Collettea coralensis, Bird, 2020

Bird, Graham J., 2020, Additions to the Tanaidacea (Crustacea: Peracarida) of Rangitâhua, the Kermadec Islands, from the Southwest Pacific Expedition 2017, Zootaxa 4860 (2), pp. 151-178 : 155-161

publication ID	https://doi.org/ 10.11646/zootaxa.4860.2.1
publication LSID	lsid:zoobank.org:pub:4A6F899C-DCB6-4A05-B4FB-C07EC8219951
DOI	https://doi.org/10.5281/zenodo.4537432
persistent identifier	https://treatment.plazi.org/id/EA6D843E-D6C3-4B96-B3C8-4F24C74AE59F
taxon LSID	lsid:zoobank.org:act:EA6D843E-D6C3-4B96-B3C8-4F24C74AE59F
treatment provided by	Plazi
scientific name	Collettea coralensis
status	sp. nov.

Treatment

Collettea coralensis View in CoL n. sp.

Figs 2–5 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 , 12H View FIGURE 12

Material examined. Holotype —non-ovigerous (non-ov.) ♀, 1.15 mm, AIM MA73607 View Materials , SWP2017-137 View Materials -3; Boat Cove , Raoul Island, Rangitâhua-Kermadecs, 9–15 m, coral rubble (see Table 1 View TABLE 1 ).

Paratypes —4 non-ov. ♀♀ (1 partly dissected on 1 microslide, AIM MA73609 View Materials ), two juvenile (juv.) ♂♂, AMS P.105579, SWP2017-135-2; 1 non-ov. ♀♀, AIM MA73611 View Materials , 1 View Materials non-ov. ♀ dissected on 2 microslides ( AIM MA73610 View Materials ), SWP2017-143-2 .

Diagnosis. Body about eight or nine times longer than broad (ltb). Cephalothorax elongate, 1.6–1.8 times ltb, shorter than pereonites 1–3 combined; carapace without lateral setules. Pereonites 1‒6 shorter than broad; pereonites 2–3 slightly longer than pereonite-1; pereonite-6 clearly shorter than pereonite-4. Pleon (excluding pleotelson) longer than pereonites 5–6 but shorter than pereonites 4–6 combined. Pleotelson about as long as broad, longer than pleonites 4–5. Antennule article-1 longer than articles 2–4 combined. Antenna article-4 without fusion line. Cheliped carpus with weak distoventral shield; propodus fixed finger with two simple ventral setae. Pereopods 2–3 spines short; pereopods 4–6 carpus with seta and three spines. Uropod about half as long as pleotelson; endopod two-segmented; exopod rudimentary, shorter than half length of endopod segment-1.

Etymology. Latin specific epithet after the habitat from which it was collected, unique so far for the genus.

Type locality. Boat Cove, Raoul Island, Rangitâhua-Kermadecs, 9–15 m, coral rubble.

Description. Holotype non-ovigerous female (AIM MA73607). Habitus ( Fig. 2 View FIGURE 2 A–B, 12H) slender, 8.6 times ltb; length 1.15 mm. Cephalothorax 18% of body length, longer than pereonites 1–2 combined, 1.6 times ltb; carapace entire, lateral margins with seta just posterior to antennule; rostrum weakly produced, acute. Pereon 48% of body length, with weakly convex margins of pereonites 1–6; sternites of pereonites 1–4 sinuate in lateral view; all shorter than broad, 0.5, 0.6, 0.6, 0.8, 0.8, and 0.6 times ltb respectively, all with pair of dorsal anterolateral setae. Pleon (excluding pleotelson) 21% of body length, as long as pereonites 5–6 and half of pereonite-4 combined, 1.7 times ltb, sternites slightly rounded; epimera indistinct, naked except for pleonite-5 ( Fig. 2C View FIGURE 2 ) also with dorsolateral setae. Pleotelson 23% of body length, ( Fig. 2 View FIGURE 2 A–B, 2D) length of pleonites 4–5 and half of pleonite-3 together ( Fig. 2 View FIGURE 2 A–B), 0.9 times as long as broad, slightly narrower posteriorly, in dorsal view with apex acute (full profile—ho-lotype) or rounded (deflexed); with seta ventral seta anterior to uropod insertion; posterior margin with two simple setae and two pinnate sensory setae (PSS); anal valves large and prominent ( Fig. 2D View FIGURE 2 ).

