Namanereis socotrensis, Glasby & Fiege & Damme, 2014

Glasby, Christopher J., Fiege, Dieter & Damme, Kay Van, 2014, Stygobiont polychaetes: notes on the morphology and the origins of groundwater Namanereis (Annelida: Nereididae: Namanereidinae), with a description of two new species, Zoological Journal of the Linnean Society 171 (1), pp. 22-37 : 26-30

NAMANEREIS SOCOTRENSIS SP. NOV.

( FIGS 4A, B , 5A–F , 6A–F )

Specimens examined

Holotype: Indian Ocean , Republic of Yemen, Socotra Island, coastal well at northern coast, Expedition Socotra Karst Project 3 ( SKP3 ). Coll. Dr Stefano Taiti and Dr Abdul Karim Nasher, i.2003, cs in two parts [ SMF 22368: SEM stub 1131 (af) and 1134 (pf)] . Paratypes: location and collecting data same as holotype. Two specimens ( SMF 23315) , one paratype marked for deposition in NHCY is kept provisionally at Senckenberg; three specimens ( NTM 25485) ; one specimen, KVD personal collection.

Type locality

Coastal well at northern coast of Socotra Island ( Yemen), Indian Ocean, between Hadiboh and Riy di Irriseyl.

Etymology

Species name based on region of occurrence.

Diagnosis

Prostomium not cleft anteriorly. Antennae short, subconical. Eyes absent. Three pairs of tentacular cirri. Jaws with bifid terminal teeth, and broad ‘wing’ covering subterminal teeth. Notochaetae absent. Neurochaetae in type C arrangement as defined by Glasby (1999). Supraneuroacicular falcigers of chaetiger 10 with blades about four to five times longer than width of shaft head, blades moderately coarsely serrated, six to nine teeth. Subacicular neurochaetae represented by two or three heterogomph falcigers only.

Description

Body elongate, uniform width along most of body, slightly tapering over far posterior body ( Fig. 4A ). Dorsal side convex, ventral side flattened. Colour in alcohol specimens yellow-white; epidermal pigment absent ( Fig. 4A ). Holotype cs (af + pf), 17.5 mm long, 1.5 mm

bj, bifid jaws; hf, heterogomph falcigers; hp, heterogomph pseudospinigers; hs, heterogomph spinigers; sj, serrated jaws; Tent., tentacular.

neuropodial ligule. Ventral cirri cirriform, one-third to one-half length of, and more slender than, dorsal cirri ( Figs 5C , 6A, B ).

Notochaetae absent. Neurochaetae in type C arrangement, i.e. supraneuroacicular chaetae consisting of one to two (paratypes none to two) sesquigomph spinigers in postacicular fascicles and one (paratypes none to one) heterogomph falciger in preacicular fascicles. Subneuroacicular fascicle in postacicular position comprising two to three heterogomph falcigers with blades of about same size ( Figs 5D , 6A–D ). Subneuroacicular spinigers and pseudospinigers absent.

Supraneuroacicular sesquigomph spinigers with boss about 1.5–1.7 times length of collar. Supraneuroacicular falcigers of chaetiger 10 with blades about four to five times longer than width of shaft head, moderately serrated, six to nine teeth ( Fig. 6D ). Subneuroacicular falcigers of chaetiger 10 with moderately to coarsely serrated blades, seven (to nine?) teeth, about four times longer than width of shaft ( Figs 5E , 6D ).

Pygidium tripartite, with small subpointed dorsal lobe and two larger ventral lobes bearing pair of smooth, subconical anal cirri ( Fig. 5F ). Anus terminal.

wide at chaetiger 10 including parapodia and chaetae, 95 chaetigers. Paratypes (cs) ranging in size from 19.2–31.0 mm long, 1.3–1.6 mm wide, 82–123 chaetigers (N = 7).

