Grania homochaeta, Wit, Pierre De, Rota, Emilia & Erséus, Christer, 2009

Wit, Pierre De, Rota, Emilia & Erséus, Christer, 2009, Grania (Annelida: Clitellata: Enchytraeidae) of the Great Barrier Reef, Australia, including four new species and a re-description of Grania trichaeta Jamieson, 1977, Zootaxa 2165, pp. 16-38 : 23-25

Grania homochaeta sp. n.

( Figs. 5 , 10 C)

Holotype: AMS type coll. W.35544, whole-mounted specimen from Heron Island, stn. H4.

Paratype: SMNH type coll. 7767, whole-mounted specimen (posteriorly amputated) from the type locality.

Description: Body 3.0 mm long (holotype, only complete specimen), 0.08 mm wide at III, 0.08–0.09 mm at clitellum (n=2). Segment number 35 (n=1). Prostomium rounded, 35–50 µm wide, 25–30 µm long (n=2); epidermis 9–11 µm thick dorsally and anteriorly, 8 µm ventrally (n=2). Peristomium 65–80 µm wide at 1/2 (n=2). Both ventral and lateral chaetae commencing in XVII. Chaetae increasing in size toward posterior body end, from 40 to 55 µm long (n=6); chaetal shaft widest at base, tapering distally, L-shaped; foot 10–15 µm long, with moderate instep and marked heel; chaetal index=4.84, n=6 sd=0.548 ( Figs. 5 A, 10C). Epidermal gland cells inconspicuous. Clitellum 8–13 µm thick, extending from anterior of XII to mid XIII, with transverse rows of granular gland cells interspersed with hyaline cells at a frequency of 5–6:1 ( Fig. 5 B), except near male pores where hyaline cells are absent, and midventrally, where no gland cells are present. Midventral copulatory gland in XIV. Spermathecal pores lateral, located immediately behind 4/5. Male pores located ventrolaterally in mid XII.

Brain posteriorly indented. Head organ absent. Pharyngeal glands in IV–VI; dorsal lobes present in IV–VI, ventral lobes present in V (2 pairs) and VI (2 pairs); not connected dorsally. First pair of nephridia at 7/8. Dorsal blood vessel commencing in XVI–XVII. Chloragogen cells small (5–7 µm tall). Coelomocytes not observed. Sperm sac extending posteriorly from clitellum as far back as XIV. Sperm funnels of uniform width, 20–25 µm wide, 8–10 times as long as wide. Heads of spermatozoa 10 µm long. Vasa deferentia unmodified, loosely coiled in XII–XVII; 6 µm wide, internally ciliated. Penial apparatuses ( Fig. 5 C) with uniform oval glandular structures, 40–50 µm long, 30–40 µm wide, next to epidermal invaginations (the latter 5 µm wide and 35–40 µm deep); vasa deferentia opening into epidermal invaginations; stylets absent (penial bulb type 3). Egg sac reaching as far back as XV. Spermathecae ( Fig. 5 D) attached to oesophagus near 5/6; ampullae roughly spherical, 30–35 µm in diameter, ducts 16–18 µm wide at spermathecal pores, tapering entally to 7–9 µm near ampullae, 50–55 µm long, wedged about 10 µm into ampullae; 8–9 sperm rings per spermatheca, 6 µm in diameter; no glands at spermathecal pores.

Etymology: From the Greek homo, meaning equal, and chaeta, referring to the fact that ventral and lateral chaetae have the same distribution along the body.

Remarks: As only two specimens of this species are available, it is not possible to draw conclusions concerning intraspecific variation. However, it is clear that this is a distinct species based on its unique chaetal distribution. No other species of Grania has been described with both ventral and lateral chaetae first occurring in the same segment (see Discussion).

Both the spermathecae and the penial bulbs, however, lack obvious distinguishing features, and closely resemble those of G. c o l o r a t a sp. n., described below. In fact, apart from the different location of the first ventral chaetae (XVII in G. homochaeta , XIV in G. c o l o r a t a), the pattern of the clitellum, the number of sperm rings in the spermathecal ampullae of G. homochaeta (few sperm rings in G. colorata ), and the shape of the sperm funnel (width is 8–10 times length in G. homochaeta , only 1.5 times in G. c o l o r a t a), these two species are very similar. We do not know whether G. h o m o c h a e t a shares in vivo the unusual color (bright greenishyellow) of G. colorata : unfortunately, we have so far only been able to study fixed and stained material of this species, where the original coloration, if present, has been lost. The penial bulbs also resemble those of G. curta De Wit & Erséus, 2007 , and both penial apparatuses and spermathecae resemble those of G. galbina De Wit & Erséus, 2007 , both of which are New Caledonian species, and the latter of which is colored greenishyellow. Grania curta , however, is unique in its low number of segments and has a large gland on the ectal part of the spermathecal duct, characters lacking in G. homochaeta . Grania galbina , is much larger than G. homochaeta , and differs in chaetal distribution, possessing ventral chaetae from IV or V.

Distribution and habitat: Heron Island, Great Barrier Reef; 18 m, gravelly fine sand.

Figures

FIGURE 5. Grania homochaeta sp. n. (Holotype, stn. H 4). A: Chaetae. B: Clitellar gland cell pattern, dorsal view, anterior end to the right. C: Penial apparatus, side view, anterior end to the top. D: Spermatheca, side view, anterior end to the bottom.

FIGURE 10. Chaetae. A: G. breviductus sp. n.. B: G. regina sp. n.. C: G. ho m o c ha e ta sp. n.. D: G. c o lor at a sp. n.. E: G. trichaeta Jamieson 1977.