Polycheria spongoteras, Peart & Spong & Sutherland & Kelly, 2019

Peart, Rachael A., Spong, Keren, Sutherland, Judy & Kelly, Michelle, 2019, A new species of sponge-dwelling amphipod, Polycheria spongoteras sp. nov., from Spirits Bay, Northland, New Zealand, Zootaxa 4674 (1), pp. 127-141 : 129-136

Polycheria spongoteras sp. nov.

( Figs 1–4 )

Type material. Holotype — NIWA 143339 , female, 5.5 mm, +1 permanent slide, NIWA Stn KAH1706/10-A1, Spirits (Piwhane) Bay, Northland, New Zealand, 34.384°S, 172.802°W, 42 m, grab sample, 31 May 2017 . Paratypes — NIWA 143340 , male, 5.0 mm, + 1 permanent slide , NIWA 143341 , juvenile, 2.5 mm, ibid .

Additional material examined. NIWA 143342 , 12 specimens, males and females , NIWA Stn KAH1706/10- A1, Spirits (Piwhane) Bay, Northland, New Zealand, 34.384°S, 172.802°W, 42 m, grab sample 31 May 2017 .

Description. Based on holotype, female, 5.5 mm, NIWA 143339. Head eye large, diameter approximately half head length; anteroventral margin angled/narrowly rounded; length subequal to pereonites 1 and 2. Rostrum absent. Antenna 1 subequal in length to antenna 2; peduncle article 1 shorter than article 2 (0.8 ×), article 2 longer than article 3 (3.3 ×); accessory flagellum absent; primary flagellum with 18 articles. Antenna 2 peduncle article 4 subequal to article 5; flagellum with 13 articles. Mandible incisor with 4 teeth on right and 5 teeth on left side; left lacinia mobilis with 4 teeth, right lacinia mobilis with only 2 teeth; molar large, triturative, asymmetrical; palp absent. Lower lip with outer lobe not projecting laterally. Upper lip with apical margin broadly rounded with fine lateral and facial setae. Maxilla 2 with inner plate apically narrowly rounded, 1 terminal seta; outer plate apically truncated with 7 simple and 3 toothed robust setae; palp linear (not tapering distally), with 8 medial and lateral slender simple setae and 2 long, terminal robust setae and 2 acute teeth; palp extending past distal tips of outer plate robust setae. Maxilla 2 inner and outer plates subequal lengths, both plates narrow and slightly curved; outer plate bearing 8 slender simple setae; inner plate bearing 15 slender simple setae. Maxilliped palp with 4 articles, slightly shorter than distal margin of outer plate, article 4 without nail; outer plate medial margin concave and lined with 11 short robust setae and no facial setae; inner plate about 1/3 length of outer plate, tipped with 4 slender setae.

Pereon. Gnathopod 1 coxa anteroventral margin not produced, narrowly rounded, ventral margin bearing 3 small slender setae; basis linear, slightly shorter than distal articles combined, anteromedial margin with 7 elongate slender setae and several shorter lateral slender setae; merus shorter than carpus; carpus length subequal to propodus, posterior margin densely lined with long slender setae, anterior margin sparsely lined; propodal palm entire and convex, dactylus reaching length of palm; dactylus weakly curved, apically smooth.

Gnathopod 2 coxa with anteroventral margin rounded, no defining corners or teeth, ventral margin bearing 1 slender seta; basis long and slender, linear, length subequal to sum of distal articles, with 3 long slender simple setae on posterior margin, anterior margin lined with small slender setae; merus shorter than carpus (0.65 ×), posterior margin with long slender setae; carpus length subequal to propodus, posterior and anterior margins lined with long slender setae; propodus subovoid, anterior and posterior margins lined with long, slender simple setae, palm entire and slightly convex, defined by robust seta; dactylus reaching to end of palm, dactylus inner margin smooth.

Pereopod 3 anteroventral margin of coxa produced to form strong ventrally directed acute tooth (reaching ¼ length of basis); posteroventral corner produced to form bluntly rounded tooth, reaching to about half length of anteroventral tooth, ventral margin concave bearing 1 robust seta; basis slightly expanded, width approximately 0.5 × length, anterior margin with 4 robust setae, posterior with 3 robust setae and 1 long slender, simple seta; merus shorter than basis (0.75 ×), longer than carpus (1.5 ×), posterior margin with 3 marginal robust setae and 2 distal robust setae, anterior margin with 1 robust seta; carpus length subequal to propodus, posterior margin with 1 robust seta, anterior margin without setae; propodus posterior margin slightly concave, without robust setae, anterior margin with row of 3 robust setae and long tuft of slender simple setae; propodal palm acutely excavate, produced at posterior corner to form acute tooth, defined on posterior corner by 2 robust setae, anteriorly (at base of dactylus) by 1 robust seta; dactylus strongly curved, reaching defining corner of palm.

