Two new meiofaunal species of Trilobodrilus (Dinophilidae, Annelida) from California, USA

Abstract

Abstract. We describe two new species of the annelid genus Trilobodrilus Remane, 1925 (Dinophilidae Verill, 1892 from an intertidal and a subtidal location in San Diego, California. These two species show morphological and molecular divergences between each other and the previously described, geographically distant species. Intertidal T. windansea sp. nov. differs from subtidal T. ellenscrippsae sp. nov. most remarkably in the number and pattern of ciliary tufts and bands on the prostomium and along the body length, besides showing ca. 15% difference in gene fragments of COI and CytB. Trilobodrilus windansea sp. nov., though nesting with T. ellenscrippsae sp. nov. in the molecular phylogenetic analyses, morphologically resembles the Japanese T. itoi Kajihara, Ikoma, Yamasaki & Hiruta, 2015 most closely, but still differs from this species in the higher number of apical ciliary tufts, an additional ciliary row posterior to the second ciliary band, and by lacking a forth ciliary band and segmentally arranged lateral ciliary tufts. Trilobodrilus ellenscrippsae sp. nov. is morphologically most similar to the Japanese T. nipponicus Uchida & Okuda, 1943, but is much shorter, has more apical ciliary tufts, and less regularly arranged lateral ciliary tufts along the body. All species differ significantly in all compared gene fragments, and no obvious correlation was found between habitat and the species morphology or relationships.

Broad North Atlantic distribution of a meiobenthic annelid – against all odds

“…3). Systematically, these clades include Dimorphilus gen. nov., representing the smallest dinophilids (females ≤ 1.3 mm), displaying strong sexual dimorphism with completely hyaline dwarf males and females with a single ciliary band per segment and a rapid life cycle; Trilobodrilus (≤2.0 mm), being hyaline with a distinctive trilobed prostomium and limited ciliation on the trunk 30,31,52 ; and Dinophilus , being the largest dinophilids (≤3 mm), with easily recognizable orange-red pigmentation and two transverse ciliary bands on each trunk segment or a more random and occasionally denser distribution of ciliary tufts 34,35,40,44 . From a strictly morphological standpoint, Dimorphilus ( e.g., D. gyrociliatus ) shares several diagnostic morphological features of Dinophilus ( e.g., D. taeniatus ), so their previously proposed affinity had never come into question.…”

“…Detailed morphological examinations were made using a JEOL JSM-63335F field emission scanning electron microscope (SEM) at the Natural History Museum of Denmark, University of Copenhagen. Specimens were prepared for SEM following previously published protocols that included fixation in glutaraldehyde, postfixation in osmium tetroxide, and dehydration by an ascending ethanol series 30,54 . Prior to imaging, all specimens were critical-point dried, mounted on aluminum stubs, and sputter-coated with platinum/palladium.…”

“…Samples were prepared for polymerase chain reactions (PCR), sequenced and aligned according to methods previously outlined 30 .…”

“…Among meiofaunal groups, various annelid families are common throughout a broad range of environments and across vast geographical distances, yet densely sampled population genetic studies are rare 7,23 and cosmopolitan species have not yet been genetically proven. The meiofaunal annelid family Dinophilidae has been recorded across the world for the last 150 years and is common in narrowly demarcated beach localities, often specific to either inter- or subtidal regions 30,31 . The family contains 18 valid species in two genera 31 , which lack significant annelid characters such as appendages, parapodia or chaetae and a free-swimming larval stage, but all show direct development of six, only internally discernible body segments and an external ventral ciliary tract used for gliding movement 31–34 .…”

Interstitial Annelida

“…Description of coloration, glandular structures or epidermal patterns, as well as some internal structures (e.g., nephridia), demands observations on live individuals. External ciliary structures (i.e., ciliary bands, ciliary tufts) are better studied using scanning electron microscopy (SEM) [37,42,60], whereas internal ciliated structures such as nephridia and gonoducts are better revealed using confocal laser scanning microscopy (CLSM) and immunolabelling [42,61].…”