Crenicarpus secundus, Drumm, David T. & Bird, Graham J., 2016

Drumm, David T. & Bird, Graham J., 2016, New deep-sea Paratanaoidea (Crustacea: Peracarida: Tanaidacea) from the northeastern Gulf of Mexico, Zootaxa 4154 (4), pp. 389-414 : 405-409

Crenicarpus secundus n. sp.

( Figs 10–12 )

Diagnosis. Monotypic genus, no species diagnosis given.

Material examined. Holotype: manca-II, 1.5 mm, ( USNM 1411520 ), northeastern Gulf of Mexico, App. Sed. 2, coll. F. Qu, 12 June 2014.

Paratype: one manca-II, 1.6 mm, (USNM 1411 521), App. Sed. 11, coll. F. Qu, 10 June 2014.

Description. Manca-II. Body ( Figs 10 , 11 A). Fairly stout, about five times as long as broad; length 1.5–1.6 mm (n = 2). Cephalothorax slightly longer than broad, longer than pereonites 1 and 2 combined, broadest medially. Pereonites all broader than long, pereonite-4 longest, pereonites 3–5 bulging mid-laterally. Pleonites subequal, last pleonite with pair of lateral setae. Pleotelson with rounded apex, not tapering, with pair of setae, longer than combined length of two pleonites.

Antennule ( Figs 11 A, B) shorter than cephalothorax; article-1 slightly shorter than rest of articles combined, with one seta and several PSS on outer margin; article-2 as long as broad, with one distolateral seta and two PSS; article-3 half as long as article-2, with one subdistal seta, one simple seta on inner margin, and one PSS; article-4 subequal to combined length of articles 2 and 3, with four or five distal simple setae, one subdistal simple seta, one PSS, and one aesthetasc.

Antenna ( Fig. 11 C) with six articles; articles 1–3 naked, articles 2 and 3 short and subequal; article-4 2.8 times as long as broad, with two distal simple and PSS; article-5 with distal seta; article-6 small, with two long and two short setae.

Mouthparts. Labrum ( Fig. 11 D) conical, broader than deep. Mandibles (not fully seen) with long, simple incisor (not illustrated). Maxillule (not fully seen) endite with five terminal spiniform setae (not illustrated). Maxilliped ( Fig. 11 E) basis and endites naked; palp article-1 naked, article-2 with three setae on inner margin, article-3 with three long and one short seta on inner margin, article-4 with five setae on inner margin. Epignath not recovered.

Cheliped ( Fig. 11 F–H). Pseudocoxa naked; basis with one seta on ventral margin; merus triangular, with cluster of at least five distal setae; carpus about 1.4 times as long as broad, crenulate mid-ventrally and on outer surface, two ventral and one dorsodistal seta; propodus inner surface ( Fig. 11 H) with long seta near dactylus insertion, outer surface with large lobe covering portions of the fixed finger and dactylus; fixed finger with one (holotype: Figs 11 G–H) or two (paratype: Fig. 11 F) ventral setae, two small setae ( Figs 11 G–H) near incisive margin, and bifid terminal claw; dactylus with one long proximal seta on inner surface.

Pereopod-1 ( Fig. 12 A). Coxa with one seta; basis 3.2 times as long as broad, naked; ischium with one ventrodistal seta; merus longer than carpus, about two times as long as broad, naked; carpus with three distal setae; propodus longer than carpus, with two subdistal setae; dactylus and unguis subequal to propodus length, dactylus with accessory seta longer than combined length of dactylus and unguis.

Pereopod-2 ( Fig. 12 B) and pereopod–3 ( Fig. 12 C). Similar to pereopod-1 except: merus and carpus subequal.

Pereopod-4 ( Fig. 12 D). Basis 2.7 times as long as broad, with one PSS on ventral margin; ischium with one ventrodistal seta; merus shorter than carpus, with two distal, simple spiniform setae; carpus 1.7 times as long as broad, with three distal, simple spiniform setae; propodus subequal to carpus, with three distal, simple spiniform setae; dactylus and unguis combined length shorter than propodus.

Pereopod-5 ( Fig. 12 E) identical to pereopod-4.

Pereopod-6. Absent.

Pleopods absent.

Uropod ( Fig. 12 F). About half as long as pleotelson, exopod shorter than basal article and fused medially, with one long and one short seta; endopod two-articled, article-1 naked, article-2 slightly longer than article-1, with five simple setae.

Etymology. Latin secundus , meaning ‘second, following’. This is the second species in the family Anarthruridae described from the Gulf of Mexico.

Distribution. Northeastern Gulf of Mexico (offshore Alabama) at the depth range 2233–2282 m.

Remarks. The two specimens available for examination are at the manca-II stage (sixth pereonite not fully formed and lacking pereopods). This is not without precedent as Bamber & Błażewicz-Paszkowycz (2013) described a new anarthrurid genus and species from one manca specimen. The mancae in this family tend to be large and relatively abundant. Bird (2004) found over half of the specimens in his material of Thorkelius latiremis (Hansen) were mancae, and Larsen’s (2005) material of Anarthruropsis edentula included 13 specimens, all of them at the manca-II stage. A similar phenomenon pertains to several undescribed anarthrurids, including Siphonolabrum , in New Zealand waters. Larsen (2005) attributed this to possible neoteny; however, more material is needed to confirm this.

Contrary to the situation in Collettea , the number of ventral setae on the fixed finger of the cheliped is not a consistent character here, as the holotype exhibits one seta and the paratype two; however, both are still at the manca stage and therefore not fully developed, although two setae are likely in mature specimens.

Figures

FIGURE 10. Crenicarpus n. gen. secundus n. sp., manca-II. Habitus (dorsal view).

FIGURE 11. Crenicarpus n. gen. secundus n. sp., manca-II. A, habitus (dorsal view); B, antennule; C, antenna; D, labrum; E, maxilliped; F, cheliped (outer); G, carpus, propodus, and dactylus of cheliped (outer); H, basis, merus, carpus, propodus, and dactylus of cheliped (inner). Scale bars: A = 0.5 mm; B, C = 0.05 mm; E = 0.03 mm; F, H = 0.1 mm.

FIGURE 12. Crenicarpus n. gen. secundus n. sp., manca-II. A, pereopod- 1; B, pereopod- 2; C, pereopod- 3; D, pereopod- 4; E, pereopod- 5; F, uropod. Scale bars: A – E = 0.1 mm; F = 0.03 mm.