Pereopod 4 with anteroventral corner of coxa produced to form acute, ventrally directed tooth, reaching to about 1/5 length of basis, posterior margin strongly convex/sinuous, extending to form acute posteroventral corner resembling shape of claw due to concave shape of ventral margin, ventral margin bearing large robust seta and 2 slender setae; basis narrower than pereopod 3 basis, posterior margin with 3 robust setae on margin, 3 small slender setae on medial surface, anterior margin bare except for 2 small distal robust setae; merus linear, shorter than basis (0.76 ×), posterior margin with 2 marginal and 3 distal robust setae, anterior margin with 1 marginal and 1 distal robust seta, longer than carpus (1.9 ×); carpus posterior margin with 1 marginal and 1 distal robust seta, anterior margin without marginal setae and 2 small distal robust setae, shorter than propodus (0.78 ×); propodus posterior margin slightly concave, no marginal setae; anterior margin with 2 robust setae in row and long tuft of slender simple setae distally; palm acutely excavate defined posteriorly by acute tooth surrounded by 2 robust setae, palm bearing 2 slender, simple midpalmar setae and 2 robust setae at base of dactylus; dactylus strongly curved, reaching to end of palm and with smooth inner margin.

Pereopod 5 with anteroventral and posteroventral corners rounded and not extended, ventral margin sinuous, bearing slender seta located posteriorly; basis expanded width 0.6 × length, posterior and anterior margins with small robust and slender setae; merus subequal in length to basis, posterior margin with 2 marginal and 2 distal robust setae, anterior margin with 4 marginal and 2 distal robust setae, longer than carpus; carpus longer than propodus, posterior margin with marginal and 2 distal robust setae, anterior margin with 3 marginal and 3 long distal robust setae; propodus posterior margin slightly sinuous and without marginal setae, anterior margin with bunch of 3 marginal robust setae and tuft of long slender simple distal setae; palm acutely excavate, defined by acute posterodistal corner, bearing 2 small robust setae, palm bearing 2 robust setae at base of dactylus; dactylus strongly curved, reaching to end of palm, with smooth inner margin.

Pereopod 6 coxa posteroventral corner softly subquadrate, anteroventral corner produced to form small acute ventrally pointing tooth, ventral margin bearing 1 robust and 1 slender seta; basis subrectangular but expanded, posteroproximal corner slightly expanded and rounded, proximal posterior margin bearing 4 slender setae and 2 distal robust setae, anterior margin with 3 slender marginal and 2 robust distal setae; merus shorter than basis (0.72 ×), longer than carpus (2.2 ×), posterior margin with marginal and 2 distal robust setae, anterior margin lined with 7 long marginal and 3 distal robust setae; carpus shorter than propodus, posterior margin without marginal but with 3 distal robust setae, anterior margin with bunch of 3 marginal and 4 long distal robust setae; propodus posterior margin slightly concave without marginal setae, anterior margin with row of 3 marginal robust and tuft of long, slender distal setae; palm acutely excavate and defined by acute posterodistal corner and 2 robust setae, with robust seta at base of dactylus; dactylus strongly curved reaching to the end of palm, inner margin smooth.

Pereopod 7 coxa posteroventral corner narrowly rounded bearing small slender seta, anteroventral corner extended ventrally slightly forming small subacute tooth; basis similar shape to pereopod 6 with rounded posteroproximal corner, posterior margin lined along complete length with small slender and robust setae, ending distally with group of 3 long robust setae, anterior margin lined with 3 small slender marginal and slender distal setae; merus shorter than basis (0.7 ×), longer than carpus (2 ×), posterior margin with group of 2 marginal and 4 distal robust setae, anterior margin with 4 marginal and 4 distal long robust setae; carpus subequal length to propodus, posterior margin without marginal, with 3 distal robust setae, anterior margin with 2 marginal and 4 distal robust setae; propodus posterior margin slightly concave without robust setae, anterior margin with 3 marginal robust setae and distal tuft of long slender setae; palm smoothly excavate defined by small acute posteroventral tooth and 2 robust setae, with robust seta at base of dactylus; dactylus curved reaching to end of palm with inner margin smooth.

Pleon. Epimeron 1 posteroventral corner subquadrate, ventral margin with slender seta near anterior corner, with lateral suture/line prominent. Epimeron 2 with posteroventral corner subquadrate with softly rounded small tooth, ventral margin with slender seta near anterior corner, lateral suture/line prominent. Epimeron 3 with posteroventral corner subquadrate, no obvious tooth, ventral margin with slender seta near anterior corner, lateral suture/ line prominent.

Urosomite 1 without setae; dorsal margin with prominent carination, produced to form large dorsally rounded, posterior directed boss.

