 0.8 as long as endopod, 5.2 times as long as greatest width, extending slightly beyond apex of endopod, straight, margins weakly convex, converging to sub­acute apex; endopod 4.8 as long as basal width, straight, apex bluntly rounded; both rami rounded in cross section with fine nodules and abundant simples and sparsely plumose setae.

Female. Similar to male. Coxa 6 not expanded.

Size. To 5.9 mm; many specimens were received damaged, and the size range for adults could not be determined.

Remarks: Exosphaeroma waitemata sp. nov. is immediately recognised by thick, setose uropods with a terminally acute exopod, in conjunction with heavily setose pereopods. The expanded and posteriorly acute male coxa 6 is a further character with which to confirm identity. These characters separate the species from all other Exosphaeroma as well as from all other New Zealand Sphaeromatidae .

Exosphaeroma falcatum Tattersall, 1921 , known only from northern North Island is similar in appearance, with similar uropodal exopods. Exosphaeroma falcatum is far smaller than E. waitemata (up to 2.5 mm compared to nearly 6 mm), lacks setose body margins and uropods, has a more elongate epistome, and has notably more slender pereopods 5–7. The adult female of E. falcatum has a conspicuous hook­shaped process on the uropodal endopod.

Despite the superficially rather different appearance to most species of Exosphaeroma , notably the strongly setose pereopods and males with an expanded sixth coxal plate, the new species is retained within Exosphaeroma , with the proviso that it is regarded as incertae sedis. The pereopod morphology, with strongly developed setae, is of the same pattern as shown by some other species such as Exosphaeroma agmokara Bruce, 2003 , and the form of the penial processes and pleopods accords entirely with that of Exosphaeroma . The most significant difference is that in E. waitemata sp. nov. the dorsal surface of the posterior margin of pleonite 1 lacks the two flush, sub­median lobes that are typical of Exosphaeroma , and which are a possible generic apomorphy. Other differences include pereopod 1 with a pectinate secondary unguis on the dactylus (otherwise always simple in Exosphaeroma s. str.), and the thick (in section) uropodal rami (always lamellar in Exosphaeroma s. str.), male coxae 6 expanded and posteriorly produced (not so in Exosphaeroma s. str.), and the posterior margin of pereonite 7 without a median angle (present in species close to the type species of Exosphaeroma s. str.). In the absence of any phylogenetic hypotheses for the Sphaeromatidae , and given the similarity of penial and appendage morphology, the species is provisionally retained within Exosphaeroma .

Superficially Exosphaeroma waitemata sp. nov. is similar to species of Tholozodium Eleftheriou, Holdich & Harrison, 1980 (see Harrison & Ellis 1991, p. 921 for discussion of the synonymy of Basphaeroma Taberner, 1988a with Tholozodium ), a genus known from sandy, exposed beaches northern Indian Ocean ( Eleftheriou et al. 1980), and sheltered freshwater sandy habitats in Brazil and Argentina ( Pires 1982; Taberner 1988). Given that E. waitemata sp. nov. and Tholozodium are both sand dwellers, a large part of that similarity may result from convergent adaptations to a similar habitat, specifically the long setae on the pereopods. The pleotelson segmentation, pereopod 1 shape and pleopod morphology, among other characters, all differ substantially.

Etymology. The name of the type locality, the Waitemata Estuary (noun in apposition).