Prostomium subtriangular, wider than long, 2.1 × (paratypes 2.33–2.75 ×; N = 6) with widest part near posterior end; anterior margin entire without cleft, shallow dorsal depression present. One pair of antennae inserted above inner half of palps; subconical, inflated basally. Antennae short, conical, not extending beyond tip of palps. Palps massive, biarticulate. Eyes absent ( Figs 4A, B , 5A, B ).

Peristomium with three pairs of tentacular cirri with indistinct cirrophores; smooth to slightly wrinkled cirrostyles. Anterodorsal and posterodorsal cirri of about same length, anteroventral slightly shorter. Posterodorsal cirri extending to chaetiger 2 ( Fig. 5A ). Pharynx retracted in all specimens. Jaws of paratypes with bifid terminal teeth, and wing covering subterminal teeth ( Fig. 6E, F ).

Parapodia with conical acicular neuropodial ligule. Dorsal cirri cirriform, similar in length throughout, extending just short of or slightly beyond acicular Remarks

Namanereis socotrensis sp. nov. resembles N. serratis Glasby, 1999 , from the Caribbean and N. gesae from Abd al-Kuri, another island in the Socotra Archipelago. It can be distinguished from the latter by the absence of heterogomph pseudospinigers in the subneuroacicular fascicles. It differs from N. serratis not only in the geographical distribution but also by the shape of the antennae, i.e. subconical rather than cirriform. The number of teeth on the supraneuroacicular falcigers and the subneuroacicular falcigers appear to be in the same range as N. serratis but the teeth are relatively large in this species (coarse serrations), whereas in comparison those of N. socotrensis sp. nov. are rather small (moderate serrations) ( Table 1).

Habitat

Specimens of N. socotrensis sp. nov. were collected ‘accidentally’ by Drs S. Taiti and A. K. Nasher, in search of isopod crustaceans (see Taiti & Ferrara, 2004; Taiti & Checcucci, 2009), using small funnel traps ( Taiti & Ferrara, 2004), hand-made from 10 mL plastic tubes, with meat as bait, left overnight in an old, manmade well. These old coastal wells, about 2–5 km from the sea and quite numerous, are drilled through the thin (10–20 m) Quaternary fossil dune and reef deposits and the (Cretaceous−)Cenozoic karstic limestone that cover the granite base on the northern coastal plain of Socotra Island. The wells contain pure (drinkable) fresh water, yet at times of drought they may turn brackish, as there is the potential for seawater infiltration. Thus, N. socotrensis sp. nov. was found in a coastal groundwater pocket in a karstic environment that serves (served) as drinking water by local people, yet at times fluctuates between brackish and fresh water. It is probably not a purely benthic/ hyporheic species, as the animals will have needed to move at least partly freely in the water in order to get into the trap. Nothing else was found in this trap except these polychaetes.

Distribution

Socotra Island, Yemen. Namanereis socotrensis sp. nov. has only been found so far in a single locality on Socotra Island, in a coastal well on the northern coast at about 10–15 m asl, between Hadiboh and Riy di Irriseyl.

Figures

Figure 4. Namanereis socotrensis sp. nov. Paratype (NTM W25485). A, whole animal, dorsal view; B, whole animal, ventral view. Scale bars = 1.0 mm.

Figure 5. Namanereis socotrensis sp. nov. Holotype (SMF 22368). Scanning electron micrograph. A, anterior end, right side, lateral view. B, anterior end, left side, lateral view. C, 25–18 posterior-most chaetigers, left side, lateral view. D, chaetae, chaetiger 7, right side. E, chaetae, chaetiger 10, left side. F, posterior end, posterior view. Scale bars: A−C = 300 μm; D, E = 30 μm; F = 100 μm.

Figure 6. Namanereis socotrensis sp. nov. Paratype NTM W25485. A, parapodium, chaetiger 10; B, parapodium, chaetiger 60; C, heterogomph spiniger, chaetiger 60; D, subacicular heterogomph falciger, chaetiger 60 (left); supra-acicular heterogomph falciger, chaetiger 60 (right); E, F, left and right side jaws, respectively, ventral view. Scale bars: A, B = 0.2 mm; C, D = 0.02 mm; E, F = 0.1 mm.