Urosomites 2–3 fused to form one segment. In situ, uropod 1 and 2 subequal and both shorter than uropod 3.

Uropod 1 peduncle fringed with long slender simple setae on lateral margins, medial margin with 7 short robust setae, 1 large distolateral robust seta, outer ramus subequal in length to inner, both rami with 7–9 slender setae, both tipped with long robust seta. Uropod 2 peduncle without lateral setae, with 4 medial robust setae and distolateral long robust seta, outer ramus slightly longer than inner ramus, with 4 lateral and 1 distal robust seta, inner ramus without marginal but with 3 distal robust setae. Uropod 3 peduncle with 4 short marginal slender/robust setae, outer ramus subequal to inner ramus. Telson not extending beyond uropod, reaching only halfway along rami; subtriangular; deeply cleft to near the base (90%); lateral margins convex, bearing 2 robust and 2 or 3 slender setae on each lobe, each lobe apex acute, subapical notch and large cusp at base of distalmost robust seta.

Variations. Based on paratype male, 5.0 mm length, NIWA 143340. Sexual dimorphism minimal; eye smaller (than female); urosomite 1 carination smaller than female. There is minimal variation within the samples. With size, there are slight variations in the shapes of the coxae (angles less pronounced) and the amount of setation on the antennae. The key characters of the mouthparts and the setation on the telson do not vary within the sample size.

Molecular data. Sequence data from the COI marker is deposited in GenBank (Accession no. MN082372.1). The placement of the new species within the greater dexaminoid group is shown in Fig. 5 .

Etymology. The species name, spongoteras (sponge-watcher, Greek), was used by the ancient Greeks for a small creature that inhabited sponges. Noun used in apposition.

Remarks. Polycheria spongoteras sp. nov. is most closely comparable to the only other known New Zealand species, Polycheria obtusa , and can also be compared to P. antarctica , as this species was previously documented from New Zealand.

The type material of P. obtusa was unable to be located and so the original description and illustrations were used for comparison with the present material. The new species aligns with the diagnosis of Polycheria provided by Thomson (1882), but there are several differences between P. obtusa and P. spongoteras sp. nov. In P. spongoteras sp. nov., the antennae are about half of the body length, compared to two-thirds body length in P. obtusa ; antenna 1 article 1 0.8 × length of article 2 (0.5 × length in P. obtusa ); antenna 1 subequal in length to antenna 2 (longer than antenna 2 in P. obtusa ); gnathopod 2 propodus ovoid (oblong in P. obtuse ) also pereopod 7 is the shortest pereopod in P. spongoteras (rather than the longest in P. obtusa ); the number of robust setae on the telson and the shape varies between the two species (the new species has two robust and two or three slender setae on each lobe, with dominant sub-apical cusps and telson is approximately 1.7 × longer than wide; P. obtusa has 6 large robust setae per lobe, minute subapical cusps and is 2.5 × longer than wide).

Barnard (1972) documented P. obtusa from Blueskin Bay, Otago. The illustrations ( Barnard 1972: figs 26, 27) indicate that P. obtusa is morphologically similar to the new species but differs in the shape of the propodi (straightsided in Barnard’s material, diverging in P. spongoteras sp. nov.) and the setal arrangement on the maxilliped inner plate (six slender apical setae in Barnard’s material and three more robust setae and one longer slender seta in P. spongoteras sp. nov.). The key difference, however, appears to be the shape of the head (anteriorly narrow in P. spongoteras sp. nov. and broad in P. obtusa as per Barnard’s illustrations).

Foster (2008: figs 35–36) also illustrated several specimens from New Zealand that he assigned to P. obtusa , but these specimens seem to differ again from those described by both Thomson (1882) and Barnard (1972) under that name, as well as P. spongoteras sp. nov. (see Table 1 for the diagnostic differences). The significance of these differences is that the key characters for distinguishing between species of Polycheria include the proportions of the antennae; the shape of coxae; the robustness of the pereopods; and the setation on the uropods and telson. The most variable characters seem to be the associated with eye shape. The other indication is that instead of just one species occurring in New Zealand, there are probably multiple cryptic species and filling specific habitats, providing a situation similar to the deep-sea environment where convergent evolution to live in a specific environment (i.e. in association with a soft-bodied organism) produces very conservative morphology.