Holotype non-ovigerous female ( AIM MA73607 View Materials ). Antennule ( Fig. 2 View FIGURE 2 A–B, 2E) 0.6 times length of cephalothorax, 4.2 times ltb; article-1 0.6 times total length, 2.6 times ltb, lateral margin with three PSS, one distal seta, and at least one PSS; article-2 1.4 times ltb, with distolateral seta, and at least one PSS; article-3 shorter than article-2, about as long as broad, with two distal setae and one PSS; article-4 as long as article-3, with aesthetasc and five setae.

Paratype non-ovigerous females ( AIM MA73609 View Materials and AIM MA73610 View Materials ), all following. Antenna ( Fig. 2F View FIGURE 2 ) 0.8 times length of antennule; article-1 shorter than broad, naked; article-2 just longer than broad, with dorsodistal seta on slight apophysis; article-3 0.7 times length of article-2, as long as broad, with dorsodistal seta longer than article; article-4 as long as articles 1–3 combined, three times ltb, without fusion line, with at least two simple distal setae; article-5 about half as long as article-4, about three times ltb, with two unequal setae; article-6 small, with at least four setae, the longest pair possibly fused .

Mouthparts. Labrum ( Fig. 3A View FIGURE 3 ) typical, hood-shaped. Mandibles ( Fig. 3 View FIGURE 3 B–E) with left ( Fig. 3B View FIGURE 3 ) incisor weakly crenulate, lacinia broad and distally crenulate, molar ( Fig. 3C View FIGURE 3 ) larger than incisor, weakly acute, with sub-coronal array of four or five spines (difficult to resolve in this minute specimen); incisor of right mandible ( Fig. 3D View FIGURE 3 ) weakly trifid, molar ( Fig. 3E View FIGURE 3 ) as in left mandible. Labium ( Fig. 3F View FIGURE 3 ) typical, outer lobes absent, inner lobe subtriangular. Maxillule ( Fig. 3G View FIGURE 3 ) endite with at least eight terminal spines. Maxilla ( Fig. 3H View FIGURE 3 ) linguiform, naked.

Maxilliped ( Fig. 3 View FIGURE 3 I–L) combined bases deltoid, basis naked. Endite just shorter than basis, subrectangular, distal margin with one short blunt tubercle, and with two setae, the mesial larger. Palp as long as endite and basis combined; article-1 shorter than broad, naked, article-2 largest, with lateral seta and three unequal mesial setae; article-3 with at least two mesial setae; article-4 with superodistal seta and five apical setae. Epignath not observed.

Cheliped ( Fig. 3 View FIGURE 3 M–O) coxal sclerite triangular, reaching posterior of cephalothorax, naked; basis about twice as long as broad, posterior lobe reaching pereonite-1, as long as anterior mass, latter with dorsolateral seta; merus ventral margin occluding about two-thirds that of carpus, with one seta; carpus stout, 1.5 times ltb, two dorsal setae and two unequal ventral setae; chela about as long as but narrower than carpus, twice as long as broad, palm 1.5 times ltb, with mesial comb of two spines ( Fig. 3O View FIGURE 3 ); fixed finger 0.4 times length of palm, with two simple ventral setae and three near incisive margin, with about four subtriangular teeth; dactylus with small proximomesial spine.

Pereopod-1 ( Fig. 4A View FIGURE 4 ) coxa annular, with seta; basis 3.2 times ltb, with proximal superior seta; ischium with seta; merus 1.8 times ltb, with slender inferodistal spine; carpus 0.7 times as long as merus, just longer than broad, with two distal spines (superior and inferior) and one distal seta; propodus 0.75 times as long as merus and carpus combined, three times ltb, with one superodistal seta, and one co-axial inferodistal spine; dactylus twice as long as unguis, with proximal accessory seta; unguis together with dactylus just shorter than propodus.

Pereopod-2 ( Fig. 4B View FIGURE 4 ) similar to pereopod-1 but basis with a small proximal superior PSS; merus slightly broad- er, with both inferodistal spine and seta (mesial); carpus with three distal spines; propodus slightly shorter, without superodistal seta; claw shorter.

Pereopod-3 ( Fig. 4C View FIGURE 4 ) like pereopod-2 but propodus slightly shorter.

