FIGURE 9

Holotype

USNM1283175, CE11659, whole-mounted, sexually mature specimen, eight posterior segments amputat- ed, from North Carolina, USA, 34°47′22″N, 76°13′43″W. Sublitoral, 17 m in depth, sand. Collected by C. Erséus, 24 May 2011. COI barcode sequence, GenBank acc. no. KT428113; for other sequences, see Table 1.

Etymology

Named unitheca for its single spermatheca.

Description

Body> 8.56 mm long, 61 segments (including segments used for DNA analysis), 0.09 mm wide at segment V, 0.09 mm at segment XII. Prostomium rounded, 40 μm long, 60 μm wide, epidermis not reduced at front tip, 6 μm thick. Ventral chaetae from segment XV, lateral chaetae absent. Chaetae (Fig. 9A) 50–62 μm long, shaft straight, 3.7–5.0 μm thick at midpoint, hook-shaped. Epidermal gland cells inconspicuous. Clitellum not well developed. Spermathecal pore unpaired, mid dorsal, just posterior to 4/5. Male pores ventrolateral in middle of segment XII. Female pores not observed.

Brain posteriorly indented. Head organ (sensu Rota & Erséus, 1996) absent. Pharyngeal glands in segments IV–VI, dorsal lobes in segment IV (one pair), in segment V (one pair), and in segment VI (one pair), ventral lobes present in segment IV (one pair), in segment V (two pairs), and in segment VI (two pairs); glands not connected dorsally. Nephridia not observed. Chloragogen cells not observed. Dorsal blood vessel commencing in segment XV. Coelomocytes not observed. Sperm sac extending to segment XIV, egg sac in segment XVII. Sperm funnels as long as wide (Fig. 9D). Vasa deferentia observed in segments XII– XIII, internally ciliated, coiled, 8 μm wide. Penial apparatus type 1 (sensu Coates, 1984), small, compact glandular bulb, 44 μm long, 39 μm wide; stylet absent (Fig. 9C). Midventral copulatory gland (in segment XIV) present. Spermatheca attached to oesophagus near 5/6. Ampulla nearly spherical, 52 μm long, 54 μm wide. Sperm rings maximally 9 μm wide (Fig. 9B). Ectal duct, 61 μm long, 35 μm wide at midcourse. No gland at spermathecal pore.

Remarks

An unpaired spermatheca is unusual in enchytraeids and, among Grania species, it has been only report- ed for Grania monospermatheca Erséus & Lasserre, 1976, also known from the continental shelf off the eastern USA. In fact, G. unitheca sp. nov. is morphologically similar to G. monospermatheca in almost all characters observed; however, it may be distinguished from G. monospermatheca by its small and compact penial bulb, with no stylet. Grania monospermatheca has a more complex penial apparatus, with a large glandular structure attached to the penial bulb, and the presence of a stylet. Furthermore, G. unitheca sp. nov. possesses a midventral copulatory gland in segment XIV. This gland was not observed in G. monospermatheca (see Erséus & Lasserre, 1976 and Coates & Erséus, 1985).

Genetically, these two species are well distinguished from each other; however, the phylogenetic analysis, as well as the fact that the two species are from the same geographical area, suggest that G. unitheca sp. nov. and G. monospermatheca are closely related (see ‘Phylogenetic analysis’ below).