As mentioned in the introduction, specimens assigned to Polycheria antarctica have been recorded from New Zealand on numerous occasions. Polycheria antarctica appears to a catch-all species that requires revision. In a move by Chilton (1912), a number of Polycheria species were placed into synonymy with P. antarctica including P. obtusa from New Zealand. This was synonymy was rejected by subsequent studies ( Barnard 1972; Barnard & Karaman 1991; Bousfield & Kendall 1994). Polycheria obtusa differs from P. antarctica sensu stricto (taken from the original description by Stebbing 1875 and opposed to P. antarctica acanthopoda Thurston, 1974 ) by the shape of pereopod 4 coxa (anteroventral corner subquadrate in P. antarctica and acutely produced ventrally in P. spongoteras ), the broad bases on pereopods 3–7 on P. antarctica (narrow to moderately expanded on pereopods 3–5 in P. spongoteras ), and greatly extended meri on the pereopods 3–7 on P. antarctica producing the impression of long slender pereopods (relatively shorter meri on the pereopods giving the impression of shorter pereopds in P. spongoteras ).

Molecular sequencing of the material at hand was undertaken to place the new species in context of other dexaminoids. As expected, the COI sequence obtained from P. spongoteras formed a well-supported clade (alrt 98.8%, bootstrap 98%, posterior probability 1.0) with the single Polycheria COI sequence available in GenBank, P. osborni from the northeastern Pacific (GenBank Accession number MH242935.1) ( Fig. 5 ). The Polycheria clade is recovered as sister to Dexamine corroborating its placement in Dexaminidae , which received moderate support (92.4/66/1.0). Pairwise divergence between the sequences of P. spongoteras and P. osborni , at 22.5%, corroborates their specific distinctness. The placement of the species of Polycheria in the molecular tree indicates that the genus belongs in the super family Dexaminoidea and that has closer affinities to the dexaminids as opposed to the atylids and lepichinellids. Beyond that very little can be said until further sequencing is done.

Habitat. Type material was obtained from a specimen of the sponge Homaxinella erecta , at 42 m depth ( Fig. 1B ).

Ecology. The exact nature of this sponge/amphipod relationship is unknown, but we assume that it is commensal, with the amphipods feeding on particulate matter brought to the sponge via the aquiferous incurrent flow. Such a relationship has been recorded in several other sponges and ascidians ( Foster 2008; White 2011; Bergquist 1968); it is assumed that the modified leg claws enable the amphipod to burrow into sponge tissue or hold tight to the pinacoderm until the sponge overgrows them ( Bergquist 1968). The cavities are not typical of Homaxinella erecta : the surface of this species, and indeed most other suberitid sponges, is usually waxy-smooth with no cavities except TABLE 1. Diagnostic differences between allied species and specimens of New Zealand Polycheria . the large exhalent oscules, but even oscules are not apparent in H. erecta in life. The amphipods described here were positioned dorsally to the body of the sponge, in cavities longer than wide, with the appendages able to reach beyond the cavity. Only a single individual per cavity was observed and there were over 20 cavities evident in the sponge body, which measured 53 mm long and 8 mm maximum diameter ( Fig. 1B ). Each cavity has a well-formed, smooth, opaque margin, suggesting that the layer of fibrillar collagen, common to the ectosome (outer surface) of all suberitid sponges, extends around the lining of the cavity as it would at a site of injury in these sponges (see Kelly- Borges & Bergquist 1988). Finally, as this is the only specimen of Homaxinella erecta examined that has revealed amphipod dwellers, we can only assume that P. spongoteras sp. nov. is opportunistic as opposed to specific in its host selection.

Figures

FIGURE 1. A. Type locality of Polycheria spongoteras sp. nov. Spirits Bay, Northland, New Zealand. B. Homaxinella erecta (Brondsted, 1924), 53 mm total length, with amphipod Polycheria spongoteras sp. nov. in residence (upper middle) in pocket 1.5 mm long (framed in box).

FIGURE 2. Polycheria spongoteras sp. nov. Paratype, male, 5.0 mm, NIWA 143340. Holotype, female, 5.5 mm, NIWA 143339. Scale bars represent 0.2 mm.

FIGURE 3. Polycheria spongoteras sp. nov. Holotype, female, 5.5 mm, NIWA 143339. Mouthparts, antennae, uropods and telson. Scale bars represent 0.2 mm.

FIGURE 4. Polycheria spongoteras sp. nov. Holotype, female, 5.5 mm, NIWA 143339, gnathopods 1–2, pereopods 3–7, scales bars represent 0.5 mm. Paratype, male, 5.0 mm, NIWA 143340, gnathopods 1–2 propodus and dactylus, scale bars represent 0.2 mm.

FIGURE 5. Maximum-likelihood phylogram estimated from the COI dataset. Support values are shown on each branch: approximate Likelihood Ratio Test (aLRT) values and ML bootstrap (%) above, and Bayesian PP values below. Only values greater than 70% (aLRT), 70% (bootstrap) and 0.9 (PP) are shown, but all support values are shown if two support methods reach the cut-off value. Scale bar represents substitutions per site. GenBank accession numbers or BOLD accession number (for Nicippe tumida) are appended to taxon names.