Achaeta borbonica sp. nov.

(Figure 1)

Achaeta sp. 1, Rota et al. 2013, table 1 and figure 3 (species ‘s1’); Rota et al. 2014, tables 1, 2 and Suppl. 1.

Type material

Holotype. MCZR Oligochaeta 0174, whole-mounted specimen, fully mature.

Type locality

Italy, Campania (Ca-1), Astroni State Nature Reserve, 8.5 km to the northwest of Naples, under the canopy of the oldest Q. ilex trees surviving in the crater (40.8490°N, 14.1499°E, 50 m asl). Thick coarse litter on loose, organic-rich soil with volcanic ash and pumice, pH 5.8, 27.10.2009, E. Rota coll.

Paratype. MCZR Oligochaeta 0175, one whole-mounted specimen, fully mature, from type locality, 14.05.2009 .

Other material. One whole-mounted specimen from type locality, 14.05.2009, in the author’ s collection.

Etymology

Discovered within a former hunting preserve for the Bourbon royal family.

Diagnosis

Small species, with flask-shaped glands occurring dorsally from V, clitellum including two mid-dorsally contiguous hyaline bands, male pores in XI, preclitellar nephridia one pair at 7/8, spermathecae short, confined to V, opening ventrally.

Description

Small, filiform species (Figure 1A). Live body length 2.2–3.2 mm, width 0.125 – 0.150 mm at XII; after fixation, length 1.3–2.0 mm, width 0.10 mm at clitellum. Segment number 20–22. Prostomium (Figure 1A) rounded both in frontal and lateral views, pointing forwards, one-fourth longer than peristomium (32 μm after fixation). Flask-shaped glands present dorsally from V (Figure 1B), conspicuous (30–35 μm long in vivo, about 25 μm in fixed material), absent ventrally. Knob-like glands and lentiform glands absent. Clitellum (Figure 1A, G, H) in XI–1/2XII, gland cells in 18 transverse rows, hyaline cells present only dorsolaterally, forming one longitudinal band per side, the two hyaline bands dorsally contiguous; granular cells covering all other sides of clitellum but absent in its middle along the midventral line.

Head pore at 0/1. Spermathecal pores ventral at 4/5. Male pores in XI (Figure 1A, G, H).

Cuticle and body wall thin. No thickened septa. Brain twice longer than broad (60 μm long when fixed), posteriorly rounded. Oesophageal outer ridge dorsal on III–V (Figure 1B). Pharyngeal glands, three pairs, all well developed and connected dorsally, secondary lobes absent (Figure 1A). One pair of preclitellar nephridia, anchored (but not constricted) by septum 7/8 (Figure 1A, E).

Coelomocytes smaller than flask-shaped glands, oval or drop-shaped, finely rugose and grained, pale (Figure 1B, F). Transition between oesophagus and intestine gradual. Gut constantly forming a loop in IX (Figure 1A). Intestinal floor of 1/2XV–XVII modified as an inner ridge of tall cells (ventral intestinal ridge). Chloragogenous cells in vivo filled with large (3 μm) opaque inclusions (Figure 1B–F), somewhat resembling the oil globules filling of Enchytraeus species, but rendering the sides of gut dark-brown in transmitted light. Dorsal blood vessel arising in VI.

Seminal vesicle absent. Sperm funnels (Figure 1D) twice longer than broad, in vivo 60 by 30 μm, with distinct collar (7 μm high). Heads of spermatozoa about 10 μm long and vasa deferentia 4.5 μm thick in vivo. Penial bulbs small, oval, compact, 25 μm long in vivo, 21 μm after fixation (Figure 1A, G, H). One egg mature, conspicuous, generally stretching through two whole segments (Figure 1A). Spermathecae (Figure 1B, C) short, confined to V, club-shaped, thicker-walled in their distal half (ectal duct), totally about 50 μm long and 15 μm across (live). Sperm arranged as a straight bundle inside ampulla.

Remarks

This new species resembles A. minima Southern, 1907 in body size, dorsal occurrence of the flask-shaped glands and position and size of the spermathecae ( A. minima and A. borbonica sp. nov. are the only known Achaeta species possessing flask-shaped glands with spermathecae confined to V), but differs from it by the cephalic displacement of the genital organs, the size of the sperm funnels and the location of the first preclitellar nephridia. An identical cephalic displacement of the genital organs, combined with ventral spermathecal pores, dorsal flask-shaped glands and possession of one pair of preclitellar nephridia, as in the new species, is observed in the northern European A. abulba Graefe, 1989 and A. bibulba Graefe, 1989 . From the latter two, the new species appears different because: (1) the nephridia comprise an anteseptal part and occur preclitellarly at 7/8 rather than at 6/7; (2) compact penial bulbs are present; (3) the spermathecae are confined to V and lack any glandular formation at pore.

Distribution

Only recorded in the Astroni State Nature Reserve, sexually mature both in spring and autumn.