Pereopod-4 ( Fig. 4D View FIGURE 4 ) coxa annular, with seta; basis slightly broader than in pereopods 1–3, 3.1 times as ltb, with inferior PSS; ischium with one seta; merus geniculate, about twice as long as broad, with two inferodistal spines; carpus about length of merus, about twice as long as broad, subrectangular with three distal spines and one superodistal rod-like seta; propodus slightly longer than carpus, 2.5 times ltb, superior margin with PSS, with one slender superodistal spine just longer than dactylus, and two shorter inferodistal spines; dactylus and unguis about equal in length, as long as propodus.

Pereopod-5 ( Fig. 4E View FIGURE 4 ) as pereopod-4.

Pereopod-6 ( Fig. 4F View FIGURE 4 ) like pereopods 4–5 but basis naked; propodus with several inferior setules, without supe- rior PSS, and with two slender superodistal distal spines.

Pleopod. Absent.

Uropod ( Fig. 2G View FIGURE 2 ) [of holotype] over half length of pleotelson; peduncle longer than broad, naked; endopod 1.3 times longer than peduncle, weakly two-segmented, segment-1 larger than segment-2, with one distal simple seta and two distomesial PSS, segment-2 with one short and three long setae, and one PSS; exopod one-segmented, caplike, articulation with peduncle indistinct, with two distal setae.

Intraspecific variation. Non-ovigerous female: Habitus as holotype, 7.9–8.4 times ltb (n=2), body length 1.07– 1.25 mm (n=6). Pleon 17–23% of body length (n=6). Pleotelson 0.46–0.68 times as long as pleon (n=6).

Juvenile male: Habitus ( Fig. 5A View FIGURE 5 ) similar to non-ovigerous female, eight times ltb (n=1), body length 0.89–0.93 mm (n=2). Pereonite-6 proportionately shorter. Pleon ( Fig. 5B View FIGURE 5 ) 17–18% of body length (n=2). Antennule ( Fig. 5C View FIGURE 5 ) stouter than female, four times ltb, article-1 2.3 times ltb. Pleopod ( Fig. 5B View FIGURE 5 ) rami oval, without setae, endopod and exopod uniarticled. Uropod ( Fig. 5D View FIGURE 5 ) similar to female.

Distribution. Raoul and Macauley islands, coral rubble, encrusted coral on rocks, and red algae, 4– 18 m.

Remarks. This Collettea species has tanaellid-like features such as the stout cheliped and the short, almost fused, uropod exopod. It also differs from most other Collettea species in the relatively short pleotelson, narrow mandibular molar, and short pereopodal spines. Collettea coralensis n. sp. is perhaps closest to C. humbolti and C. minima in general habitus, but differs in its molar shape, its pereopodal spines, and uropod, inter alia (see above).

Compared to the type species C. cylindrata , C. coralensis has a 6-articled antenna (vs. 7-articled; equivalent of article-4 divided), its cheliped carpus is stout with a ventral shield (vs. not stout, without shield), the pereopods are stout ( v. slender , almost sticklike), the spines of pereopods 3–6 are short (vs. slender), and the carpus of pereopods 4–6 has three distal spines (vs. four).

It is tempting to erect a new genus for this taxon but C. coralensis may just be exhibiting adaptive characters associated with its small size and presumed interstitial habitat, as has been implicated for other tanaids (e.g., Bamber 2012; Bamber & Marshall 2015). Collettea coralensis is perhaps the smallest species of the genus yet described ( Table 2 View TABLE 2 .) although published data on body length are (frustratingly) largely confined to measurement of the holotype, even if multiple specimens are available.

The genus Collettea is cosmopolitan in distribution, with an extensive reported bathymetric range from shelf to hadal depths ( Table 2 View TABLE 2 .). At least two other species of Collettea have been recorded by me (unpublished) from cooler bathyal New Zealand waters to the South of the Kermadecs: C. cylindratoides Larsen, 2000 (Chatham Rise and Hikurangi Margin, 670–1237 m), and C. cf. alicjae Błażewicz-Paszkowycz & Larsen, 2005 (Hikurangi Margin and Bounty Trough, 693–1320 m), although the full extent and composition of these data have yet to be investigated. At some stage, the genus may be revised based on molecular studies.

available; ** measurement from holotype only, single specimen.