Caulleriella murilloi Dean & Blake, 2007, sp. nov.

Caulleriella murilloi sp. nov.

Figures 11 A–G; 12 A–D.

Material Examined Costa Rica, Golfo Dulce. Holotype: Mangrove sediments, mud, Jan 1996, (MCZ 67154). Paratypes: Mangrove sediments, mud, Jan 1996, (1 MCZ 67155) (2 UCRMZ 133). Costa Rica, Golfo de Nicoya. Jicaral, mangrove sediments, mud, Jan 1996, (1 HKD).

Holotype 6.4 mm long, 0.6 mm wide for 94 setigers, paratypes ranging from 5.3 mm long, 0.6 mm wide for 84 setigers up to 10.7 mm long, 0.7 mm wide for 111 setigers. Body long, uniformly wide; approximately rectangular in cross-section with dorsal and ventral surfaces slightly depressed relative to noto- and neuropodial lobes; area between noto- and neuropodia forming a groove-like depression in posterior region; segments short throughout. Pygidium long cone; anus dorsal with digitate ventral cirrus (Fig. 11 C). Color in alcohol light tan.

Prostomium short, tapered, peristomium with deep grooves anteriorly, exposing circular, rimmed nuchal organs within grooves (Fig. 11 A B; 12A); peristomium with three annulations and wide dorsal crest; first annulation long, approximately 2.5× length of second annulation; border between first and second annulation indistinct ventrally; third annulation approximately 2× length of second, with wide dorsal caruncle-like ridge extending over setigers 1– 2(Fig. 11 A B; 12A). Posterior extension of peristomium carries paired dorsal tentacles posteriorly with these arising at posterior border of setiger 2; first pair of branchiae on setiger 1 at dorsal edge of swollen notopodial lobe; branchiae arising from similar position in subsequent setigers.

Notosetae of anterior region including 4–6 smooth capillaries, accompanied by two weakly curved spines from setiger 25 in holotype (25–27 in other specimens), capillaries reduced in number in subsequent setigers with spines gradually increasing to 4–5 per fascicle with capillaries reduced to single fine, tessellated capillary emerging from base of ventralmost spine (Fig. 12B); posterior setigers with 1–3 spines or hooks with single fine capillary seta. Anterior neurosetae 3–5 smooth capillaries accompanied by 2–4 slightly curved spines; middle setigers with 4–6 spines, reduced to 2–3 spines in posterior setigers. Notopodial spines bidentate in few anterior setigers (Fig. 11 E), spines of middle and posterior setigers with large, rounded distal tooth encircled by short hood interpreted as derived from subdistal tooth (Fig. 12B); many notopodial spines in posterior body appearing unidentate most likely due to wear of hood. Neuropodial spines slightly curved, shorter than notopodial spines; some ventralmost spines in setal bundle bidentate with well-developed, subequal teeth (Fig. 11 F) or with spine-like subdistal tooth (Fig. 12C), remainder of spines weakly bidentate with low, subequal teeth; in middle and posterior setigers spines weakly bidentate (Fig. 11 G) or subdistal tooth forming an encircling hood around distal tooth, encircling hood may slightly project dorsally giving appearance of bidentate spine with weakly developed tooth subdistally on convex surface (Fig. 12D).

Methyl green staining pattern. Entire body staining uniformly blue-green with exception of prostomium and peristomium.

Habitat. Known only from sediments associated with the roots of mangrove trees in Golfo Dulce and Golfo de Nicoya, Costa Rica.

Remarks. The unusual structure of the spines in this species makes classification difficult. Most of the spines in each rami appear to be either unidentate (at low magnification) or weakly bidentate; bidentate spines with well developed teeth are rare. The recognition of the low-lying subequal teeth or the presence of a thin hood, which may be worn, requires the use of oil immersion or SEM.

The tips of the weakly bidentate spines are reminiscent of species of Tharyx as described by Blake (1991) but this is interpreted as an apparent convergence of characters. The genus Tharyx is characterized as having closely situated notosetal and neurosetal bundles with the first pair of branchiae found immediately posterior to the dorsal tentacles (Blake 1991). In C. murilloi sp. nov. the setal bundles are widely separated as is characteristic of the genus Caulleriella and the first branchiae emerge from the first setiger while the dorsal tentacles occur at the posterior border of setiger 2.

Within the genus Caulleriella, C. murilloi sp. nov. is most similar to C. lajolla in the posterior extension of the peristomium over anterior setigers resulting in the position of paired dorsal tentacles from setiger 2. Furthermore, first occurrence of notopodial (approximately setiger 25) and neuropodial hooks (setiger 1) are also similar. The two species differ most obviously in the morphology of the hooks because C. lajolla has easily recognizable bidentate hooks throughout. C. lajolla also differs from C. murilloi sp. nov. in the absence of capillary setae accompanying the neuropodial hooks which are found in all setigers in C. murilloi sp. nov.

Etymology. This species is named for Dr. Manuel Murillo, marine biologist and founding father of essentially all marine and limnological sciences in Costa Rica. As Vice-Recktor Dr. Murillo provided training opportunities for all the original members of, and was the prime mover in the establishment of, CIMAR at the Universidad de Costa Rica.